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  • 1.
    Ahad, Abdul
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Nick, Peter
    Actin is bundled in activation-tagged tobacco mutants that tolerate aluminum2007In: Planta, ISSN 0032-0935, E-ISSN 1432-2048, Vol. 225, no 2, p. 451-468Article in journal (Refereed)
    Abstract [en]

    A panel of aluminum-tolerant (AlRes) mutants was isolated by protoplast-based T-DNA activation tagging in the tobacco cultivar SR1. The mutants fell into two phenotypic classes: a minority of the mutants were fertile and developed similarly to the wild type (type I), the majority was male-sterile and grew as semi-dwarfs (type II). These traits, along with the aluminum tolerance, were inherited in a monogenic dominant manner. Both types of mutants were characterized by excessive bundling of actin microfilaments and by a strongly increased abundance of actin, a phenotype that could be partially phenocopied in the wild type by treatment with aluminum chloride. The actin bundles could be dissociated into finer strands by addition of exogenous auxin in both types of mutants. However, actin microfilaments and leaf expansion were sensitive to blockers of actin assembly in the wild type and in the mutants of type I, whereas they were more tolerant in the mutants of type II. The mutants of type II displayed a hypertrophic development of vasculature, manifest in form of supernumerary leaf veins and extended xylem layers in stems and petioles. Whereas mutants of type I were characterized by a normal, but aluminum-tolerant polar auxin-transport, auxin-transport was strongly promoted in the mutants of type II. The phenotype of these mutants is discussed in terms of reduced endocytosis leading, concomitantly with aluminum tolerance, to changes in polar auxin transport.

  • 2. Andersson-Gunnerås, Sara
    et al.
    Mellerowicz, Ewa J
    Love, Jonathan
    Segerman, Bo
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Ohmiya, Yasunori
    Coutinho, Pedro M
    Nilsson, Peter
    Henrissat, Bernard
    Moritz, Thomas
    Sundberg, Björn
    Biosynthesis of cellulose-enriched tension wood in Populus: global analysis of transcripts and metabolites identifies biochemical and developmental regulators in secondary wall biosynthesis2006In: The Plant Journal, ISSN 0960-7412, E-ISSN 1365-313X, Vol. 45, no 2, p. 144-165Article in journal (Refereed)
    Abstract [en]

    Stems and branches of angiosperm trees form tension wood (TW) when exposed to a gravitational stimulus. One of the main characteristics of TW, which distinguishes it from normal wood, is the formation of fibers with a thick inner gelatinous cell wall layer mainly composed of crystalline cellulose. Hence TW is enriched in cellulose, and deficient in lignin and hemicelluloses. An expressed sequence tag library made from TW-forming tissues in Populus tremula (L.) x tremuloides (Michx.) and data from transcript profiling using microarray and metabolite analysis were obtained during TW formation in Populus tremula (L.) in two growing seasons. The data were examined with the aim of identifying the genes responsible for the change in carbon (C) flow into various cell wall components, and the mechanisms important for the formation of the gelatinous cell wall layer (G-layer). A specific effort was made to identify carbohydrate-active enzymes with a putative function in cell wall biosynthesis. An increased C flux to cellulose was suggested by a higher abundance of sucrose synthase transcripts. However, genes related to the cellulose biosynthetic machinery were not generally affected, although the expression of secondary wall-specific CesA genes was modified in both directions. Other pathways for which the data suggested increased activity included lipid and glucosamine biosynthesis and the pectin degradation machinery. In addition, transcripts encoding fasciclin-like arabinogalactan proteins were particularly increased and found to lack true Arabidopsis orthologs. Major pathways for which the transcriptome and metabolome analysis suggested decreased activity were the pathway for C flux through guanosine 5'-diphosphate (GDP) sugars to mannans, the pentose phosphate pathway, lignin biosynthesis, and biosynthesis of cell wall matrix carbohydrates. Several differentially expressed auxin- and ethylene-related genes and transcription factors were also identified.

  • 3.
    Auffret, Alistair G
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Meineri, Eric
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Bruun, Hans Henrik
    Ejrnaes, Rasmus
    Graae, Bente J
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Ontogenetic niche shifts in three Vaccinium species on a sub-alpine mountain side2010In: Plant Ecology & Diversity, ISSN 1755-0874, E-ISSN 1755-1668, Vol. 3, no 2, p. 131-139Article in journal (Refereed)
    Abstract [en]

    Background: Climate warming in arctic and alpine regions is expected to result in the altitudinal migration of plant species, but current predictions neglect differences between species' regeneration niche and established niche.

    Aims: To examine potential recruitment of Vaccinium myrtillus, V. uliginosum and V. vitis-idaea on a mountain slope in northern Sweden in relation to current adult occurrence.

    Methods: We combined a seed-sowing experiment in seven community types with adult occurrence observations and species distribution mapping. Results: Emergence of V. myrtillus and V. vitis-idaea seedlings was significantly related to community type, while V. uliginosum was indifferent, but exhibited the highest average emergence. Adult occurrence was related to community, and ontogenetic niche shifts were observed for all three study species. V. myrtillus was shown to have the highest potential recruitment in habitats at altitudes above its current populations.

    Conclusions: The potential for migration exists, but incongruence between regenerative and established niches presents a challenge for colonisers, as well as for plant migration modelling.

  • 4.
    Barajas-Lopez, Juan de Dios
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Kremnev, Dmitry
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Shaikhali, Jehad
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Pinas-Fernandez, Aurora
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Strand, Åsa
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    PAPP5 is involved in the tetrapyrrole mediated plastid signalling during chloroplast development2013In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 8, no 3, article id e60305Article in journal (Refereed)
    Abstract [en]

    The initiation of chloroplast development in the light is dependent on nuclear encoded components. The nuclear genes encoding key components in the photosynthetic machinery are regulated by signals originating in the plastids. These plastid signals play an essential role in the regulation of photosynthesis associated nuclear genes (PhANGs) when proplastids develop into chloroplasts. One of the plastid signals is linked to the tetrapyrrole biosynthesis and accumulation of the intermediates the Mg-ProtoIX and its methyl ester Mg-ProtoIX-ME. Phytochrome-Associated Protein Phosphatase 5 (PAPP5) was isolated in a previous study as a putative Mg-ProtoIX interacting protein. In order to elucidate if there is a biological link between PAPP5 and the tetrapyrrole mediated signal we generated double mutants between the Arabidopsis papp5 and the crd mutants. The crd mutant over-accumulates Mg-ProtoIX and Mg-ProtoIX-ME and the tetrapyrrole accumulation triggers retrograde signalling. The crd mutant exhibits repression of PhANG expression, altered chloroplast morphology and a pale phenotype. However, in the papp5crd double mutant, the crd phenotype is restored and papp5crd accumulated wild type levels of chlorophyll, developed proper chloroplasts and showed normal induction of PhANG expression in response to light. Tetrapyrrole feeding experiments showed that PAPP5 is required to respond correctly to accumulation of tetrapyrroles in the cell and that PAPP5 is most likely a component in the plastid signalling pathway down stream of the tetrapyrrole Mg-ProtoIX/Mg-ProtoIX-ME. Inhibition of phosphatase activity phenocopied the papp5crd phenotype in the crd single mutant demonstrating that PAPP5 phosphatase activity is essential to mediate the retrograde signal and to suppress PhANG expression in the crd mutant. Thus, our results suggest that PAPP5 receives an inbalance in the tetrapyrrole biosynthesis through the accumulation of Mg-ProtoIX and acts as a negative regulator of PhANG expression during chloroplast biogenesis and development.

  • 5. Benson, Samuel L
    et al.
    Maheswaran, Pratheesh
    Ware, Maxwell A
    Hunter, C Neil
    Horton, Peter
    Jansson, Stefan
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Ruban, Alexander V
    Johnson, Matthew P
    An intact light harvesting complex I antenna system is required for complete state transitions in Arabidopsis2015In: Nature plants, ISSN 2055-026X, Vol. 1, no 12, article id 15176Article in journal (Refereed)
    Abstract [en]

    Efficient photosynthesis depends on maintaining balance between the rate of light-driven electron transport occurring in photosystem I (PSI) and photosystem II (PSII), located in the chloroplast thylakoid membranes. Balance is achieved through a process of 'state transitions' that increases energy transfer towards PSI when PSII is overexcited (state II), and towards PSII when PSI is overexcited (state I). This is achieved through redox control of the phosphorylation state of light-harvesting antenna complex II (LHCII). PSI is served by both LHCII and four light-harvesting antenna complex I (LHCI) subunits, Lhca1, 2, 3 and 4. Here we demonstrate that despite unchanged levels of LHCII phosphorylation, absence of specific Lhca subunits reduces state transitions in Arabidopsis. The severest phenotype-observed in a mutant lacking Lhca4 (Delta Lhca4)-displayed a 69% reduction compared with the wild type. Yet, surprisingly, the amounts of the PSI-LHCI-LHCII supercomplex isolated by blue native polyacrylamide gel electrophoresis (BN-PAGE) from digitonin-solubilized thylakoids were similar in the wild type and Delta Lhca mutants. Fluorescence excitation spectroscopy revealed that in the wild type this PSI-LHCI-LHCII supercomplex is supplemented by energy transfer from additional LHCII trimers in state II, whose binding is sensitive to digitonin, and which are absent in Delta Lhca4. The grana margins of the thylakoid membrane were found to be the primary site of interaction between this 'extra' LHCII and the PSI-LHCI-LHCII supercomplex in state II. The results suggest that the LHCI complexes mediate energetic interactions between LHCII and PSI in the intact membrane.

  • 6. Bitocchi, Elena
    et al.
    Rau, Domenico
    Benazzo, Andrea
    Bellucci, Elisa
    Goretti, Daniela
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Biagetti, Eleonora
    Panziera, Alex
    Laido, Giovanni
    Rodriguez, Monica
    Gioia, Tania
    Attene, Giovanna
    McClean, Phillip
    Lee, Rian K.
    Jackson, Scott A.
    Bertorelle, Giorgio
    Papa, Roberto
    High Level of Nonsynonymous Changes in Common Bean Suggests That Selection under Domestication Increased Functional Diversity at Target Traits2017In: Frontiers in Plant Science, ISSN 1664-462X, E-ISSN 1664-462X, Vol. 7, article id 2005Article in journal (Refereed)
    Abstract [en]

    Crop species have been deeply affected by the domestication process, and there have been many efforts to identify selection signatures at the genome level. This knowledge will help geneticists to better understand the evolution of organisms, and at the same time, help breeders to implement successful breeding strategies. Here, we focused on domestication in the Mesoamerican gene pool of Phaseolus vulgaris by sequencing 49 gene fragments from a sample of 45 P. vulgaris wild and domesticated accessions, and as controls, two accessions each of the closely related species Phaseolus coccineus and Phaseolus dumosus. An excess of nonsynonymous mutations within the domesticated germplasm was found. Our data suggest that the cost of domestication alone cannot explain fully this finding. Indeed, the significantly higher frequency of polymorphisms in the coding regions observed only in the domesticated plants (compared to noncoding regions), the fact that these mutations were mostly nonsynonymous and appear to be recently derived mutations, and the investigations into the functions of their relative genes (responses to biotic and abiotic stresses), support a scenario that involves new functional mutations selected for adaptation during domestication. Moreover, consistent with this hypothesis, selection analysis and the possibility to compare data obtained for the same genes in different studies of varying sizes, data types, and methodologies allowed us to identify four genes that were strongly selected during domestication. Each selection candidate is involved in plant resistance/tolerance to abiotic stresses, such as heat, drought, and salinity. Overall, our study suggests that domestication acted to increase functional diversity at target loci, which probably controlled traits related to expansion and adaptation to new agro-ecological growing conditions.

  • 7.
    Bollhöner, Benjamin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Jokipii-Lukkari, Soile
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Bygdell, Joakim
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Stael, Simon
    Adriasola, Mathilda
    Muñiz, Luis
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Van Breusegem, Frank
    Ezcurra, Inés
    Wingsle, Gunnar
    Tuominen, Hannele
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    The function of two type II metacaspases in woody tissues of Populus trees2018In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 217, no 4, p. 1551-1565Article in journal (Refereed)
    Abstract [en]

    Metacaspases (MCs) are cysteine proteases that are implicated in programmed cell death of plants. AtMC9 (Arabidopsis thaliana Metacaspase9) is a member of the Arabidopsis MC family that controls the rapid autolysis of the xylem vessel elements, but its downstream targets in xylem remain uncharacterized. PttMC13 and PttMC14 were identified as AtMC9 homologs in hybrid aspen (Populustremulaxtremuloides). A proteomic analysis was conducted in xylem tissues of transgenic hybrid aspen trees which carried either an overexpression or an RNA interference construct for PttMC13 and PttMC14. The proteomic analysis revealed modulation of levels of both previously known targets of metacaspases, such as Tudor staphylococcal nuclease, heat shock proteins and 14-3-3 proteins, as well as novel proteins, such as homologs of the PUTATIVE ASPARTIC PROTEASE3 (PASPA3) and the cysteine protease RD21 by PttMC13 and PttMC14. We identified here the pathways and processes that are modulated by PttMC13 and PttMC14 in xylem tissues. In particular, the results indicate involvement of PttMC13 and/or PttMC14 in downstream proteolytic processes and cell death of xylem elements. This work provides a valuable reference dataset on xylem-specific metacaspase functions for future functional and biochemical analyses.

  • 8.
    Boutté, Yohann
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Frescatada-Rosa, Márcia
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Men, Shuzhen
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Chow, Cheung-Ming
    Ebine, Kazuo
    Gustavsson, Anna
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Johansson, Lenore
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Ueda, Takashi
    Moore, Ian
    Jürgens, Gerd
    Grebe, Markus
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Endocytosis restricts Arabidopsis KNOLLE syntaxin to the cell division plane during late cytokinesis2010In: EMBO Journal, ISSN 0261-4189, E-ISSN 1460-2075, Vol. 29, no 3, p. 546-58Article in journal (Refereed)
    Abstract [en]

    Cytokinesis represents the final stage of eukaryotic cell division during which the cytoplasm becomes partitioned between daughter cells. The process differs to some extent between animal and plant cells, but proteins of the syntaxin family mediate membrane fusion in the plane of cell division in diverse organisms. How syntaxin localization is kept in check remains elusive. Here, we report that localization of the Arabidopsis KNOLLE syntaxin in the plane of cell division is maintained by sterol-dependent endocytosis involving a clathrin- and DYNAMIN-RELATED PROTEIN1A-dependent mechanism. On genetic or pharmacological interference with endocytosis, KNOLLE mis-localizes to lateral plasma membranes after cell-plate fusion. Fluorescence-loss-in-photo-bleaching and fluorescence-recovery-after-photo-bleaching experiments reveal lateral diffusion of GFP-KNOLLE from the plane of division to lateral membranes. In an endocytosis-defective sterol biosynthesis mutant displaying lateral KNOLLE diffusion, KNOLLE secretory trafficking remains unaffected. Thus, restriction of lateral diffusion by endocytosis may serve to maintain specificity of syntaxin localization during late cytokinesis.

  • 9.
    Bygdell, Joakim
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Srivastava, Vaibhav
    Obudulu, Ogonna
    Srivastava, Manoj K.
    Nilsson, Robert
    Sundberg, Björn
    Trygg, Johan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Mellerowicz, Ewa J.
    Wingsle, Gunnar
    Protein expression in tension wood formation monitored at high tissue resolution in Populus2017In: Journal of Experimental Botany, ISSN 0022-0957, E-ISSN 1460-2431, Vol. 68, no 13, p. 3405-3417Article in journal (Refereed)
    Abstract [en]

    Tension wood (TW) is a specialized tissue with contractile properties that is formed by the vascular cambium in response to gravitational stimuli. We quantitatively analysed the proteomes of Populus tremula cambium and its xylem cell derivatives in stems forming normal wood (NW) and TW to reveal the mechanisms underlying TW formation. Phloem-, cambium-, and wood-forming tissues were sampled by tangential cryosectioning and pooled into nine independent samples. The proteomes of TW and NW samples were similar in the phloem and cambium samples, but diverged early during xylogenesis, demonstrating that reprogramming is an integral part of TW formation. For example, 14-3-3, reactive oxygen species, ribosomal and ATPase complex proteins were found to be up-regulated at early stages of xylem differentiation during TW formation. At later stages of xylem differentiation, proteins involved in the biosynthesis of cellulose and enzymes involved in the biosynthesis of rhamnogalacturonan-I, rhamnogalacturonan-II, arabinogalactan-II and fasciclin-like arabinogalactan proteins were up-regulated in TW. Surprisingly, two isoforms of exostosin family proteins with putative xylan xylosyl transferase function and several lignin biosynthesis proteins were also up-regulated, even though xylan and lignin are known to be less abundant in TW than in NW. These data provided new insight into the processes behind TW formation.

  • 10.
    Chen, Yang-Er
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry. College of Life Sciences, Sichuan Agricultural University, Ya'an, China.
    Yuan, Shu
    Schröder, Wolfgang P.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Comparison of methods for extracting thylakoid membranes of Arabidopsis plants2016In: Physiologia Plantarum: An International Journal for Plant Biology, ISSN 0031-9317, E-ISSN 1399-3054, Vol. 156, no 1, p. 3-12Article in journal (Refereed)
    Abstract [en]

    Robust and reproducible methods for extracting thylakoid membranes are required for the analysis of photosynthetic processes in higher plants such as Arabidopsis. Here, we compare three methods for thylakoid extraction using two different buffers. Method I involves homogenizing the plant material witha metal/glass blender; method II involves manually grinding the plant materialin ice-cold grinding buffer with a mortar and method III entails snap-freezing followed by manual grinding with a mortar, after which the frozen powder is thawed in isolation buffer. Thylakoid membrane samples extracted using each method were analyzed with respect to protein and chlorophyll content, yields relative to starting material, oxygen-evolving activity, protein complex content and phosphorylation. We also examined how the use of fresh and frozen thylakoid material affected the extracts’ contents of protein complexes. The use of different extraction buffers did not significantly alter the protein contentof the extracts in any case. Method I yielded thylakoid membranes with the highest purity and oxygen-evolving activity. Method III used low amounts of starting material and was capable of capturing rapid phosphorylation changes in the sample at the cost of higher levels of contamination. Method II yielded thylakoid membrane extracts with properties intermediate between those obtained with the other two methods. Finally, frozen and freshly isolated thylakoid membranes performed identically in blue native-polyacrylamide gel electrophoresis experiments conducted in order to separate multimeric protein supracomplexes.

  • 11. Chow, Wah Soon
    et al.
    Lee, Hae-Youn
    He, Jie
    Hendrickson, Luke
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Research School of Biological Sciences, Australian National University, GPO Box 475, Canberra, ACT 2601, Australia.
    Hong, Young-Nam
    Matsubara, Shizue
    Photoinactivation of photosystem II in leaves2005In: Photosynthesis Research, ISSN 0166-8595, E-ISSN 1573-5079, Vol. 84, no 1-3, p. 35-41Article in journal (Refereed)
    Abstract [en]

    Photoinactivation of Photosystem II (PS II), the light-induced loss of ability to evolve oxygen, inevitably occurs under any light environment in nature, counteracted by repair. Under certain conditions, the extent of photoinactivation of PS II depends on the photon exposure (light dosage, x), rather than the irradiance or duration of illumination per se, thus obeying the law of reciprocity of irradiance and duration of illumination, namely, that equal photon exposure produces an equal effect. If the probability of photoinactivation (p) of PS II is directly proportional to an increment in photon exposure (p = kDeltax, where k is the probability per unit photon exposure), it can be deduced that the number of active PS II complexes decreases exponentially as a function of photon exposure: N = Noexp(-kx). Further, since a photon exposure is usually achieved by varying the illumination time (t) at constant irradiance (I), N = Noexp(-kI t), i.e., N decreases exponentially with time, with a rate coefficient of photoinactivation kI, where the product kI is obviously directly proportional to I. Given that N = Noexp(-kx), the quantum yield of photoinactivation of PS II can be defined as -dN/dx = kN, which varies with the number of active PS II complexes remaining. Typically, the quantum yield of photoinactivation of PS II is ca. 0.1micromol PS II per mol photons at low photon exposure when repair is inhibited. That is, when about 10(7) photons have been received by leaf tissue, one PS II complex is inactivated. Some species such as grapevine have a much lower quantum yield of photoinactivation of PS II, even at a chilling temperature. Examination of the longer-term time course of photoinactivation of PS II in capsicum leaves reveals that the decrease in N deviates from a single-exponential decay when the majority of the PS II complexes are inactivated in the absence of repair. This can be attributed to the formation of strong quenchers in severely-photoinactivated PS II complexes, able to dissipate excitation energy efficiently and to protect the remaining active neighbours against damage by light.

  • 12.
    Decker, Daniel
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    UDP-sugar metabolizing pyrophosphorylases in plants: formation of precursors for essential glycosylation-reactions2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    UDP-sugar metabolizing pyrophosphorylases provide the primary mechanism for de novo synthesis of UDP-sugars, which can then be used for myriads of glycosyltranferase reactions, producing cell wall carbohydrates, sucrose, glycoproteins and glycolipids, as well as many other glycosylated compounds. The pyrophosphorylases can be divided into three families: UDP-Glc pyrophosphorylase (UGPase), UDP-sugar pyrophosphorylase (USPase) and UDP-N-acety lglucosamine pyrophosphorylase (UAGPase), which can be discriminated both by differences in accepted substrate range and amino acid sequences.

    This thesis focuses both on experimental examination (and re-examination) of some enzymatic/ biochemical properties of selected members of the UGPases and USPases and UAGPase families and on the design and implementation of a strategy to study in vivo roles of these pyrophosphorylases using specific inhibitors. In the first part, substrate specificities of members of the Arabidopsis UGPase, USPase and UAGPase families were comprehensively surveyed and kinetically analyzed, with barley UGPase also further studied with regard to itspH dependency, regulation by oligomerization, etc. Whereas all the enzymes preferentially used UTP as nucleotide donor, they differed in their specificity for sugar-1-P. UGPases had high activity with D-Glc-1-P, but could also react with Frc-1-P, whereas USPase reacted with arange of sugar-1-phosphates, including D-Glc-1-P, D-Gal-1-P, D-GalA-1-P, β-L-Ara-1-P and α-D-Fuc-1-P. In contrast, UAGPase2 reacted only with D-GlcNAc-1-P, D-GalNAc-1-P and, to some extent, with D-Glc-1-P. A structure activity relationship was established to connect enzyme activity, the examined sugar-1-phosphates and the three pyrophosphorylases. The UGPase/USPase/UAGPase active sites were subsequently compared in an attempt to identify amino acids which may contribute to the experimentally determined differences in substrate specificities.

    The second part of the thesis deals with identification and characterization of inhibitors of the pyrophosphorylases and with studies on in vivo effects of those inhibitors in Arabidopsis-based systems. A novel luminescence-based high-throughput assay system was designed, which allowed for quantitative measurement of UGPase and USPase activities, down to a pmol per min level. The assay was then used to screen a chemical library (which contained 17,500 potential inhibitors) to identify several compounds affecting UGPase and USPase. Hit-optimization on one of the compounds revealed even stronger inhibitors of UGPase and USPase which also strongly inhibited Arabidopsis pollen germination, by disturbing UDP-sugar metabolism. The inhibitors may represent useful tools to study in vivo roles of the pyrophosphorylases, as a complement to previous genetics-based studies.

    The thesis also includes two review papers on mechanisms of synthesis of NDP-sugars. The first review covered the characterization of USPase from both prokaryotic and eukaryotic organisms, whereas the second review was a comprehensive survey of NDP-sugar producing enzymes (not only UDP-sugar producing and not only pyrophosphorylases). All these enzymes were discussed with respect to their substrate specificities and structural features (if known) and their proposed in vivo functions.

  • 13.
    Decker, Daniel
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Öberg, Christopher
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Kleczkowski, Leszek A.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Identification and characterization of inhibitors of UDP-glucose and UDP-sugar pyrophosphorylases for in vivo studies2017In: The Plant Journal, ISSN 0960-7412, E-ISSN 1365-313X, Vol. 90, no 6, p. 1093-1107Article in journal (Other academic)
    Abstract [en]

    UDP-sugars serve as ultimate precursors in hundreds of glycosylation reactions (e.g. for protein and lipid glycosylation, synthesis of sucrose, cell wall polysaccharides, etc.), underlying an important role of UDP-sugar-producing enzymes in cellular metabolism. However, genetic studies on mechanisms of UDP-sugar formation were frequently hampered by reproductive impairment of the resulting mutants, making it difficult to assess an in vivo role of a given enzyme. Here, a chemical library containing 17 500 compounds was separately screened against purified UDP-glucose pyrophosphorylase (UGPase) and UDP-sugar pyrophosphorylase (USPase), both enzymes representing the primary mechanisms of UDP-sugar formation. Several compounds have been identified which, at 50 μm, exerted at least 50% inhibition of the pyrophosphorylase activity. In all cases, both UGPase and USPase activities were inhibited, probably reflecting common structural features of active sites of these enzymes. One of these compounds (cmp #6), a salicylamide derivative, was found as effective inhibitor of Arabidopsis pollen germination and Arabidopsis cell culture growth. Hit optimization on cmp #6 yielded two analogs (cmp #6D and cmp #6D2), which acted as uncompetitive inhibitors against both UGPase and USPase, and were strong inhibitors in the pollen test, with apparent inhibition constants of less than 1 μm. Their effects on pollen germination were relieved by addition of UDP-glucose and UDP-galactose, suggesting that the inhibitors targeted UDP-sugar formation. The results suggest that cmp #6 and its analogs may represent useful tools to study in vivo roles of the pyrophosphorylases, helping to overcome the limitations of genetic approaches.

  • 14.
    Dobrenel, Thomas
    et al.
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Institut Jean-Pierre Bourgin, Institut National de la Recherche Agronomique, AgroParisTech, Centre National de la Recherche Scientifique, Université Paris-Saclay, Versailles, France; Université Paris-Sud–Université Paris-Saclay, Orsay, France.
    Mancera-Martinez, Eder
    Forzani, Celine
    Azzopardi, Marianne
    Davanture, Marlene
    Moreau, Manon
    Schepetilnikov, Mikhail
    Chicher, Johana
    Langella, Olivier
    Zivy, Michel
    Robaglia, Christophe
    Ryabova, Lyubov A.
    Hanson, Johannes
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Meyer, Christian
    The Arabidopsis TOR Kinase Specifically Regulates the Expression of Nuclear Genes Coding for Plastidic Ribosomal Proteins and the Phosphorylation of the Cytosolic Ribosomal Protein S62016In: Frontiers in Plant Science, ISSN 1664-462X, E-ISSN 1664-462X, Vol. 7, article id 1611Article in journal (Refereed)
    Abstract [en]

    Protein translation is an energy consuming process that has to be fine-tuned at both the cell and organism levels to match the availability of resources. The target of rapamycin kinase (TOR) is a key regulator of a large range of biological processes in response to environmental cues. In this study, we have investigated the effects of TOR inactivation on the expression and regulation of Arabidopsis ribosomal proteins at different levels of analysis, namely from transcriptomic to phosphoproteomic. TOR inactivation resulted in a coordinated down-regulation of the transcription and translation of nuclear-encoded mRNAs coding for plastidic ribosomal proteins, which could explain the chlorotic phenotype of the TOR silenced plants. We have identified in the 5' untranslated regions (UTRs) of this set of genes a conserved sequence related to the 5' terminal oligopyrimidine motif, which is known to confer translational regulation by the TOR kinase in other eukaryotes. Furthermore, the phosphoproteomic analysis of the ribosomal fraction following TOR inactivation revealed a lower phosphorylation of the conserved Ser240 residue in the C-terminal region of the 40S ribosomal protein S6 (RPS6). These results were confirmed by Western blot analysis using an antibody that specifically recognizes phosphorylated Ser240 in RPS6. Finally, this antibody was used to follow TOR activity in plants. Our results thus uncover a multi-level regulation of plant ribosomal genes and proteins by the TOR kinase.

  • 15.
    Erik, Edlund
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Regulatory Control of Autumn Senescence in Populus tremula2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Autumn senescence is a visually spectacular phenomenon in which trees prepare for the oncoming winter. The mechanism for regulation of autumn senescence in trees has been very hard to pinpoint. In this thesis the main focus is to investigate how autumn senescence is regulated in aspens (Populus tremula).

    Previous work has established that autumn senescence in aspens is under daylight control, in this thesis the metabolic status and the effect on autumn senescence was investigated. The metabolic status was altered by girdling which leads to accumulation of photosynthates in the canopy. This resulted in an earlier onset of senescence but also the speed of senescence was changed. At the onset of senescence the girdled trees also accumulated or retained anthocyanins.

    The nitrogen status of aspens during autumn senescence was also investigated, we found that high doses of fertilization could significantly delay the onset of senescence. The effects of various nitrogen forms was investigated by delivering organic and inorganic nitrogen through a precision fertilization delivery system that could inject solutes directly into the xylem of the mature aspens. The study showed that addition of nitrate delayed senescence, addition of arginine did not have any effect on the autumn senescence in aspens, and furthermore the nitrate altered the trees leaf metabolism that was more profound in high dosages of supplied nitrate. 

    Cytokinins are plant hormones believed to delay or block senescence, studies have suggested that the decrease of cytokinins and/or cytokinin signalling may precede senescence in some plants. To investigate how cytokinin regulates autumn senescence in aspens we profiled 34 cytokinin types in a free growing mature aspen. The study begun before autumn senescence was initiated and ended with the shedding of the leaves, and spanned three consecutive years. The study showed that the individual cytokinin profiles varied significantly between the years, this despite that senescence was initiated at the same time each year. Senescence was furthermore not connected to the depletion of either active or total cytokinins levels. The gene pattern of genes known to be associated with cytokinin was also studied, but no gene expression pattern that the profile generated could explain the onset of senescence. These results suggest that the depletion of cytokinins is unlikely to explain the tightly regulated onset of autumn leaf senescence in aspen.

  • 16.
    Escamez, Sacha
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Latha Gandla, Madhavi
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Derba-Maceluch, Marta
    Lundqvist, Sven-Olof
    Mellerowicz, Ewa J.
    Jönsson, Leif J.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Tuominen, Hannele
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    A collection of genetically engineered Populus trees reveals wood biomass traits that predict glucose yield from enzymatic hydrolysis2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 15798Article in journal (Refereed)
    Abstract [en]

    Wood represents a promising source of sugars to produce bio-based renewables, including biofuels. However, breaking down lignocellulose requires costly pretreatments because lignocellulose is recalcitrant to enzymatic saccharification. Increasing saccharification potential would greatly contribute to make wood a competitive alternative to petroleum, but this requires improving wood properties. To identify wood biomass traits associated with saccharification, we analyzed a total of 65 traits related to wood chemistry, anatomy and structure, biomass production and saccharification in 40 genetically engineered Populus tree lines. These lines exhibited broad variation in quantitative traits, allowing for multivariate analyses and mathematical modeling. Modeling revealed that seven wood biomass traits associated in a predictive manner with saccharification of glucose after pretreatment. Four of these seven traits were also negatively associated with biomass production, suggesting a trade-off between saccharification potential and total biomass, which has previously been observed to offset the overall sugar yield from whole trees. We therefore estimated the "total-wood glucose yield" (TWG) from whole trees and found 22 biomass traits predictive of TWG after pretreatment. Both saccharification and TWG were associated with low abundant, often overlooked matrix polysaccharides such as arabinose and rhamnose which possibly represent new markers for improved Populus feedstocks.

  • 17. Felten, Judith
    et al.
    Kohler, Annegret
    Morin, Emmanuelle
    Bhalerao, Rishikesh P
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Palme, Klaus
    Martin, Francis
    Ditengou, Franck A
    Legue, Valerie
    The ectomycorrhizal fungus laccaria bicolor stimulates lateral root formation in poplar and arabidopsis through auxin transport and signaling2009In: Plant Physiology, ISSN 0032-0889, E-ISSN 1532-2548, Vol. 151, no 4, p. 1991-2005Article in journal (Refereed)
    Abstract [en]

    The early phase of the interaction between tree roots and ectomycorrhizal fungi, prior to symbiosis establishment, is accompanied by a stimulation of lateral root (LR) development. We aimed to identify gene networks that regulate LR development during the early signal exchanges between poplar (Populus tremula x Populus alba) and the ectomycorrhizal fungus Laccaria bicolor with a focus on auxin transport and signaling pathways. Our data demonstrated that increased LR development in poplar and Arabidopsis (Arabidopsis thaliana) interacting with L. bicolor is not dependent on the ability of the plant to form ectomycorrhizae. LR stimulation paralleled an increase in auxin accumulation at root apices. Blocking plant polar auxin transport with 1-naphthylphthalamic acid inhibited LR development and auxin accumulation. An oligoarray-based transcript profile of poplar roots exposed to molecules released by L. bicolor revealed the differential expression of 2,945 genes, including several components of polar auxin transport (PtaPIN and PtaAUX genes), auxin conjugation (PtaGH3 genes), and auxin signaling (PtaIAA genes). Transcripts of PtaPIN9, the homolog of Arabidopsis AtPIN2, and several PtaIAAs accumulated specifically during the early interaction phase. Expression of these rapidly induced genes was repressed by 1-naphthylphthalamic acid. Accordingly, LR stimulation upon contact with L. bicolor in Arabidopsis transgenic plants defective in homologs of these genes was decreased or absent. Furthermore, in Arabidopsis pin2, the root apical auxin increase during contact with the fungus was modified. We propose a model in which fungus-induced auxin accumulation at the root apex stimulates LR formation through a mechanism involving PtaPIN9-dependent auxin redistribution together with PtaIAA-based auxin signaling.

  • 18. Gauslaa, Yngvar
    et al.
    Palmqvist, Kristin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Solhaug, Knut Asbjørn
    Hilmo, Olga
    Holien, Håkon
    Nybakken, Line
    Ohlson, Mikael
    Size-dependent growth of two old-growth associated macrolichen species2009In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 181, no 3, p. 683-692Article in journal (Refereed)
    Abstract [en]

    Relationships between thallus size and growth variables were analysed for the foliose Lobaria pulmonaria and the pendulous Usnea longissima with the aim of elucidating their morphogenesis and the factors determining thallus area (A) versus biomass (dry weight (DW) gain. Size and growth data originated from a factorial transplantation experiment that included three boreal climate zones (Atlantic, suboceanic and continental), each with three successional forest stands (clear-cut, young and old). When A was replaced by the estimated photobiont layer area in an area-DW scatterplot including all thalli (n = 1080), the two separate species clusters merged into one, suggesting similar allocation patterns between photobionts and mycobionts across growth forms. During transplantation, stand-specific water availability boosted area gain in foliose transplants, consistent with a positive role of water in fungal expansion. In pendulous lichens, A gain greatly exceeded DW gain, particularly in small transplants. The A gain in U. longissima increased with increasing DW:A ratio, consistent with a reallocation of carbon, presumably mobilized from the dense central chord. Pendulous lichens with cylindrical photobiont layers harvest light from all sides. Rapid and flexible three-dimensional A gain allows the colonization of spaces between canopy branches to utilize temporary windows of light in a growing canopy. Foliose lichens with a two-dimensional photobiont layer have more coupled A and DW gains.

  • 19. Granado-Yela, C
    et al.
    García-Verdugo, C
    Carrillo, K
    Rubio DE Casas, R
    Kleczkowski, Leszek A
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Balaguer, L
    Temporal matching among diurnal photosynthetic patterns within the crown of the evergreen sclerophyll Olea europaea L2011In: Plant, Cell and Environment, ISSN 0140-7791, E-ISSN 1365-3040, Vol. 34, no 5, p. 800-810Article in journal (Refereed)
    Abstract [en]

    Trees are modular organisms that adjust their within-crown morphology and physiology in response to within-crown light gradients. However, whether within-plant variation represents a strategy for optimizing light absorption has not been formally tested. We investigated the arrangement of the photosynthetic surface throughout one day and its effects on the photosynthetic process, at the most exposed and most sheltered crown layers of a wild olive tree (Olea europaea L.). Similar measurements were made for cuttings taken from this individual and grown in a greenhouse at contrasted irradiance-levels (100 and 20% full sunlight). Diurnal variations in light interception, carbon fixation and carbohydrate accumulation in sun leaves were negatively correlated with those in shade leaves under field conditions when light intensity was not limiting. Despite genetic identity, these complementary patterns were not found in plants grown in the greenhouse. The temporal disparity among crown positions derived from specialization of the photosynthetic behaviour at different functional and spatial scales: architectural structure (crown level) and carbon budget (leaf level). Our results suggest that the profitability of producing a new module may not only respond to construction costs or light availability, but also rely on its spatio-temporal integration within the productive processes at the whole-crown level.

  • 20. Hartmann, Laura
    et al.
    Pedrotti, Lorenzo
    Weiste, Christoph
    Fekete, Agnes
    Schierstaedt, Jasper
    Göttler, Jasmin
    Kempa, Stefan
    Krischke, Markus
    Dietrich, Katrin
    Mueller, Martin J
    Vicente-Carbajosa, Jesus
    Hanson, Johannes
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Department of Molecular Plant Physiology, Utrecht University, The Netherlands .
    Dröge-Laser, Wolfgang
    Crosstalk between Two bZIP Signaling Pathways Orchestrates Salt-Induced Metabolic Reprogramming in Arabidopsis Roots2015In: The Plant Cell, ISSN 1040-4651, E-ISSN 1532-298X, Vol. 27, no 8, p. 2244-2260Article in journal (Refereed)
    Abstract [en]

    Soil salinity increasingly causes crop losses worldwide. Although roots are the primary targets of salt stress, the signaling networks that facilitate metabolic reprogramming to induce stress tolerance are less understood than those in leaves. Here, a combination of transcriptomic and metabolic approaches was performed in salt-treated Arabidopsis thaliana roots, which revealed that the group S1 basic leucine zipper transcription factors bZIP1 and bZIP53 reprogram primary C- and N-metabolism. In particular, gluconeogenesis and amino acid catabolism are affected by these transcription factors. Importantly, bZIP1 expression reflects cellular stress and energy status in roots. In addition to the well-described abiotic stress response pathway initiated by the hormone abscisic acid (ABA) and executed by SnRK2 (Snf1-RELATED-PROTEIN-KINASE2) and AREB-like bZIP factors, we identify a structurally related ABA-independent signaling module consisting of SnRK1s and S1 bZIPs. Crosstalk between these signaling pathways recruits particular bZIP factor combinations to establish at least four distinct gene expression patterns. Understanding this signaling network provides a framework for securing future crop productivity.

  • 21.
    Ishikawa, Yasuo
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Schröder, Wolfgang P
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Funk, Christiane
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Functional analysis of the PsbP-like protein (sll1418) in Synechocystis sp PCC 68032005In: Photosynthesis Research, ISSN 0166-8595, E-ISSN 1573-5079, Vol. 84, no 1-3, p. 257-262Article in journal (Refereed)
    Abstract [en]

    A recent proteomic analysis of the thylakoid lumen of Arabidopsis thaliana revealed the presence of several PsbP-like proteins, and a homologue to this gene family was detected in the genome of the cyanobacterium Synechocystis sp. PCC 6803 (Schubert M, Petersson UA, Haas BJ, Funk C, Schroder WP, Kieselbach T (2002) J Biol Chem 277, 8354-8365). Using a peptide-directed antibody against this cyanobacterial PsbP-like protein (sll1418) we could show that it was localized in the thylakoid membrane and associated with Photosystem II. While salt washes did not remove the PsbP-like protein from the thylakoid membrane, it was partially lost during the detergent-based isolation of PSII membrane fractions. In total cell extracts this protein is present in the same amount as the extrinsic PsbO protein. We did not see any significant functional difference between the wild-type and a PsbP-like insertion mutant.

  • 22.
    Jiao, Xiang
    et al.
    College of Mechanical and Electronic Engineering, Nanjing Forestry University.
    Zhang, Huichun
    College of Mechanical and Electronic Engineering, Nanjing Forestry University.
    Zheng, Jiaqiang
    College of Mechanical and Electronic Engineering, Nanjing Forestry University.
    Yin, Yue
    College of Mechanical and Electronic Engineering, Nanjing Forestry University.
    Wang, Guosu
    College of Mechanical and Electronic Engineering, Nanjing Forestry University.
    Chen, Ying
    College of Forestry, Nanjing Forestry University.
    Ge, Yufeng
    Department of Biological Systems Engineering, University of Nebraska-Lincoln.
    Yu, Jun
    Umeå University, Faculty of Science and Technology, Department of Mathematics and Mathematical Statistics.
    Comparative analysis of nonlinear growth curve models for Arabidopsis thaliana rosette leaves2018In: Acta Physiologiae Plantarum, ISSN 0137-5881, E-ISSN 1861-1664, Vol. 40, no 6, article id 114Article in journal (Refereed)
    Abstract [en]

    As a model organism, modeling and analysis of the phenotype of Arabidopsis thaliana (A. thaliana) leaves for a given genotype can help us better understand leaf growth regulation. A. thaliana leaves growth trajectories are to be nonlinear and the leaves contribute most to the above-ground biomass. Therefore, analysis of their change regulation and development of nonlinear growth models can better understand the phenotypic characteristics of leaves (e.g., leaf size) at different growth stages. In this study, every individual leaf size of A. thaliana rosette leaves was measured during their whole life cycle using non-destructive imaging measurement. And three growth models (Gompertz model, logistic model and Von Bertalanffy model) were analyzed to quantify the rosette leaves growth process of A. thaliana. Both graphical (plots of standardized residuals) and numerical measures (AIC, R2 and RMSE) were used to evaluate the fitted models. The results showed that the logistic model fitted better in describing the growth of A. thaliana leaves compared to Gompertz model and Von Bertalanffy model, as it gave higher R2 and lower AIC and RMSE for the leaves of A. thaliana at different growth stages (i.e., early leaf, mid-term leaf and late leaf).

  • 23.
    Johansson, Mikael
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    The circadian clock in annuals and perennials: coordination of Growth with Environmental Rhythms2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Since the first signs of life on planet earth, organisms have had to adapt to the daily changes between light and dark, and high and low temperatures. This has led to the evolution of an endogenous time keeper, known as the circadian clock. This biological timing system helps the organism to synchronize developmental and metabolic events to the most favorable time of the day. Such a mechanism is of considerable value to plants, since they in contrast to animals cannot change location when the environment becomes unfavorable. Thus is the ability to predict coming events of central importance in a plants life. This thesis is a study of the molecular machinery behind the clockwork in the small weed plant Arabidopsis thaliana as well as its close relative perennial; the woody species Populus. We have characterized a novel component of the circadian clock, EARLY BIRD (EBI). EBI is involved in transcriptional and translational regulation, via interaction with the known post-translational clock regulator ZEITLUPE (ZTL). In Populus, we describe the role of the circadian clock and its components with respect to entry and exit of dormancy and show that gene expression of the Populus LATE ELONATED HYPOCOTYL (LHY) genes are crucial importance for freezing tolerance and thereby survival at high latitudes. Furthermore, the input to the Populus clock is mediated via the phytochrome A (phyA) photoreceptor.

  • 24. Jonsell, Bengt
    et al.
    Ericsson, Stefan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Fröberg, Lars
    Rosta´nski, Krzysztof
    Snogerup, Sven
    Widen, Björn
    Nomenclatural notes to Flora Nordica Vol. 6 (Thymelaeaceae-Apiaceae)2009In: Nordic Journal of Botany, ISSN 0107-055X, E-ISSN 1756-1051, Vol. 27, no 2, p. 138-140Article in journal (Refereed)
    Abstract [en]

    The following names in Flora Nordica Vol. 6 are subject to nomenclatural action: Helianthemum oelandicum var. canescens (typified), Epilobium hornemannii (typified), Oenothera nuda (validated), Myriophyllum spicatum (emendation of typification), Viola rupestris subsp. relicta (typified), Hippophae rhamnoides (typified), Angelica archangelica subsp. littoralis (typified). - Flora Nordica Note no. 35.

  • 25.
    Klemenčič, Marina
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Funk, Christiane
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Department of Chemistry and Biochemistry, Faculty of Chemistry and Chemical Technology, University of Ljubljana, Vecna pot 113, SI-1000 Ljubljana, Slovenia.
    Type III metacaspases: calcium-dependent activity proposes new function for the p10 domain2018In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 218, no 3 Special issue, p. 1179-1191Article in journal (Refereed)
    Abstract [en]

    Metacaspases are a subgroup of caspase homologues represented in bacteria, algae and plants. Although type I and type II metacaspases are present in plants, recently discovered and uncharacterized type III metacaspases can only be found in algae which have undergone secondary endosymbiosis. We analysed the expression levels of all 13 caspase homologues in the cryptophyte Guillardia theta in vivo and biochemically characterized its only type III metacaspase, GtMC2, in vitro. Type III metacaspase GtMC2 was shown to be an endopeptidase with a preference for basic amino acids in the P1 position, which exhibited specific N-terminal proteolytic cleavage for full catalytic efficiency. Autolytic processing, as well as the activity of the mature enzyme, required the presence of calcium ions in low millimolar concentrations. In GtMC2, two calcium-binding sites were identified, one with a dissociation constant at low and the other at high micromolar concentrations. We show high functional relatedness of type III metacaspases to type I metacaspases. Moreover, our data suggest that the low-affinity calcium-binding site is located in the p10 domain, which contains a well-conserved N-terminal region. This region can only be found in type I/II/III metacaspases, but is absent in calcium-independent caspase homologues.

  • 26. Klenell, Markus
    et al.
    Morita, Shigeto
    Tiemblo-Olmo, Mercedes
    Mühlenbock, Per
    Karpinski, Stanislaw
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Department of Botany, Stockholm University, SE-106 91 Stockholm, Sweden .
    Karpinska, Barbara
    Involvement of the chloroplast signal recognition particle cpSRP43 in acclimation to conditions promoting photooxidative stress in Arabidopsis2005In: Plant and Cell Physiology, ISSN 0032-0781, E-ISSN 1471-9053, Vol. 46, no 1, p. 118-129Article in journal (Refereed)
    Abstract [en]

    In this study, we have investigated the role of the CAO gene (coding for the chloroplast recognition particle cpSRP43) in the protection against and acclimation to environmental conditions that promote photooxidative stress. Deficiency of cpSRP43 in the Arabidopsis mutant chaos has been shown previously to lead to partial loss of a number of proteins of the photosystem II (PSII) antennae. In addition, as reported here, mutant plants have lower growth rates and reduced lignin contents under laboratory conditions. However, chaos seedlings showed significantly higher tolerance to photooxidative stress under both tightly controlled laboratory conditions and highly variable conditions in the field. This greater tolerance of chaos plants was manifested in less photooxidative damage together with faster growth recovery in young seedlings. It was also associated with a lower production of H2O2, lower ascorbate levels and less induction of ascorbate peroxidases. Under field conditions, chaos exhibited better overall photosynthetic performance and had higher survival rates. Expression of the CAO gene may be regulated by a light-dependent chloroplastic redox signalling pathway, and was inhibited during acclimation to high light and chilling temperatures, simultaneously with induction of ascorbate peroxidases. It is concluded that the presence/absence of the CAO gene has an impact on photo-produced H2O2, lignification in the hypocotyls and on the plant's susceptibility to photooxidative stress. Therefore, regulation of the CAO gene may be part of the plant's system for acclimation to high light and chilling temperatures.

  • 27.
    Kloth, Karen J.
    et al.
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Laboratory of Entomology, Wageningen University, 6700 AA Wageningen, The Netherlands; Laboratory of Plant Physiology, Wageningen University, 6700 AA Wageningen, The Netherlands; Bioscience, Wageningen University & Research, 6708 PB Wageningen, The Netherlands.
    Busscher-Lange, Jacqueline
    Wiegers, Gerrie L.
    Kruijer, Willem
    Buijs, Gonda
    Meyer, Rhonda C.
    Albrectsen, Benedicte R.
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Bouwmeester, Harro J.
    Dicke, Marcel
    Jongsma, Maarten A.
    SIEVE ELEMENT-LINING CHAPERONE1 Restricts Aphid Feeding on Arabidopsis during Heat Stress2017In: The Plant Cell, ISSN 1040-4651, E-ISSN 1532-298X, Vol. 29, no 10, p. 2450-2464Article in journal (Refereed)
    Abstract [en]

    The role of phloem proteins in plant resistance to aphids is still largely elusive. By genome-wide association mapping of aphid behavior on 350 natural Arabidopsis thaliana accessions, we identified the small heat shock-like SIEVE ELEMENT-LINING CHAPERONE1 (SLI1). Detailed behavioral studies on near-isogenic and knockout lines showed that SLI1 impairs phloem feeding. Depending on the haplotype, aphids displayed a different duration of salivation in the phloem. On sli1 mutants, aphids prolonged their feeding sessions and ingested phloem at a higher rate than on wild-type plants. The largest phenotypic effects were observed at 26 degrees C, when SLI1 expression is upregulated. At this moderately high temperature, sli1 mutants suffered from retarded elongation of the inflorescence and impaired silique development. Fluorescent reporter fusions showed that SLI1 is confined to the margins of sieve elements where it lines the parietal layer and colocalizes in spherical bodies around mitochondria. This localization pattern is reminiscent of the clamp-like structures observed in previous ultrastructural studies of the phloem and shows that the parietal phloem layer plays an important role in plant resistance to aphids and heat stress.

  • 28.
    Kullman, Leif
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Alpine flora dynamics: a critical review of responses to climate change in the Swedish Scandes since the early 1950s2010In: Nordic Journal of Botany, ISSN 0107-055X, E-ISSN 1756-1051, Vol. 28, no 4, p. 398-408Article in journal (Refereed)
    Abstract [en]

    Reports about changes of alpine plant species richness over the past 60 years in the Swedish Scandes are reviewed, synthesized and updated with data from recent reinventories. Methodologically, this endeavour is based on resurveys of the floristic composition on the uppermost 20 m of four high-mountain summits. The key finding is that the species pool has increased by 60-170% since the 1950s and later. Some of the invading species are new to the alpine tundra, with more silvine and thermophilic properties than the extant alpine flora. Not a single species of the original flora has disappeared from any of the summits. This circumstance is discussed in perspective of widespread expectations of pending temperature-driven extinction of alpine species in an alleged future warmer climate. These progressive changes coincided with distinct warming (summer and winter) since the late 1980s. During a short cooler period (1974-1994), the species numbers decreased and the upper elevational limits of some ground cover species descended. Thus, discernible responses, concurrent with both warming and cooling intervals, sustain a strong causal link between climate variability and alpine plant species richness. Methodologically, plot-less revisitation studies of the present kind are beset with substantial uncertainties, which may overstate floristic changes over time. However, it is argued here that carefully executed and critically interpreted, no other method can equally effectively sense the earliest phases of plant invasions into alpine vegetation.

  • 29. Le Hir, Rozenn
    et al.
    Castelain, Mathieu
    Chakraborti, Dipankar
    Moritz, Thomas
    Dinant, Sylvie
    Bellini, Catherine
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Institut Jean-Pierre Bourgin, INRA, AgroParisTech, CNRS, Université Paris-Saclay, Versailles, France.
    AtbHLH68 transcription factor contributes to the regulation of ABA homeostasis and drought stress tolerance in Arabidopsis thaliana2017In: Physiologia Plantarum: An International Journal for Plant Biology, ISSN 0031-9317, E-ISSN 1399-3054, Vol. 160, no 3, p. 312-327Article in journal (Refereed)
    Abstract [en]

    Basic helix-loop-helix (bHLH) transcription factors are involved in a wide range of developmental processes and in response to biotic and abiotic stresses. They represent one of the biggest families of transcription factors but only few of them have been functionally characterized. Here we report the characterization of AtbHLH68 and show that, although the knock out mutant did not have an obvious development phenotype, it was slightly more sensitive to drought stress than the Col-0, and AtbHLH68 overexpressing lines displayed defects in lateral root (LR) formation and a significant increased tolerance to drought stress, likely related to an enhanced sensitivity to abscisic acid (ABA) and/or increased ABA content. AtbHLH68 was expressed in the vascular system of Arabidopsis and its expression was modulated by exogenously applied ABA in an organ-specific manner. We showed that the expression of genes involved in ABA metabolism [AtAAO3 (AtALDEHYDE OXIDASE 3) and AtCYP707A3 (AtABSCISIC ACID 8HYDROXYLASE 3)], in ABA-related response to drought-stress (AtMYC2, AtbHLH122 and AtRD29A) or during LRs development (AtMYC2 and AtABI3) was de-regulated in the overexpressing lines. We propose that AtbHLH68 has a function in the regulation of LR elongation, and in the response to drought stress, likely through an ABA-dependent pathway by regulating directly or indirectly components of ABA signaling and/or metabolism.

  • 30.
    Liebsch, Daniela
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Keech, Olivier
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Dark-induced leaf senescence: new insights into a complex light-dependent regulatory pathway2016In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 212, no 3, p. 563-570Article, review/survey (Refereed)
    Abstract [en]

    Leaf senescence - the coordinated, active process leading to the organized dismantling of cellular components to remobilize resources - is a fundamental aspect of plant life. Its tight regulation is essential for plant fitness and has crucial implications for the optimization of plant productivity and storage properties. Various investigations have shown light deprivation and light perception via phytochromes as key elements modulating senescence. However, the signalling pathways linking light deprivation and actual senescence processes have long remained obscure. Recent analyses have demonstrated that PHYTOCHROME-INTERACTING FACTORS (PIFs) are major transcription factors orchestrating dark-induced senescence (DIS) by targeting chloroplast maintenance, chlorophyll metabolism, hormone signalling and production, and the expression of senescence master regulators, uncovering potential molecular links to the energy deprivation signalling pathway. PIF-dependent feed-forward regulatory modules might be of critical importance for the highly complex and initially light-reversible DIS induction.

  • 31.
    Mauriat, Melanie
    et al.
    Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, Umeå, Sweden ; Institut National de la Recherche Agronomique, Cestas Cedex, France.
    Petterle, Anna
    Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Bellini, Catherine
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Institut Jean-Pierre Bourgin, UMR 1318 INRA–AgroParisTech, Institut National de la Recherche Agronomique Centre de Versailles–Grignon, Versailles Cedex, France.
    Moritz, Thomas
    Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Gibberellins inhibit adventitious rooting in hybrid aspen and Arabidopsis by affecting auxin transport2014In: The Plant Journal, ISSN 0960-7412, E-ISSN 1365-313X, Vol. 78, no 3, p. 372-384Article in journal (Refereed)
    Abstract [en]

    Knowledge of processes involved in adventitious rooting is important to improve both fundamental understanding of plant physiology and the propagation of numerous plants. Hybrid aspen (Populus tremula x tremuloides) plants overexpressing a key gibberellin (GA) biosynthesis gene (AtGA20ox1) grow rapidly but have poor rooting efficiency, which restricts their clonal propagation. Therefore, we investigated the molecular basis of adventitious rooting in Populus and the model plant Arabidopsis. The production of adventitious roots (ARs) in tree cuttings is initiated from the basal stem region, and involves the interplay of several endogenous and exogenous factors. The roles of several hormones in this process have been characterized, but the effects of GAs have not been fully investigated. Here, we show that a GA treatment negatively affects the numbers of ARs produced by wild-type hybrid aspen cuttings. Furthermore, both hybrid aspen plants and intact Arabidopsis seedlings overexpressing AtGA20ox1, PttGID1.1 or PttGID1.3 genes (with a 35S promoter) produce few ARs, although ARs develop from the basal stem region of hybrid aspen and the hypocotyl of Arabidopsis. In Arabidopsis, auxin and strigolactones are known to affect AR formation. Our data show that the inhibitory effect of GA treatment on adventitious rooting is not mediated by perturbation of the auxin signalling pathway, or of the strigolactone biosynthetic and signalling pathways. Instead, GAs appear to act by perturbing polar auxin transport, in particular auxin efflux in hybrid aspen, and both efflux and influx in Arabidopsis.

  • 32. Merritt, David M.
    et al.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Roland
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Consequences of propagule dispersal and river fragmentation for riparian plant community diversity and turnover2010In: Ecological Monographs, ISSN 0012-9615, E-ISSN 1557-7015, Vol. 80, no 4, p. 609-626Article in journal (Refereed)
    Abstract [en]

    The spatial distribution and temporal availability of propagules fundamentallyconstrain plant community development. This study experimentally tested several hypothesesabout the relative roles of wind and water dispersal in colonization and development ofriparian communities along rivers. Through controlling the source of propagules (dispersed bywind, water, or both) reaching newly created, bare river margin sites, we isolated the relativeroles of dispersal and other factors in plant community development over five years.Replicated treatments were established at 12 sites spanning 400 km along two adjacent riversin northern Sweden, one fragmented by a series of dams, the other free-flowing. Bare rivermargins receiving only water-dispersed propagules had significantly higher species richnesscompared to plots receiving only wind-dispersed propagules during the initial two years ofcolonization. Species richness increased annually throughout the study along tranquil andturbulent reaches of the free-flowing river but reached an asymptote at comparatively lowrichness after a single year on the impounded river. Propagule source strongly influencedspecies richness during the initial establishment along both rivers, with richness beingsignificantly higher in plots receiving water-dispersed seeds. This strong treatment effectcontinued to be important through time along the regulated river but diminished inimportance along the free-flowing river where other factors such as soil moisture, lightavailability, and exposure of sites to fluvial disturbance overshadowed the influence ofdispersal pathway in mediating species richness. This suggests that hydrochory (plantdispersal by water) may be more important for maintenance of diversity in regulated systemswhere long-distance dispersal is absent or negligible, but that the rich local propagule sourcealong free-flowing rivers supports high species richness. The number of unique species washigher in water-dispersal plots along both the regulated and free-flowing rivers. This resultsuggests that hydrochory may contribute to temporal variability of sites, may enhance richnessover time, and may have an important role in meta-population and meta-communitydynamics of plant communities through long-distance (and local) dispersal and chancecolonization. Our findings provide experimental evidence that water dispersal of plantpropagules influences colonization dynamics and is important for long-term communitydevelopment in riparian zones.

  • 33. Myouga, Fumiyoshi
    et al.
    Takahashi, Kaori
    Tanaka, Ryoichi
    Nagata, Noriko
    Kiss, Anett Z.
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Funk, Christiane
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Nomura, Yuko
    Nakagami, Hirofumi
    Jansson, Stefan
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Shinozaki, Kazuo
    Stable accumulation of photosystem II requires one-helix protein1 (OHP1) of the light harvesting-like family2018In: Plant Physiology, ISSN 0032-0889, E-ISSN 1532-2548, Vol. 176, no 3, p. 2277-2291Article in journal (Refereed)
    Abstract [en]

    The cellular functions of two Arabidopsis (Arabidopsis thaliana) one-helix proteins, OHP1 and OHP2 (also named LIGH-THARVESTING-LIKE2 [LIL2] and LIL6, respectively, because they have sequence similarity to light-harvesting chlorophyll a/b-binding proteins), remain unclear. Tagged null mutants of OHP1 and OHP2 (ohp1 and ohp2) showed stunted growth with pale-green leaves on agar plates, and these mutants were unable to grow on soil. Leaf chlorophyll fluorescence and the composition of thylakoid membrane proteins revealed that ohp1 deletion substantially affected photosystem II (PSII) core protein function and led to reduced levels of photosystem I core proteins; however, it did not affect LHC accumulation. Transgenic ohp1 plants rescued with OHP1-HA or OHP1-Myc proteins developed a normal phenotype. Using these tagged OHP1 proteins in transgenic plants, we localized OHP1 to thylakoid membranes, where it formed protein complexes with both OHP2 and High Chlorophyll Fluorescence244 (HCF244). We also found PSII core proteins D1/D2, HCF136, and HCF173 and a few other plant-specific proteins associated with the OHP1/OHP2-HCF244 complex, suggesting that these complexes are early intermediates in PSII assembly. OHP1 interacted directly with HCF244 in the complex. Therefore, OHP1 and HCF244 play important roles in the stable accumulation of PSII.

  • 34. Nakamura, Moritaka
    et al.
    Claes, Andrea R.
    Grebe, Tobias
    Hermkes, Rebecca
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Viotti, Corrado
    Ikeda, Yoshihisa
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Grebe, Markus
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Auxin and ROP GTPase Signaling of Polar Nuclear Migration in Root Epidermal Hair Cells2018In: Plant Physiology, ISSN 0032-0889, E-ISSN 1532-2548, Vol. 176, no 1, p. 378-391Article in journal (Refereed)
    Abstract [en]

    Polar nuclear migration is crucial during the development of diverse eukaryotes. In plants, root hair growth requires polar nuclear migration into the outgrowing hair. However, knowledge about the dynamics and the regulatory mechanisms underlying nuclear movements in root epidermal cells remains limited. Here, we show that both auxin and Rho-of-Plant (ROP) signaling modulate polar nuclear position at the inner epidermal plasma membrane domain oriented to the cortical cells during cell elongation as well as subsequent polar nuclear movement to the outer domain into the emerging hair bulge in Arabidopsis (Arabidopsis thaliana). Auxin signaling via the nuclear AUXIN RESPONSE FACTOR7 (ARF7)/ARF19 and INDOLE ACETIC ACID7 pathway ensures correct nuclear placement toward the inner membrane domain. Moreover, precise inner nuclear placement relies on SPIKE1 Rho-GEF, SUPERCENTIPEDE1 Rho-GDI, and ACTIN7 (ACT7) function and to a lesser extent on VTI11 vacuolar SNARE activity. Strikingly, the directionality and/or velocity of outer polar nuclear migration into the hair outgrowth along actin strands also are ACT7 dependent, auxin sensitive, and regulated by ROP signaling. Thus, our findings provide a founding framework revealing auxin and ROP signaling of inner polar nuclear position with some contribution by vacuolar morphology and of actin-dependent outer polar nuclear migration in root epidermal hair cells.

  • 35.
    Pacurar, Daniel Ioan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Pacurar, Monica Lacramioara
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Lakehal, Abdellah
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Pacurar, Andrea Mariana
    Ranjan, Alok
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Bellini, Catherine
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    The Arabidopsis Cop9 signalosome subunit 4 (CNS4) is involved in adventitious root formation2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 628Article in journal (Refereed)
    Abstract [en]

    The COP9 signalosome (CSN) is an evolutionary conserved multiprotein complex that regulates many aspects of plant development by controlling the activity of CULLIN-RING E3 ubiquitin ligases (CRLs). CRLs ubiquitinate and target for proteasomal degradation a vast number of specific substrate proteins involved in many developmental and physiological processes, including light and hormone signaling and cell division. As a consequence of CSN pleiotropic function, complete loss of CSN activity results in seedling lethality. Therefore, a detailed analysis of CSN physiological functions in adult Arabidopsis plants has been hampered by the early seedling lethality of csn null mutants. Here we report the identification and characterization of a viable allele of the Arabidopsis COP9 signalosome subunit 4 (CSN4). The allele, designated csn4-2035, suppresses the adventitious root (AR) phenotype of the Arabidopsis superroot2-1 mutant, potentially by altering its auxin signaling. Furthermore, we show that although the csn4-2035 mutation affects primary and lateral root (LR) formation in the 2035 suppressor mutant, CSN4 and other subunits of the COP9 complex seem to differentially control AR and LR development.

  • 36. Pawar, Prashant Mohan-Anupama
    et al.
    Derba-Maceluch, Marta
    Chong, Sun-Li
    Gandla, Madhavi Latha
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Bashar, Shamrat Shafiul
    Sparrman, Tobias
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ahvenainen, Patrik
    Hedenström, Mattias
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ozparpucu, Merve
    Ruggeberg, Markus
    Serimaa, Ritva
    Lawoko, Martin
    Tenkanen, Maija
    Jönsson, Leif J.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Mellerowicz, Ewa J.
    In muro deacetylation of xylan affects lignin properties and improves saccharification of aspen wood2017In: Biotechnology for Biofuels, ISSN 1754-6834, E-ISSN 1754-6834, Vol. 10, article id 98Article in journal (Refereed)
    Abstract [en]

    Background: Lignocellulose from fast growing hardwood species is a preferred source of polysaccharides for advanced biofuels and “green” chemicals. However, the extensive acetylation of hardwood xylan hinders lignocellulose saccharification by obstructing enzymatic xylan hydrolysis and causing inhibitory acetic acid concentrations during microbial sugar fermentation. To optimize lignocellulose for cost-effective saccharification and biofuel production, an acetyl xylan esterase AnAXE1 from Aspergillus niger was introduced into aspen and targeted to cell walls.

    Results: AnAXE1-expressing plants exhibited reduced xylan acetylation and grew normally. Without pretreatment, their lignocellulose yielded over 25% more glucose per unit mass of wood (dry weight) than wild-type plants. Glucose yields were less improved (+7%) after acid pretreatment, which hydrolyses xylan. The results indicate that AnAXE1 expression also reduced the molecular weight of xylan, and xylan–lignin complexes and/or lignin co-extracted with xylan, increased cellulose crystallinity, altered the lignin composition, reducing its syringyl to guaiacyl ratio, and increased lignin solubility in dioxane and hot water. Lignin-associated carbohydrates became enriched in xylose residues, indicating a higher content of xylo-oligosaccharides.

    Conclusions: This work revealed several changes in plant cell walls caused by deacetylation of xylan. We propose that deacetylated xylan is partially hydrolyzed in the cell walls, liberating xylo-oligosaccharides and their associated lignin oligomers from the cell wall network. Deacetylating xylan thus not only increases its susceptibility to hydrolytic enzymes during saccharification but also changes the cell wall architecture, increasing the extractability of lignin and xylan and facilitating saccharification.

  • 37. Pawar, Prashant Mohan-Anupama
    et al.
    Derba-Maceluch, Marta
    Chong, Sun-Li
    Gomez, Leonardo D.
    Miedes, Eva
    Banasiak, Alicja
    Ratke, Christine
    Gaertner, Cyril
    Mouille, Grégory
    McQueen-Mason, Simon J.
    Molina, Antonio
    Sellstedt, Anita
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Tenkanen, Maija
    Mellerowicz, Ewa J.
    Expression of fungal acetyl xylan esterase in Arabidopsis thaliana improves saccharification of stem lignocellulose2016In: Plant Biotechnology Journal, ISSN 1467-7644, E-ISSN 1467-7652, Vol. 14, no 1, p. 387-397Article in journal (Refereed)
    Abstract [en]

    Cell wall hemicelluloses and pectins are O-acetylated at specific positions, but the significance of these substitutions is poorly understood. Using a transgenic approach, we investigated how reducing the extent of O-acetylation in xylan affects cell wall chemistry, plant performance and the recalcitrance of lignocellulose to saccharification. The Aspergillus niger acetyl xylan esterase AnAXE1 was expressed in Arabidopsis under the control of either the constitutively expressed 35S CAMV promoter or a woody-tissue-specific GT43B aspen promoter, and the protein was targeted to the apoplast by its native signal peptide, resulting in elevated acetyl esterase activity in soluble and wall-bound protein extracts and reduced xylan acetylation. No significant alterations in cell wall composition were observed in the transgenic lines, but their xylans were more easily digested by a beta-1,4-endoxylanase, and more readily extracted by hot water, acids or alkali. Enzymatic saccharification of lignocellulose after hot water and alkali pretreatments produced up to 20% more reducing sugars in several lines. Fermentation by Trametes versicolor of tissue hydrolysates from the line with a 30% reduction in acetyl content yielded similar to 70% more ethanol compared with wild type. Plants expressing 35S: AnAXE1 and pGT43B:AnAXE1 developed normally and showed increased resistance to the biotrophic pathogen Hyaloperonospora arabidopsidis, probably due to constitutive activation of defence pathways. However, unintended changes in xyloglucan and pectin acetylation were only observed in 35S: AnAXE1-expressing plants. This study demonstrates that postsynthetic xylan deacetylation in woody tissues is a promising strategy for optimizing lignocellulosic biomass for biofuel production.

  • 38.
    Pesquet, Edouard
    et al.
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Tuominen, Hannele
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Unravelling ethylene biosynthesis and its role during tracheary element formation in Zinnia elegans2007In: Advances in plant ethylene research: proceedings of the 7th international symposium on the plant hormone ethylene / [ed] Angelo Ramina, Caren Chang, Jim Giovannoni, Harry Klee, Pierdomenico Perata, Ernst Woltering, Dordrecht: Springer Netherlands, 2007, p. 147-149Conference paper (Refereed)
    Abstract [en]

    Xylem is the plant vascular tissue responsible for raw sap conduction. It comprises two main types of cells that are derived from differentiating cambium: tracheary elements (TEs) and fibres that have conducting and mechanical role, respectively. Xylem formation is a developmental process and is under strict hormonal control involving a stew of phytohormones including auxin, cytokinin and ethylene.

  • 39. Podgorska, Anna
    et al.
    Ostaszewska, Monika
    Gardeström, Per
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Rasmusson, Allan G.
    Szal, Bozena
    In comparison with nitrate nutrition, ammonium nutrition increases growth of the frostbite1 Arabidopsis mutant2015In: Plant, Cell and Environment, ISSN 0140-7791, E-ISSN 1365-3040, Vol. 38, no 1, p. 224-237Article in journal (Refereed)
    Abstract [en]

    Ammonium nutrition inhibits the growth of many plant species, including Arabidopsis thaliana. The toxicity of ammonium is associated with changes in the cellular redox state. The cellular oxidant/antioxidant balance is controlled by mitochondrial electron transport chain. In this study, we analysed the redox metabolism of frostbite1 (fro1) plants, which lack mitochondrial respiratory chain complex I. Surprisingly, the growth of fro1 plants increased under ammonium nutrition. Ammonium nutrition increased the reduction level of pyridine nucleotides in the leaves of wild-type plants, but not in the leaves of fro1 mutant plants. The observed higher activities of type II NADH dehydrogenases and cytochrome c oxidase in the mitochondrial electron transport chain may improve the energy metabolism of fro1 plants grown on ammonium. Additionally, the observed changes in reactive oxygen species (ROS) metabolism in the apoplast may be important for determining the growth of fro1 under ammonium nutrition. Moreover, bioinformatic analyses showed that the gene expression changes in fro1 plants significantly overlap with the changes previously observed in plants with a modified apoplastic pH. Overall, the results suggest a pronounced connection between the mitochondrial redox system and the apoplastic pH and ROS levels, which may modify cell wall plasticity and influence growth. In this paper, we analysed the redox metabolism of frostbite1 (fro1) plants lacking Complex I under ammonium nutrition. We showed that, although ammonium leads to stress in wild type plants, ammonium does not cause reductive stress in fro1 plants. Our experimental and bioinformatic analyses indicated that mtETC dysfunction strongly influences apoplastic reactive oxygen species content and pH, and suggested that the faster growth of fro1 plants under ammonium nutrition probably results from modification of the cell wall.

  • 40. Podgorska, Anna
    et al.
    Ostaszewska-Bugajska, Monika
    Tarnowska, Agata
    Burian, Maria
    Borysiuk, Klaudia
    Gardeström, Per
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Szal, Bozena
    Nitrogen Source Dependent Changes in Central Sugar Metabolism Maintain Cell Wall Assembly in Mitochondrial Complex I-Defective frostbite1 and Secondarily Affect Programmed Cell Death2018In: International Journal of Molecular Sciences, ISSN 1422-0067, E-ISSN 1422-0067, Vol. 19, no 8, article id 2206Article in journal (Refereed)
    Abstract [en]

    For optimal plant growth, carbon and nitrogen availability needs to be tightly coordinated. Mitochondrial perturbations related to a defect in complex I in the Arabidopsis thalianafrostbite1 (fro1) mutant, carrying a point mutation in the 8-kD Fe-S subunit of NDUFS4 protein, alter aspects of fundamental carbon metabolism, which is manifested as stunted growth. During nitrate nutrition, fro1 plants showed a dominant sugar flux toward nitrogen assimilation and energy production, whereas cellulose integration in the cell wall was restricted. However, when cultured on NH4+ as the sole nitrogen source, which typically induces developmental disorders in plants (i.e., the ammonium toxicity syndrome), fro1 showed improved growth as compared to NO3- nourishing. Higher energy availability in fro1 plants was correlated with restored cell wall assembly during NH4+ growth. To determine the relationship between mitochondrial complex I disassembly and cell wall-related processes, aspects of cell wall integrity and sugar and reactive oxygen species signaling were analyzed in fro1 plants. The responses of fro1 plants to NH4+ treatment were consistent with the inhibition of a form of programmed cell death. Resistance of fro1 plants to NH4+ toxicity coincided with an absence of necrotic lesion in plant leaves.

  • 41. Poxson, David J.
    et al.
    Karady, Michal
    Gabrielsson, Roger
    Alkattan, Aziz Y.
    Gustavsson, Anna
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Doyle, Siamsa M.
    Robert, Stephanie
    Ljung, Karin
    Grebe, Markus
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Plant Physiology, Institute of Biochemistry and Biology, University of Potsdam, 14476 Potsdam, Golm, Germany.
    Simon, Daniel T.
    Berggren, Magnus
    Regulating plant physiology with organic electronics2017In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 114, no 18, p. 4597-4602Article in journal (Refereed)
    Abstract [en]

    The organic electronic ion pump (OEIP) provides flow-free and accurate delivery of small signaling compounds at high spatio-temporal resolution. To date, the application of OEIPs has been limited to delivery of nonaromatic molecules to mammalian systems, particularly for neuroscience applications. However, many long-standing questions in plant biology remain unanswered due to a lack of technology that precisely delivers plant hormones, based on cyclic alkanes or aromatic structures, to regulate plant physiology. Here, we report the employment of OEIPs for the delivery of the plant hormone auxin to induce differential concentration gradients and modulate plant physiology. We fabricated OEIP devices based on a synthesized dendritic polyelectrolyte that enables electrophoretic transport of aromatic substances. Delivery of auxin to transgenic Arabidopsis thaliana seedlings in vivo was monitored in real time via dynamic fluorescent auxin-response reporters and induced physiological responses in roots. Our results provide a starting point for technologies enabling direct, rapid, and dynamic electronic interaction with the biochemical regulation systems of plants.

  • 42. Ratke, Christine
    et al.
    Terebieniec, Barbara K.
    Department of Forest Genetics and Plant Physiology, SLU, Umeå Plant Science Centre (UPSC), Umeå, Sweden.
    Winestrand, Sandra
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Derba-Maceluch, Marta
    Department of Forest Genetics and Plant Physiology, SLU, Umeå Plant Science Centre (UPSC), Umeå, Sweden.
    Grahn, Thomas
    Schiffthaler, Bastian
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Ulvcrona, Thomas
    Ozparpucu, Merve
    Rüggeberg, Markus
    Lundqvist, Sven-Olof
    Street, Nathaniel
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Jönsson, Leif J.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Mellerowicz, Ewa J.
    Downregulating aspen xylan biosynthetic GT43 genes in developing wood stimulates growth via reprograming of the transcriptome2018In: New Phytologist, ISSN 0028-646X, Vol. 219, no 1, p. 230-245Article in journal (Refereed)
    Abstract [en]

    Xylan is one of the main compounds determining wood properties in hardwood species. The xylan backbone is thought to be synthesized by a synthase complex comprising two members of the GT43 family. We downregulated all GT43 genes in hybrid aspen (Populus tremulaxtremuloides) to understand their involvement in xylan biosynthesis.

    All three clades of the GT43 family were targeted for downregulation using RNA interference individually or in different combinations, either constitutively or specifically in developing wood.

    Simultaneous downregulation in developing wood of the B (IRX9) and C (IRX14) clades resulted in reduced xylan Xyl content relative to reducing end sequence, supporting their role in xylan backbone biosynthesis. This was accompanied by a higher lignocellulose saccharification efficiency. Unexpectedly, GT43 suppression in developing wood led to an overall growth stimulation, xylem cell wall thinning and a shift in cellulose orientation. Transcriptome profiling of these transgenic lines indicated that cell cycling was stimulated and secondary wall biosynthesis was repressed. We suggest that the reduced xylan elongation is sensed by the cell wall integrity surveying mechanism in developing wood.

    Our results show that wood-specific suppression of xylan-biosynthetic GT43 genes activates signaling responses, leading to increased growth and improved lignocellulose saccharification.

  • 43. Rende, Umut
    et al.
    Wang, Wei
    Gandla, Madhavi Latha
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Jönsson, Leif J.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Niittylä, Totte
    Cytosolic invertase contributes to the supply of substrate for cellulose biosynthesis in developing wood2017In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 214, no 2, p. 796-807Article in journal (Refereed)
    Abstract [en]

    Carbon for cellulose biosynthesis is derived from sucrose. Cellulose is synthesized from uridine 5'-diphosphoglucose (UDP-glucose), but the enzyme(s) responsible for the initial sucrose cleavage and the source of UDP-glucose for cellulose biosynthesis in developing wood have not been defined. We investigated the role of CYTOSOLIC INVERTASEs (CINs) during wood formation in hybrid aspen (Populus tremula × tremuloides) and characterized transgenic lines with reduced CIN activity during secondary cell wall biosynthesis. Suppression of CIN activity by 38–55% led to a 9–13% reduction in crystalline cellulose. The changes in cellulose were reflected in reduced diameter of acid-insoluble cellulose microfibrils and increased glucose release from wood upon enzymatic digestion of cellulose. Reduced CIN activity decreased the amount of the cellulose biosynthesis precursor UDP-glucose in developing wood, pointing to the likely cause of the cellulose phenotype. The findings suggest that CIN activity has an important role in the cellulose biosynthesis of trees, and indicate that cellulose biosynthesis in wood relies on a quantifiable UDP-glucose pool. The results also introduce a concept of altering cellulose microfibril properties by modifying substrate supply to cellulose biosynthesis.

  • 44. Schrader, Jarmo
    et al.
    Moyle, Richard
    Bhalerao, Rupali
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Hertzberg, Magnus
    Lundeberg, Joakim
    Nilsson, Peter
    Bhalerao, Rishikesh P
    Cambial meristem dormancy in trees involves extensive remodelling of the transcriptome2004In: The Plant Journal, ISSN 0960-7412, E-ISSN 1365-313X, Vol. 40, no 2, p. 173-187Article in journal (Refereed)
    Abstract [en]

    The establishment of the dormant state in meristems involves considerable physiological and metabolic alterations necessary for surviving unfavourable growth conditions. However, a global molecular analysis of dormancy in meristems has been hampered by the difficulty in isolating meristem cells. We used cryosectioning to isolate purified cambial meristem cells from the woody plant Populus tremula during active growth and dormancy. These samples were used to generate meristem-specific cDNA libraries and for cDNA microarray experiments to define the global transcriptional changes underlying cambial dormancy. The results indicate a significant reduction in the complexity of the cambial transcriptome in the dormant state. Although cell division is terminated in the dormant cambium, the cell cycle machinery appears to be maintained in a skeletal state as suggested by the continued presence of transcripts for several cell cycle regulators. The downregulation of PttPIN1 and PttPIN2 transcripts explains the reduced basipetal polar auxin transport during dormancy. The induction of a member of the SINA family of ubiquitin ligases implicated in auxin signalling indicates a potential mechanism for modulation of auxin sensitivity during cambial dormancy. The metabolic alterations during dormancy are mirrored in the induction of genes involved in starch breakdown and the glyoxysomal cycle. Interestingly, the induction of RGA1 like gene suggests modification of gibberellin signalling in cambial dormancy. The induction of genes such as poplar orthologues of FIE and HAP2 indicates a potential role for these global regulators of transcription in orchestrating extensive changes in gene expression during dormancy.

  • 45.
    Shaikhali, Jehad
    et al.
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Baier, Margarete
    Ascorbate regulation of 2-Cys peroxiredoxin-A promoter activity is light-dependent2010In: Journal of plant physiology (Print), ISSN 0176-1617, E-ISSN 1618-1328, Vol. 167, no 6, p. 461-467Article in journal (Refereed)
    Abstract [en]

    The 2-Cys peroxiredoxin-A (2CPA) promoter is a model promoter to study redox and ABA-dependent stress signaling. Here, an Arabidopsis reporter gene line expressing luciferase under control of the 2CPA promoter was used to study the impact of ascorbate on reporter gene transcription in a series of protoplast and leaf slice incubation experiments. It was shown that ascorbate has a dual function on gene expression regulation. First, a comparison of responses to ascorbate, dehydroascorbate and reduced and oxidized glutathione demonstrated that ascorbate feeding supports gene expression regulation by increasing the catalytic capacity in redox signaling, as defined by the concentration of low molecular weight antioxidants and their oxidized counterparts. Second, ascorbate had a specific and light-dependent effect on 2CPA transcription, which cannot be substituted by reduced glutathione. Based on the differences between ascorbate and glutathione in the subcellular redox-cycling capacities, it is concluded that ascorbate feeding modulates chloroplast-specific regulation of 2CPA expression. (C) 2009 Elsevier GmbH. All rights reserved.

  • 46.
    Stagge, Stefan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Cavka, Adnan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Jönsson, Leif J
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Identification of benzoquinones in pretreated lignocellulosic feedstocks and inhibitory effects on yeast2015In: AMB Express, ISSN 2191-0855, E-ISSN 2191-0855, Vol. 5, article id 62Article in journal (Refereed)
    Abstract [en]

    Pretreatment of lignocellulosic biomass under acidic conditions gives rise to by-products that inhibit fermenting microorganisms. An analytical procedure for identification of p-benzoquinone (BQ) and 2,6-dimethoxybenzoquinone (DMBQ) in pretreated biomass was developed, and the inhibitory effects of BQ and DMBQ on the yeast Saccharomyces cerevisiae were assessed. The benzoquinones were analyzed using ultra-high performance liquid chromatographyelectrospray ionization-triple quadrupole-mass spectrometry after derivatization with 2,4-dinitrophenylhydrazine. Pretreatment liquids examined with regard to the presence of BQ and DMBQ originated from six different lignocellulosic feedstocks covering agricultural residues, hardwood, and softwood, and were produced through impregnation with sulfuric acid or sulfur dioxide at varying pretreatment temperature (165-204 degrees C) and residence time (6-20 min). BQ was detected in all six pretreatment liquids in concentrations ranging up to 6 mg/l, while DMBQ was detected in four pretreatment liquids in concentrations ranging up to 0.5 mg/l. The result indicates that benzoquinones are ubiquitous as by-products of acid pretreatment of lignocellulose, regardless of feedstock and pretreatment conditions. Fermentation experiments with BQ and DMBQ covered the concentration ranges 2 mg/l to 1 g/l and 20 mg/l to 1 g/l, respectively. Even the lowest BQ concentration tested (2 mg/l) was strongly inhibitory to yeast, while 20 mg/l DMBQ gave a slight negative effect on ethanol formation. This work shows that benzoquinones should be regarded as potent and widespread inhibitors in lignocellulosic hydrolysates, and that they warrant attention besides more well-studied inhibitory substances, such as aliphatic carboxylic acids, phenols, and furan aldehydes.

  • 47.
    Terebieniec, Barbara
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Gene Expression and Growth Analyses in Populus RNAi lines Targeting Xylan Biosynthetic Gene Family GT 432012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Wood biomass is coming into focus as a good alternative renewable energy feedstock. Fast-growing woody plants, such as Populus species, offer potential as a bioenergy crop mediated by their abundance of energy containing cell wall polysaccharides.

    Furthermore, the first tree genome sequencing of Populus trichocarpa (poplar) offers an opportunity for genetic manipulation of woody cell components in order to optimize it for instance as an energy crop. Plant cell walls are very complex structures consisting of biopolymers, which form a network in the secondary wall. Cellulose, for instance, is organized as microfibrils consisting of β‐1,4‐glucan chains, whereas the hemicelluloses present heterogeneous polysaccharide groups. Within the hemicelluloses, xylans are the most abundant. The biosynthesis of hemicelluloses is still poorly understood.

    In order to investigate the biological role of GT43 genes during wood formation, transgenic hybrid aspen RNAi lines targeting GT43 have been created (Ratke et al., unpublished). Three GT43 genes (GT43B, GT43C and GT43F), and their double (GT43BC, GT43BF, GT43CF) and triple (GT43BCF) combinations, were selected to be targeted by RNAi. All the constructs were fused to the constitutive cauliflower 35 (CaM35S) and a wood-specific (WP) promoter and transformed into hybrid aspen (Populus tremula x tremuloides).

    The first part of the study focuses on selecting the most down‐regulated GT43 RNAi lines by using real‐time quantitative PCR analysis. We used a stepwise screening strategy starting from 20 individual in vitro transformant lines per construct. During the two in vitro screening steps we used in vitro grown stem tissue as an RNA source. The first in vitro screening narrowed down the number of lines to eight per each construct. After second in vitro screening, four most down regulated lines per construct were selected in order to grow them in greenhouse conditions and obtain woody tissue for further analyses. Third screening was applied when the GT43 RNAi plants were growing under greenhouse conditions and it used petioles as an RNA source. After the third screening, three best lines were selected per construct based on RNA analysis and additional chemical analyses not presented here. For the final gene expression analysis of selected three best lines per construct, we used freeze-dried wood or bark powder as an RNA source. The GT43 gene expression analysis base on quantitative real‐time PCR.

    These results are promising for developing Populus into a bioenergy crop. The use of molecular tools such a quantitative real-time PCR in stepwise screenings in order to select most down‐regulated lines of hybrid aspen resulted in selection of significantly altered lines as compared to the wild type. The future development of this technology should possibly use a higher number of transgenic lines as a starting point for selection.

  • 48.
    Trygg, Johan
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Hertzberg, Magnus
    Swetree technologies.
    Sundberg, Björn
    UPSC.
    Sandberg, Göran
    UPSC.
    Schrader, Jarmo
    UPSC.
    Teeri, Tuula
    Aspeborg, Henrik
    Wallbäcks, Lars
    Bhalerao, Rishi
    UPSC.
    Johansson, Karin
    Swetree technologies.
    Jonsson, Pär
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Vegetabile material, plants and a method of producing a plant having altered lignin properties2012Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    Abstract: The present invention is related to a set of genes, which when modified in plants gives altered lignin properties. The invention provides DNA construct such as a vector useful in the method of the invention. Further, the invention relates to a plant cell or plant progeny of the plants and wood produced by the plants according to the invention Lower lignin levels will result in improved saccharification for bio-refining and ethanol production and improved pulp and paper. Increased lignin levels will utilise lignin properties for energy production. The genes and DNA constructs may be used for the identification of plants having altered lignin characteristics as compared to the wild-type. According to the invention genes and DNA constructs may also be used as candidate genes in marker assisted breeding.

  • 49.
    von Sydow, Lotta
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Characterization of auxiliary membrane proteins in the chloroplast of Arabidopsis thaliana2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In nature, sessile plants have to adapt to their environment and to the never ending changes they are exposed to. They do so mainly by proteomic and metabolomic changes. In all cells, there are complex networks of auxiliary proteins that are responsible for quality control of all the cell's proteins. The auxiliary proteins are divided into chaperones and proteases, and these are further separated into different groups. Chaperones help other proteins in terms of stability and folding. In order for a protein to achieve its function, the three-dimensional structure has to be precise. A protease is a helper protein that is able to break peptide bonds in a process termed proteolysis. Chaperones and proteases can work independently, but sometimes the chaperone unfolds the substrate of the protease to ensure full degradation of the protein. In some cases, the chaperone and the protease functions are combined in one protein.

    All proteins studied within this thesis are localized in the chloroplast, the organelle that originated from cyanobacteria, in which plants and algae convert the energy from sunlight into carbohydrates in the process called photosynthesis. Molecular oxygen is released as a by-product, and carbon dioxide is consumed. Photosystem II (PSII), one of the major protein complexes involved in photosynthesis, consists of more than 30 protein subunits, where around half of them are termed low molecular weight (LMW) proteins with a molecular size less than 10 kDa. In this thesis, data identifying one PSII LMW protein, PsbY, as a chaperone for the PSII subcomplex Cytochrome b559 are presented. In the absence of PsbY, Arabidopsis plants were more sensitive to photoinhibition, and the protective circular electron transport around PSII is completely blocked.

    Data on members of the Filamentation temperature sensitive protein H (FtsH) protease family are also discussed, with a focus on FtsH11 and FtsHi1-i5. Members of the FtsH protease family carry a protease domain and a chaperone domain. Our data show that FtsH11 has an influence on the structure and function of chloroplasts of Arabidopsis plants grown under continuous light along with protein import into the same. FtsHi1-5 are five members with mutations within the proteolytic motif, most probably rendering them proteolytically inactive, hence they are referred to as ''inactive FtsH proteases''. Knock-out plants of the inactive members are embryo lethal, and knock-down plants grow slower than wild type, probably because of an affected level of plastid proteins at the translational level.

  • 50.
    von Sydow, Lotta
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Mielke, Kati
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Funk, Christiane
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Characterization of the plastid-localized inactive FtsHis of Arabidopsis thalianaManuscript (preprint) (Other academic)
    Abstract [en]

    In the genome of Arabidopsis thaliana five genes encode members of the FtsH (Filamentation temperature sensitive protein H) protease family with mutations or deletions in their proteolytic site. Despite of not being active proteases these so called FtsHi (i for inactive) enzymes still seem to be highly important for plant development. All five enzymes have been localized within the plant chloroplast, most of them seem to be inserted in the chloroplast envelope. As homozygous ftshi mutants are seed lethal, here we compared different heterozygous ftshi mutants with respect to their growth at various light periods and at semi-natural growth conditions in the field. Their photosynthetic efficiency was evaluated by pulse-amplitude modulated fluorescence and the composition of their photosynthetic complexes was analysed by native polyacrylamide gel electrophoresis. Co-expression analyses were performed to find clues about the function of the five FtsHi inactive proteases.

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