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  • 1. Andersson, Anders
    et al.
    Keskitalo, Johanna
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Sjödin, Andreas
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Bhalerao, Rupali
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Sterky, Fredrik
    Wissel, Kirsten
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Tandre, Karolina
    Aspeborg, Henrik
    Moyle, Richard
    Ohmiya, Yasunori
    Bhalerao, Rishikesh
    Brunner, Amy
    Gustafsson, Petter
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Lundeberg, Joakim
    Nilsson, Ove
    Sandberg, Göran
    Strauss, Steven
    Sundberg, Björn
    Uhlen, Mathias
    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).
    Nilsson, Peter
    A transcriptional timetable of autumn senescence2004In: Genome Biology, ISSN 1465-6906, E-ISSN 1474-760X, Vol. 5, no 4, p. R24-Article in journal (Refereed)
    Abstract [en]

    Background We have developed genomic tools to allow the genus Populus (aspens and cottonwoods) to be exploited as a full-featured model for investigating fundamental aspects of tree biology. We have undertaken large-scale expressed sequence tag (EST) sequencing programs and created Populus microarrays with significant gene coverage. One of the important aspects of plant biology that cannot be studied in annual plants is the gene activity involved in the induction of autumn leaf senescence. Results On the basis of 36,354 Populus ESTs, obtained from seven cDNA libraries, we have created a DNA microarray consisting of 13,490 clones, spotted in duplicate. Of these clones, 12,376 (92%) were confirmed by resequencing and all sequences were annotated and functionally classified. Here we have used the microarray to study transcript abundance in leaves of a free-growing aspen tree (Populus tremula) in northern Sweden during natural autumn senescence. Of the 13,490 spotted clones, 3,792 represented genes with significant expression in all leaf samples from the seven studied dates. Conclusions We observed a major shift in gene expression, coinciding with massive chlorophyll degradation, that reflected a shift from photosynthetic competence to energy generation by mitochondrial respiration, oxidation of fatty acids and nutrient mobilization. Autumn senescence had much in common with senescence in annual plants; for example many proteases were induced. We also found evidence for increased transcriptional activity before the appearance of visible signs of senescence, presumably preparing the leaf for degradation of its components.

  • 2. ANDERSSON, B
    et al.
    SANDBERG, G
    IDENTIFICATION OF ENDOGENOUS N-(3-INDOLEACETYL)ASPARTIC ACID IN SCOTS PINE (PINUS-SYLVESTRIS L) BY COMBINED GAS CHROMATOGRAPHY-MASS SPECTROMETRY, USING HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY FOR QUANTIFICATION1982In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 238, no 1, p. 151-156Article in journal (Refereed)
  • 3. Fuchs, I
    et al.
    Philippar, K
    Ljung, K
    Sandberg, G
    Hedrich, R
    Blue light regulates an auxin-induced K+-channel gene in the maize coleoptile2003In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 100, no 20, p. 11795-11800Article in journal (Refereed)
    Abstract [en]

    Auxin redistribution along gravistimulated maize coleoptiles causes differential expression of the auxin-induced K+-channel gene ZMK1 (Zea mays K+ channel 1) and precedes the curvature response. To evaluate the role of ZMK1 during phototropism, we here investigated blue light-stimulated coleoptiles. Four hours of blue light stimulation resulted in phototropic bending (23degrees). Rotation on a clinostat, at nominally "zero" gravity, and simultaneous stimulation with unidirectional blue light, however, resulted in up to 510 bending toward the light. Differential ZMK1 transcription reached a maximum after 90 min of blue light stimulation under gravity, whereas ZMK1 expression remained asymmetric for at least 180 min in photostimulated coleoptiles on a clinostat. We therefore conclude that the stronger phototropic bending under nominally "zero" gravity results from prolonged differential expression of ZMK1. Under both conditions, asymmetric expression of ZMK1 could be superimposed on the lateral auxin gradient across the coleoptile tip, whereas the gene for the blue light receptor phototropin 1 (PHOT1), expressed in the tip only, was not differentially regulated in response to blue light. The activation of the two different receptors eliciting the photo- and gravitropic response of the coleoptile thus feeds into a common signaling pathway, resulting in auxin redistribution in the coleoptile tip and finally in differential transcription of ZMK1. In the process of signal integration, gravity transduction restricts the magnitude of the blue light-inducible ZMK1 gradient. The spatial and temporal distribution of ZMK1 transcripts and thus differential K+ uptake in both flanks of the coleoptile seem to limit the stimulus-induced bending of this sensory organ.

  • 4.
    Jones, Brian
    et al.
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Gunnerås, Sara Andersson
    Petersson, Sara V
    Tarkowski, Petr
    Graham, Neil
    May, Sean
    Dolezal, Karel
    Sandberg, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Ljung, Karin
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Cytokinin regulation of auxin synthesis in Arabidopsis involves a homeostatic feedback loop regulated via auxin and cytokinin signal transduction.2010In: The Plant Cell, ISSN 1040-4651, E-ISSN 1532-298X, Vol. 22, no 9, p. 2956-2969Article in journal (Refereed)
    Abstract [en]

    Together, auxin and cytokinin regulate many of the processes that are critical to plant growth, development, and environmental responsiveness. We have previously shown that exogenous auxin regulates cytokinin biosynthesis in Arabidopsis thaliana. In this work, we show that, conversely, the application or induced ectopic biosynthesis of cytokinin leads to a rapid increase in auxin biosynthesis in young, developing root and shoot tissues. We also show that reducing endogenous cytokinin levels, either through the induction of CYTOKININ OXIDASE expression or the mutation of one or more of the cytokinin biosynthetic ISOPENTENYLTRANSFERASE genes leads to a reduction in auxin biosynthesis. Cytokinin modifies the abundance of transcripts for several putative auxin biosynthetic genes, suggesting a direct induction of auxin biosynthesis by cytokinin. Our data indicate that cytokinin is essential, not only to maintain basal levels of auxin biosynthesis in developing root and shoot tissues but also for the dynamic regulation of auxin biosynthesis in response to changing developmental or environmental conditions. In combination with our previous work, the data suggest that a homeostatic feedback regulatory loop involving both auxin and cytokinin signaling acts to maintain appropriate auxin and cytokinin concentrations in developing root and shoot tissues.

  • 5.
    Nilsson, Jeanette
    et al.
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Karlberg, Anna
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Antti, Henrik
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Lopez-Vernaza, Manuel
    Mellerowicz, Ewa
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Perrot-Rechenmann, Catherine
    Sandberg, Göran
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Bhalerao, Rishikesh P
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Dissecting the Molecular Basis of the Regulation of Wood Formation by Auxin in Hybrid Aspen2008In: The Plant Cell, Vol. 20, p. 843-55Article in journal (Refereed)
    Abstract [en]

    Indole acetic acid (auxin) is a key regulator of wood formation, and an observed overlap between auxin concentration gradient and developing secondary xylem cells has led to the hypothesis that auxin regulates wood formation by acting as a morphogen. We dissected the role of auxin in wood formation by identifying the auxin-responsive transcriptome in wood-forming tissues and investigating alterations in wood formation in transgenic hybrid aspen plants (Populus tremula x Populus tremuloides) with perturbed auxin signaling. We showed that auxin-responsive genes in wood-forming tissues respond dynamically to changes in cellular auxin levels. However, the expression patterns of most of the auxin-responsive genes displayed limited correlation with the auxin concentration across this developmental zone. Perturbing auxin signaling by reducing auxin responsiveness reduced the cambial cell division activity, caused spatial deregulation of cell division of the cambial initials, and led to reductions in not only radial but also axial dimensions of fibers and vessels. We propose that, instead of acting as a morphogen, changes in auxin concentration in developing secondary xylem cells may provide important regulatory cues that modulate the expression of a few key regulators; these, in turn, may control the global gene expression patterns that are essential for normal secondary xylem development.

  • 6. NILSSON, O
    et al.
    MORITZ, T
    IMBAULT, N
    SANDBERG, G
    OLSSON, O
    HORMONAL CHARACTERIZATION OF TRANSGENIC TOBACCO PLANTS EXPRESSING THE ROLC GENE OF AGROBACTERIUM-RHIZOGENES TL-DNA1993In: Plant Physiology, ISSN 0032-0889, E-ISSN 1532-2548, Vol. 102, no 2, p. 363-371Article in journal (Refereed)
    Abstract [en]

    Transgenic tobacco (Nicotiana tabacum L. cv Wisconsin 38) plants expressing the Agrobacterium rhizogenes rolC gene under the control of the cauliflower mosaic virus 35S RNA promoter were constructed. These plants displayed several morphological alterations reminiscent of changes in indole-3-acetic acid (IAA), cytokinin, and gibberellin (GA) content. However, investigations showed that neither the IAA pool size nor its rate of turnover were altered significantly in the rolC plants. The biggest difference between rolC and wild-type plants was in the concentrations of the cytokinin, isopentenyladenosine (iPA) and the gibberellin GA19. Radioimmunoassay and liquid chromatography-mass spectrometry measurements revealed a drastic reduction in rolC plants of iPA as well as in several other cytokinins tested, suggesting a possible reduction in the synthesis rate of cytokinins. Furthermore, gas chromatography-mass spectrometry quantifications of GA19 showed a 5- to 6-fold increase in rolC plants compared with wild-type plants, indicating a reduced activity of the GA19 oxidase, a proposed regulatory step in the gibberellin biosynthesis. Thus, we conclude that RolC activity in transgenic plants leads to major alterations in the metabolism of cytokinins and gibberellins.

  • 7.
    Nordström, Anders
    et al.
    Swedish University of Agricultural Sciences.
    Tarkowski, Petr
    Tarkowska, Danuse
    Dolezal, Karel
    Astot, Crister
    Sandberg, Göran
    Moritz, Thomas
    Derivatization for LC-electrospray ionization-MS: a tool for improving reversed-phase separation and ESI responses of bases, ribosides, and intact nucleotides.2004In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 76, no 10, p. 2869-77Article in journal (Refereed)
    Abstract [en]

    We have developed a method for analyzing polar compounds by reversed-phase LC-ESI-MS following esterification of the analytes' free hydroxyl groups with propionyl or benzoyl acid anhydride. The method was applied to members of the plant hormone group cytokinins, which includes adenine bases, ribosides/glycosides, and nucleotides substituted at N-6 with an isoprenoid side chain, spanning a wide range of polarity. It was also used to analyze other compounds of biological importance, e.g., the nucleotides AMP, ADP, and ATP. The formation of more hydrophobic derivatives had a significant impact on two aspects of the analysis. The retention on a reversed-phase material was greatly increased without the use of any acetate/formate buffer or ion pairing reagent, and the ESI response was enhanced, due to the higher surface activities of the derivatives. Detection limits of propionylated cytokinins were in the high-attomole to low-femtomole range, an improvement by factors of 10-100 compared to previously reported figures. Using an automated SPE-based purification method, 12 endogenous cytokinins were quantified in extracts from 20- to 100-mg samples of leaves (from the plant Arabidopsis thaliana) with high accuracy and precision. Furthermore, the chromatographic properties of the benzoylated AMP, ADP, and ATP in the reversed-phase LC-MS system were much better in terms of retention, separation, and sensitivity than those of their underivatized counterparts, even without the use of any ion pairing reagent. Our data show that derivatization followed by LC-ESI-MS is an effective strategy for analyzing low molecular weight compounds, enabling compounds with a wide range of polarity to be determined in a single-injection LC-MS analysis.

  • 8.
    Nordström, Anders
    et al.
    Umeå Plant Science Centre, Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences.
    Tarkowski, Petr
    Tarkowska, Danuse
    Norbaek, Rikke
    Astot, Crister
    Dolezal, Karel
    Sandberg, Göran
    Auxin regulation of cytokinin biosynthesis in Arabidopsis thaliana: a factor of potential importance for auxin-cytokinin-regulated development.2004In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 101, no 21, p. 8039-44Article in journal (Refereed)
    Abstract [en]

    One of the most long-lived models in plant science is the belief that the long-distance transport and ratio of two plant hormones, auxin and cytokinin, at the site of action control major developmental events such as apical dominance. We have used in vivo deuterium labeling and mass spectrometry to investigate the dynamics of homeostatic cross talk between the two plant hormones. Interestingly, auxin mediates a very rapid negative control of the cytokinin pool by mainly suppressing the biosynthesis via the isopentenyladenosine-5'-monophosphate-independent pathway. In contrast, the effect of cytokinin overproduction on the entire auxin pool in the plant was slower, indicating that this most likely is mediated through altered development. In addition, we were able to confirm that the lateral root meristems are likely to be the main sites of isopentenyladenosine-5'-monophosphate-dependent cytokinin synthesis, and that the aerial tissue of the plant surprisingly also was a significant source of cytokinin biosynthesis. Our demonstration of shoot-localized synthesis, together with data demonstrating that auxin imposes a very rapid regulation of cytokinin biosynthesis, illustrates that the two hormones can interact also on the metabolic level in controlling plant development, and that the aerial part of the plant has the capacity to synthesize its own cytokinin independent of long-range transport from the root system.

  • 9. Pencik, Ales
    et al.
    Simonovik, Biljana
    Petersson, Sara V.
    Henykova, Eva
    Simon, Sibu
    Greenham, Kathleen
    Zhang, Yi
    Kowalczyk, Mariusz
    Estelle, Mark
    Zazimalova, Eva
    Novak, Ondrej
    Sandberg, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Ljung, Karin
    Regulation of Auxin Homeostasis and Gradients in Arabidopsis Roots through the Formation of the Indole-3-Acetic Acid Catabolite 2-Oxindole-3-Acetic Acid2013In: The Plant Cell, ISSN 1040-4651, E-ISSN 1532-298X, Vol. 25, no 10, p. 3858-3870Article in journal (Refereed)
    Abstract [en]

    The native auxin, indole-3-acetic acid (IAA), is a major regulator of plant growth and development. Its nonuniform distribution between cells and tissues underlies the spatiotemporal coordination of many developmental events and responses to environmental stimuli. The regulation of auxin gradients and the formation of auxin maxima/minima most likely involve the regulation of both metabolic and transport processes. In this article, we have demonstrated that 2-oxindole-3-acetic acid (oxIAA) is a major primary IAA catabolite formed in Arabidopsis thaliana root tissues. OxIAA had little biological activity and was formed rapidly and irreversibly in response to increases in auxin levels. We further showed that there is cell type-specific regulation of oxIAA levels in the Arabidopsis root apex. We propose that oxIAA is an important element in the regulation of output from auxin gradients and, therefore, in the regulation of auxin homeostasis and response mechanisms.

  • 10. Peret, Benjamin
    et al.
    Middleton, Alistair M.
    French, Andrew P.
    Larrieu, Antoine
    Bishopp, Anthony
    Njo, Maria
    Wells, Darren M.
    Porco, Silvana
    Mellor, Nathan
    Band, Leah R.
    Casimiro, Ilda
    Kleine-Vehn, Juergen
    Vanneste, Steffen
    Sairanen, Ilkka
    Mallet, Romain
    Sandberg, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Ljung, Karin
    Beeckman, Tom
    Benkova, Eva
    Friml, Jiri
    Kramer, Eric
    King, John R.
    De Smet, Ive
    Pridmore, Tony
    Owen, Markus
    Bennett, Malcolm J.
    Sequential induction of auxin efflux and influx carriers regulates lateral root emergence2013In: Molecular Systems Biology, ISSN 1744-4292, E-ISSN 1744-4292, Vol. 9, p. Article number 699-Article in journal (Refereed)
    Abstract [en]

    In Arabidopsis, lateral roots originate from pericycle cells deep within the primary root. New lateral root primordia ( LRP) have to emerge through several overlaying tissues. Here, we report that auxin produced in new LRP is transported towards the outer tissues where it triggers cell separation by inducing both the auxin influx carrier LAX3 and cell-wall enzymes. LAX3 is expressed in just two cell files overlaying new LRP. To understand how this striking pattern of LAX3 expression is regulated, we developed a mathematical model that captures the network regulating its expression and auxin transport within realistic three-dimensional cell and tissue geometries. Our model revealed that, for the LAX3 spatial expression to be robust to natural variations in root tissue geometry, an efflux carrier is required-later identified to be PIN3. To prevent LAX3 from being transiently expressed in multiple cell files, PIN3 and LAX3 must be induced consecutively, which we later demonstrated to be the case. Our study exemplifies how mathematical models can be used to direct experiments to elucidate complex developmental processes.

  • 11.
    Petersson, Sara V
    et al.
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Johansson, Annika I
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Kowalczyk, Mariusz
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Makoveychuk, Alexander
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Wang, Jean Y
    Department of Biology and Institute for Genome Sciences & Policy, Center for Systems Biology, Duke University, Durham, North Carolina 27708, USA.
    Moritz, Thomas
    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).
    Benfey, Philip N
    Department of Biology and Institute for Genome Sciences & Policy, Center for Systems Biology, Duke University, Durham, North Carolina 27708, USA.
    Sandberg, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Ljung, Karin
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    An auxin gradient and maximum in the arabidopsis root apex shown by high-resolution cell-specific analysis of IAA distribution and synthesis2009In: The Plant Cell, ISSN 1040-4651, E-ISSN 1532-298X, Vol. 21, no 6, p. 1659-1668Article in journal (Refereed)
    Abstract [en]

    Local concentration gradients of the plant growth regulator auxin (indole-3-acetic acid [IAA]) are thought to instruct the positioning of organ primordia and stem cell niches and to direct cell division, expansion, and differentiation. High-resolution measurements of endogenous IAA concentrations in support of the gradient hypothesis are required to substantiate this hypothesis. Here, we introduce fluorescence-activated cell sorting of green fluorescent protein-marked cell types combined with highly sensitive mass spectrometry methods as a novel means for analyses of IAA distribution and metabolism at cellular resolution. Our results reveal the presence of IAA concentration gradients within the Arabidopsis thaliana root tip with a distinct maximum in the organizing quiescent center of the root apex. We also demonstrate that the root apex provides an important source of IAA and that cells of all types display a high synthesis capacity, suggesting a substantial contribution of local biosynthesis to auxin homeostasis in the root tip. Our results indicate that local biosynthesis and polar transport combine to produce auxin gradients and maxima in the root tip.

  • 12. Sairanen, Ilkka
    et al.
    Novak, Ondrej
    Pencik, Ales
    Ikeda, Yoshihisa
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Jones, Brian
    Sandberg, Göran
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Ljung, Karin
    Soluble Carbohydrates Regulate Auxin Biosynthesis via PIF Proteins in Arabidopsis2012In: The Plant Cell, ISSN 1040-4651, E-ISSN 1532-298X, Vol. 24, no 12, p. 4907-4916Article in journal (Refereed)
    Abstract [en]

    Plants are necessarily highly competitive and have finely tuned mechanisms to adjust growth and development in accordance with opportunities and limitations in their environment. Sugars from photosynthesis form an integral part of this growth control process, acting as both an energy source and as signaling molecules in areas targeted for growth. The plant hormone auxin similarly functions as a signaling molecule and a driver of growth and developmental processes. Here, we show that not only do the two act in concert but that auxin metabolism is itself regulated by the availability of free sugars. The regulation of the biosynthesis and degradation of the main auxin, indole-3-acetic acid (IAA), by sugars requires changes in the expression of multiple genes and metabolites linked to several IAA biosynthetic pathways. The induction also involves members of the recently described central regulator PHYTOCHROME-INTERACTING FACTOR transcription factor family. Linking these three known regulators of growth provides a model for the dynamic coordination of responses to a changing environment.

  • 13. SANDBERG, G
    et al.
    ANDERSSON, B
    DUNBERG, A
    IDENTIFICATION OF 3-INDOLEACETIC ACID IN PINUS-SYLVESTRIS L BY GAS CHROMATOGRAPHY-MASS SPECTROMETRY, AND QUANTITATIVE-ANALYSIS BY ION-PAIR REVERSED-PHASE LIQUID-CHROMATOGRAPHY WITH SPECTROFLUORIMETRIC DETECTION1981In: Journal of Chromatography A, ISSN 0021-9673, E-ISSN 1873-3778, Vol. 205, no 1, p. 125-137Article in journal (Refereed)
  • 14.
    SANDBERG, G
    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).
    DUNBERG, A
    PRECISION AND ACCURACY OF INDOLE-3-ACETIC-ACID ANALYSES PERFORMED WITH THE 2-METHYLINDOLO-ALPHA-PYRONE FLUORESCENCE ASSAY AND WITH A HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY TECHNIQUE WITH SPECTROFLUORIMETRIC DETECTION, EXEMPLIFIED ON PINE TISSUE (PINUS-SYLVESTRIS L)1982In: Physiologia Plantarum: An International Journal for Plant Biology, ISSN 0031-9317, E-ISSN 1399-3054, Vol. 55, no 3, p. 315-322Article in journal (Refereed)
  • 15. SANDBERG, G
    et al.
    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).
    SITBON, F
    OLSSON, O
    PRESENCE OF INDOLE-3-ACETIC-ACID IN CHLOROPLASTS OF NICOTIANA-TABACUM AND PINUS-SYLVESTRIS1990In: Planta, ISSN 0032-0935, E-ISSN 1432-2048, Vol. 180, no 4, p. 562-568Article in journal (Refereed)
  • 16.
    Schrader, Jarmo
    et al.
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre. Department of Forest Genetics and Plant Physiology.
    Nilsson, Jeanette
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre. Department of Forest Genetics and Plant Physiology.
    Mellerowicz, Ewa
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre. Department of Forest Genetics and Plant Physiology.
    Berglund, Anders
    Chemistry.
    Nilsson, Peter
    Hertzberg, Magnus
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre. Department of Forest Genetics and Plant Physiology.
    Sandberg, Göran
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre. Department of Forest Genetics and Plant Physiology.
    A High-Resolution Transcript Profile across the Wood-Forming Meristem of Poplar Identifies Potential Regulators of Cambial Stem Cell Identity2004In: The Plant Cell, ISSN 1040-4651, Vol. 16, no 9, p. 2278-92Article in journal (Refereed)
    Abstract [en]

    Plant growth is the result of cell proliferation in meristems, which requires a careful balance between the formation of new tissue and the maintenance of a set of undifferentiated stem cells. Recent studies have provided important information on several genetic networks responsible for stem cell maintenance and regulation of cell differentiation in the apical meristems of shoots and roots. Nothing, however, is known about the regulatory networks in secondary meristems like the vascular cambium of trees. We have made use of the large size and highly regular layered organization of the cambial meristem to create a high-resolution transcriptional map covering 220 µm of the cambial region of aspen (Populus tremula). Clusters of differentially expressed genes revealed substantial differences in the transcriptomes of the six anatomically homogenous cell layers in the meristem zone. Based on transcriptional and anatomical data, we present a model for the position of the stem cells and the proliferating mother cells in the cambial zone. We also provide sets of marker genes for different stages of xylem and phloem differentiation and identify potential regulators of cambial meristem activity. Interestingly, analysis of known regulators of apical meristem development indicates substantial similarity in regulatory networks between primary and secondary meristems.

  • 17. SITBON, F
    et al.
    EDLUND, A
    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).
    OLSSON, O
    SANDBERG, G
    COMPARTMENTATION OF INDOLE-3-ACETIC-ACID METABOLISM IN PROTOPLASTS ISOLATED FROM LEAVES OF WILD-TYPE AND IAA-OVERPRODUCING TRANSGENIC TOBACCO PLANTS1993In: Planta, ISSN 0032-0935, E-ISSN 1432-2048, Vol. 191, no 2, p. 274-279Article in journal (Refereed)
    Abstract [en]

    Cellular compartmentation of indole-3-acetamide (IAM), indole-3-acetic acid (IAA), and [N-15(1)]IAA synthesised from [N-15(1)]tryptophan was monitored in protoplasts isolated from sterile wild-type tobacco SR1 plants, and in IAA-overproducing plants expressing the Agrobacterium tumefaciens T-DNA IAA genes iaaM and iaaH. Indole-3-acetamide was located exclusively in the cytosol of both iaaM and iaaM/iaaH protoplasts, being 75% lower than in iaaM protoplasts, presumably because of conversion into IAA by action of the iaaH-encoded hydrolase. The free-IAA level, however, was raised only 8% in iaaM/iaaH compared to iaaM protoplasts, whereas the level of IAA-conjugates was increased more than fivefold. For both genotypes, the location of IAA conjugates was restricted to the cytosol, while one-third of the free-IAA pool was present in chloroplasts. Transcription of the iaaM gene was increased by fusion to the strong cautiflower mosaic virus (CaMV) 35S promoter. Compared with the wildtype, this led to an 18-fold higher conversion of [N-15(1)]tryptophan to [N-15(1)]IAA, a three- to fourfold increase in free IAA, and a tenfold higher level of IAA conjugates in 35S-iaaM/iaaH protoplasts. Also in these genotypes, IAA conjugates were exclusively cytosolic. There was no major difference between transgenic and wildtype protoplasts in the proportion of chloroplastic to total cellular IAA, although the chloroplastic IAA and [N-15(1)]IAA pools in the transformant were threefold and eightfold higher, respectively. Since the IAM pool in transgenic plants is exclusively cytosolic, these findings suggest that the increased chloroplastic [N-15(1)]IAA pool in 35S-iaaM/iaaH protoplasts is synthesised in the cytosol but rapidly transported into the chloroplast. Furthermore, the presence of IAA in the chloroplast together with the exclusively cytosolic location of IAA conjugates, suggests the presence of two differentially subcellular pools of IAA. The first is located in the cytosol and mainly regulated by non-decarboxylative catabolism and conjugation (Sandberg et al. 1990, Planta 180, 562-568), whereas the second is located in the chloroplast and is seemingly not directly regulated inside the organelle by either of these two processes. The cytosolic IAA control mechanisms, however, also affect the chloroplastic pool size due to the rapid transport of IAA between the two compartments.

  • 18.
    Sjödin, Andreas
    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.
    Street, Nathaniel R
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Sandberg, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Gustafsson, Petter
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    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).
    The populus genome integrative explorer (PopGenIE): a new resource for exploring the populus genome2009In: New Phytologist, ISSN 0028-646X, E-ISSN 1469-8137, Vol. 182, no 4, p. 1013-1025Article in journal (Refereed)
    Abstract [en]

    * Populus has become an important model plant system. However, utilization of the increasingly extensive collection of genetics and genomics data created by the community is currently hindered by the lack of a central resource, such as a model organism database (MOD). Such MODs offer a single entry point to the collection of resources available within a model system, typically including tools for exploring and querying those resources. * As a starting point to overcoming the lack of such an MOD for Populus, we present the Populus Genome Integrative Explorer (PopGenIE), an integrated set of tools for exploring the Populus genome and transcriptome. The resource includes genome, synteny and quantitative trait locus (QTL) browsers for exploring genetic data. * Expression tools include an electronic fluorescent pictograph (eFP) browser, expression profile plots, co-regulation within collated transcriptomics data sets, and identification of over-represented functional categories and genomic hotspot locations. A number of collated transcriptomics data sets are made available in the eFP browser to facilitate functional exploration of gene function. Additional homology and data extraction tools are provided. * PopGenIE significantly increases accessibility to Populus genomics resources and allows exploration of transcriptomics data without the need to learn or understand complex statistical analysis methods. PopGenIE is available at http://www.popgenie.org or via http://www.populusgenome.info.

  • 19. Sterky, F
    et al.
    Regan, S
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Hertzberg, M
    Rohde, A
    Holmberg, A
    Amini, B
    Bhalerao, R
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Larsson, M
    Villarroel, R
    Van Montagu, M
    Sandberg, G
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Olsson, O
    Teeri, T T
    Boerjan, W
    Gustafsson, Petter
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Uhlen, M
    Sundberg, B
    Lundeberg, J
    Gene discovery in the wood-forming tissues of poplar: Analysis of 5,692 expressed sequence tags1998In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 95, no 22, p. 13330-13335Article in journal (Refereed)
    Abstract [en]

    A rapidly growing area of genome research is the generation of expressed sequence tags (ESTs) in which large numbers of randomly selected cDNA clones are partially sequenced. The collection of ESTs reflects the level and complexity of gene expression in the sampled tissue, To date, the majority of plant ESTs are from nonwoody plants such as Arabidopsis, Brassica, maize, and rice. Here, we present a large-scale production of ESTs from the wood-forming tissues of two poplars, Populus tremula L, x tremuloides Michx, and Populus trichocarpa 'Trichobel.' The 5,692 ESTs analyzed represented a total of 3,719 unique transcripts for the two cDNA libraries, Putative functions could be assigned to 2,245 of these transcripts that corresponded to 820 protein functions. Of specific interest to forest biotechnology are the 4% of ESTs involved in various processes of cell wall formation, such as lignin and cellulose synthesis, 5% similar to developmental regulators and members of known signal transduction pathways, and 2% involved in hormone biosynthesis. An additional 12% of the ESTs show ed no significant similarity to any other DNA or protein sequences in existing databases. The absence of these sequences from public databases may indicate a specific role for these proteins in wood formation. The cDNA libraries and the accompanying database are valuable resources for forest research directed toward understanding the genetic control of wood formation and future endeavors to modify wood and fiber properties for industrial use.

  • 20. Sterky, Fredrik
    et al.
    Bhalerao, Rupali R
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Unneberg, Per
    Segerman, Bo
    Nilsson, Peter
    Brunner, Amy M
    Charbonnel-Campaa, Laurence
    Lindvall, Jenny Jonsson
    Tandre, Karolina
    Strauss, Steven H
    Sundberg, Björn
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Gustafsson, Petter
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Uhlén, Mathias
    Bhalerao, Rishikesh P
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Nilsson, Ove
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Sandberg, Göran
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Lundeberg, Joakim
    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).
    A Populus EST resource for plant functional genomics.2004In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, Vol. 101, no 38, p. 13951-6Article in journal (Refereed)
    Abstract [en]

    Trees present a life form of paramount importance for terrestrial ecosystems and human societies because of their ecological structure and physiological function and provision of energy and industrial materials. The genus Populus is the internationally accepted model for molecular tree biology. We have analyzed 102,019 Populus ESTs that clustered into 11,885 clusters and 12,759 singletons. We also provide >4,000 assembled full clone sequences to serve as a basis for the upcoming annotation of the Populus genome sequence. A public web-based EST database (POPULUSDB) provides digital expression profiles for 18 tissues that comprise the majority of differentiated organs. The coding content of Populus and Arabidopsis genomes shows very high similarity, indicating that differences between these annual and perennial angiosperm life forms result primarily from differences in gene regulation. The high similarity between Populus and Arabidopsis will allow studies of Populus to directly benefit from the detailed functional genomic information generated for Arabidopsis, enabling detailed insights into tree development and adaptation. These data will also valuable for functional genomic efforts in Arabidopsis.

  • 21. Swarup, Kamal
    et al.
    Benková, Eva
    Swarup, Ranjan
    Casimiro, Ilda
    Péret, Benjamin
    Yang, Yaodong
    Parry, Geraint
    Nielsen, Erik
    De Smet, Ive
    Vanneste, Steffen
    Levesque, Mitch P
    Carrier, David
    James, Nicholas
    Calvo, Vanessa
    Ljung, Karin
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre.
    Kramer, Eric
    Roberts, Rebecca
    Graham, Neil
    Marillonnet, Sylvestre
    Patel, Kanu
    Jones, Jonathan D G
    Taylor, Christopher G
    Schachtman, Daniel P
    May, Sean
    Sandberg, Göran
    Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre.
    Benfey, Philip
    Friml, Jiri
    Kerr, Ian
    Beeckman, Tom
    Laplaze, Laurent
    Bennett, Malcolm J
    The auxin influx carrier LAX3 promotes lateral root emergence.2008In: Nature Cell Biology, ISSN 1476-4679, Vol. 10, no 8, p. 946-54Article in journal (Refereed)
    Abstract [en]

    Lateral roots originate deep within the parental root from a small number of founder cells at the periphery of vascular tissues and must emerge through intervening layers of tissues. We describe how the hormone auxin, which originates from the developing lateral root, acts as a local inductive signal which re-programmes adjacent cells. Auxin induces the expression of a previously uncharacterized auxin influx carrier LAX3 in cortical and epidermal cells directly overlaying new primordia. Increased LAX3 activity reinforces the auxin-dependent induction of a selection of cell-wall-remodelling enzymes, which are likely to promote cell separation in advance of developing lateral root primordia.

  • 22. Swarup, Ranjan
    et al.
    Perry, Paula
    Hagenbeek, Dik
    Van Der Straeten, Dominique
    Beemster, Gerrit T S
    Sandberg, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Bhalerao, Rishikesh
    Ljung, Karin
    Bennett, Malcolm J
    Ethylene upregulates auxin biosynthesis in Arabidopsis seedlings to enhance inhibition of root cell elongation.2007In: The Plant Cell, ISSN 1040-4651, E-ISSN 1532-298X, Vol. 19, no 7, p. 2186-96Article in journal (Refereed)
    Abstract [en]

    Ethylene represents an important regulatory signal for root development. Genetic studies in Arabidopsis thaliana have demonstrated that ethylene inhibition of root growth involves another hormone signal, auxin. This study investigated why auxin was required by ethylene to regulate root growth. We initially observed that ethylene positively controls auxin biosynthesis in the root apex. We subsequently demonstrated that ethylene-regulated root growth is dependent on (1) the transport of auxin from the root apex via the lateral root cap and (2) auxin responses occurring in multiple elongation zone tissues. Detailed growth studies revealed that the ability of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid to inhibit root cell elongation was significantly enhanced in the presence of auxin. We conclude that by upregulating auxin biosynthesis, ethylene facilitates its ability to inhibit root cell expansion.

  • 23. Tao, Yi
    et al.
    Ferrer, Jean-Luc
    Ljung, Karin
    Pojer, Florence
    Hong, Fangxin
    Long, Jeff A
    Li, Lin
    Moreno, Javier E
    Bowman, Marianne E
    Ivans, Lauren J
    Cheng, Youfa
    Lim, Jason
    Zhao, Yunde
    Ballaré, Carlos L
    Sandberg, Göran
    Umeå University, Faculty of Science and Technology, Plant Physiology. Umeå Plant Science Centre.
    Noel, Joseph P
    Chory, Joanne
    Rapid synthesis of auxin via a new tryptophan-dependent pathway is required for shade avoidance in plants.2008In: Cell, ISSN 1097-4172, Vol. 133, no 1, p. 164-76Article in journal (Refereed)
    Abstract [en]

    Plants grown at high densities perceive a decrease in the red to far-red (R:FR) ratio of incoming light, resulting from absorption of red light by canopy leaves and reflection of far-red light from neighboring plants. These changes in light quality trigger a series of responses known collectively as the shade avoidance syndrome. During shade avoidance, stems elongate at the expense of leaf and storage organ expansion, branching is inhibited, and flowering is accelerated. We identified several loci in Arabidopsis, mutations in which lead to plants defective in multiple shade avoidance responses. Here we describe TAA1, an aminotransferase, and show that TAA1 catalyzes the formation of indole-3-pyruvic acid (IPA) from L-tryptophan (L-Trp), the first step in a previously proposed, but uncharacterized, auxin biosynthetic pathway. This pathway is rapidly deployed to synthesize auxin at the high levels required to initiate the multiple changes in body plan associated with shade avoidance.

  • 24. Tuskan, G A
    et al.
    Difazio, S
    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).
    Bohlmann, J
    Grigoriev, I
    Hellsten, U
    Putnam, N
    Ralph, S
    Rombauts, S
    Salamov, A
    Schein, J
    Sterck, L
    Aerts, A
    Bhalerao, Rupali R
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Bhalerao, Rishikesh P
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Blaudez, D
    Boerjan, W
    Brun, A
    Brunner, A
    Busov, V
    Campbell, M
    Carlson, J
    Chalot, M
    Chapman, J
    Chen, G-L
    Cooper, D
    Coutinho, P M
    Couturier, J
    Covert, S
    Cronk, Q
    Cunningham, R
    Davis, J
    Degroeve, S
    Déjardin, A
    Depamphilis, C
    Detter, J
    Dirks, B
    Dubchak, I
    Duplessis, S
    Ehlting, J
    Ellis, B
    Gendler, K
    Goodstein, D
    Gribskov, M
    Grimwood, J
    Groover, A
    Gunter, L
    Hamberger, B
    Heinze, B
    Helariutta, Y
    Henrissat, B
    Holligan, D
    Holt, R
    Huang, W
    Islam-Faridi, N
    Jones, S
    Jones-Rhoades, M
    Jorgensen, R
    Joshi, C
    Kangasjärvi, J
    Karlsson, Jan
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Kelleher, C
    Kirkpatrick, R
    Kirst, M
    Kohler, A
    Kalluri, U
    Larimer, F
    Leebens-Mack, J
    Leplé, J-C
    Locascio, P
    Lou, Y
    Lucas, S
    Martin, F
    Montanini, B
    Napoli, C
    Nelson, D R
    Nelson, C
    Nieminen, K
    Nilsson, Ove
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Pereda, V
    Peter, G
    Philippe, R
    Pilate, G
    Poliakov, A
    Razumovskaya, J
    Richardson, P
    Rinaldi, C
    Ritland, K
    Rouzé, P
    Ryaboy, D
    Schmutz, J
    Schrader, J
    Segerman, Bo
    Shin, H
    Siddiqui, A
    Sterky, Fredrik
    Terry, A
    Tsai, C-J
    Uberbacher, E
    Unneberg, P
    Vahala, J
    Wall, K
    Wessler, S
    Yang, G
    Yin, T
    Douglas, C
    Marra, M
    Sandberg, Göran
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Van de Peer, Y
    Rokhsar, D
    The genome of black cottonwood, Populus trichocarpa (Torr. & Gray).2006In: Science, ISSN 1095-9203, Vol. 313, no 5793, p. 1596-604Article in journal (Refereed)
    Abstract [en]

    We report the draft genome of the black cottonwood tree, Populus trichocarpa. Integration of shotgun sequence assembly with genetic mapping enabled chromosome-scale reconstruction of the genome. More than 45,000 putative protein-coding genes were identified. Analysis of the assembled genome revealed a whole-genome duplication event; about 8000 pairs of duplicated genes from that event survived in the Populus genome. A second, older duplication event is indistinguishably coincident with the divergence of the Populus and Arabidopsis lineages. Nucleotide substitution, tandem gene duplication, and gross chromosomal rearrangement appear to proceed substantially more slowly in Populus than in Arabidopsis. Populus has more protein-coding genes than Arabidopsis, ranging on average from 1.4 to 1.6 putative Populus homologs for each Arabidopsis gene. However, the relative frequency of protein domains in the two genomes is similar. Overrepresented exceptions in Populus include genes associated with lignocellulosic wall biosynthesis, meristem development, disease resistance, and metabolite transport.

  • 25.
    Wang, Jiehua
    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). Tianjin Univ, Coll Agr & Bioengn, Tianjin 300072, Peoples R China.
    Andersson-Gunneras, Sara
    Gaboreanu, Ioana
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Hertzberg, Magnus
    Tucker, Matthew R.
    Zheng, Bo
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Lesniewska, Joanna
    Mellerowicz, Ewa J.
    Laux, Thomas
    Sandberg, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Jones, Brian
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Reduced expression of the SHORT-ROOT gene increases the rates of growth and development in hybrid poplar and arabidopsis2011In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 6, no 12, article id e28878Article in journal (Refereed)
    Abstract [en]

    SHORT-ROOT (SHR) is a well characterized regulator of cell division and cell fate determination in the Arabidopsis primary root. However, much less is known about the functions of SHR in the aerial parts of the plant. In this work, we cloned SHR gene from Populus trichocarpa (PtSHR1) as an AtSHR ortholog and down-regulated its expression in hybrid poplar (Populus tremula x P. tremuloides Michx-clone T89) in order to determine its physiological functions in shoot development. Sharing a 90% similarity to AtSHR at amino acid level, PtSHR1 was able to complement the Arabidopsis shr mutant. Down regulation of PtSHR1 led to a strong enhancement of primary (height) and secondary (girth) growth rates in the transgenic poplars. A similar approach in Arabidopsis showed a comparable accelerated growth and development phenotype. Our results suggest that the response to SHR could be dose-dependent and that a partial down-regulation of SHR could lead to enhanced meristem activity and a coordinated acceleration of plant growth in woody species. Therefore, SHR functions in plant growth and development as a regulator of cell division and meristem activity not only in the roots but also in the shoots. Reducing SHR expression in transgenic poplar was shown to lead to significant increases in primary and secondary growth rates. Given the current interest in bioenergy crops, SHR has a broader role as a key regulator of whole plant growth and development and SHR suppression has considerable potential for accelerating biomass accumulation in a variety of species.

  • 26. Wang, Jiehua
    et al.
    Kucukoglu, Melis
    Zhang, Linbin
    Chen, Peng
    Decker, Daniel
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Nilsson, Ove
    Jones, Brian
    Sandberg, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Zheng, Bo
    The Arabidopsis LRR-RLK, PXC1, is a regulator of secondary wall formation correlated with the TDIF-PXY/TDR-WOX4 signaling pathway2013In: BMC Plant Biology, ISSN 1471-2229, E-ISSN 1471-2229, Vol. 13, p. 94-Article in journal (Refereed)
    Abstract [en]

    Background: Although a number of leucine-rich repeat receptor-like kinase-encoding genes (LRR-RLKs) have been identified in plants, a functional role has been determined for only a few. Recent studies have demonstrated that an LRR-RLK, PXY/TDR, is important for the process of secondary vascular development. Other studies have indicated that PXY/TDR is unlikely to be the sole LRR-RLK involved in this complex process.

    Results: In this study, in silico analyses led to the identification of three Arabidopsis LRR-RLK genes (PXY-correlated; PXC1, 2, 3) with transcript accumulation profiles that correlated strongly with several key regulators of vascular development, including PXY/TDR, HB-8, REV, and CLE41. Expression profiling using qPCR and promoter: reporter lines indicated that all three PXC genes are associated with the vasculature. One in particular, PXC1 (At2g36570), had a strong correlation with PXY/TDR. Shifting pxc1 mutants from long-days to short-days showed that loss of the gene led to a dramatic reduction in secondary wall formation in xylem fibers. Transcript analysis of mutants for a variety of secondary cell wall-associated genes, including PXY/TDR indicated that the pathways mediated by PXC1 connect with those mediated by the TDIF-PXY/TDR-WOX4 system.

    Conclusions: The data indicate that the LRR-RLK, PXC1 is involved in secondary cell wall formation in xylem fibers. Whereas further study is needed to identify the ligands and mode of action of the PXC1 protein, it is clear from this work that similarly to the shoot apical meristem (SAM), secondary vascular development requires contributions from a number of LRR-RLKs.

  • 27. Yin, Xiao-Jun
    et al.
    Volk, Sara
    Ljung, Karin
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Mehlmer, Norbert
    Dolezal, Karel
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Laboratory of Growth Regulators, Palacky University and Institute of Experimental Botany, Academy of Sciences of the Czech Republic, CZ-78371 Olomouc, Czech Republic.
    Ditengou, Franck
    Hanano, Shigeru
    Davis, Seth J
    Schmelzer, Elmon
    Sandberg, Göran
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Teige, Markus
    Palme, Klaus
    Pickart, Cecile
    Bachmair, Andreas
    Ubiquitin lysine 63 chain forming ligases regulate apical dominance in Arabidopsis2007In: The Plant Cell, ISSN 1040-4651, E-ISSN 1532-298X, Vol. 19, no 6, p. 1898-1911Article in journal (Refereed)
    Abstract [en]

    Lys-63-linked multiubiquitin chains play important roles in signal transduction in yeast and in mammals, but the functions for this type of chain in plants remain to be defined. The RING domain protein RGLG2 (for RING domain Ligase2) from Arabidopsis thaliana can be N-terminally myristoylated and localizes to the plasma membrane. It can form Lys-63-linked multiubiquitin chains in an in vitro reaction. RGLG2 has overlapping functions with its closest sequelog, RGLG1, and single mutants in either gene are inconspicuous. rglg1 rglg2 double mutant plants exhibit loss of apical dominance and altered phyllotaxy, two traits critically influenced by the plant hormone auxin. Auxin and cytokinin levels are changed, and the plants show a decreased response to exogenously added auxin. Changes in the abundance of PIN family auxin transport proteins and synthetic lethality with a mutation in the auxin transport regulator BIG suggest that the directional flow of auxin is modulated by RGLG activity. Modification of proteins by Lys-63-linked multiubiquitin chains is thus important for hormone-regulated, basic plant architecture.

  • 28. Åstot, C
    et al.
    Dolezal, K
    Nordström, A
    Wang, Q
    Kunkel, T
    Moritz, T
    Chua, N H
    Sandberg, G
    An alternative cytokinin biosynthesis pathway2000In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 97, no 26, p. 14778-14783Article in journal (Refereed)
    Abstract [en]

    Studies of de novo cytokinin biosynthesis in isopentenyltransferase (ipt)-transformed Arabidopsis thaliana, involving in vivo deuterium labeling and mass spectrometry, showed that the biosynthetic rate of zeatinriboside-5'-monophosphate was around 66-fold higher than that of isopentenyladenosine-5'-monophosphate (iPMP), the proposed primary product of the Agrobacterium ipt. Double tracer analysis, using [(2)H(6)] isopentenyladenosine and deuterium oxide, provided evidence for an alternative, iPMP-independent, biosynthetic pathway for zeatin-type cytokinins, present in both ipt-expressing and wild-type Arabidopsis thaliana. Reduction of the biosynthetic flux in the alternative pathway by use of mevastatin, an inhibitor for 3-hydroxy-3-methylglutaryl CoA reductase, indicated a terpenoid origin for the side-chain precursor of the iPMP independent pathway.

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