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  • 51.
    Kunz, Sabine
    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.
    Gardeström, Per
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Pesquet, Edouard
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Kleczkowski, Leszek
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Hexokinase 1 is required for glucose-induced repression of bZIP63, At5g22920, and BT2 in Arabidopsis2015In: Frontiers in Plant Science, ISSN 1664-462X, E-ISSN 1664-462X, Vol. 6, article id 525Article in journal (Refereed)
    Abstract [en]

    Simple sugars, like glucose (Glc) and sucrose (Suc), act as signals to modulate the expression of hundreds of genes in plants. Frequently, however, it remains unclear whether this regulation is induced by the sugars themselves or by their derivatives generated in the course of carbohydrate (CH) metabolism. In the present study, we tested the relevance of different CH metabolism and allocation pathways affecting expression patterns of five selected sugar-responsive genes (bZIP63, At5g22920, BT2, MGD2, and TPS9) in Arabidopsis thaliana. In general, the expression followed diurnal changes in the overall sugar availability. However, under steady growth conditions, this response was hardly impaired in the mutants for CH metabolizing/transporting proteins (adg1, sex1, sus1-4, sus5/6, and tpt2), including also hexokinase1 (HXK1) loss- and gain-of-function plants—gin2.1 and oe3.2, respectively. In addition, transgenic plants carrying pbZIP63::GUS showed no changes in reporter-gene-expression when grown on sugar under steady-state conditions. In contrast, short-term treatments of agar-grown seedlings with 1% Glc or Suc induced pbZIP63::GUS repression, which became even more apparent in seedlings grown in liquid media. Subsequent analyses of liquid-grown gin2.1 and oe3.2 seedlings revealed that Glc -dependent regulation of the five selected genes was not affected in gin2.1, whereas it was enhanced in oe3.2 plants for bZIP63, At5g22920, and BT2. The sugar treatments had no effect on ATP/ADP ratio, suggesting that changes in gene expression were not linked to cellular energy status. Overall, the data suggest that HXK1 does not act as Glc sensor controlling bZIP63, At5g22920, and BT2 expression, but it is nevertheless required for the production of a downstream metabolic signal regulating their expression.

  • 52.
    Kunz, Sabine
    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).
    Pesquet, Edouard
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    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).
    Functional Dissection of Sugar Signals Affecting Gene Expression in Arabidopsis thaliana2014In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 9, no 6, p. e100312-Article in journal (Refereed)
    Abstract [en]

    Background: Sugars modulate expression of hundreds of genes in plants. Previous studies on sugar signaling, using intact plants or plant tissues, were hampered by tissue heterogeneity, uneven sugar transport and/or inter-conversions of the applied sugars. This, in turn, could obscure the identity of a specific sugar that acts as a signal affecting expression of given gene in a given tissue or cell-type. Methodology/Principal Findings: To bypass those biases, we have developed a novel biological system, based on stem-cell-like Arabidopsis suspension culture. The cells were grown in a hormone-free medium and were sustained on xylose as the only carbon source. Using functional genomics we have identified 290 sugar responsive genes, responding rapidly (within 1 h) and specifically to low concentration (1 mM) of glucose, fructose and/or sucrose. For selected genes, the true nature of the signaling sugar molecules and sites of sugar perception were further clarified using non-metabolizable sugar analogues. Using both transgenic and wild-type A. thaliana seedlings, it was shown that the expression of selected sugar-responsive genes was not restricted to a specific tissue or cell type and responded to photoperiod-related changes in sugar availability. This suggested that sugar-responsiveness of genes identified in the cell culture system was not biased toward heterotrophic background and resembled that in whole plants. Conclusions: Altogether, our research strategy, using a combination of cell culture and whole plants, has provided an unequivocal evidence for the identity of sugar-responsive genes and the identity of the sugar signaling molecules, independently from their inter-conversions or use for energy metabolism.

  • 53. Kwiatkowski, B A
    et al.
    Zielińska-Kwiatkowska, A G
    Migdalski, A
    Kleczkowski, L A
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Wasilewska, L D
    Cloning of two cDNAs encoding calnexin-like and calreticulin-like proteins from maize (Zea mays) leaves: identification of potential calcium-binding domains.1995In: Gene, ISSN 0378-1119, E-ISSN 1879-0038, Vol. 165, no 2, p. 219-22Article in journal (Refereed)
    Abstract [en]

    Two cDNAs encoding calnexin (Cln)-like and calreticulin (Crl)-like proteins have been isolated by immunoscreening of a maize leaf cDNA library. In the deduced amino acid (aa) sequences, several regions that are conserved for Cln and Crl proteins from all sources have been identified. These regions can be classified into two distinct motifs which are repeated four times each in Cln and three times each in Crl sequences. One of these motifs, containing a highly acidic 17-aa sequence, has high homology to a Ca(2+)-binding domain previously characterized in both Cln and Crl from mammalian tissues. Motifs for retention in endoplasmic reticulum (Crl) and for an integral membrane-spanning sequence (Cln) have also been identified.

  • 54. Lesniewska, Joanna
    et al.
    Ohman, David
    Krzeslowska, Magdalena
    Kushwah, Sunita
    Barciszewska-Pacak, Maria
    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).
    Sundberg, Bjorn
    Moritz, Thomas
    Mellerowicz, Ewa J.
    Defense Responses in Aspen with Altered Pectin Methylesterase Activity Reveal the Hormonal Inducers of Tyloses2017In: Plant Physiology, ISSN 0032-0889, E-ISSN 1532-2548, Vol. 173, no 2, p. 1409-1419Article in journal (Refereed)
    Abstract [en]

    Tyloses are ingrowths of parenchyma cells into the lumen of embolized xylem vessels, thereby protecting the remaining xylem from pathogens. They are found in heartwood, sapwood, and in abscission zones and can be induced by various stresses, but their molecular triggers are unknown. Here, we report that down-regulation of PECTIN METHYLESTERASE1 (PtxtPME1) in aspen (Populus tremula 3 tremuloides) triggers the formation of tyloses and activation of oxidative stress. We tested whether any of the oxidative stress-related hormones could induce tyloses in intact plantlets grown in sterile culture. Jasmonates, including jasmonic acid (JA) and methyl jasmonate, induced the formation of tyloses, whereas treatments with salicylic acid (SA) and 1-aminocyclopropane-1carboxylic acid (ACC) were ineffective. SA abolished the induction of tyloses by JA, whereas ACC was synergistic with JA. The ability of ACC to stimulate tyloses formation when combined with JA depended on ethylene (ET) signaling, as shown by a decrease in the response in ET-insensitive plants. Measurements of internal ACC and JA concentrations in wild-type and ET-insensitive plants treated simultaneously with these two compounds indicated that ACC and JA regulate each other's concentration in an ET-dependent manner. The findings indicate that jasmonates acting synergistically with ethylene are the key molecular triggers of tyloses.

  • 55. Luo, C
    et al.
    Dejardin, A
    Villand, P
    Doan, D N P
    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).
    Differential processing of homologues of the small subunit of ADP-glucose pyrophosphorylase from barley (Hordeum vulgare) tissues1997In: Zeitschrift für Naturforschung C - A Journal of Biosciences, ISSN 0939-5075, E-ISSN 1865-7125, Vol. 52, no 11-12, p. 807-811Article in journal (Refereed)
    Abstract [en]

    ADP-glucose pyrophosphorylase (AGPase), a two-gene-encoded enzyme, is the key component of starch synthesis in all plants. In the present study, we have used an E. coli expres sion system for the (over)production of proteins derived from both full length and specifically truncated cDNAs encoding small subunits of AGPase from seed endosperm (AGPase-B1) and leaves (AGPase-B2) of barley (Hordeum vulgare). Based on immunoblot analyses, the molecular mass of the expressed AGPase-B1 (52 kD) was similar to that from endosperm extracts, whereas the expressed AGPase-B2 (56 kD) was larger than that in barley leaves (51 kD). Expression of truncated cDNAs for both the seed and leaf proteins has allowed for a direct verification of molecular masses that were earlier proposed for mature AGPases in barley tissues. The data suggest that seed AGPase-B1 does not undergo any post-translational proteolytic processing in barley, whereas the leaf homologue is processed to a smaller protein. Possible implications of these findings are discussed.

  • 56. Luo, C
    et al.
    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).
    Expression of barley ADP-glucose pyrophosphorylase in Escherichia coli: processing and regulatory considerations1999In: Phytochemistry, ISSN 0031-9422, E-ISSN 1873-3700, Vol. 50, no 2, p. 209-214Article in journal (Refereed)
    Abstract [en]

    Full length cDNAs for barley ADP-glucose pyrophosphorylase (AGPase) coding for the large subunits of the endosperm and leaf homologues of the enzyme (AGPase-S1 and -S2, respectively) and for the small subunit protein from endosperm (AGPase-B1), have been expressed in Escherichia coli. The cDNAs for AGPase-S1 and -S2 required different induction conditions for their maximal expression and they encoded immunologically distinct proteins. The AGPase-S1 that was produced by E. coli had the same M-r (58 kDa) as the corresponding protein in barley crude endosperm extracts, whereas the bacteria-produced AGPase-S2 (55 kDa) was larger than its counterpart from barley leaf preparations (53 kDa). An enzymatically active ACPase expressed in E. coli from a double construct containing cDNAs for AGPase-S1 and -B1 subunits was insensitive to the activation by 3-phosphoglycerate and to inhibition by inorganic phosphate, similarly to the enzyme in barley endosperm. Neither AGPase-S1 nor -B1 were active when expressed alone in the bacteria. The data are discussed with respect to possible mechanisms of intracellular targeting of immature AGPase-S proteins in barley tissues and regarding previous data on effector regulation of the barley enzyme. (C) 1998 Elsevier Science Ltd. All rights reserved.

  • 57.
    Martz, Françoise
    et al.
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Wilczynska, Malgorzata
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Kleczkowski, Leszek A
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC). Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
    Oligomerization status, with the monomer as active species, defines catalytic efficiency of UDP-glucose pyrophosphorylase2002In: Biochemical Journal, ISSN 0264-6021, E-ISSN 1470-8728, Vol. 367, no 1, p. 295-300Article in journal (Refereed)
    Abstract [en]

    Barley UDP-glucose pyrophosphorylase (UGPase), a key enzyme for the synthesis of sucrose, cellulose and other saccharides, was expressed in Escherichia coli and purified. Using both native electrophoresis and gel filtration, the recombinant and crude leaf UGPase proteins were found to exist as a mixture of monomers, dimers and higher-order polymers. In order to understand the molecular basis for the oligomerization of UGPase, a conserved Cys residue was replaced (C99S mutant) and several amino acids were substituted (LIV to NIN, KK to LL and LLL to NNN) in a conserved hydrophobic domain (amino acids 117-138). The C99S mutant had about half the V (max) of the wild-type and a 12-fold higher K (m) for PP(i), whereas NIN and LL mutations lowered the V (max) by 12- and 2-fold, respectively, with relatively small effects on substrate K (m) values (the NNN mutant was insoluble/inactive). The NIN mutation resulted in a low-activity oligomerized enzyme form, with very little monomer formation. Activity staining on native PAGE gels as well as gel-filtration studies demonstrated that the monomer was the sole enzymically active form. Possible implications of the oligomerization status of UGPase for post-translational regulation of the enzyme are discussed.

  • 58.
    Meng, Meng
    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).
    Fitzek, Elisabeth
    Gajowniczek, Agnieszka
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Wilczynska, Malgorzata
    Umeå University, Faculty of Medicine, Department of Medical Biochemistry and Biophysics.
    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).
    Domain-specific determinants of catalysis/ substrate binding and the oligomerization status of barley UDP-glucose pyrophosphorylase2009In: Biochimica et Biophysica Acta - Proteins and Proteomics, ISSN 1570-9639, E-ISSN 1878-1454, Vol. 1794, p. 1734-1742Article in journal (Refereed)
    Abstract [en]

    UDP-glucose (UDPG) pyrophosphorylase (UGPase) produces UDPG for sucrose and polysaccharide synthesis and glycosylation reactions. In this study, several barley UGPase mutants were produced, either single amino acid mutants or involving deletions of N- and C-terminal domains (Ncut and Ccut mutants, respectively) and of active site region ("NB loop"). The Del-NB mutant yielded no activity, whereas Ncut deletions and most of Ccut mutants, including short deletions at the so called "I-loop" region of C-terminal domain, as well as a single K260A mutant resulted in very low activity. For wt and the mutants, kinetics with UDPG were linear on reciprocal plots, whereas PPi at concentrations above 1mM exerted strong substrate inhibition. Both K260A and most of the Ccut mutants had very high K(m) with PPi (up to 33mM), whereas Ncut deletions had greatly increased K(m) with UDPG (up to 57mM). Surprisingly, an 8 amino acid deletion from end of the C-terminus resulted in an enzyme (Ccut-8 mutant) with 44% higher activity when compared to wt, but with similar K(m) values. Whereas Ccut-8 existed solely as a monomer, other deletion mutants had a more oligomerized status, e.g. Ncut mutants existing primarily as dimers. Overall, the data confirmed the essential role of NB loop in catalysis, but also pointed out to the role of both N- and C-termini for activity, substrate binding and oligomerization. The importance of oligomerization status for enzymatic activity of UGPase is discussed.

  • 59.
    Meng, Meng
    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).
    Geisler, Matt
    Department of Plant Biology, Southern Illinois University.
    Johansson, Henrik
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Harholt, Jesper
    Department of Plant Physiology, University of Copenhagen.
    Scheller, Henrik V.
    Department of Plant Physiology, University of Copenhagen, .
    Mellerowicz, Ewa J.
    Department of Forest Genetics and Plant Physiology, SLU, Umeå, Sweden.
    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).
    UDP-glucose pyrophosphorylase is not rate limiting, but is essential in arabidopsis2009In: Plant and Cell Physiology, ISSN 0032-0781, E-ISSN 1471-9053, Vol. 50, no 5, p. 998-1011Article in journal (Refereed)
    Abstract [en]

    UDP-glucose pyrophosphorylase (UGPase) produces UDP-glucose which is essential for sucrose and polysaccharide synthesis. Using Arabidopsis, we demonstrated that two UGPase genes (UGP1 and UGP2) are differentially expressed in a variety of organs, with UGP1 being pre-dominant. Co-expression analyses of UGP genes suggest that UGP1 is closely co-regulated with carbohydrate metabolism genes, late embryogenesis and seed loading, while UGP2 is co-regulated with stress response genes, fertilized flowers and photosynthetic genes. We have used Arabidopsis mutants for the UGP genes to characterize the role of both genes. The UGPase activity/protein was reduced by 70, 10 and 85% in ugp1, ugp2 and ugp1/ugp2 double mutant (DK) plants, respectively. A decrease in UGPase activity/protein was accompanied by an increase in expression of USP, a gene for UDP-sugar pyrophos-phorylase, suggesting a compensatory mechanism. Generally, the mutants had no effects on soluble sugar/starch content (except in certain cases for DK plants), and there were no differences in cell wall composition/content between the wild type and the mutants. On the other hand, DK plants had greater hypocotyl and root lengths. When grown in the field, the mutants had as much as a 50% decrease in the number of seeds produced (consistent with a substantial decrease in field fitness), suggesting that they would be outcompeted in the field in a few generations. Overall, the data suggest that UGPase is not rate limiting for sucrose/starch and cell wall synthesis, but that it is essential in Arabidopsis.

  • 60.
    Meng, Meng
    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).
    Geisler, Matt
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Johansson, Henrik
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Mellerowicz, Ewa J
    Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Karpinski, Stanislaw
    Department of Botany, Stockholm University.
    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).
    Differential tissue/organ-dependent expression of two sucrose- and cold-responsive genes for UDP-glucose pyrophosphorylase in Populus.2007In: Gene, ISSN 0378-1119, E-ISSN 1879-0038, Vol. 389, no 2, p. 186-95Article in journal (Refereed)
    Abstract [en]

    Plant UDP-glucose (UDPG) pyrophosphorylase (UGPase) is involved in the production/metabolism of UDPG, a key metabolite for sucrose and cell wall biosynthesis. Two highly similar cDNAs (UGP1 and UGP2) corresponding to UGPase were isolated from cDNA libraries of hybrid aspen (Populus tremula x tremuloides). Expression of both UGPs, as studied by DNA microarrays and EST abundance, was compared to that of three sucrose synthase genes (SUS1–3), also involved in UDPG synthesis. Generally, the UGPs had lower expression than SUS1 and SUS2 genes (especially in tension wood and cambium), with the notable exception of leaves, primary roots and flowers. Based on real-time quantitative PCR, UGP1 in root xylem, leaves and male flowers was by far the predominant transcript, while in other tissues both UGP1 and UGP2 had comparable expression. In leaves, the UGP1 gene, but not UGP2, was upregulated by light and short-term sucrose feeding. Cold treatment led to dramatic organ-specific changes in relative expression of both genes, with UGP2 being upregulated either transiently (leaves), long-term (stems) or not at all (roots), whereas UGP1 was cold-upregulated in all organs. Individual or overall UGP expression patterns only weakly correlated with UGPase activity/protein; however, UGPase activity and protein were correlated in all tissues/conditions. The data suggest that UGPs are differentially expressed at the tissue level and in response to metabolic feedback (sucrose) and cold stress, and point to a tight posttranscriptional/translational control and, possibly, distinct roles for those genes.

  • 61.
    Meng, Meng
    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).
    Wilczynska, Malgorzata
    Umeå University, Faculty of Medicine, Department of Medical Biochemistry and Biophysics.
    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).
    Molecular and kinetic characterization of two UDP-glucose pyrophosphorylases, products of distinct genes, from Arabidopsis2008In: Biochimica et Biophysica Acta - Proteins and Proteomics, ISSN 1570-9639, E-ISSN 1878-1454, Vol. 1784, no 6, p. 967-972Article in journal (Refereed)
    Abstract [en]

    UDP-glucose pyrophosphorylase (UGPase) is an important enzyme in the production (and conversions) of UDP-glucose, a key precursor for carbohydrate biosynthesis. cDNAs corresponding to two UGPase isozymes in Arabidopsis were overexpressed in Escherichia coli and, subsequently, the recombinant proteins were purified and characterized. Both proteins were highly conserved, sharing 93% identity. Based on crystal structure-derived images, the main amino acid differences mapped to N- and C-termini domains, but not to central active site region. The two proteins existed mainly as monomers, and they had similar molecular masses of ca. 53 kDa. However, comparison of molecular masses of UGPases from Arabidopsis root and leaf extracts revealed that the root protein was slightly larger, suggesting a post-translational modification. Specific activity of the purified UGPase-1 was ca. 10–30% lower than that of UGPase-2, depending on direction of the reaction, whereas its Km values with all substrates in both directions of the reaction were consistently ca. twice lower than those of UGPase-2 (0.03–0.14 mM vs. 0.07–0.36 mM, respectively). Both proteins were “true” UGPases, and had no activity with ADP-glucose/ATP or galactose-1-P. Equilibrium constant for both proteins was ca. 0.3, suggesting preference for the pyrophosphorolysis direction of the reaction. The data are discussed with respect to potential roles of UGPase in carbohydrate synthesis/metabolism in Arabidopsis.

  • 62. Siedlecka, A
    et al.
    Ciereszko, I
    Mellerowicz, E
    Martz, F
    Chen, J
    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).
    The small subunit ADP-glucose pyrophosphorylase (ApS) promoter mediates okadaic acid-sensitive uidA expression in starch-synthesizing tissues and cells in Arabidopsis2003In: Planta, ISSN 0032-0935, E-ISSN 1432-2048, Vol. 217, no 2, p. 184-192Article in journal (Refereed)
    Abstract [en]

    Transgenic plants of Arabidopsis thaliana Heynh., transformed with a bacterial beta-glucuronidase (GUS) gene under the control of the promoter of the small subunit (ApS) of ADP-glucose pyrophosphorylase (AGPase), exhibited GUS staining in leaves (including stomata), stems, roots and flowers. Cross-sections of stems revealed GUS staining in protoxylem parenchyma, primary phloem and cortex. In young roots, the staining was found in the root tips, including the root cap, and in vascular tissue, while the older root-hypocotyl axis showed prominent staining in the secondary phloem and paratracheary parenchyma of secondary xylem. The GUS staining co-localized with ApS protein, as found by tissue printing using antibodies against ApS. Starch was found only in cell and tissue types exhibiting GUS staining and ApS labelling, but not in all of them. For example, starch was lacking in the xylem parenchyma and secondary phloem of the root-hypocotyl axis. Sucrose potently activated ApS gene expression in leaves of wild-type (wt) plants, and in transgenic seedlings grown on sucrose medium where GUS activity was quantified with 4-methylumbelliferyl-beta-glucuronide as substrate. Okadaic acid, an inhibitor of protein phosphatases 1 and 2A, completely blocked expression of ApS in mature leaves of wt plants and prevented GUS staining in root tips and flowers of the transgenic plants, suggesting a similar signal transduction mechanism for ApS expression in various tissues. The data support the key role of AGPase in starch synthesis, but they also underlie the ubiquitous importance of the ApS gene for AGPase function in all organs/tissues of Arabidopsis.

  • 63. Siedlecka, A
    et al.
    Gardestrom, P
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Samuelsson, G
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Kleczkowski, L A
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Krupa, Z
    A relationship between carbonic anhydrase and rubisco in response to moderate cadmium stress during light activation of photosynthesis1999In: Zeitschrift für Naturforschung C - A Journal of Biosciences, ISSN 0939-5075, E-ISSN 1865-7125, Vol. 54, no 9-10, p. 759-763Article in journal (Refereed)
    Abstract [en]

    In our previous research, we showed that low Cd concentration increases the effectiveness of the process es leading to activation of ribulose-1,5-bisphosphate carboxylase/oxygen ase (Rubisco). This stimulation was dependent on carbonic anhydrase (CA) activity and resulted in protecting Rubisco activity against Cd toxicity. The aim of the present paper was to test whether this mechanism has any influence on light activation of photosynthesis during the first 2 h of illumination. Both the "activation mechanism" of plant response to Cd-stress conditions and its full efficiency at low Cd concentration were confirmed. The CA-dependent light activation of Rubisco at low Cd level was correlated with accelerated attaining of the maximum Rubisco activity by these plants. The amount of Rubisco was also Cd- and time-dependent and varied from continuous accumulation in control plants till reaching the maximum level within 30 minutes for the high Cd concentration. An increase in CA activity that was found to be parallel to the decrease of the amount of CA suggested activation of the enzyme by low Cd concentration.

  • 64. Sokolov, L N
    et al.
    Dejardin, A
    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).
    Sugars and light/dark exposure trigger differential regulation of ADP-glucose pyrophosphorylase genes in Arabidopsis thaliana (thale cress)1998In: Biochemical Journal, ISSN 0264-6021, E-ISSN 1470-8728, Vol. 336, p. 681-687Article in journal (Refereed)
    Abstract [en]

    Expression of four Arabidopsis (thale cress) genes corresponding to the small (ApS) and large subunits (ApL1, ApL2, ApL3) of ADP-glucose pyrophosphorylase (AGPase), a key enzyme of starch biosynthesis, was found to be profoundly and differentially regulated by sugar and light/dark exposures. Transcript levels of both ApL2 and ApL3, and to a lesser extent ApS, increased severalfold upon feeding sucrose or glucose to the detached leaves in the dark, whereas the mRNA content for ApL1 decreased under the same conditions. Glucose was, in general, less effective than sucrose in inducing regulation of AGPase genes, possibly due to observed limitations in its uptake when compared with sucrose uptake by detached leaves. Osmotic agents [sorbitol, poly(ethylene glycol)] had no effect on ApS, ApL2 and ApL3 transcript level, but they did mimic the effect of sucrose on ApL1 gene, suggesting that the latter is regulated by osmotic pressure rather than any particular sugar. For all the genes the sugar effect was closely mimicked by an exposure of the dark-pre-adapted leaves to the light. Under both dark and light conditions, sucrose fed to the detached leaves was found to be rapidly metabolized to hexoses and, to some extent, starch. Starch production reflected most probably an increase in substrate availability for AGPase reaction rather than being due to changes in AGPase protein content, since both the sugar feeding and light exposure had little or no effect on the activity of AGPase or on the levels of its small and large subunit proteins in leaf extracts. The data suggest tight translational or posttranslational control, but they may also reflect spatial control of AGPase gene expression within a leaf. The sugar/light-dependent regulation of AGPase gene expression may represent a part of a general cellular response to the availability/allocation of carbohydrates during photosynthesis.

  • 65. Thorbjornsen, T
    et al.
    Villand, P
    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).
    Olsen, O A
    A single gene encodes two different transcripts for the ADP-glucose pyrophosphorylase small subunit from barley (Hordeum vulgare)1996In: Biochemical Journal, ISSN 0264-6021, E-ISSN 1470-8728, Vol. 313, p. 149-154Article in journal (Refereed)
    Abstract [en]

    ADP-glucose pyrophosphorylase (AGPase), a heterotetrameric enzyme composed of two small and two large subunits, catalyses the first committed step of starch synthesis in plant tissues. In an attempt to learn more about the organization and expression of the small-subunit gene of AGPase, we have studied the small-subunit transcripts as well as the structure of the gene encoding these transcripts in barley (Hordeum vulgare L. cv. Bomi). Two different transcripts (bepsF1 and blps14) were identified: bepsF1 was abundantly expressed in the starchy endosperm but not in leaves, whereas blps14 was isolated from leaves but was also found to be present at a moderate level in the starchy endosperm. The sequences for the two transcripts are identical over approx. 90% of the length, with differences being confined solely to their 5' ends. In blps14, the unique 5' end is 259 nt long and encodes a putative plastid transit peptide sequence. For the 178-nt 5' end of bepsF1, on the other hand, no transit peptide sequence could be recognized. A lambda clone that hybridized to the AGPase transcripts was isolated from a barley genomic library and characterized. The restriction map has suggested a complex organization of the gene, with alternative exons encoding the different 5' ends of the two transcripts followed by nine exons coding for the common part of the transcripts. The sequence of a portion of the genomic clone, covering the alternative 5'-end exons as well as upstream regions, has verified that both transcripts are encoded by the gene. The results suggest that the small-subunit gene of barley AGPase transcribes two different mRNAs by a mechanism classified as alternative splicing.

  • 66. Timm, Stefan
    et al.
    Nunes-Nesi, Adriano
    Pärnik, Tiit
    Morgenthal, Katja
    Wienkoop, Stefanie
    Keerberg, Olav
    Weckwerth, Wolfram
    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).
    Fernie, Alisdair R
    Bauwe, Hermann
    A Cytosolic Pathway for the Conversion of Hydroxypyruvate to Glycerate during Photorespiration in Arabidopsis.2008In: The Plant Cell, ISSN 1040-4651, Vol. 20, p. 2848-2859Article in journal (Refereed)
    Abstract [en]

    Deletion of any of the core enzymes of the photorespiratory cycle, one of the major pathways of plant primary metabolism, results in severe air-sensitivity of the respective mutants. The peroxisomal enzyme hydroxypyruvate reductase (HPR1) represents the only exception to this rule. This indicates the presence of extraperoxisomal reactions of photorespiratory hydroxypyruvate metabolism. We have identified a second hydroxypyruvate reductase, HPR2, and present genetic and biochemical evidence that the enzyme provides a cytosolic bypass to the photorespiratory core cycle in Arabidopsis thaliana. Deletion of HPR2 results in elevated levels of hydroxypyruvate and other metabolites in leaves. Photosynthetic gas exchange is slightly altered, especially under long-day conditions. Otherwise, the mutant closely resembles wild-type plants. The combined deletion of both HPR1 and HPR2, however, results in distinct air-sensitivity and a dramatic reduction in photosynthetic performance. These results suggest that photorespiratory metabolism is not confined to chloroplasts, peroxisomes, and mitochondria but also extends to the cytosol. The extent to which cytosolic reactions contribute to the operation of the photorespiratory cycle in varying natural environments is not yet known, but it might be dynamically regulated by the availability of NADH in the context of peroxisomal redox homeostasis.

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