The plastidic glutamine synthetase activity is directly modulated by means of redox change at two unique cysteine residues

Choi, Yang Ae; Kim, Sang Gu; Kwon, Young Jun

doi:10.1016/s0168-9452(99)00163-6

Cited by 39 publications

(35 citation statements)

References 25 publications

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“…It will be interesting to determine whether T6P also regulates other thioredoxin-dependent processes in the plastid, such as fatty acid (35) or amino acid synthesis (36). This may allow global control of diverse pathways of carbon utilization in plants in response to short-term changes in the carbon status.…”

Section: Discussionmentioning

confidence: 99%

Trehalose 6-phosphate regulates starch synthesis via posttranslational redox activation of ADP-glucose pyrophosphorylase

Kolbe

Tiessen

Schluepmann³

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

355

320

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Trehalose is the most widespread disaccharide in nature, occurring in bacteria, fungi, insects, and plants. Its precursor, trehalose 6-phosphate (T6P), is also indispensable for the regulation of sugar utilization and growth, but the sites of action are largely unresolved. Here we use genetic and biochemical approaches to investigate whether T6P acts to regulate starch synthesis in plastids of higher plants. Feeding of trehalose to Arabidopsis leaves led to stimulation of starch synthesis within 30 min, accompanied by activation of ADP-glucose pyrophosphorylase (AGPase) via posttranslational redox modification. The response resembled sucrose but not glucose feeding and depended on the expression of SNF1-related kinase. We also analyzed transgenic Arabidopsis plants with T6P levels increased by expression of T6P synthase or decreased by expression of T6P phosphatase (TPP) in the cytosol. Compared with wild type, leaves of T6P synthase-expressing plants had increased redox activation of AGPase and increased starch, whereas TPP-expressing plants showed the opposite. Moreover, TPP expression prevented the increase in AGPase activation in response to sucrose or trehalose feeding. Incubation of intact isolated chloroplasts with 100 M T6P significantly and specifically increased reductive activation of AGPase within 15 min. Results provide evidence that T6P is synthesized in the cytosol and acts on plastidial metabolism by promoting thioredoxin-mediated redox transfer to AGPase in response to cytosolic sugar levels, thereby allowing starch synthesis to be regulated independently of light. The discovery informs about the evolution of plant metabolism and how chloroplasts of prokaryotic origin use an intermediate of the ancient trehalose pathway to report the metabolic status of the cytosol.SNF1 kinase ͉ sugar signaling ͉ thioredoxin S tarch is the major carbon store in plants consisting of an insoluble polymer of ␣-1,4-and ␣-1,6-linked glucose units (1). In the chloroplast of leaves, starch is synthesized during the day as a transient store, which is degraded during the night to support nonphotosynthetic leaf metabolism and sucrose export. In heterotrophic storage organs such as potato tubers, most of the incoming sucrose is converted to starch as a long-term carbon store for reproductive growth. In addition to its central role in carbon metabolism of plants, starch is also of great economical importance and is used for food and feed purposes and many industrial applications (2).ADP-glucose pyrophosphorylase (AGPase) catalyzes the first committed step of starch synthesis in the plastid, converting glucose 1-phosphate and ATP to ADP-glucose and PP i . ADP-glucose is subsequently used by starch synthases and branching enzymes to elongate the glucan chains of the starch granule. AGPase is a heterotetramer that contains two large (AGPS, 51 kDa) and two slightly smaller subunits (AGPB, 50 kDa) (3, 4). Work with Arabidopsis mutants (5) and potato tubers (6) showed that the enzyme catalyzes a near rate-limiting step in the pat...

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Section: Discussionmentioning

confidence: 99%

Trehalose 6-phosphate regulates starch synthesis via posttranslational redox activation of ADP-glucose pyrophosphorylase

Kolbe

Tiessen

Schluepmann³

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

355

320

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“…A. thaliana GS-2 possesses two Cys residues, Cys-306 and Cys-371, absent in cytosolic isoforms (Figure 1) but highly conserved in plastidic GS-2 of all tested angiosperms. As evidenced by site-specific mutageneses, both Cys-306 and Cys-371 are critical for light stability; presumably, internal, oxidative, disulfide bond formation between Cys-306 and Cys-371 results in loss of plastidic GS-2 activity (Choi et al, 1999). Conceivably, stable GS activity in dark-shifted A. thaliana mitochondria might be owed to thioredoxin activity, which would both maintain Cys sulfhydryl groups chemically reduced and prevent formation of any internal disulfide bonds.…”

Section: Leaf Mitochondrial Gs Activity Is Dark Stable and Induced Bymentioning

confidence: 99%

Arabidopsis thaliana GLN2-Encoded Glutamine Synthetase Is Dual Targeted to Leaf Mitochondria and Chloroplasts

et al. 2004

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In higher plants, photorespiratory Gly oxidation in leaf mitochondria yields ammonium in large amounts. Mitochondrial ammonium must somehow be recovered as glutamate in chloroplasts. As the first step in that recovery, we report glutamine synthetase (GS) activity in highly purified Arabidopsis thaliana mitochondria isolated from light-adapted leaf tissue. Leaf mitochondrial GS activity is further induced in response to either physiological CO2 limitation or transient darkness. Historically, whether mitochondria are fully competent for oxidative phosphorylation in actively photorespiring leaves has remained uncertain. Here, we report that light-adapted, intact, leaf mitochondria supplied with Gly as sole energy source are fully competent for oxidative phosphorylation. Purified intact mitochondria efficiently use Gly oxidation (as sole energy, NH3, and CO2 source) to drive conversion of l-Orn to l-citrulline, an ATP-dependent process. An A. thaliana genome-wide search for nuclear gene(s) encoding mitochondrial GS activity yielded a single candidate, GLN2. Stably transgenic A. thaliana ecotype Columbia plants expressing a p35S∷GLN2∷green fluorescent protein (GFP) chimeric reporter were constructed. When observed by laser scanning confocal microscopy, leaf mesophyll and epidermal tissue of transgenic plants showed punctate GFP fluorescence that colocalized with mitochondria. In immunoblot experiments, a 41-kD chimeric GLN2∷GFP protein was present in both leaf mitochondria and chloroplasts of these stably transgenic plants. Therefore, the GLN2 gene product, heretofore labeled plastidic GS-2, functions in both leaf mitochondria and chloroplasts to faciliate ammonium recovery during photorespiration

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“…The decrease of a-ketoglutarate and stimulation of amino acid synthesis after DTT treatment may be indicative for regulation of the GS/GOGAT cycle via posttranslational redox regulation. Fd-GOGAT and GS are subject to thioredoxin-dependent redox regulation in vitro (Choi et al, 1999;Motohashi et al, 2001;Balmer et al, 2003).…”

Section: Thiol-disulfide Exchange Leads To Global Changes In Leaf Metmentioning

confidence: 99%

Combined Transcript and Metabolite Profiling of Arabidopsis Leaves Reveals Fundamental Effects of the Thiol-Disulfide Status on Plant Metabolism

et al. 2006

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In this study, we used gas chromatography-mass spectrometry analysis in combination with flux analysis and the Affymetrix ATH1 GeneChip to survey the metabolome and transcriptome of Arabidopsis (Arabidopsis thaliana) leaves in response to manipulation of the thiol-disulfide status. Feeding low concentrations of the sulfhydryl reagent dithiothreitol for 1 h at the end of the dark period led to posttranslational redox activation of ADP-glucose pyrophosphorylase and major alterations in leaf carbon partitioning, including an increased flux into major respiratory pathways, starch, cell wall, and amino acid synthesis, and a reduced flux to sucrose. This was accompanied by a decrease in the levels of hexose phosphates, while metabolites in the second half of the tricarboxylic acid cycle and various amino acids increased, indicating a stimulation of anaplerotic fluxes reliant on a-ketoglutarate. There was also an increase in shikimate as a precursor of secondary plant products and marked changes in the levels of the minor sugars involved in ascorbate synthesis and cell wall metabolism. Transcript profiling revealed a relatively small number of changes in the levels of transcripts coding for components of redox regulation, transport processes, and cell wall, protein, and amino acid metabolism, while there were no major alterations in transcript levels coding for enzymes involved in central metabolic pathways. These results provide a global picture of the effect of redox and reveal the utility of transcript and metabolite profiling as systemic strategies to uncover the occurrence of redox modulation in vivo.

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The plastidic glutamine synthetase activity is directly modulated by means of redox change at two unique cysteine residues

Cited by 39 publications

References 25 publications

Trehalose 6-phosphate regulates starch synthesis via posttranslational redox activation of ADP-glucose pyrophosphorylase

Trehalose 6-phosphate regulates starch synthesis via posttranslational redox activation of ADP-glucose pyrophosphorylase

Arabidopsis thaliana GLN2-Encoded Glutamine Synthetase Is Dual Targeted to Leaf Mitochondria and Chloroplasts

Combined Transcript and Metabolite Profiling of Arabidopsis Leaves Reveals Fundamental Effects of the Thiol-Disulfide Status on Plant Metabolism

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