Redox regulation of carbon storage and partitioning in response to light and sugars
TLDR
Experimental data will be provided showing that the isozyme from pea leaf chloroplasts is activated by reduced thioredoxin f or m in a similar way, and recent evidence will be discussed showing that key enzymes of de novo fatty acid synthesis and ammonium assimilation are regulated by reversible disulphide-bond formation similar to AGPase.Abstract:
Redox signals generated by the photosynthetic electron transport chain are known to be involved in regulating the Calvin cycle, ATP synthesis, and NADPH export from chloroplasts in response to light. The signal cascade involves transfer of electrons from photosystem I via the ferredoxin-thioredoxin system to target enzymes that are activated by reduction of regulatory disulphide bonds. The purpose of this review is to discuss recent findings showing that this concept can be extended to the regulation of carbon storage and partitioning in plants. Starch is the major carbon store in plants, and ADP-glucose pyrophosphorylase (AGPase) is the key regulatory enzyme of starch synthesis in the plastid. It has been shown that AGPase from potato tubers is subject to post-translational redox modification, and here experimental data will be provided showing that the isozyme from pea leaf chloroplasts is activated by reduced thioredoxin f or m in a similar way. Recent reports will be summarized providing in planta evidence that this mechanism regulates storage starch synthesis in response to light and sugars. Post-translational redox activation of AGPase in response to sugars is part of a signalling mechanism linking the rate of starch synthesis to the availability of carbon in diverse plant tissues. Some of the components of the signalling pathway reporting changes in the cytosolic sugar status to the plastid have been postulated, but detailed work is in progress to confirm the exact mode of action. Recent evidence will be discussed showing that key enzymes of de novo fatty acid synthesis (acetyl-CoA carboxylase) and ammonium assimilation (glutamine synthetase and glutamine:oxoglutarate amino transferase) are regulated by reversible disulphide-bond formation similar to AGPase. Redox regulation is proposed to be the preferred strategy of plastidial enzymes to regulate various metabolic processes such as carbon fixation, starch metabolism, lipid synthesis, and amino acid synthesis in response to physiological and environmental inputs.read more
Citations
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References
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TL;DR: In this paper, a light-dependent Enzyme Activation and Deactivation in the Dark (DEAD) mechanism was found to increase the pH of the stromal pH.
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Sugar-induced signal transduction in plants
TL;DR: The role of sugar signaling in seed development and in seed germination is discussed, especially with respect to the various mechanisms by which sugar signaling controls gene expression.
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The molecular-genetics of nitrogen assimilation into amino acids in higher plants
TL;DR: The recent progress in using molecular-genetic approaches to delineate the regulatory mechanisms controlling nitrogen assimilation into amino acids and to define the physiological role of each isoenzyme involved in this metabolic pathway is reviewed.
Journal ArticleDOI
Steps towards an integrated view of nitrogen metabolism
Mark Stitt,Cathrin Müller,Petra Matt,Yves Gibon,Petronia Carillo,Rosa Morcuende,Wolf-Rüdiger Scheible,Anne Krapp +7 more
TL;DR: Comparison across genotypes and conditions reveals that NIA transcript levels are always closely related to the balance between nitrate influx and assimilation, but are unrelated to changes of glutamine or 2-oxoglutarate.