Abstract
Post-translational modifications (PTMs) of proteins enable fast modulation of protein function in response to metabolic and environmental changes. Phosphorylation is known to play a major role in regulating distribution of light energy between the Photosystems (PS) I and II (state transitions) and in PSII repair cycle. In addition, thioredoxin-mediated redox regulation of Calvin cycle enzymes has been shown to determine the efficiency of carbon assimilation. Besides these well characterized modifications, recent methodological progress has enabled identification of numerous other types of PTMs in various plant compartments, including chloroplasts. To date, at least N-terminal and Lys acetylation, Lys methylation, Tyr nitration and S-nitrosylation, glutathionylation, sumoylation and glycosylation of chloroplast proteins have been described. These modifications impact DNA replication, control transcriptional efficiency, regulate translational machinery and affect metabolic activities within the chloroplast. Moreover, light reactions of photosynthesis as well as carbon assimilation are regulated at multiple levels by a number of PTMs. It is likely that future studies will reveal new metabolic pathways to be regulated by PTMs as well as detailed molecular mechanisms of PTM-mediated regulation.
Highlights
Chloroplasts are surrounded by the envelope membrane, and the majority of nuclear-encoded chloroplast proteins are imported through the envelope into the plastid via the Toc/Tic machinery
Another well-studied phosphorylation process is involved in the balancing electron transfer between PSII and PSI according to ambient environmental cues
In poplar trees sedoheptulose-bisphosphatase (SBPase), Rubisco activase (RA), ribose-5-phosphate isomerase (RPI), phosphoribulokinase (PRK), Glyceraldehyde 3-phosphate dehydrogenase (GAPDH), triosephosphate isomerase (TPI), and Phosphoglycerate kinase (PGK) were S-nitrosylated during short-term oxidative stress induced by nitric oxide (NO) treatment (Vanzo et al, 2014, 2016), but the functional importance has not been described yet (Lindermayr et al, 2005; Abat et al, 2008; Romero-Puertas et al, 2008; Abat and Deswal, 2009)
Summary
The subchloroplastic destination of a specific protein is determined by the information buried within the primary amino acid sequence, either in the form of cleavable transit peptide or as an internal targeting signal Due to their endosymbiotic origin, biosynthesis and function of chloroplasts is dependent on nuclear control, and on the expression of approximately 120 plastome encoded genes, mostly involved in photosynthesis and plastid gene expression (Sugiura, 1992; Green, 2011). Post-translational Modifications of Chloroplast Proteins as integration of plastid metabolism with the rest of the cell are required to induce appropriate physiological responses to various environmental stimuli, thereby enabling successful growth and reproduction of the plants This coordination takes place at many different levels, including the control of nuclear and plastid transcription, RNA processing and translation, protein translocation and assembly of protein complexes as well as functional adjustments of specific enzymes and/or pathways. We will draw together the current understanding of the PTMs regulating distinct metabolic processes in chloroplasts, and review the known physiological effects of these modifications
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