Two opposing redox signals mediated by 2-Cys peroxiredoxin shape the redox proteome during photosynthetic induction
Photosynthetic induction, characterized by the lag in CO2 assimilation rates typically observed upon plant transition from darkness to light, has traditionally been attributed to Rubisco activase activity and stomatal opening. Yet, the faster induction of photosynthesis in the 2-Cys peroxiredoxins (Prxs) mutant (2cpab) highlighted the critical role of chloroplast redox state in regulating photosynthetic rates during this phase. Since 2-Cys Prxs are involved in transmission of oxidative signals to target enzymes, it was hypothesized that it slows down photosynthesis during the induction phase. SPEAR, a redox proteomics approach for simultaneous protein expression and redox analysis, was used to systematically map redox changes occurring at the proteome level during photosynthesis induction and to unravel the role of 2-Cys Prxs in shaping these redox alterations. No significant difference was observed in protein expression levels between WT and 2cpab plants, suggesting that protein abundance does not account for the 2cpab phenotype. During the transition from dark to low light, 82 and 54 cysteine-containing peptides were reduced or oxidized, respectively, in WT plants. Most redox-regulated cysteines in photosynthetic proteins were found oxidized in the dark and became reduced in response to light, including ATP synthase gamma chain 1 (ATPC1) and glyceraldehyde-3-phosphate dehydrogenase (GAPB). A reverse pattern was observed among redox-regulated cysteines in proteins involved in starch degradation and chloroplast glycolysis, which shifted from a reduced to an oxidized state in response to light. These findings demonstrate the initiation of two opposing redox responses, affecting distinct sets of metabolic proteins during the induction phase. Remarkably, a significantly lower number of cysteines were reduced or oxidized in 2cpab plants, highlighting the crucial role 2-Cys Prxs play in shaping both signals. Taken together, rotational shifts between metabolic pathways during the photosynthesis induction phase are regulated by two opposing redox signals mediated by 2-Cys Prx activity.