![]() For Arabidopsis, five more Ser and Thr residues are present in phosphopeptides for which the exact phosphoresidue was not determined. Residues for which phosphorylation was shown unambiguously are indicated by a purple box. Those organisms, for which phosphoproteomics data on CAS are available, are listed separately. For dicots, monocots, gymnosperms and green algae, a consensus sequence was created based on alignments shown in Supplementary Data S1–S4. (B) Sequence alignment of the CAS C-terminal domain from organisms throughout the Viridiplantae clade. Thr and Ser residues that were unambiguously identified by phospho-proteomic studies are marked by an asterisk, while sites that are part of a phosphopeptide (tentative sites) are marked by a hash. The predicted transit sequence and the transmembrane domain are marked by a solid line and a gray box, respectively. (A) Amino acid sequence of the CAS (At5g23060) protein of A. ![]() Together with the observation of a strong concomitant phosphorylation of light harvesting complex II (LHCII) and photosynthetic core proteins under high irradiance in the cas mutant this suggests a role for CAS in the STN7/STN8/TAP38 network of phosphorylation-mediated photoacclimation processes in Arabidopsis.ĬAS STN7 STN8 calcium sensor protein chloroplast phosphorylation photoacclimation state transition.ĬAS domain structure and phylogenetic conservation of phosphorylation sites. Spectroscopic analyses of chlorophyll fluorescence emission at 77K further showed that, while the cas mutant is not affected in state transition, it displays a persistent strong excitation of PSI under high light exposure, similar to the phenotype previously observed in other mutants defective in photoacclimation mechanisms. ![]() ![]() Phosphoproteomics analysis and in vitro phosphorylation assays on CAS variants identified the phylogenetically conserved residues Thr-376, Ser-378, and Thr-380 as the major phosphorylation sites of the STN kinases. Here we show that in Arabidopsis thaliana, CAS is also phosphorylated by the state transition kinase 7 (STN7), as well as by another, so-far unknown, Ca 2+-dependent kinase. The calcium sensor receptor protein (CAS) has previously been indicated as one of the targets of the state transition kinase 8 (STN8). However, the precise functional role of many of the described phosphorylation events on thylakoid proteins remains elusive. When facing difficulties with puzzles or our website in general, feel free to drop us a message at the contact page.Reversible phosphorylation of thylakoid proteins contributes to photoacclimation responses in photosynthetic organisms, enabling the fine-tuning of light harvesting under changing light conditions and promoting the onset of photoprotective processes.
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