From targets to function: Crosstalk between STN7/8 and pCK2 during photosynthetic acclimation

• Applicant: Professor Dr. Sacha Baginsky
• Subject Area: Plant Biochemistry and Biophysics
• Term: since 2011
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 204473045

The research project proposed here continues our long-term efforts to decipher chloroplast phosphorylation networks and understand the crosstalk between different plastid protein kinases. We have generated the triple mutant stn7/stn8/pck2 and will characterize it phenotypically and biochemically. A special emphasis will be laid on the functional characterization of photosynthetic acclimation to unravel processes that depend on the crosstalk between these three protein kinases. Since the stn7/stn8/pck2 phenotype is severe and the growth defects partially exceed those of the stn7/stn8 double and the pck2 single mutants, we assume cooperativity between the different chloroplast kinases in the regulation of chloroplast functions. Obvious cooperation exists in the phosphorylation of at least two proteins of the thylakoid membrane system, i.e. PsbH and PSI-P. To understand the function of light-independent phosphorylations of these proteins by pCK2, we will test the ability of the triple mutant to assemble the two photosystems, to assess the repair characteristics after photoinhibition and to systematically assess the impact of the triple mutation on the metabolome. While these experiments are targeted at rather short-term acclimation processes, we will strive for a deeper understanding of the function of phosphorylation in long-term acclimation. To this end, we will perform detailed analyses of plastid ribosomal phosphorylation patterns and analyze the utilization of ribosomal phosphorylation sites in kinase mutants, light- and dark-adapted chloroplasts and in polysomes compared to free ribosomes. This will provide a deeper understanding on how phosphorylation regulates translation and provide links between chloroplast kinases and photosynthetic acclimation processes.

• DFG Programme: Research Grants