Turnover rates of photosynthetic proteins indicate a correlation with photosynthetic capacity under state transitions

Abstract State transitions in algae and higher plants involve the phosphorylation and dephosphorylation of light-harvesting complex II, which are regulated by the kinase STN7 and phosphatase TAP38/PPH1. We systematically measured thylakoid protein turnover in stn7-1 and tap38-1 Arabidopsis (Arabidopsis thaliana) mutants, which are locked in permanent State I and State II, respectively. Although the abundance of photosynthetic proteins such as D1, LHCII, and PSAB remained unchanged, their turnover rates were antagonistically altered compared to wild-type plants. These changes correlated with differences in excitation energy distribution and electron transport rates. Our findings reveal that the thylakoid state minimally affects protein abundance but markedly impacts protein complex maintenance by altering protein turnover. This provides insights into the costs and benefits of thylakoid state transitions in plants, the impact of excitation energy distribution between photosynthetic electron transport pathways on their maintenance, and a potential method for quantifying long-term energy distribution changes.