The STN8 kinase-PBCP phosphatase system is responsible for high-light-induced reversible phosphorylation of the PSII inner antenna subunit CP29 in rice

This article is protected by copyright. All rights reserved. SUMMARY Reversible phosphorylation of thylakoid lightharvesting proteins is a mechanism to compensate for unbalanced excitation of PSI vs PSII under limiting light. In monocots, an additional phosphorylation event on the PSII antenna CP29 occurs upon exposure to excess light, enhancing resistance to light stress. Different from the case of the major LHCII antenna complex, the STN7 kinaseand its related PPH1 phosphatase were proven not to be involved in CP29 phosphorylation, indicating that a different set of enzymes act in the high-light response. Here, we analyze a rice stn8mutant in which both PSII core proteins and CP29 phosphorylation are suppressed in high light, implying that STN8 is the kinase catalyzing this reaction. In order to identify the phosphatase involved, we produced a recombinant enzyme encoded by the rice ortholog of AtPBCP, antagonist of AtSTN8, which catalyzes the dephosphorylation of PSII core proteins. The recombinant protein was active in dephosphorylating P-CP29. Based on these data, we propose that the activities of the OsSTN8 kinase and the antagonistic OsPBCP phosphatase, in addition to being involved in the repair of photo-damaged PSII, are also responsible for the high light-dependent reversiblephosphorylation of the inner antenna CP29.