DEPHOSPHORYLATION OF PHOTOSYSTEM-II CORE PROTEINS IS LIGHT-REGULATED IN-VIVO

A number of photosystem II (PSII)-associated proteins, including D1, D 2, CP43 and LHCII, are phosphorylated post-translationally by a membra ne-bound, redox-regulated kinase activity. In vitro studies have demon strated that these proteins can be dephosphorylated by membrane-bound phosphatase activity, reportedly insensitive to light or redox control . We demonstrate here that the PSII core proteins, D1, D2 and CP43, un dergo light-stimulated, linear electron-transport-independent dephosph orylation in vivo. The in vivo dephosphorylation of D1 was characteriz ed further and shown to depend upon light intensity, and to occur thro ughout the visible light spectrum with characteristics most consistent with light absorption by chlorophyll. PSII core protein dephosphoryla tion in vivo was stimulated by photosystem I (PSI)-specific far-red li ght, and inhibited by 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone, an inhibitor of plastoquinol oxidation by the cytochrome b6f complex. Based on these findings, we propose that PSI excitation is involved i n regulating dephosphorylation of PSII core proteins in vivo.