PsbE:Phe10 of Cytochrome b₅₅₉ Modifies Inactivation and Recovery of Photosystem II in Response to High-Light Stress

Cytochrome b₅₅₉ (Cyt b₅₅₉) is a Photosystem II (PS II) protein formed by PsbE (the α-subunit) and PsbF (the β-subunit) that is essential for the biogenesis of the photosystem and may contribute to photoprotection via cyclic electron flow; however, the precise roles of Cyt b₅₅₉ and its molecular interactions with other proteins and cofactors remain unknown. We have introduced an Ala substitution in the α-subunit of Cyt b₅₅₉ at PsbE:Phe10 in the cyanobacterium Synechocystis sp. PCC 6803. The conserved PsbE:Phe10 residue interacts with surrounding proteins and cofactors in the vicinity of the secondary plastoquinone electron acceptor Q_B. Oxygen evolution in the F10A mutant underwent rapid inactivation in high light, which did not recover during darkness, but rapid recovery of PS II activity was induced by subsequent low-light exposure. Lincomycin added before the high-light treatment prevented the recovery of PS II activity under low light, whereas the addition of lincomycin after the high-light treatment did not block recovery. These findings indicate exchanging PsbE:Phe10 for Ala resulted in the formation of a dark-stable inactive PS II complex upon exposure to high light and that light-induced protein synthesis during high-light exposure conditioned the inactivated PS II for recovery via a process triggered by low light. Ala substitutions introduced at the neighboring PsbE:Pro9 and PsbE:Ser11 residues did not introduce the high-light sensitive phenotype, indicating that the sensitivity to high light and the formation of the dark-stable PS II complex were unique to the PsbE:F10A strain.