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

Cytochrome b 559 (Cyt b 559 ) 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 b 559 and its molecular interactions with other proteins and cofactors remain unknown. We have introduced an Ala substitution in the α‐subunit of Cyt b 559 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.