The lumenal domain of Cyt b 559 interacting with extrinsic subunits is crucial for accumulation of functional photosystem II

Cytochrome b₅₅₉ (Cyt b₅₅₉) is an essential component of the photosystem II (PSII) reaction center core. It consists of two subunits, PsbE and PsbF, which together coordinate a redox-active heme. While extensive studies have revealed the importance of Cyt b₅₅₉, its structural and functional roles are not fully understood. Previous studies have implied that the lumenal region of Cyt b₅₅₉, interacting with the PSII extrinsic subunit PsbP in green plant PSII, may have important roles. However, few studies have investigated its lumenal region. Here, we have focused on a well-conserved lumenal region of PsbE, which was found to interact with the N-terminal region of PsbP in green-lineage PSII (from green algae and land plants). In red-lineage PSII (from red algae and algae possessing red algal-derived plastids), very similar interactions were observed between the same lumenal region of PsbE and the N-terminal region of PsbQ′. We generated Arabidopsis thaliana mutants harboring mutations in the well-conserved lumenal region of PsbE through targeted base editing of the plastid genome by ptpTALECD. The mutations led to strong growth defects and extremely low F_v/F_m. This study suggests the importance of the lumenal regions of Cyt b₅₅₉, and gives insight into possible structural and functional compensation between the N-terminal regions of PsbP in green-lineage PSII and PsbQ′ in red-lineage PSII.