Abstract
Higher plants have a number of PsbP homologs (PsbP-like proteins: PPLs, PsbP-domain proteins: PPDs) in addition to the authentic PsbP, which regulates the oxygen-evolving reaction in photosystem II (PSII). Among the PsbP homologs, PPL1 is the most homologous protein to a cyanobacterial PsbP (cyanoP), and we previously reported that PPL1 is involved in the repair of photo-damaged PSII under high light condition (Ishihara et al. 2007, Plant Physiol. 145, 668-679). However, functional role of PPL1 in the PSII repair cycle has not been clarified yet. In this study, we further characterized molecular function of PPL1. Although the growth of PPL1 knockdown plants (ppl1i) under low intensity light was comparable with that of wild type plants, the PSII activity of ppl1i was more sensitive to high intensity light. In a sucrose density gradient centrifuge analysis, PPL1 was fractionated in relatively high density fraction and seemed to be co-migrated with the PSII reaction center D1 protein suggesting that PPL1 seems to interact the PSII subcomplexes during the repair of photo-damaged PSII. Further characterization of PPL1 in PSII repair cycle will be reported.
