Identification of a Novel Mutation Exacerbated the PSI Photoinhibition in / Mutants; Caution for Overestimation of the Phenotypes in Arabidopsis Mutant.

PSI photoinhibition is usually avoided through P700 oxidation. Without this protective mechanism, excess light represents a potentially lethal threat to plants. PGR5 is suggested to be a major component of cyclic electron transport around PSI and is important for P700 oxidation in angiosperms. The known Arabidopsis PGR5 deficient mutant, , is incapable of P700 oxidation regulation and has been used in numerous photosynthetic studies. However, here it was revealed that was a double mutant with exaggerated PSI photoinhibition. significantly reduced growth compared to the newly isolated PGR5 deficient mutant, . The introduction of PGR5 into restored P700 oxidation regulation, but remained a pale-green phenotype, indicating that had additional mutations. Both and tended to cause PSI photoinhibition by excess light, but exhibited an enhanced reduction in PSI activity. Introducing AT2G17240, a candidate gene for the second mutation into restored the pale-green phenotype and partially restored PSI activity. Furthermore, a deficient mutant of PGRL1 complexing with PGR5 significantly reduced PSI activity in the double-deficient mutant with AT2G17240. From these results, we concluded that AT2G17240, named PSI photoprotection 1 (PTP1), played a role in PSI photoprotection, especially in PGR5/PGRL1 deficient mutants.