psbA gene family coding D1 proteins of photosystem II of cyanobacteria Synechocystis PCC 6803 is essential for DNA repair/protection

Synechocystis PCC 6803 wild type (WT) switches from UV-resistant to UV-sensitive state on shifting from photoautotrophic to photoheterotrophic mode of growth. The strain also displays the differential UV sensitivity between the light and dark phase in the photoautotrophic mode of growth. Here we provide genetic evidence for the role of D1 polypeptide in repair/protective activity in the UV sensitivity switching phenomenon. The strain used can switch between photoautotrophy and photoheterotrophy, thereby permitting assessment of the role of photosystem II (PSII) components in functions other than photosynthesis. We show that D1 mutants selected for altered UV sensitivity are novel and different from those known to affect the electron transport function or PSII assembly. To our knowledge this is the first report on the involvement of any PSII constituent in genome housekeeping activity. The observation suggests a new pathway for stress management in cyanobacteria and, by implication, also in higher plants.