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The Ability of Cyanobacterial Cells to Restore UV‐B Radiation Induced Damage to Photosystem II is Influenced by Photolyase Dependent DNA Repair

Damage of DNA and Photosystem‐II are among the most significant effects of UV‐B irradiation in photosynthetic organisms. Both damaged DNA and Photosystem‐II can be repaired, which represent important defense mechanisms against detrimental UV‐B effects. Correlation of Photosystem‐II damage and repair with the concurrent DNA damage and repair was investigated in the cyanobacterium Synechocystis PCC6803 using its wild type and a photolyase deficient mutant, which is unable to repair UV‐B induced DNA damages. A significant amount of damaged DNA accumulated during UV‐B exposure in the photolyase mutant concomitant with decreased Photosystem‐II activity and D1 protein amount. The transcript level of psbA3, which is a UV‐responsive copy of the psbA gene family encoding the D1 subunit of the Photosystem‐II reaction center, is also decreased in the photolyase mutant. The wild‐type cells, however, did not accumulate damaged DNA during UV‐B exposure, suffered smaller losses of Photosystem‐II activity and D1 protein, and maintained higher level of psbA3 transcripts than the photolyase mutant. It is concluded that the repair capacity of Photosystem‐II depends on the ability of cells to repair UV‐B‐damaged DNA through maintaining the transcription of genes, which are essential for protein synthesis‐dependent repair of the Photosystem‐II reaction center.