The mechanisms of high light regulation in cyanobacteria play a vital role in allowing cyanobacteria to cope with high light stress. Orange Carotenoid Protein (OCP)-related quenching is the primary regulatory response to high light and has been extensively studied in the cyanobacterium Synechocystis sp. PCC6803 (hereafter Synechocystis sp.). However, the difference in the efficiency of this OCP-related quenching for optimal regulation of high light is still unclear among different cyanobacterial species. Therefore, we evaluated the efficiency of the OCP-related quenching mechanisms in Synechocystis sp. and Microcystis aeruginosa FACHB905 (hereafter M. aeruginosa ). We found that M. aeruginosa had higher OCP-related quenching than Synechocystis sp. under high light stress. Interestingly, M. aeruginosa also showed faster OCP-related quenching under high light and faster recovery of OCP-related quenching when high light was turned off, compared to Synechocystis sp. Moreover, M. aeruginosa showed a higher ability to regulate high light stress than Synechocystis sp., suggesting that OCP-related quenching is more efficient in M. aeruginosa than in Synechocystis sp., permitting the former to cope with high light stress. The tertiary structures of OCP in Synechocystis sp. and M. aeruginosa demonstrate structural variations based on key amino acid substitution that may be responsible for the observed differences in the efficiency of OCP. These results suggest that OCP could have different structures with varied key amino acids, providing cyanobacteria with varied efficiencies to adapt to their environment.
Xu et al. (Fri,) studied this question.