Cyanobacterial photosynthetic reaction center in wobbly light: Modulation of light energy by orange carotenoid proteins (OCPs)

Abstract High irradiance and fluctuating light boons substantial risk to photosynthetic life forms by summoning responsive oxygen species (ROS). To bear the high irradiance level, plants, algae, and cyanobacteria have developed mechanisms to diminution the energy hitting at reaction centers to protect it from high irradiance by a photo-defensive system. In cyanobacteria, these photoprotection systems reduce the light energy arriving at the reaction centers by reducing photosynthesis and enhancing thermal energy dissipation at the level of the phycobilisome (PB), the extra-membranous light-harvesting antenna. Fluorescence recovery proteins (FRPs) and orange carotenoid proteins (OCPs) alluded to as essential elements for this mechanism by nonphotochemical quenching (NPQ). Initially, cyanobacteria were considered not to fit for performing NPQ, and the last shreds of evidence advocated NPQ as a crucial and primary photoprotective tool. OCP comprises two domains, (1) N-terminal domain (NTD) and (2) C-terminal domain (CTD), with a solitary carotenoid as a chromophore traversing evenly in the two areas. Blue-green or high irradiance light actuates the transformation of OCP from a dormant orange state (OCPO) to a dynamic red state (OCPR). Dynamic OCP (OCPR) ties to the center of the light-harvesting antenna complex, phycobilisomes (PBs), extinguishes fluorescence, and aids dispersal abundance energy’s nonradiative pathway. OCP-intervened photoprotection mechanism effectively managed by FRP by accelerating the OCP transformation of active OCP (OCPR) to the resting state (OCPO) under light-limiting conditions. However, numerous inquiries concerning the working of FRP have stayed dubious. This chapter summarizes the current information and comprehension of the FRP and OCP in cyanobacterial photoprotection and the possibilities of exploiting these systems for plant resilience to high irradiance.