Chlororespiration Serves as Photoprotection for Photo-Inactivated Oxygen-Evolving Complex in Zostera Marina, a Marine Angiosperm

Plant Cell Physiol. 2020 Jun 3;pcaa075. doi: 10.1093/pcp/pcaa075. Online ahead of print.

Abstract

As an alternative electron sink, chlororespiration, comprised of the NAD(P)H dehydrogenase complex and plastid terminal plastoquinone oxidase, may play a significant role for sustaining the redox equilibrium between stroma and thylakoid membrane. This study identified a distinct role of chlororespiration in the marine angiosperm Zostera marina, whose oxygen evolving complex (OEC) is prone to photo-inactivation as a result of its inherent susceptibility to excess irradiation. The strong connectivity between OEC peripheral proteins and key chlororespiratory enzymes, as demonstrated in the interaction network of differentially expressed genes, suggested that the recovery of photo-inactivated OEC was connected with chlororespiration. Chlorophyll fluorescence, transcriptome, and Western blot data verified a new physiological role of chlororespiration to function as photoprotection and generate proton gradient across the thylakoid membrane for the recovery of photo-inactivated OEC. Chlororespiration was only activated in darkness following excess irradiation exposure, which might be related to the electron deficiency in the electron transport chain because of the continuous impairment of OEC. The activation of chlororespiration in Z. marina was prone to proactivity, which was also supported by the further activation of the oxidative pentose-phosphate pathway synthesizing NADPH to meet the demand of chlororespiration during darkness. This phenomenon is distinct from the common assumption that chlororespiration is prone to consuming redundant reducing power during the short transition phase from light to dark.

Keywords: Zostera marina; Chlororespiration; NADPH dehydrogenase-like complex; Oxygen evolving complex; Trans-thylakoid proton gradient.