A chloroplast thylakoid lumen protein is required for proper photosynthetic acclimation of plants under fluctuating light environments

Photosynthesis harnesses sunlight to assimilate carbon dioxide and produce biomass essential for life on earth. Photosystem integrity and activity are negatively impacted by fluctuations in incident light from the sun. How plants regulate photosynthetic dynamics under natural fluctuating growth light is relatively poorly understood. Loss of the Arabidopsis thaliana chloroplast lumenal protein MPH2 causes photosystem II (PSII) repair deficiency under changing light. PSII repair mutants are impaired in growth under greenhouse fluctuating light environments, while photoprotection mutants grow normally. These findings inform strategies for engineering plant photosynthetic performance under field conditions, to sustainably address increasing needs for food, fiber, and fuel at a time of changing climate and rapid population growth.