The unique mechanisms that enable Chlorella ohadii to thrive in light intensities that are fatal to most photosynthetic organisms
Although light is required for photosynthesis, too much light is harmful and may cause damage to the photosynthetic proteins in a process known as photoinhibition. During photoinhibition, photosynthesis is inhibited in plants, algae, and cyanobacteria, and may lead to retarded growth and death. Improving photoinhibition resistance to increase crop production is a long-standing goal for plant scientists worldwide. Here we reveal the unique mechanisms of photoinhibition resistance in the desert green algae Chlorella ohadii, one of the most high-light tolerant organisms on the planet. We show that C. ohadii lacks some of the most important photoinhibition resistance mechanisms in other model organisms, such as non-photochemical quenching (NPQ), the PsbS and LhcSR proteins, and state transitions. Instead, C. ohadii protects photosynthesis by eliminating the photosynthetic antenna and minimizing excess energy uptake, while maximizing cyclic electron flow around photosystem I and antioxidant activity via carotenoids and enzymatic detoxification, thus protecting the photosynthetic proteins. Our work describes a new efficient mechanism for photoinhibition resistance under extreme light intensities and provides potential targets for improving photoinhibition resistance in crop plants.
