Prof. Roman Sobotka, Microbology, Photosynthetic Pigments, Czech Academy of Sciences, Třeboň, Tschechien

Oxygenic photosynthesis is a fundamental biochemical process on our planet, responsible for almost all primary production and for the oxygenation of the Earth’s atmosphere. Key components of the photosynthetic apparatus are two light‐driven photo‐oxidoreductases called Photosystem I and Photosystem II (PSII). Although photosynthesis is an amazingly successful metabolic strategy, the robustness of the photosynthetic apparatus is not so great and can be inactivated relatively easily. This typically happens when the light input exceeds the maximum photosynthetic rate. The absorbed energy cannot be used efficiently and the PSII complexes begin to produce harmful oxygen radicals and are destroyed. The photosynthetic cell must then synthesize new PSIIs even under severe stress, but the process of PSII assembly is a delicate task. The building blocks of PSII (called assembly modules) and the partially assembled PSIIs already absorb light, but are not connected to the electron transport chain and can be easily damaged (oxidized). To protect the biogenesis of PSIIs, cyanobacteria have evolved so‐called high light inducible proteins (Hlips) that bind to the PSII intermediates. Hlips are small (4‐6 KDa), single-transmembrane helix proteins that bind chlorophyll and carotenoid molecules and are capable to dissipate the absorbed light energy very quickly (in a few ps) as heat. Proteins, homologous to Hlips, are present also in algae and plants. The model cyanobacterium Synechocystis PCC 6803 contains four Hlips (HliA-D). In my talk, I will describe how these proteins are organized and how they interact with the PSII subunits to photoprotect each step of PSII assembly.