Engineering light robustness: Adaptive evolution uncovers new genetic determinants of HL tolerance in Synechocystis

Excess light absorption is lethal to photosynthetic organisms. Increased tolerance and utilization to high light (HL) are beneficial to primary productivity of photosynthetic microorganisms and plants. Here, with photosynthetic cyanobacterium Synechocystis sp. PCC 6803 (Syn6803) as a model, we obtained 8 independent strains tolerant to 2000 μmol photons/m²/s HL via about 2 years’ adaptive laboratory evolution. Interestingly, 4 of them exhibited increased biomass accumulation by 121.71%-168.36% compared to that of wild type under HL condition. A total of 77 mutations was investigated in ALE strains and 33 responsive genes like two RNA-binding proteins slr0193 and slr0320 were identified. Accompanied by phenotypes examination and mechanisms elucidation, we found both slr0193 and slr0320 could regulate the genes related with photosynthesis, promoting the HL acclimation via excluding the excess light harvesting. Our findings provide new insights for photosynthesis reinforcement.