Alka(e)nes contribute to membrane lipid homeostasis and resilience of photosynthesis to high light in cyanobacteria

Alka(e)nes are produced by many living organisms and exhibit diverse physiological roles, reflecting a high functional versatility. Alka(e)nes serve as water proof wax in plants, communicating pheromones for insects, and microbial signaling molecules in some bacteria. Although alka(e)nes have been found in cyanobacteria and algal chloroplasts, a possible role in photosynthesis and chloroplast function remains elusive. In this study, we investigated the consequences of the absence of alka(e)nes on membrane lipid remodeling and photosynthesis using the cyanobacteria Synechocystis PCC6803 as a model organism. By following the dynamics of membrane lipids and the photosynthetic performance in strains defected and altered in alka(e)ne biosynthesis, we show that a profound remodeling of the membrane lipidome and carotenoid content occur in the absence of alka(e)nes, including a decrease in the membrane carotenoid content, a decrease in some digalactosyldiacylglycerol (DGDG) species and a parallel increase in monogalactosyldiacylglycerol (MGDG) species. Under high light, this effect is accompanied in alka(e)ne deficient strains by a higher susceptibility of photosynthesis and growth, the effect being reversed by expressing an algal photoenzyme producing alka(e)nes from fatty acids. We conclude that alka(e)nes play a crucial role in maintaining lipid homeostasis of photosynthetic membranes, thereby contributing to the proper functioning of photosynthesis, particularly under elevated light intensities. ### Competing Interest Statement The authors have declared no competing interest.