Algal carbon concentrating drives fatty acid biosynthesis beyond photosynthesis
Tingting You, Yuqing Yang, Tianjun Cao, Lianyong Wang, Xiaobo Li
Abstract
Algal photosynthesis contributes to half of global carbon fixation and is enhanced by CO 2 -concentrating mechanisms (CCMs), which depend on the pyrenoid organelle in eukaryotic species. Despite its importance, the coordination between photosynthesis and other inorganic-carbon using pathways like fatty acid biosynthesis (FAS) remains underexplored. Here, we investigate this interplay using the green alga Chlamydomonas reinhardtii . We find that subunits of the acetyl-CoA carboxylase, key in FAS, form protein condensates at the pyrenoid periphery under limiting CO 2 and redistribute throughout the chloroplast stroma under high CO 2 . The condensate structures form via liquid-liquid phase separation and are located in the pyrenoid's outer layer, which contains the bicarbonate-generating enzymes. Pyrenoid function-deficient mutants display impaired FAS, supporting a model where CCMs supply carbon to FAS. Our results unveil a moonlighting function of the pyrenoid and have implications for global carbon cycle, algal biotechnology, and the transfer of pyrenoids into crops for photosynthesis improvements.