Evolution of Ycf54-independent chlorophyll biosynthesis in cyanobacteria

Significance Photosynthesis uses chlorophylls to utilize solar energy. In oxygenic phototrophs, formation of the isocyclic fifth ring chlorophyll, responsible for its green color, is catalyzed by AcsF/CycI and auxiliary protein Ycf54. Removal Ycf54 causes severe chlorophyll deficiency impaired photoautotrophic growth. We analyzed laboratory-evolved suppressor mutants a Ycf54-less strain cyanobacterium Synechocystis where biosynthesis phototrophy were restored. A single point mutation in CycI significantly weakens dependence on Ycf54, mimicking natural evolution enzyme marine cyanobacteria that lack second resulting overaccumulation inactivates an with vitro dephytylase activity. Our results provide insights into important regulatory role biosynthesis.