The transcription factor RppA regulates chlorophyll and carotenoid biosynthesis to improve photoprotection in cyanobacteria.

This article focuses on the role of the transcription factor RppA in regulating chlorophyll (Chl) and carotenoid (CAR) biosynthesis to enhance photoprotection in the cyanobacterium Synechocystis sp. PCC 6803. RppA directly binds to the promoter of chlG, the gene encoding chlorophyll synthase, repressing its expression during dark–light transitions to prevent excessive chlorophyll accumulation and associated reactive oxygen species (ROS) production. Concurrently, RppA promotes the transcription of key carotenoid biosynthesis genes (crtB and crtP), increasing carotenoid synthesis that aids in ROS scavenging and photoprotection. This dual regulatory mechanism balances photosynthetic pigment production and oxidative stress, facilitating cyanobacterial acclimation to fluctuating light environments; similar regulatory roles of RppA were also suggested in the marine cyanobacterium Synechococcus sp. PCC 7002.