Coordinate up‐regulation of carotenoid biosynthesis as a response to light stress in Synechococcus PCC7942

ABSTRACT Carotenoid biosynthesis is up‐regulated by strong light in the cyanobacterium Synechococcus. By blocking off the pathway at the level of phytoene conversion, light‐dependent accumulation of phytoene was observed. Real‐time PCR studies demonstrated that four genes of the carotenogenic pathway are under transcriptional control. These were the genes encoding phytoene synthase, phytoene desaturase, ζ‐carotene desaturase and β‐carotene hydroxylase. The transcript of the first three follow a similar kinetics, whereas the transcript of β‐carotene hydroxylase increased much faster upon transfer to high light. Promoter activities were determined with transcriptional fusions to chloramphenicol acyltransferase as reporter enzyme. The activity of the promoter of the phytoene desaturase/synthase operon was higher under strong light.