Light‐dependent regulation of photosynthesis genes in Rhodobacter sphaeroides 2.4.1 is coordinately controlled by photosynthetic electron transport via the PrrBA two‐component system and the photoreceptor AppA

Summary Formation of the photosynthetic apparatus in Rhodobacter is regulated by oxygen tension and light intensity. Here we show that in anaerobically grown Rhodobacter cells a light‐dependent increase in expression of the puc and puf operons encoding structural proteins of the photosynthetic complexes requires an active photosynthetic electron transport. The redox‐sensitive CrtJ/PpsR repressor of photosynthesis genes, which was suggested to mediate electron transport‐dependent signals, is not involved in this light‐dependent signal chain. Our data reveal that the signal initiated in the photosynthetic reaction centre is transmitted via components of the electron transport chain and the PrrB/PrrA two‐component system in Rhodobacter sphaeroides . Under blue light illumination in the absence of oxygen this signal leads to activation of photosynthesis genes and interferes with a blue‐light repression mediated by the AppA photoreceptor and the PpsR transcriptional repressor in R. sphaeroides . Thus, light either sensed by a photoreceptor or initiating photosynthetic electron transport has opposite effects on the transcription of photosynthesis genes. Both signalling pathways involve redox‐dependent steps that finally determine the effect of light on gene expression.