Function of and signaling by blue light photoreceptors in Rhodobacter sphaeroides

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Although photoreceptors have now been identified in many bacterial species, their biological function and signaling downstream from signal perception are mostly elusive. In the past we identified the BLUF domain of the AppA protein from R. sphaeroides as a new type of photoreceptor. It is involved in a blue light-dependent repression of photosynthesis genes at elevated oxygen levels. Recently we revealed that the cryptochrome-like CryB protein and the LOV-domain protein of R. sphaeroides bind flavins and undergo a photocycle. We could show that CryB strongly affects the expression of photosynthesis genes. Thus a clear biological function can be assigned to a bacterial cryptochrome for the first time. In the proposed project we want to unravel the signal chain from CryB to the expression of photosynthesis genes, to characterize the flavin binding domain of CryB, and to elucidate, how the photocycle of CryB relates to downstream signaling. A search for interaction partners of the LOV protein by a yeast two-hybrid screening suggests its involvement in the regulation of capsule synthesis. The role of light in capsule synthesis and signaling by LOV will be analysed in detail. We expect that our results will provide new insights into the biological role of bacterial photoreceptors and the mechanisms of signaling downstream of light perception.