Regulation of Genes by Light

Abstract

Our current understanding of light-dependent regulation of gene expression in purple bacteria is summarized. Most of the regulatory systems utilize photoreceptor proteins that transmit a light-dependent signal to different downstream components to control a wide variety of physiological responses. The photoreceptors identified so far are (bacterio)phytochrome, sensory rhodopsin, phototropin-related proteins, BLUF domain proteins, cryptochrome, and photoactive yellow protein. They use different chromophores such as bilin, retinal, flavin or p-coumaric acid that absorb different wavelengths of light. Based on structural and spectroscopic studies, photochemical reaction mechanisms are beginning to be revealed, which show how the photoreceptors translate a light signal into protein structural changes. On the other hand, downstream factors as well as their signaling pathways are still largely unknown. Purple bacteria also respond to the light environment independently of the photoreceptors. Recent biochemical and genetic data have established that the responses involve photosynthetic and respiratory electron transport chains as well as reactive oxygen species such as singlet oxygen. Regulatory mechanisms of the photoreceptor-independent light responses are also discussed.