Elucidation of Primary Events in Bacteriophytochrome Photoreceptors

Abstract

Plants, fungi, and bacteria regulate many physiological responses using phytochrome photoreceptors that absorb light in the red and infrared wavelength ranges (1). For example, growth of plants toward sunlight, germination of seeds, and flowering are all regulated by the phytochrome system. As shown in Fig. 1, the functionality of phytochromes in bacteria is controlled by the geometry of an open-chain tetrapyrrole cofactor known as a bilin. Absorption of red light initiates isomerization of one of the carbon-carbon double bonds in the bilin, which ultimately transforms the protein from inactive to functional forms, respectively denoted as “Pr” and “Pfr”.