Photochemistry and Signaling Activity of Plant Cryptochromes: A Review

-Cryptochromes constitute an extensive class of blue-light sensory receptors that regulate the processes of development and circadian rhythm in plants. These photoreceptors can also act as magnetoreceptors. As a chromophore, cryptochromes bind the flavin adenine dinucleotide (FAD) in the photolyase homology region (PHR) domain; near the FAD-binding site, a C-terminal extension CCE is attached to it. The cryptochrome activation is initiated by FAD photoreactions with electron/proton transfer and formation of redox forms. During FAD photoreduction, the protein is exposed to a conformational change causing a separation of the PHR domain and CCE, which is accompanied by the formation of functionally active oligomers of cryptochrome molecules. Photooligomerization is considered as a key process required for a signaling activity of cryptochromes.