Phytochrome: structural basis for its functions

Phytochrome mediates various physiological as well as developmental responses to light stimuli in plants. Phytochrome is a soluble chromoprotein consisting of the N-terminal photosensory and C-terminal dimerization moieties. Close homologues of plant phytochromes are widely found in prokaryotes. Recently, the crystal structures of the core photosensory module of bacterial phytochromes are resolved. Intriguingly, three sub-domains (PAS, GAF and PHY) in the module are connected by unusual structures named ‘light-sensing knot’ and ‘tongue’, which are in tight contact with the chromophore. These findings enable us to review previous data on the structure–function relationships in phytochrome. Consequently, functional importance of these peculiar structures is further highlighted. Thus, the three-dimensional structure provides a framework for understanding how phytochrome processes the light signals.

Research highlights▶ The crystal structure of phytochrome has been resolved. ▶ The PAS/GAF domain constitutes the core signaling structure. ▶ The other domains modify the functions of phytochrome.