How Does Photoreceptor UVR8 Perceive a UV-B Signal?

UVR8 is the only known plant photoreceptor that mediates light responses to UV‐B (280–315 nm) of the solar spectrum. UVR8 perceives a UV‐B signal via light‐induced dimer dissociation, which triggers a wide range of cellular responses involved in photomorphogenesis and photoprotection. Two recent crystal structures of Arabidopsis thaliana UVR8 (AtUVR8) have revealed unusual clustering of UV‐B‐absorbing Trp pigments at the dimer interface and provided a structural framework for further mechanistic investigation. This review summarizes recent advances in spectroscopic, computational and crystallographic studies on UVR8 that are directed toward full understanding of UV‐B perception at the molecular level. Light perception of UV‐B photoreceptor UVR8 is triggered by light‐induced molecular events originating in two epicenters located at the dimer interface. Clustered tryptophan residues serve as UV‐B pigments and undergo concerted conformational changes upon absorbing UV‐B photons, which disrupt the dimer interface and lead to dimer dissociation of UVR8.