Abstract

Donuts Dissociate In Arabidopsis , the UVR8 protein responds to ultraviolet-B (UV-B) light by dissociating into monomers, which are then available to interact with downstream factors that enact the plant's response to light. Christie et al. (p. 1492 , published online 9 February; see the cover and see the Perspective by Gardner and Correa ) have now determined the crystal structure of UVR8. Without ultraviolet-B light, UVR8 dimerizes, with two donut-shaped monomers joined by a network of salt bridges. Close-packing of a pyramid of tryptophan residues permits exciton coupling that is key to UV-B perception. Electron transfer after UV-B perception could dissociate the salt bridges that hold the dimer together and release monomeric UVR8 to initiate light-induced signaling.