Although UV-B makes up only a small fraction of the sunlight that reaches the Earth’s surface, it serves as an important signal in plants, with effects on plant architecture and metabolism, for instance (reviewed in Jenkins, 2009). Arabidopsis thaliana UV RESISTANCE LOCUS8 (UVR8) has recently been established to be a UV-B photoreceptor, opening the door to elucidating UV-B signaling pathways in plants (reviewed in Heijde and Ulm, 2012). As it mediates the activation of downstream genes in response to UV-B, UVR8 changes from a dimer to monomer and interacts with the E3 ubiquitin ligase CONSTITUTIVELY PHOTOMORPHOGENIC1 (COP1). UVR8 is a β-propeller protein with several conserved Trp residues that have been suggested to be important for its function. Now, O’Hara and Jenkins (pages 3755–3766) have thoroughly characterized the roles of these residues.
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