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Nancy R. Hofmann, The Molecular Mechanism of the UVR8 UV-B Photoreceptor, The Plant Cell, Volume 24, Issue 9, September 2012, Page 3485, https://doi.org/10.1105/tpc.112.240910
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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.
O’Hara and Jenkins mutated each of the 14 Trp residues in UVR8 and analyzed their effects on several aspects of UVR8 function. First, the authors examined whether the mutations abolished the UV-B–dependent interaction between UVR8 and COP1 proteins heterologously expressed in yeast. In addition, they tested whether green fluorescent protein fusions of the mutated proteins could complement the uvr8 mutant in terms of restoring UV-B–induced expression of ELONGATED HYPOCOTYL5 and CHALCONE SYNTHASE and UV-B suppression of hypocotyl extension. They also tested whether the mutants rescued the UV-B sensitivity of the uvr8 mutant. Eight of the single mutations and some combinations of double mutants were still able to interact with COP1 in response to UV-B and rescued the uvr8 phenotypes, suggesting that most of the Trp residues in UVR8 are not necessary for its function.
