title: Photoactivated UVR8-COP1 module determines photomorphogenic UV-B signaling output in Arabidopsis.
abstract: In Arabidopsis, ultraviolet (UV)-B-induced photomorphogenesis is initiated by a unique photoreceptor UV resistance locus 8 (UVR8) which utilizes its tryptophan residues as internal chromophore to sense UV-B. As a result of UV-B light perception, the UVR8 homodimer shaped by its arginine residues undergoes a conformational switch of monomerization. Then UVR8 associates with the constitutively photomorphogenic 1-suppressor of PHYA (COP1-SPA) core complex(es) that is released from the cullin 4-damaged dna binding protein 1 (CUL4-DDB1) E3 apparatus. This association, in turn, causes COP1 to convert from a repressor to a promoter of photomorphogenesis. It is not fully understood, however, regarding the biological significance of light-absorbing and dimer-stabilizing residues for UVR8 activity in photomorphogenic UV-B signaling. Here, we take advantage of transgenic UVR8 variants to demonstrate that two light-absorbing tryptophans, W233 and W285, and two dimer-stabilizing arginines, R286 and R338, play pivotal roles in UV-B-induced photomorphogenesis. Mutation of each residue results in alterations in UV-B light perception, UVR8 monomerization and UVR8-COP1 association in response to photomorphogenic UV-B. We also identify and functionally characterize two constitutively active UVR8 variants, UVR8W285A and UVR8R338A, whose photobiological activities are enhanced by the repression of CUL4, a negative regulator in this pathway. Based on our molecular and biochemical evidence, we propose that the UVR8-COP1 affinity in plants critically determines the photomorphogenic UV-B signal transduction coupling with UVR8-mediated UV-B light perception.
authors.affiliation: Peking-Yale Joint Center for Plant Molecular Genetics and Agro-Biotechnology, State Key Laboratory of Protein and Plant Gene Research, Peking-Tsinghua Center for Life Sciences, College of Life Sciences, Peking University, Beijing, China.
authors.forename: Xi
authors.initials: X
authors.lastname: Huang
authors.affiliation: Peking-Yale Joint Center for Plant Molecular Genetics and Agro-Biotechnology, State Key Laboratory of Protein and Plant Gene Research, Peking-Tsinghua Center for Life Sciences, College of Life Sciences, Peking University, Beijing, China; Department of Botany, College of Life Sciences, Hunan Normal University, Changsha, China.
authors.forename: Panyu
authors.initials: P
authors.lastname: Yang
authors.affiliation: Peking-Yale Joint Center for Plant Molecular Genetics and Agro-Biotechnology, State Key Laboratory of Protein and Plant Gene Research, Peking-Tsinghua Center for Life Sciences, College of Life Sciences, Peking University, Beijing, China.
authors.forename: Xinhao
authors.initials: X
authors.lastname: Ouyang
authors.affiliation: Department of Botany, College of Life Sciences, Hunan Normal University, Changsha, China.
authors.forename: Liangbi
authors.initials: L
authors.lastname: Chen
authors.affiliation: Peking-Yale Joint Center for Plant Molecular Genetics and Agro-Biotechnology, State Key Laboratory of Protein and Plant Gene Research, Peking-Tsinghua Center for Life Sciences, College of Life Sciences, Peking University, Beijing, China; Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, Connecticut, United States of America.
authors.forename: Xing Wang
authors.initials: XW
authors.lastname: Deng
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D002868:Chromosomal Proteins, Non-Histone / Q000235:genetics* / Q000378:metabolism; D044842:Cullin Proteins / Q000235:genetics; D018506:Gene Expression Regulation, Plant / Q000528:radiation effects; D047468:Immunoprecipitation; D009154:Mutation; D063245:Plant Development / Q000235:genetics* / Q000528:radiation effects; D015398:Signal Transduction / Q000528:radiation effects; D044767:Ubiquitin-Protein Ligases / Q000235:genetics* / Q000378:metabolism; D014466:Ultraviolet Rays
chemical_list: D029681:Arabidopsis Proteins; C514806:CULLIN4 protein, Arabidopsis; D002868:Chromosomal Proteins, Non-Histone; D044842:Cullin Proteins; C525052:Uvr8 protein, Arabidopsis; C471983:AT2G32950 protein, Arabidopsis; D044767:Ubiquitin-Protein Ligases