title: UV-B Perception and Acclimation in Chlamydomonas reinhardtii.
abstract: Plants perceive UV-B, an intrinsic component of sunlight, via a signaling pathway that is mediated by the photoreceptor UV RESISTANCE LOCUS8 (UVR8) and induces UV-B acclimation. To test whether similar UV-B perception mechanisms exist in the evolutionarily distant green alga Chlamydomonas reinhardtii, we identified Chlamydomonas orthologs of UVR8 and the key signaling factor CONSTITUTIVELY PHOTOMORPHOGENIC1 (COP1). Cr-UVR8 shares sequence and structural similarity to Arabidopsis thaliana UVR8, has conserved tryptophan residues for UV-B photoreception, monomerizes upon UV-B exposure, and interacts with Cr-COP1 in a UV-B-dependent manner. Moreover, Cr-UVR8 can interact with At-COP1 and complement the Arabidopsis uvr8 mutant, demonstrating that it is a functional UV-B photoreceptor. Chlamydomonas shows apparent UV-B acclimation in colony survival and photosynthetic efficiency assays. UV-B exposure, at low levels that induce acclimation, led to broad changes in the Chlamydomonas transcriptome, including in genes related to photosynthesis. Impaired UV-B-induced activation in the Cr-COP1 mutant hit1 indicates that UVR8-COP1 signaling induces transcriptome changes in response to UV-B. Also, hit1 mutants are impaired in UV-B acclimation. Chlamydomonas UV-B acclimation preserved the photosystem II core proteins D1 and D2 under UV-B stress, which mitigated UV-B-induced photoinhibition. These findings highlight the early evolution of UVR8 photoreceptor signaling in the green lineage to induce UV-B acclimation and protection.
authors.affiliation: Department of Botany and Plant Biology, University of Geneva, Sciences III, CH-1211 Geneva 4, Switzerland.
authors.forename: Kimberley
authors.identifier: 0000-0001-5394-1996
authors.initials: K
authors.lastname: Tilbrook
authors.affiliation: Department of Botany and Plant Biology, University of Geneva, Sciences III, CH-1211 Geneva 4, Switzerland.
authors.forename: Marine
authors.identifier: 0000-0003-3579-1829
authors.initials: M
authors.lastname: Dubois
authors.affiliation: Department of Botany and Plant Biology, University of Geneva, Sciences III, CH-1211 Geneva 4, Switzerland.
authors.forename: Carlos D
authors.identifier: 0000-0002-6026-4003
authors.initials: CD
authors.lastname: Crocco
authors.affiliation: Department of Botany and Plant Biology, University of Geneva, Sciences III, CH-1211 Geneva 4, Switzerland.
authors.forename: Ruohe
authors.identifier: 0000-0001-6782-4651
authors.initials: R
authors.lastname: Yin
authors.affiliation: Department of Botany and Plant Biology, University of Geneva, Sciences III, CH-1211 Geneva 4, Switzerland.
authors.forename: Richard
authors.initials: R
authors.lastname: Chappuis
authors.affiliation: Department of Botany and Plant Biology, University of Geneva, Sciences III, CH-1211 Geneva 4, Switzerland.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Allorent
authors.affiliation: SIB-Swiss Institute of Bioinformatics, University of Lausanne, CH-1015 Lausanne, Switzerland.
authors.forename: Emanuel
authors.identifier: 0000-0003-1339-5120
authors.initials: E
authors.lastname: Schmid-Siegert
authors.affiliation: Department of Botany and Plant Biology, University of Geneva, Sciences III, CH-1211 Geneva 4, Switzerland Institute of Genetics and Genomics of Geneva (iGE3), University of Geneva, CH-1211 Geneva 4, Switzerland.
authors.forename: Michel
authors.identifier: 0000-0003-1224-5868
authors.initials: M
authors.lastname: Goldschmidt-Clermont
authors.affiliation: Department of Botany and Plant Biology, University of Geneva, Sciences III, CH-1211 Geneva 4, Switzerland Institute of Genetics and Genomics of Geneva (iGE3), University of Geneva, CH-1211 Geneva 4, Switzerland roman.ulm@unige.ch.
authors.forename: Roman
authors.identifier: 0000-0001-8014-7392
authors.initials: R
authors.lastname: Ulm
mesh_terms: D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D016825:Chlamydomonas reinhardtii / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects*; D002868:Chromosomal Proteins, Non-Histone / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant / Q000235:genetics / Q000528:radiation effects; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000528:radiation effects; D044767:Ubiquitin-Protein Ligases; D014466:Ultraviolet Rays
chemical_list: D029681:Arabidopsis Proteins; D002868:Chromosomal Proteins, Non-Histone; D010940:Plant Proteins; C525052:Uvr8 protein, Arabidopsis; C471983:AT2G32950 protein, Arabidopsis; D044767:Ubiquitin-Protein Ligases