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Plant Cell. 2016 Apr;28(4):966-83. doi: 10.1105/tpc.15.00287. Epub 2016 Mar 28.

UV-B Perception and Acclimation in Chlamydomonas reinhardtii.

Author information

1
Department of Botany and Plant Biology, University of Geneva, Sciences III, CH-1211 Geneva 4, Switzerland.
2
SIB-Swiss Institute of Bioinformatics, University of Lausanne, CH-1015 Lausanne, Switzerland.
3
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.
4
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.

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.

PMID:
27020958
PMCID:
PMC4863380
DOI:
10.1105/tpc.15.00287
[Indexed for MEDLINE]
Free PMC Article

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