UV-B Perception and Acclimation in Chlamydomonas reinhardtii

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


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.

MeSH terms

  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism
  • Chlamydomonas reinhardtii / genetics
  • Chlamydomonas reinhardtii / metabolism*
  • Chlamydomonas reinhardtii / radiation effects*
  • Chromosomal Proteins, Non-Histone / genetics
  • Chromosomal Proteins, Non-Histone / metabolism
  • Gene Expression Regulation, Plant / genetics
  • Gene Expression Regulation, Plant / radiation effects
  • Plant Proteins / genetics
  • Plant Proteins / metabolism
  • Signal Transduction / radiation effects
  • Ubiquitin-Protein Ligases
  • Ultraviolet Rays*


  • Arabidopsis Proteins
  • Chromosomal Proteins, Non-Histone
  • Plant Proteins
  • Uvr8 protein, Arabidopsis
  • AT2G32950 protein, Arabidopsis
  • Ubiquitin-Protein Ligases