How plants cope with UV-B: from perception to response

• The homodimeric UV-B photoreceptor UVR8 monomerizes in response to UV-B reception.
• Monomeric UVR8 interacts with the E3 ubiquitin ligase COP1 via two distinct domains.
• Active UVR8 accumulates in the nucleus in a COP1-dependent manner.
• Pathway is evolutionarily conserved from a unicellular green alga to higher plants.
• UVR8 induces UV-B acclimation, which contributes to enhanced UV-B tolerance.

Ultraviolet-B radiation (UV-B) is an intrinsic part of the solar radiation that reaches the Earth’s surface and affects the biosphere. Plants have evolved a specific UV-B signaling pathway mediated by the UVR8 photoreceptor that regulates growth, development, and acclimation. Major recent advances have contributed to our understanding of the UVR8 photocycle, UV-B-responsive protein-protein interactions, regulation of UVR8 subcellular localization, and UVR8-regulated physiological responses. Here, we review the latest progress in our understanding of UVR8 signaling and UV-B responses, which includes studies in the unicellular alga Chlamydomonas reinhardtii and the flowering plant Arabidopsis.