Ultraviolet-B light (UV-B) is an inherent part of sunlight, which has significant biological effects on plants. Low level, non-damaging UV-B serves as a photomorphogenic signal to regulate photomorphogenesis.

UV RESISTANCE LOCUS 8 (UVR8) is a UV-B photoreceptor that mediates light responses in plant. The mechanism by which UVR8 triggers UV-B photomophogenic responses in the nucleus and whether or not UVR8 interacts with transcription factors to directly regulate transcription is still unknown. 

Dr. LIU Hongtao's group at Shanghai Institute of Plant Physiology and Ecology, CAS Center for Excellence in Molecular Plant Sciences, Chinese Academy of Sciences, provided evidence that UVR8 interacts with WRKY36 to regulate photomorphogeneis in response to UV-B light. This work was published online in Developmental Cell. 

The researchers demonstrated that UV-B inhibits plant growth by repressing plant steroid hormone brassinosteroid (BR)-promoted plant growth, and UVR8 physically interacts with the functional dephosphorylated BRI1-EMS-SUPPRESSOR1 (BES1) and BES1-INTERACTING MYC-LIKE 1 (BIM1) transcription factors that mediate BR-regulated gene expression and plant growth to inhibit their activities.

Genome-wide gene expression analysis defined a BES1-dependent UV-B-regulated transcriptome, which is enriched with genes involved in cell elongation and plant growth.

They further showed that UV-B activated and nucleus localized UVR8 inhibited the DNA-binding activities of BES1/BIM1 to directly regulate transcription of growth-related genes.

This study established that UVR8-BES1/BIM1 interaction represents an early photoreceptor signaling mechanism in plants and serves as an important module integrating light and BR signaling.