Analysis of Brachypodium distachyon UVR8 reveals conservation in UV-B receptors

The Ultraviolet Resistance Locus 8 (UVR8) in plants recognizes ultraviolet-B (UV-B) light and plays a crucial role in regulating plant growth through a series of signal transduction events. However, the UVR8 in monocotyledon crops has not yet been systematically analysed. We identified BdUVR8 (BRADI_3g45740) from the genome of Brachypodium distachyon, a relative of wheat, by analysing the phylogenetic tree, the gene expression pattern, detecting accumulation of UV-B response metabolites, and checking for phenotype recovery. The BdUVR8 protein sequence is similar to the known UVR8 of other species. The phylogenetic tree of UVR8 shows clear divergence between dicotyledons and monocotyledons. Expression analysis revealed that UV-B downregulates BdUVR8 by 70% and upregulates the chalcone synthase (BdCHS) gene 3.4-fold in B. distachyon. The pCAMBIA1300::BdUVR8-mCherry construct introduced into Arabidopsis uvr8 mutants showed that the BdUVR8 protein is localized in the cytoplasm and translocates into the nucleus in response to UV-B irradiation. The introduction of BdUVR8 into uvr8 rescued hypocotyl elongation caused by UV-B and restored expression of HY5, Chalcone synthase, and Flavanone 3-hydroxylase, as well as accumulation of total flavonoids. Together, our results show that BdUVR8 is a photoreceptor that perceives UV-B in B. distachyon.