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

The Ultraviolet Resistance Locus 8 (UVR8) in plants recognizes Ultraviolet-B (UV-B) and plays a crucial role by regulating plant growth through a series of signal transduction events. However, the UVR8 in monocotyledon crops has not been systematically analyzed. We identified BdUVR8 (BRADI_3g45740) from the genome of Brachypodium distachyon, a relative of wheat, by analyzing the phylogenetic tree, gene expression pattern, detecting the accumulation of UV-B response metabolites, and check the 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. The expression analysis reveals that UV-B down-regulates BdUVR8 by 70% and up-regulates the chalcone synthase (BdCHS) gene 3.4-folds in B. distachyon. The pCAMBIA1300::BdUVR8-mCherry construct introduced into Arabidopsis uvr8 mutants shows that BdUVR8 protein localized in the cytoplasm translocates into the nucleus in response to UV-B irradiation. The introduction of BdUVR8 into uvr8 rescued the hypocotyl elongation by UV-B and restored the expression of HY5, Chalcone synthase, and Flavanone 3-hydroxylase as well as the accumulation of total flavonoids. Altogether, our results show that BdUVR8 is a photoreceptor that perceives UV-B in B. distachyon.