Genome-wide analysis of the UGT gene family in Rhododendron and transcriptional correlation of RiUGT43 with anthocyanin accumulation

Abstract

UDP-glycosyltransferases (UGTs) catalyze the glycosylation of anthocyanins and are key enzymes affecting anthocyanin stability and petal coloration. However, the evolutionary characteristics of the UGT family and its regulatory roles in flower color development remain poorly understood in woody ornamental plants. In this study, we identified 137 UGT genes in the Rhododendron simsii genome. Of these, 126 were unevenly distributed across the 13 chromosomes, whereas the remaining 11 were located on unanchored scaffolds. These genes were classified into 15 distinct subfamilies (designated A-O), among which subfamilies A and E contained the most members. Bioinformatic analyses of their physicochemical properties, conserved motifs, chromosomal locations and cis-acting regulatory elements revealed substantial structural and potential regulatory diversification within the Rhododendron UGT family. Integration of genome-family analysis with transcriptomic data from white, pink and red petals of Rhododendron indicum 'Huazhui' identified RiUGT43 as a candidate associated with flower-color variation. The R. simsii gene RsUGT43 falls into group E based on the current phylogeny, while its homolog RiUGT43 shows preferential expression in flowers. RiUGT43 -GFP fluorescence and Western blot analysis in Nicotiana benthamiana leaves confirmed the fusion protein's cytoplasmic and nuclear localization and accumulation in this heterologous host. Changes in RiUGT43 transcript abundance were accompanied by corresponding changes in anthocyanin content. In conclusion, our analysis of the UGT gene family in Rhododendron identified RiUGT43 as a gene transcriptionally associated with anthocyanin accumulation, provided correlative evidence for flower color regulation in woody plants, and established a foundation for future functional studies of UGT-mediated anthocyanin regulation in woody plants.