Biochemical and molecular characterization of anthocyanidin/flavonol 3-glucosylation pathways in Rosa×hybrida

Rose petals contain 3-glucosylated anthocyanidins and flavonols. We isolated three flavonoid 3-glucosyltransferase (UF3GT) homolog genes (RhUF3GT1, RhUF3GT2, and RhUF3GT3) from rose. RhUF3GT1 encoded an amino acid sequence that is almost identical to the reported rose partial UF3GT homologs and highly homologous to strawberry and apple UF3GTs. Recombinant RhUF3GT1 expressed in yeast catalyzes 3-glucosylation of anthocyanidins but not flavonols. RhUF3GT1 was not expressed in the petals of many cultivars even when anthocyanin biosynthesis was active, while it was expressed in the mature petals of cultivars that synthesize cyanidin 3-glucoside in the mature petals. RhUF3GT2 and RhUF3GT3, sharing 79% identity, exhibit only 42% and 41% identities to RhUF3GT1, respectively, and are distantly related to strawberry and apple UF3GTs. They were expressed in coordination with the flavonol synthase gene in the petal. The recombinant RhUF3GT2 expressed in yeast catalyzed 3-glucosylation of flavonol much more efficiently than that of anthocyanidins. We suggest that RhUF3GT2 catalyzes flavonol 3-glucosylation in rose petals and that it also contributes to accumulation of anthocyanidin 3-glucoside in the petals.