**43. UDP-glucose:Flavonoid 3-O-glucosyltransferase**

The seed coats of black soybean accumulate red (cyanidin-based), orange (pelargonidinbased) blue (delphinidin-based), purple (petunidin-based), and anthocyanins almost exclu‐ sively as 3-O-glucosidesThe full-length cDNA encoding UDP-glucose:flavonoid 3-Oglucosyltransferase (UGT78K1), the enzyme which catalyzes the last step in anthocyanin biosynthesis, was isolated from black soybean seed coat using rapid amplification of cDNA ends (RACE). The recombinant enzyme glucosylated only anthocyanidins and flavonols with 3-OH regiospecificity. Galactose could also be transferred, albeit with relatively low ac‐ tivity, to the 3-position of cyanidin or delphinidin *in vitro*. The results are consistent with the presence of mainly 3-O-glucosylated and minor amounts of 3-O-galactosylated anthocya‐ nins in the black soybean seed coat. The recombinant enzyme exhibited pronounced sub‐ strate inhibition by cyanidin at 100 M acceptor concentration. The accumulation of anthocyanins and flavonols was reinstated by transfer of UGT78K1 into the *Arabidopsis* T-DNA mutant (ugt78d2) lacking in anthocyanidin and flavonol 3-O-glucosyltransferase activ‐ ity, signifying the role of the enzyme as a flavonoid 3-O-glucosyltransferase. Genomic and phylogenetic analyses suggest the presence of three additional soybean sequences with re‐ markable homology to UGT78K1. RT-PCR confirmed the co-expression of one of these genes (Glyma08g07130) with UGT78K1 in the black soybean seed coat, suggesting possible func‐ tional redundancies in anthocyanin biosynthesis in this tissue [47].
