Abstract
Veronica persica develops small bluish flowers. We analyzed flavonoids in the blue petals by HPLC, TOF-MS, and NMR, and determined its major anthocyanin and flavone to be delphinidin 3-O-(2-O-(6-O-coumaroyl)-glucosyl)-6-O-coumaroyl-glucoside-5-O-glucoside and apigenin 7-O-(2-O-glucuronosyl)-glucuronide, respectively. This flavone glucuronide caused a dose-dependent bathochromic shift toward a blue hue with the anthocyanin pigment, showing an intermolecular co-pigment effect. The significant co-pigmentation prompted us to explore genes responsible for these flavonoids. Based on the structural similarity to Lamiales flavonoid 7-O-glucuronosyltranferases, we isolated a cDNA encoding a UDP-sugar-dependent glycosyltransferase (UGT88D8). UGT88D8 catalyzed the 7-O-glucuronosylation of flavones. Moreover, based on the structural similarity to sugar-sugar glycosyltransferases, we also identified UGT94F1 as an anothocyanin 3-O-glucoside-2''-O-glucosyltransferase. Considering the remarkable expressions of UGT88D8 and UGT94F1 genes in petals, they are involved in the blue flower coloration of V. persica by catalyzing the co-pigment and pigment biosyntheses.
