In the presence of other necessary color factors, this glycosylation reaction allows the accumulation of anthocyanin pigments. an anthocyanidin + H(+) + UDP-alpha-D-glucose = an anthocyanidin 3-O-beta-D-glucoside + UDP Pigment biosynthesis; anthocyanin biosynthesis. Expressed in cotyledons and roots, but not in leaves. Maximum expression in cotyledons that just emerged from the seed coat. Low levels in hypocotyls and increasing levels in roots throughout this period of development. Belongs to the UDP-glycosyltransferase family.