In the presence of other necessary color factors, this glycosylation reaction allows the accumulation of anthocyanin pigments (By similarity). May be involved in glycosylation of unstable cyanohydrins to produce stable cyanoglucosides. an anthocyanidin + H(+) + UDP-alpha-D-glucose = an anthocyanidin 3-O-beta-D-glucoside + UDP Pigment biosynthesis; anthocyanin biosynthesis. Expressed in cotyledons and leaves. Expressed primarily in developing cotyledons (from emerging green cotyledons to approximately 10 days old); very low levels in hypocotyls and no measurable expression in roots. Belongs to the UDP-glycosyltransferase family.