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, hypocotyls, roots and leaves. Expressed in all tissues (cotyledon, hypocotyls and roots) at uniform levels at all stages of development. Belongs to the UDP-glycosyltransferase family.