In the presence of other necessary color factors, this glycosylation reaction allows the accumulation of anthocyanin pigments (PubMed:17573033). Anthocyanidins are the preferred substrates, while flavonols are only a minor substrate in vitro (PubMed:17573033). an anthocyanidin + H(+) + UDP-alpha-D-glucose = an anthocyanidin 3-O-beta-D-glucoside + UDP pelargonidin + UDP-alpha-D-glucose = pelargonidin 3-O-beta-D-glucoside + UDP cyanidin + UDP-alpha-D-glucose = cyanidin 3-O-beta-D-glucoside + H(+) + UDP Pigment biosynthesis; anthocyanin biosynthesis. Highest expression detected in fruit, with very low levels detected in petal and leaf. Expression in fruit is ripening-related, with highest expression levels detected in turning stage and red fruit. Belongs to the UDP-glycosyltransferase family.