Detection and identification of a UDP-glucose: flavonoid 3-Oglucosyltransferase gene involving in anthocyanin pathway in pomegranate (Punica granatum)

Pomegranate is a rich source of valuable anthocyanin pigments which constitute the colors ranging from pink to dark purple in fruit skin and arils. The UDP-glucose: flavonoid 3- Oglycosyltransferase enzyme is responsible for the formation of anthocyanins in pigmented cells and catalyze the transfer of a sugar moiety into anthocyanidin. In this study, the cDNA of UDP glucose: flavonoid 3-O-glucosyltransferase gene (UFGT), the last enzyme in anthocyanin biosynthesis was isolated from the pomegranate fruit skin and sequenced. Moreover, the expression of this gene in three distinct pomegranate accessions (Poost Siyah Yazd, Malas Isfahn and Shirin Shabad Shiraz) differing in skin color and pattern of color accumulation was monitored. The deduced amino acid sequence of the cDNAs showed high homology to the sequences of other plants in the GenBank database such as grape and peach. Our results demonstrated that the expression of PgUFGT was relatively high in flowers in the three accessions, but increasing as the fruit continued to develop and peaking in Poost Siyah Yazd over-ripe fruit. Unlike this accession, in Shirin Shaabad Shiraz, PgUFGT expression was detected at low level in all fruit development stages except flower stage. Moreover, the expression of PgUFGT declined in young developing fruits, gradually increased again as the fruit matured and reached its peak when the fruit was over-ripened in Malas Isfahan. Overall, the expression of PgUFGT indicated that the expression of this gene increased dramatically during pomegranate fruit development. Furthermore, the protein structure prediction of PgUFGT showed the similarity of 52% to three dimensional structure of UDP-glucose: flavonoid glycosyltransferase in red grape. The obtained data suggested that both of proteins likely act in similar way to produce anthocyanin. Also, the results obtained from PgUFGT expression in three pomegranate accessions confirmed it.