A Genetic Locus Determines Glycosylation Specificity of Anthocyanins in Cranberry

American cranberry (Vaccinium macrocarpon) fruit contain flavonoids known to benefit human health. Providing high antioxidant levels is one of the benefits and the main contributors to this activity are the anthocyanins. In vivo activity of these antioxidants can be limited by bioavailability. Although anthocyanidin-glucose conjugates are reported to be more bioavailable than those of other sugars, American cranberry fruit contain mainly galactosides and arabinosides of the aglycones, cyanidin and peonidin, with less than 8% glucosides. In contrast, small-fruited cranberry (V. oxycoccos) contains mostly glucose conjugates. We propose that the glycosylation difference is mediated by a 3-O-glycosyltransferase gene. We amplified the anythocyanidin 3-O-glycosyltransferase from both cranberry species using primers based on comparison of published sequences from other plant species and the cranberry genome sequence as a reference. The aligned full-length gene sequences revealed 96% identity and only 39 SNPs and 2 gaps in V. oxycoccos relative to V. macrocarpon. The SNPs resulted in 21 amino acid differences and 2 gaps in the V.oxycoccos enzyme relative to that of V. macrocarpon. The plant secondary product glycosyltransferase (PSPG) box is involved in binding to the UDP moiety of the sugar donor and is thus one of the regions of interest. The PSPG box is 44 amino acids long and 4 amino acids differ in this region between the two cranberry species (N352T, N357S, V359L, H378Q). We are sequencing this region from representative F₂ hybrids, for which the anthocyanin phenotype has been determined to confirm the amino acid differences impacting glycosylation specificity.