Preliminary results on high polymorphism of glycosyltransferase VvGT7 in grapevine (Vitis vinifera)

In our study sequencing of the glycosyltransferase gene VvGT7 in Vitis vinifera 'White Riesling' led to the identification of four sequence variants in a single plant. Single-base substitutions introduced during PCR or cloning could be excluded as source of the observed polymorphism, because they would be expected to be randomly distributed. In contrast the sequence variants of VvGT7 always share their SNPs and repeat length with at least one other variant. Possible explanations for abnormal high allele numbers are (1) the misinterpretation of highly similar genes as one locus during genome assembly, (2) the coexistence of genetically distinct cell layers in one organism and (3) recombination, either between homologous chromosomes in somatic cells or during PCR. By sequencing of VvGT7 in plants derived from somatic embryogenesis and selfings, we were able to show that VvGT7 is actually a single gene and that the four sequence variants are not originating from distinct genotypes in different cell layers. These preliminary results may be helpful to others observing similar patterns of sequence diversity.