The genetic basis of a flower color polymorphism in the common morning glory (Ipomoea purpurea).

The common morning glory (Ipomoea purpurea) is highly polymorphic for flower color. Part of this phenotypic variation is due to allelic variation at the P locus. This locus determines whether flowers will be purple or pink, where purple is dominant to pink. We have determined that the anthocyanin biosynthetic gene flavonoid 3'-hydroxylase (f3'h) corresponds to the P locus. In the pink allele of f3'h there is a large insertion in the third exon, which results in the production of a truncated transcript. This shortened transcript produces a nonfunctional F3'H enzyme, resulting in the production of pink flowers rather than purple. In addition, we describe a polymerase chain reaction (PCR)-based assay that can be used to determine the genotype of a plant at this locus.