The molecular basis of incomplete dominance at the A locus of CHS-D in the common morning glory, Ipomoea purpurea

The mutable a flaked (a f ) allele at the A locus of the common morning glory (Ipomoea purpurea) confers incomplete dominance in flower pigmentation and is caused by insertion of the DNA transposon Tip100 into CHS-D, which encodes chalcone synthase and is required for anthocyanin biosynthesis. Levels of CHS-D transcripts, CHS-D protein, and anthocyanin pigment in heterozygous flowers were about half that in homozygous flowers, indicating that dosage-dependent expression of CHS-D is the primary cause of the observed incomplete dominance. This contrasts with the Nivea locus in snapdragon (Antirrhinum majus) in which incomplete dominance is caused by semi-dominant CHS alleles.