DNA rearrangements at the region of the dihydroflavonol 4-reductase gene for flower pigmentation and incomplete dominance in morning glory carrying the mutable flaked mutation

Abstract

 The a-3 ^flecked[J] variegated line of Japanese morning glory bearing white flowers with normal-colored flecks and sectors has been shown to carry a 6.4-kb transposable element, Tpn1, inserted within the DFR-B gene, one of the anthocyanin biosynthesis genes encoding dihydroflavonol 4-reductase (DFR). The a ^flaked[M] variegated line of morning glory also bears white flowers with normal-colored flakes and sectors, and it was shown to carry multiple DNA rearrangements, including insertions of mobile element-like sequences, MELSIP1 and MELSIP2, in its DFR gene region. Unlike the a-3 ^flecked[J] mutation, the mutable a ^flaked[M] allele exhibited incomplete dominance. Interestingly, not only intensely colored flakes but also white spots and sectors were often observed in lightly colored flowers of morning glory in the heterozygous state A[M]/a ^flaked[M]. The interspecific F₁ hybrids between Japanese morning glory and morning glory carrying both a-3 ^flecked[J]/A-3[M] and A[J]/ a ^flaked[M] in the heterozygous condition bear lightly colored flowers with intensely colored sectors as well as white flakes. The results clearly demonstrated that the DFR gene in the a ^flaked[M] line of morning glory is active and complements the DFR-B gene carrying Tpn1 in the a-3 ^flecked[J] line of Japanese morning glory. Interspecific allelic interactions between the mutable a ^flaked[M] gene of morning glory and the corresponding wild-type A[J] gene of Japanese morning glory resulted in incomplete dominance and the formation of white flakes and sectors. The appearance of the white flakes may be due to a somatic mutation of the A[J] gene.