Instability at a flower color locus in the morning glory

Abstract

Genetic analyses of albino-variegated flower phenotypes of the common morning glory, Ipomoea purpurea, show that these sectoring phenotypes are caused by a mutator system that acts on white flower alleles of locus A/a. The mutator is located no further than two map units from locus A/a (and hence possibly at locus A/a itself) and is apparently cis-acting. Mutations In subdermal tissue of unstable aa genotypes result in the recovery of stable a and revertant A type gametes in high frequencies (approximately 0.005 each). In addition, different somatic sectoring rates among unrelated lineages of unstable aa genotypes are heritable, and are reflected in the frequencies of gametes from these plants that have mutant A or stable a genotypes. The differences in mutation rates between these llneages appear to be due primarlly to differences between the mutators themselves, not to other genetic factors. These results suggest that transposable elements may be responsible for the Instability of some A/a locus genotypes, analogous, for example, to the transposable element-induced Instabllity of flower color genes demonstrated in Antirrhinum majus.