Genetic analysis of instability in Petunia hybrida : 2. Unstable mutations at different loci as the result of transpositions of the genetic element inserted at the An1 locus.

In crossing experiments with Petunia hybrida, new mutations, some unstable, have been found in descendants of plants having an unstable allele of the anthocyanin gene An1. One of the unstable mutations affecting the new anthocyanin gene An11 was genetically analyzed, and it was subsequently established in which step of anthocyanin synthesis that An11 is involved. The discovery of new, unstable mutations at other loci indicates that in Petunia also a relation exists between unstable mutations and the presence of transposable elements in the genome. It was demonstrated that reverted alleles (an1 (+/+)) originating from unstable An1 alleles are less stable than the original wild-type allele An1, and that reversions do not increase the chances of occurrence of new, stable or unstable mutations at other loci. These results provide additional arguments in favour of the hypothesis posed in an earlier paper that reversions of unstable An1 alleles are not the result of excision of the inserted transposable element, but are due to the repair of secondary mutations induced by the insert in the regulatory region of the locus. Consequently, a reverted allele still contains the inserted element that may again induce mutations leading to inactivation of An1.