Analysis of flower pigmentation mutants generated by random transposon mutagenesis in Petunia hybrida

Fifty new flower pigmentation mutants in Petunia hybrida using endogenous transposable elements (TEs) as a mutagen were generated. Forty-six mutants displayed somatic and sporogenic instability indicating that they were caused by a TE. Phenotypic analysis showed that the mutation altered either anthocyanin biosynthesis (40 alleles for seven loci), the intracellular pH of petals (six alleles for three loci) or the shape of petal cells (two alleles for two loci). To identify the TEs responsible for the mutations, the authors subjected 16 alleles of the anthocyanin-3 (an3) locus, encoding flavanone 3 beta-hydroxylase, to molecular analysis. This showed that 11 out of 12 unstable an3 alleles harboured TE insertions of a single family, dTph1, while one allele harboured a new 177 bp TE designated dTph2. In addition, the authors found one an3 allele (an3-W138A) in which a dTph1 element had inserted 30 bp upstream the translation start, without inactivating the gene. This 'cryptic' element was responsible for the creation of a stable recessive (untagged) an3 allele, where a large rearrangement inactivated the gene. These findings indicate that mutants for novel loci are most likely tagged by dTph1 elements opening the way for their isolation.