The rps19 ribosomal protein gene, which has not been previously reported in any mitochondrial genome, was identified by sequence analysis in the mitochondrial DNA of the higher plant Petunia hybrida. According to the sequence of eight rps19 cDNAs, seven C to U conversions with respect to the genomic sequence are present in rps19 transcripts. Not all transcripts are fully edited at these seven sites. Six of the seven C to U conversions change the encoded amino acid sequence by altering four codons. The rps19 gene is located entirely within a repeat sequence which is present in three copies on the 443 kb genome. Due to intragenomic recombination across these repeats, Petunia rps19 is present in nine different genomic environments.

Anthocyanin biosynthesis in flowers of Petunia hybrida is controlled by the regulatory genes an1, an2 and an11. Seven classes of cDNA clones homologous to transcripts that are down-regulated in an1-, an2- and an11- mutants were isolated via differential cDNA cloning. Genetic mapping, antisense RNA experiments and analyses of mutant alleles demonstrated that one class of clones originated from the Rt locus. The rt gene has no introns and encodes a protein with homology to mammalian glucuronosyl transferases and flavonoid 3-O-glucosyltransferase (UF3GT) encoded by the bz1 gene from Zea mays. As the Rt locus controls the rhamnosylation of reddish anthocyanin-3-O-glucosides which is the first in a series of modifications that finally yield magenta or blue/purple coloured anthocyanins, this suggests that rt encodes an anthocyanin rhamnosyl transferase. Molecular analysis of two mutant rt alleles showed that their expression is blocked by different DNA insertion elements. Mutability of the rt-vu15 allele results from the presence of a 284 bp transposable element (dTph1) in the rt promoter region, causing a block in transcription. The protein coding region of the rt-r27 allele contains a 442 bp insertion (dTph3) resulting in premature polyadenylation of rt transcripts. Although dTph3 cannot transpose, it has sequence characteristics of transposable elements, suggesting that it is a defective member of a new family of transposable elements.

Overlapping open reading frames corresponding to maize mitochondrial genes rps3 and rpl16 have been found in Petunia mitochondrial DNA. The DNA region associated with these two genes is part of the Petunia mitochondrial recombination repeat and is iterated three times. Analysis of transcripts from these genes shows that there is RNA editing of the coding regions and that one of the editing sites detected in the open reading frame overlap creates a premature stop codon in the rpl16 sequence. No transcripts were detected that were unedited at this site. Thus, in Petunia editing of rpl16 appears to render this gene nonfunctional.

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.