Molecular characterization of a double-flower mutation in Matthiola incana

The double flower is one of the most important traits in the floricultural plant Matthiola incana. Although a doubleness locus (S/s) was defined by genetic analysis a century ago, the gene responsible for double flowers has not been identified in M. incana. We isolated MiAG from M. incana cultivars, and its sequence and genomic structure were found to be highly similar to the AGAMOUS gene in Arabidopsis. Two independent mutated alleles miagl and miag2 were identified from the double-flowered individuals of M. incana cultivars. Deletions of 135 bp (from the 2nd exon to the 2nd intron) and 89 bp (from the 7th intron to the 8th exon) were detected in miagl and miag2, respectively. No transcript was detected in flower buds from miagl alleles in corresponding cultivars, whereas three mRNA variants with frameshifts were transcribed from the miag2 allele in other cultivars. Thus, two mutated alleles corresponding to the s locus contributed to the 'eversporting' type double-flower cultivars in M. incana. Moreover, we also developed co-dominant molecular markers to describe the genotypes of the three alleles of MiAG. Using these DNA markers allows for selection of single- or double-flowered individuals among seedlings that do not display phenotypic differences.