Comparative analysis of floral MADS-box genes between wild-type and a putative homeotic mutant in lily

Lily is one of the most valuable garden plants, and its double flowers are highly prized. 'Aphrodite' is a double-flowered cultivar of lily in which the stamens are converted into petaloid organs in whorl 3. 'Aphrodite' differs from agamous mutants in Arabidopsis thaliana because it contains carpels in whorl 4, although the carpels are not fused at the top of the pistil. In order to explain this unique phenotype, we isolated B-, C- and D-class MADS-box genes from the well-known wild-type lily, Lilium × formolongi, and compared the expression patterns of these genes in the two cultivars. We observed reduced C-class gene expression in whorl 3 of'Aphrodite', although the expression patterns of the other genes did not appear to differ greatly. In addition, we isolated the AGAMOUS-like genes from 'Aphrodite' and compared their amino acid sequences with those from L. × formolongi. Very little difference was observed between these two cultivars. Thus, it appears that, in 'Aphrodite', reduced C-class gene expression correlates with the transformation of stamens into petaloid organs. We suggest that this transformation could be caused by transcriptional regulation of the C-class gene.