homeotic modi®cations in Arabidopsis

The ABC model for ¯oral development was proposed more than 10 years ago and since then many studies have been performed on model species, such as Arabidopsis thaliana, Antirrhinum majus, and many other species in order to con®rm this hypothesis. This led to additional information on ¯ower develop-ment and to more complex molecular models. AGAMOUS (AG) is the only C type gene in Arabidopsis and it is responsible for stamen and car-pel development as well as ¯oral determinacy. LLAG1, an AG homologue from lily (Lilium longi-¯orum Thunb.) was isolated by screening a cDNA library derived from developing ¯oral buds. The deduced amino acid sequence revealed the MIKC structure and a high homology in the MADS-box among AG and other orthologues. Phylogenetic analysis indicated a close relationship between LLAG1 and AG orthologues from monocot species. Spatial expression data showed LLAG1 transcripts exclusively in stamens and carpels, constituting the C domain of the ABC model. Functional analysis was carried out in Arabidopsis by overexpression of LLAG1 driven by the CaMV35S promoter. Transformed plants showed homeotic changes in the two outer ¯oral whorls with some plants presenting the second whorl completely converted into stamens. Altogether, these data strongly indicated the func-tional homology between LLAG1 and AG. Key words: ABCDE model, double ¯ower, ¯ower architecture, function analysis, MADS-box genes, phylogenetic study