Ectopic expression of LLAG1, an AGAMOUS homologue from lily (Lilium longiflorum Thunb.) causes floral homeotic modifications in Arabidopsis

The ABC model for floral 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 confirm this hypothesis. This led to additional information on flower development and to more complex molecular models. AGAMOUS (AG) is the only C type gene in Arabidopsis and it is responsible for stamen and carpel development as well as floral determinacy. LLAG1, an AG homologue from lily (Lilium longiflorum Thunb.) was isolated by screening a cDNA library derived from developing floral 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 floral whorls with some plants presenting the second whorl completely converted into stamens. Altogether, these data strongly indicated the functional homology between LLAG1 and AG.