Abstract

The ABC model of floral organ identity, derived from eudicot organisms such as Arabidopsis thaliana and Antirrhinum majus, has stimulated new approaches in the study of floral diversity and petal evolution. More specifically, the model suggests that MADS -box genes may play an important role in generating floral diversity through expression changes in conserved floral organ identity programs, resulting in homoeotic shifts in floral organ identity. We have been examining the role of heterotopic MADS -box gene expression in the evolution of petals in the eudicot order Caryophyllales. We previously constructed a phylogeny of the order using multiple chloroplast and nuclear gene markers, and demonstrated that numerous separate instances of petal evolution have occurred across the order. However analyses of MADS -box gene expression patterns in separate instances of petal evolution reveal little evidence for a common petal identity program, indicative of homoeosis. Therefore, within the Caryophylalles, different floral organs with a distinct developmental genetic basis appear to have converged on similar petal morphology. We are now examining how this convergence might be achieved at the developmental genetic level.