MOLECULAR EVOLUTION OF FLOWER DEVELOPMENT - DIVERSIFICATION OF THE PLANT MADS-BOX REGULATORY GENE FAMILY

Floral homeotic genes that control the specification of meristem and o rgan identity in developing flowers have been isolated from both Arabi dopsis thaliana and Antirrhinum majus. Most of these genes belong to a large family of regulatory genes and possess a characteristic DNA bin ding domain known as the MADS-box. Members of this gene family display primarily floral-specific expression and are homologous to transcript ion factors found in several animal and fungal species. Molecular evol utionary analyses reveal that there are appreciable differences in the substitution rates between different domains of these plant MADS-box genes. Phylogenetic analyses also demonstrate that members of the plan t MADS-box gene family are organized into several distinct gene groups : the AGAMOUS, APETALA3/PISTILLATA and APETALA1/AGL9 groups. The share d evolutionary history of members of a gene group appear to reflect th e distinct functional roles these MADS-box genes play in flower develo pment. Molecular evolutionary analyses also suggest that these differe nt gene groups were established in a relatively short span of evolutio nary time and that the various floral homeotic loci originated even be fore the appearance of the flowering plants.