Patterns of molecular evolution among paralogous floral homeotic genes

The plant MADS-box regularory gene family includes several loci that contro l different aspects of inflorescence and floral development. Orthologs to t he Arabidopsis thaliana MADS-box floral meristem genes APETALA1 and CAULIFL OWER and the floral organ identity genes APETALA3 and PISTILLATA were isola ted from the congeneric species Arabidopsis lyrata. Analysis of these loci between these two Arabidopsis species, as well as three other more distantl y related tare, reveal contrasting dynamics of molecular evolution between these paralogous floral regulatory genes. Among the four loci, the CAL locu s evolves at a significantly faster rate, which may be associated with the evolution of generic redundancy between CAL and API. Moreover, there are si gnificant differences in the distribution of replacement and synonymous sub stitutions between the functional gene domains of different floral homeotic loci. These results indicate thai divergence in developmental function amo ng paralogous members of regulatory gene families is accompanied by changes in rate and pattern of sequence evolution among loci.