Variation and selection at the CAULIFLOWER floral homeotic gene accompanying the evolution of domesticated Brassica oleracea

The evolution of plant morphologies during domestication events provides cl ues to the origin of crop species and the evolutionary genetics of structur al diversification. The CAULIFLOWER gene, a floral regulatory locus, has be en implicated in the cauliflower phenotype in both Arabidopsis thaliana and Brassica oleracea. Molecular population genetic analysis indicates that al leles carrying a nonsense mutation in exon 5 of the B. oleracea CAULIFLOWER (BoCAL) gene are segregating in both wild and domesticated B. oleracea sub species. Alleles carrying this nonsense mutation are nearly fixed in B. ole racea ssp. botrytis (domestic cauliflower) and B. oleracea ssp. italica (br occoli), both of which show evolutionary modifications of inflorescence str uctures. Tests for selection indicate that the pattern of variation at this locus is consistent with positive selection at BoCAL in these two subspeci es. This nonsense polymorphism, however, is also present in both B. olerace a ssp. acephala (kale) and B. oleracea ssp. oleracea (wild cabbage). These results indicate that specific alleles of BoCAL were selected by early farm ers during the domestication of modified inflorescence structures in B. ole racea.