Molecular population genetics of maize regulatory genes during maize evolution By

Maize was domesticated from its wild ancestor, teosinte, in southern Mexico between ~6,250 and ~10,000 years ago. The domestication of maize resulted in an extensive phenotypic change in female inflorescence (ear) structures from teosinte. MADS-box genes encode transcription factors which are key regulators of plant inflorescence and flower development. We examined DNA sequence variation in 32 maize MADS-box genes and 32 random loci from the maize genome and investigated their involvement in maize domestication and improvement. Domestication caused a significant loss of genetic variation in 32 MADS-box genes in maize relative to teosinte while maize improvement further reduced maize genetic variation by a slight amount. Conditioning on sequence variation in 30 neutral random genes, analysis of coalescent simulation showed that the bottleneck associated with domestication was of moderate intensity (Nb/d ! 1.8, where Nb is population size and d is the duration time of domestication) and a bottleneck with this intensity was used to test for selection in MADS-box genes. Among 32 MADS-box genes, neutrality tests and tests incorporating the bottleneck identified eight genes as putative targets of artificial selection associated with domestication. According to neutrality tests, three additional MADS-box genes appear to have been under selection during modern agricultural improvement of maize. For random loci, two genes appear to be targets of selection during domestication and four additional genes were indicated to be candidate selected loci for maize improvement. The role of MADS-box genes as more frequent targets of selection during domestication