Despite numerous quantitative trait loci and association mapping studies, our understanding of the extent to which natural allelic series contribute to the variation for complex traits is limited. In this study, we investigate the occurrence of a natural allelic series for complex traits at the teosinte branched1 (tb1) gene in natural populations of teosinte (Zea mays ssp. parviglumis, Z. mays ssp. mexicana, and Z. diploperennis). Previously, tb1 was shown to confer large effects on both plant architecture and ear morphology between domesticated maize and teosinte; however, the effect of tb1 on trait variation in natural populations of teosinte has not been investigated. We compare the effects of nine teosinte alleles of tb1 that were introgressed into an isogenic maize inbred background. Our results provide evidence for a natural allelic series at tb1 for several complex morphological traits. The teosinte introgressions separate into three distinct phenotypic classes, which correspond to the taxonomic origin of the alleles. The effects of the three allelic classes also correspond to known morphological differences between the teosinte taxa. Our results suggest that tb1 contributed to the morphological diversification of teosinte taxa as well as to the domestication of maize.
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