The origin of maize from the annual teosinte (Zea mays ssp. parviglumis; hereafter, parviglumis) has been a widely accepted hypothesis, owing to the genetic similarities between them. However, this simple model fails to explain the different geographical distributions and phenotypes between the lowland parviglumis and highland maize. Recently, a second annual teosinte — Z. mays ssp. mexicana (hereafter, mexicana), which is distributed throughout the highlands of Mexico — has been implicated in maize origins. However, how mexicana has affected the evolution of maize remains largely unknown. Taking advantage of large-scale population genetics analyses, Ning Yang, from the Huazhong Agricultural University, and colleagues find that a post-domestication admixture between ancient maize and mexicana around 6,000 years before present (bp) in the Mexico highlands substantially shaped the diversity and dispersal of maize.
N16 is a cob sample of an ancient maize (from about 5,500 years bp) from northern Peru and represents a maize lineage that had spread south before the colonization of the Mexican highlands by maize. As expected, no mexicana ancestry was found in its genome. Genetic admixture with mexicana was, however, ubiquitously found in hundreds of modern maize lines, a large panel of broadly sampled traditional lines across the Americas and China, and in archaeological samples unearthed either in central Mexico (about 5,300 years bp) or from South America (about 1,000 years bp). Basically, mexicana ancestry is present in all samples that represent maize that had dispersed after this plant had colonized the Mexican highlands. Moreover, this admixture shows high correlation features of genetic diversity, which indicate its effect on expanding maize diversity.
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