Genetic Diversity and Population Structure of Teosinte
Fukunaga, Kenji, Hill, Jason, Vigouroux, Yves, Matsuoka, Yoshihiro, et al., Genetics
The teosintes, the closest wild relatives of maize, are important resources for the study of maize genetics and evolution and for plant breeding. We genotyped 237 individual teosinte plants for 93 microsatellites. Phylogenetic relationships among species and subspecific taxa were largely consistent with prior analyses for other types of molecular markers. Plants of all species formed monophyletic clades, although relationships among species were not fully resolved. Phylogenetic analysis indicated that the Mexican annual teosintes divide into two clusters that largely correspond to the previously defined subspecies, Z mays ssp. parviglumis and ssp. mexicana, although there are a few samples that represent either evolutionary intermediates or hybrids between these two subspecies. The Mexican annual teosintes show genetic substructuring along geographic lines. Hybridization or introgression between some teosintes and maize occurs at a low level and appears most common with Z mays ssp. mexicana. Phylogeographic and phylogenetic analyses of the Mexican annual teosintes indicated that ssp. parviglumis diversified in the eastern part of its distribution and spread from east to west and that ssp. mexicana diversified in the Central Plateau of Mexico and spread along multiple paths to the north and east. We defined core sets of collections of Z mays ssp. mexicana and ssp. parviglumis that attempt to capture the maximum number of microsatellite alleles for given sample sizes.
TEOSINTE is a wild grass native to Mexico and Central America (Figure 1) and the closest wild relative of cultivated maize (Zea mays ssp. mays L.). Teosinte represents an important resource for the study of maize genetics (EVANS and KERMICLE 2001), quantitative genetics (LUKENS and DOEBLEY 1999), molecular population genetics (GAUT et al. 2000), genome evolution (SANZ-ALFEREZ et al. 2003), and crop evolution (DOEBLEY 1990a). Notably, teosinte has become one of the best-characterized systems for plant molecular population genetics, including studies utilizing DNA samples recovered from archeological specimens (JAENICKE-DESPRES et al. 2003). The teosintes also represent an important potential resource for maize breeding, although they have not yet been extensively used in this capacity. Given the breadth of use of teosinte in genetic analyses, a refined understanding of its phylogenetics and population structure can help guide further research in all of these areas.
Together, teosinte and maize compose the genus Zea, which has four species (Figure 1): (1) Z. luxurians (Durieu and Ascherson) Bird, an annual teosinte from Central America; (2) Z. diploperennis Iltis, Doebley and Guzman, a diploid perennial teosinte from Jalisco, Mexico; (3) Z. perennis (Hitchc.) Reeves and Mangelsdorf, a tetraploid perennial teosinte from Jalisco, Mexico; and (4) Z. mays, a polytypic annual species that includes four subspecies. The four subspecies are (1) ssp. mays (maize); (2) ssp. mexicana (Schrader) Iltis, a large-spikeleted teosinte adapted to the drier high elevations (~1600-2700 m) of northern and central Mexico; (3) ssp. parviglumis Iltis and Doebley, a small-spikeleted teosinte adapted to the moister middle elevation (~400-1800 m) of southwestern Mexico; and (4) ssp. huehuetenangensis (Iltis and Doebley) Doebley, an annual teosinte found only in the province of Huehuetenango in western Guatemala (DOEBLEY 199Ob). The four species of Z. mays have been placed into two sections: section Zea, which contains only Z. mays, and section Luxuriantes, which is composed of the other three species. Most of these teosinte species and subspecies have narrow geographic distributions consisting of only a few local populations; however, ssp. mexicana and ssp. parviglumis are exceptions, being widely distributed in Mexico (Figure 1). Recently, ILTIS and BENZ (2000) classified Z. luxurians from Nicaragua as a new species, Z. nicaraguensis Iltis and Benz. Here, we treat it as one geographical group of Z. …