期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2016
卷号：113
期号：49
页码：14151-14156
DOI：10.1073/pnas.1609701113
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceThe valley of Tehuacan in Mexico is an important center of early Mesoamerican agriculture. To characterize the genetic constitution of the earliest phase of maize cultivation, we reexamined San Marcos cave in Tehuacan and sequenced DNA from three newly discovered maize samples dating at a similar age of 5,000 y B.P. The genomes of these samples reveal unforeseen levels of genetic diversity as compared with modern maize, indicating that the effects of domestication were not yet complete. We find that their genetic constitution was similar and influenced by inbreeding, suggesting that the corresponding plants come from a reduced population of isolated and perhaps self-pollinated individuals. Pioneering archaeological expeditions lead by Richard MacNeish in the 1960s identified the valley of Tehuacan as an important center of early Mesoamerican agriculture, providing by far the widest collection of ancient crop remains, including maize. In 2012, a new exploration of San Marcos cave (Tehuacan, Mexico) yielded nonmanipulated maize specimens dating at a similar age of 5,300-4,970 calibrated y B.P. On the basis of shotgun sequencing and genomic comparisons to Balsas teosinte and modern maize, we show herein that the earliest maize from San Marcos cave was a partial domesticate diverging from the landraces and containing ancestral allelic variants that are absent from extant maize populations. Whereas some domestication loci, such as teosinte branched1 (tb1) and brittle endosperm2 (bt2), had already lost most of the nucleotide variability present in Balsas teosinte, others, such as teosinte glume architecture1 (tga1) and sugary1 (su1), conserved partial levels of nucleotide variability that are absent from extant maize. Genetic comparisons among three temporally convergent samples revealed that they were homozygous and identical by descent across their genome. Our results indicate that the earliest maize from San Marcos was already inbred, opening the possibility for Tehuacan maize cultivation evolving from reduced founder populations of isolated and perhaps self-pollinated individuals.
