DNA of 1,000 year-old maize sheds light on origins of globally important food crop
University of York
Researchers have tested ancient DNA from corn found at archaeological sites in Arkansas, shedding new light on the dispersal of one of the world’s most important food crops.
By reconstructing the genomes of archaeological maize cobs and kernels, the study, by researchers at the University of York and the University of Copenhagen, revealed that 1,000-year-old maize from rockshelters in the Ozark region of Arkansas, US, shares a close genetic link with modern Northern Flint varieties.
These hardy varieties are cold-adapted and are the ancestors for commercially important maize grown around the world. Researchers say that understanding its origins and journey through different geographical regions could help find new ways of sustaining and improving crops today, as pressures on global food supply increases and crop health is challenged by climate change.
Researchers showed that maize underwent selection as it was transported from the US Southwest across the Great Plains, particularly through a gene, known as waxy1. Genetic variants in the waxy1 gene affect the stickiness and chewiness of maize, traits that are still valued in some traditional cuisines today.
This suggests that farmers 1,000 years ago were not just engaged in planting and harvesting, but in selecting traits that could help in breeding and producing the best quality yield for food, not too dissimilar to farmers today.
Dr Nathan Wales, from the University of York’s Department of Archaeology, said: “We know that maize was domesticated in Mexico, but it has long been debated what route it took to regions of the US to become what it is today - one of the most globally important food crops.
“We now have a clearer idea of the journey it took from Mexico, and we better appreciate how regional varieties can become more globally significant than varieties grown near the domestication centre. It is valuable information for crop breeders because they can chart the evolution of the crop, reintroduce any lost genetic diversity or develop new varieties, which could be vital to helping food shortages in the future.”
Ancient maize genomes from the Ozark rockshelters indicated that maize entered eastern North America at least twice, tracing ancestry to both the upland US Southwest and southern Texas.
Dr Jazmín Ramos-Madrigal, from the Globe Institute at the University of Copenhagen in Denmark, said: “We also showed that maize could only be introduced into eastern North America once humans bred local varieties with the genetic tools to cope with the challenging environment of the region, which goes someway to demonstrating the skills and knowledge of farmers 1,000 years ago.”
The study is published in the journal Cell.
Journal
Cell
Ancient maize genomes reveal the early evolutionary history of commercially important flint and dent varieties
A study published today in Cell uncovers the deep evolutionary roots of flint and dent maize (also commonly known as “corn”), two foundational varieties central to modern maize breeding and cultivation. By analyzing ancient DNA from 32 maize samples spanning the last 3,000 years, researchers have reconstructed the journey of the crop into eastern North America, shedding new light on its geographic origins, dispersal routes, and history of selection.
This study was carried out by an international team of scientists and spearheaded by Jazmín Ramos Madrigal from the Center for Evolutionary Hologenomics at the University of Copenhagen, Denmark, and Nathan Wales from the Department of Archaeology at the University of York, UK.
A genetic link between Northern Flints and 1,000-year-old Ozark maize
By reconstructing the genomes of archaeological maize cobs and kernels, the study reveals that 1,000-year-old maize from rockshelters in the Ozark region of Arkansas, US, shares a close genetic link with modern Northern Flint varieties. Known for their cold tolerance and hardiness, these ancient flints form the backbone of many commercial maize hybrids cultivated today.
“Our research shows that this lineage of maize, which makes up the ancestry of most commercial maize, shares its roots with maize grown by Indigenous Peoples in the Ozark region over 1,000 years ago” explained Wales.
The long journey of maize: across the Great Plains to eastern North America
Eastern North America represents one of the last stops in maize's dispersion from its domestication center in southern Mexico. The path maize took to reach eastern North America has long been debated, with two competing hypotheses: one proposing a route through eastern Mexico and across the Gulf coast of Texas, and another suggesting maize traveled across the Great Plains from the U.S. Southwest.
The study provides clear evidence supporting the latter. Ancient maize genomes from the Ozark rockshelters indicate that maize entered eastern North America in at least two dispersion pulses, tracing ancestry to both the Upland US Southwest and southern Texas.
“One of the ancestries we find in the Ozarks comes from maize already adapted to growing in the colder and shorter days of Upland US Southwest. This suggests that maize could only be introduced into eastern North America once humans bred local varieties with the genetic tools to cope with the challenging environment of the region.” noted Ramos-Madrigal.
Evolutionary adaptations: selection on starch gene reflects early food preferences
The study also highlights repeated selection on maize's starch metabolic pathway during its dispersion into eastern North America. A key gene in this pathway, known as waxy, which influences kernel texture, showed clear signs of selection in ancient Ozark maize 1,000 years ago. Genetic variants in the waxy gene affect the stickiness and chewiness of maize, traits that are still valued in some traditional cuisines today.
“This suggests that Indigenous farmers were not only adapting maize to local climates but might also be selecting for traits that suited their specific culinary preferences,” explained Wales. “Our research provides another piece of the puzzle that is the chronology of selection and adaptation during maize domestication, by showing this gene was selected sometime between maize departure from the US Southwest and its arrival into eastern North America at least a thousand years ago” added Ramos-Madrigal.
Conclusion
This study highlights how ancient DNA can illuminate the origins and adaptations of crops that shaped human history. By tracing maize's journey and adaptation into eastern North America, the research not only advances our understanding on the early origins and evolution of maize, one of the three pillars of modern agriculture, but also provides new insights into the evolutionary history of one of the world's most important crops.
Journal
Cell
Article Title
The genomic origin of early maize in eastern North America
Article Publication Date
4-Dec-2024
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