COLLEGE STATION — Researchers have found genetic evidence linking the world’s most important cereal grains — rice, corn and sorghum — to a common ancestor that grew 65 million years ago.
The discovery that a common set of genes are largely responsible for the large seeds and high yields of modern cereal grains could unlock the door to genetic engineering of more productive and nutritious crops. The finding is reported in the Sept. 22 issue of Science magazine.
Cereal grains are the most common food source throughout the world from the richest to the poorest nations. The world’s farmers annually produce more than 1.87 billion tons of cereal crops valued at more than $200 billion worldwide — the bulk of which are rice, corn and sorghum. Together with wheat, these crops provide most of the calories consumed by humans.
Researchers have believed for years that the grains had a common ancestor, but that theory had not been proven.
Dr. Keith Schertz, U.S. Department of Agriculture-Agricultural Research Service geneticist, and Dr. Andrew Paterson, Texas Agricultural Experiment Station molecular biologist, said the common ancestor probably looked like a grassy weed, with long blades for leaves and small flowers at the tip of the stem similar to sorghum plants.
“We took new steps in looking at the evolution of agricultural productivity,” said Schertz.
Seed from the original plant spread as the earth’s land masses separated into continents millions of years ago. The plant evolved into wild rice in Asia, wild corn in America and wild sorghum in Africa. Humans began gathering the seed of these wild grasses for food some 12,000 years ago, giving preference to those plants which had large seed and were easy to harvest. Remarkably, even after 65 million years of evolution, the same genes were responsible for large seed and other characteristics in rice, corn, and sorghum.
“It’s similar to three children each inheriting blue eyes from the same great-great-grandparent, only with these cereal grains we’re talking about genetic traits that appeared after millions of generations,” Paterson said.
Schertz and Paterson began by looking at the genes that control three traits which distinguish all cereal crops from their wild ancestors — seed size, seed shattering (loss) during harvest and the effect of day length on flowering.
DNA from each crop was investigated separately — rice by Dr. Shannon Pinson, USDA-ARS, and Drs. James Stansel and Zhikang Li, Experiment Station researchers in Beaumont; maize by Dr. John Doebley at the University of Minnesota; and sorghum by Schertz and Paterson.
Then, Paterson and students Yann-rong Lin and Sin-Chieh Liu determined that the genes in the three different crops corresponded to one another at the DNA level.
“It was known that the genes of different cereals occur in similar orders along the chromosomes,” Paterson said. “What was not known was whether the same genes still controlled agriculturally important traits after 65 million years of evolution.”
“This new information is helpful to plant breeders because it says that when we learn something about sorghum we are also learning it about other grains,” he said.
Already, Paterson’s team and Dr. James Irvine, an Experiment Station scientist in Weslaco have shown that sorghum genes are predictive of the behavior of sugarcane, another major crop.
“Moreover, now we can devise a strategy to clone these genes,” Paterson said. He noted that in sorghum, only one gene controls the plant’s tendency to shatter — or lose seed at harvest time. That gene will be simplest to clone. Once cloned, the gene can be engineered to improve not only sorghum, but also many other crops.
Schertz said similarly other important genes that control digestibility and nutritional qualities, for example, might be isolated in one cereal and then used to improve others.
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