A study by a team of university and government scientists led by a Kansas State University researcher, indicates that genes responsible for seed shattering – the process by which grasses disseminate their seeds – were chosen in a similar, but independent manner during sorghum, rice and maize domestication.
“When early human groups were domesticating different wild grasses, they inadvertently or unintentionally selected the same sets of mutations that make more efficient crop production possible,” said Jianming Yu, associate professor of agronomy at K-State. “That was critical in the transition out of the hunter-gatherer phase of human history. You can call it just luck or the wisdom of ancient farmers, both of which are fascinating to know.”
Cereal crops, including sorghum, rice and maize, were domesticated from their early wild ancestors by humans thousands of years ago, because of their importance as a food source, Yu said. Although these crops were domesticated in different geographical regions, they all underwent parallel selection, which involves systemic and parallel changes during the domestication process.
The study, “Parallel domestication of the Shattering1 genes in cereals,” was published May 13 in the online version of the journal, Nature Genetics. In order to identify the molecular basis underlying seed shattering in sorghum, which is the world’s fifth major crop, the researchers conducted map-based cloning and diversity mapping in sorghum first, and then examined the identified gene in other cereals.
“Once we better understand seed shattering in sorghum, the better we will understand seed shattering and domestication in other cereal crops,” Yu said. “The discovery of the shared genetic mechanisms provides us an opportunity to better appreciate the wisdom of ancient human groups in turning wild grasses into cereals.
As the demands for food, feed and fiber increase, domesticating other grasses into crops would also benefit from the current research findings.”
The implications for sorghum alone are huge, because of sorghum’s emerging applications in bioenergy and stress management, as well as its long-time importance as a food and feed source, said Tesfaye Tesso, assistant professor of agronomy and sorghum breeder. A better understanding about the origins of sorghum, a very diverse species, helps in terms of preserving natural resources for breeding use, classifying germplasm, and facilitating the process of bringing useful genes from wild relatives to crops.
Kansas leads the nation in grain sorghum production, growing 51 percent of all grain sorghum grown in the United States in 2011, according to the Kansas Grain Sorghum Producers Association. The 2011 crop totaled 110.0 million bushels.
Seeds on wild grasses shed naturally when they mature, which ensures their natural propagation, Yu said. When humans began cultivating those crops, however, seed shattering would have caused inefficient harvesting and large losses in grain yield, because some of the seeds which were to be harvested, would have already disbursed naturally.
“Selection for non-shattering crop plants would have greatly facilitated harvesting and improved production,” said Zhongwei Lin, K-State research associate in agronomy and the first author of the publication. He noted that several other genes have been identified as being responsible for seed shattering in rice and wheat.
Prior to the most current study, however, no findings had been made on whether other cereals share the same molecular genetic basis for shattering, although such a hypothesis was proposed more than a decade ago. The highly similar genomes of these cereals and the critical role of non-shattering in their domestication make this speculation plausible.
The researchers’ discovery that seed shattering in sorghum is controlled by a single gene, Sh1, and their work in rice and maize suggest that the Sh1 genes for seed shattering have undergone parallel selection during domestication in multiple cereals.
“It is great to have this team of scientists with complementary expertise in different species to work on this project,” said Frank White, K-State professor of plant pathology. “Sorghum is important to Kansas and we appreciate the K-State Targeted Excellence Program for initiating and supporting the research.”
Other K-State researchers involved in the study were Xianran Li, research associate in agronomy, as well as Harold Trick, professor of plant pathology, and Jiarui Li, research assistant professor and Zhao Peng, Ph.D. candidate – both in plant pathology. The team also included researchers from the University of Wisconsin-Madison, Iowa State University, USDA-ARS, University of Nebraska-Lincoln, and Purdue University.