Wednesday, Nov. 28, 2012
A map that matters: Scientists shotgun sequence wheat genes, working for gold standard sequence of its genome
MANHATTAN -- A scientific breakthrough that includes two Kansas State University plant pathologists may help food producers feed a growing world population.
Sunish Sehgal, research associate in plant pathology, and Bikram S. Gill, university distinguished professor of plant pathology and director of the university's Wheat Genetics Resource Center, were part of an international collaboration that successfully sequenced most of the genes of common wheat, also known as bread wheat. Common wheat is grown in more than 95 percent of the world's wheat fields.
By sequencing its genes, scientists now have a genetic blueprint of common wheat for many traits, although associating gene sequences with traits will take many more years of work, Gill said. Researchers anticipate using this information to genetically improve wheat so that growers can meet the world's increasing demands for food and feed.
"This will be an important resource for wheat gene discovery," Gill said.
Additionally, the common wheat genome is a model genome for studying polyploidy -- a chromosomal driving force in plant genome evolution. Improved understanding of polyploidy may advance improvements in other food-producing plants, such as cabbage and broccoli.
A report of the common wheat study and its findings, titled "Analysis of the bread wheat genome using whole-genome shotgun sequencing," appears in the Nov. 29 issue of the journal Nature.
Gill and Sehgal are internationally recognized experts in wheat gene analysis and germplasm improvement. Both also are affiliated with Kansas State University's Wheat Genetics Resource Center, which is the largest contributor to wheat research in the world. The center maintains about 14,000 wild wheat species strains and about 10,000 genetic stocks. The collection is a one-stop shop for genetic resources.
"Our center has been described as a mecca for wheat genetics," Gill said.
Common wheat has one of the largest genomes among crops, and is nearly three times the size of the human genome.
Researchers used a method called whole genome shotgun sequencing that involves random bits and pieces of DNA that leaves many gaps in the sequence and is not anchored to a map.
While the reported shotgun sequence of the wheat is useful, a team of sciences at the International Wheat Genome Sequencing Consortium, or IWGSC, is working to produce a gold standard sequence of the wheat genome. The gold standard will be the complete sequence anchored to a genetic map of agronomic traits that are important to the wheat industry.
The consortium scientists are using special genetic stocks provided by the university's Wheat Genetics Resource Center, which were sent to many institutes around the world for physical mapping and sequencing of the 21 chromosomes of wheat. The center was responsible for gold standard mapping and sequencing of four of the 21 chromosomes of wheat.
"The polyploidy is both a curse and a blessing," Gill said. "It provided the evolutionary novelty that made wheat the world's most important crop, but at the same time it made the genome more complex and a hard nut to crack."
Shotgun sequencing revealed that the wheat plant has roughly 100,000 genes compared to the 30,000 genes in humans. The gene sequences were used to identify, categorize and record the potential functions of thousands of individual genes and gene cluster locations -- creating a rough map with points of interest for future studies.
"With funding from the United State Department of Agriculture and the National Science Foundation, center scientists have made sequence-ready physical maps of the four wheat chromosomes assigned to the U.S., but lack of funding is hurting the U.S. effort for gold standard sequencing of the wheat genome," Gill said.