sealPurdue News

October 1999

New approach to crop genetics:
Find genes first, ask questions later

WEST LAFAYETTE, Ind. -- A new approach to biology -- called genomics -- promises to speed the development of new crops that are able to withstand environmental stresses such as drought, heat and frost.

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Scientists predict that by creating "road maps" of all the genes in various plants and animals, they will be able to more quickly locate desirable traits and move those traits into other crops.

Genomics also has spurred change at Purdue University, which has launched two new multimillion dollar research facilities and hired several new scientists to pursue the promise of genomics.

As a result of the much-touted Human Genome Project, scientists have new tools that allow them to study organisms in new ways. For example, new automated machines can quickly determine the structure of genes. "Before, it might have taken us two years to determine the structure of one particular gene," says Jeffrey Bennetzen, Purdue's H. Edwin Umbarger Distinguished Professor of Genetic Sciences. "Now we expect to do the same region of the chromosome in a couple of weeks. It's quite a change to think that any of this is possible. Five years ago we wouldn't have even thought about doing these experiments."

In traditional genetics, scientists would select a genetic trait that they were interested in, such as resistance to a particular disease. Then they began a search that sometimes took years for the particular gene that caused, or coded, for that trait. (They did this by comparing the genes of an organism that had the trait with those that didn't.) Once the gene was located, the scientists would spend more time mapping out the biochemical structure of that particular gene.

In the new paradigm of genomics, however, scientists take the opposite approach. They use new techniques and equipment to map out the biochemical structure of all of the genes of an organism, and then they set to work to figure out what each of those millions of potential genes does. The first step is known as structural genomics, and the second step is called functional genomics.

The scientists are aided in this search for desirable genes by the discovery that the genes for various traits are found on the same place on the chromosomes of similar organisms. (A chromosome is a chain of genes inside a cell's nucleus.)

For example, the genes for traits such as digestibility, dwarfism and waxy skin (which protects a plant during times of drought) are found in the same approximate location on cereal grains such as wheat, corn, sorghum and rice. But because corn has three times as much genetic material as sorghum -- 2,000 million base pairs, or chromosome chain links, vs. 760 million-- it is easier to locate a desired trait in sorghum and then find the gene in corn than it is to search through the corn's entire genetic library.

Now Purdue scientists hope to find ways to exploit this genetic shortcut to develop improved crops.

According to John Axtell, Purdue's Lynn Distinguished Professor of Agronomy and the first chairman of the National Academy of Science's Applied Biology committee, this new way of improving the genetics of crops began in the late 1980s. "When scientists started looking at the genes of corn and comparing them to the genes of sorghum, we found some interesting things," he says. "The similarity among corn, rice and other cereal crops is so great that you can use genetic probes from corn to map genes from sorghum."

This is a potential boon to crop breeders. "I've been interested in the genetics of sorghum for many years," Axtell says, "but I often worked with corn, because the chromosomes of sorghum were so small you'd go blind looking at them. But now that smaller set of genes makes it much easier to find things at the molecular level.

"Today, the fastest way to improve corn might be to study the genetics of sorghum. By identifying genes for a desired trait, such as drought tolerance, in sorghum, researchers know where to look for it in corn."

Axtell predicts that this use of genomics will greatly speed the number of improved varieties of many crop plants. "All cereals are members of the grass family, and they are all closely related," he says. "They obviously have a lot of similarity in their origin. Now, all of the technology developed in one cereal will work for all cereals. Now when we want to improve a crop, we don't have to go through 50 years and 500 careers to do it."

At Purdue, one major area of research is looking for ways to help crops survive stresses such as drought, heat and cold.

According to Randy Woodson, associate dean of agricultural research at Purdue, it is these types of environmental stresses, and not weeds or insects, that cause the largest reductions in crop yields. "In the Midwest we don't always worry about having plants that are drought resistant, but farmers spend a certain part of every year praying for rain," he says. "If you had plants that could withstand drought better you could put marginal land into full production." A 1987 U.S. Department of Agriculture study found that drought causes an estimated 70 percent yield loss nationwide in non-irrigated crops each year.

To combat such yield losses, Purdue has received a $2.2 million grant from the National Science Foundation to study genetic factors involved with crop stresses. The grant was part of an $8.4 million "Functional Genomics of Plant Stress Tolerance Project" that is being conducted by scientists at Purdue, the University of Arizona and Oklahoma State University.

Also, Purdue has constructed a new instrumentation facility to conduct high-throughput gene sequencing. The Purdue Agricultural Genomics Center began with $1 million in seed money from the National Science Foundation and is directed by Bennetzen.

Sources: John Axtell, (765) 494-8056;

Jeffrey Bennetzen, (765) 494-4763;

Randy Woodson, (765) 494-8362;

Writer: Steve Tally, (765) 494-9809;

Purdue News Service: (765) 494-2096;


Plant scientists have discovered that if they determine the location of a gene for a specific trait in one plant, another plant in the same family is likely to have the gene in the same location on its genome. For example, the genes for digestibility, dwarfism and waxy skin are found in the same approximate locations on cereal grains such as wheat, corn, sorghum and rice. But because corn has three times as much genetic material as sorghum, it is easier to identify the location of a desired trait in sorghum and then search for that gene in corn than it is to search through the entire genome of corn. (Purdue Ag Communications Graphic by Amy Carter and Steve Tally)

Color print, electronic transmission, and Web and ftp download available. Photo ID: Axtell.genomics.

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