Locating the Blue Ribbon Winner

Developing corn hybrids today requires a blend of novel technologies. The process is a bit like trying to bake the blue ribbon-winning apple pie for the state fair. Select ingredients. Prepare the crust. Mix the filling. Heat the oven. Bake the pie. Taste-test the results. It takes a combination of skills to produce an award-winning dessert or seed product.

"Developing traits is like creating new recipes," says Matthew Mouw, Ph.D., Pioneer senior marketing manager. "Based on the ingredients being used, you can anticipate what the end result might look like and taste like, but you won't know for sure until it's cooked."

One step Pioneer uses in its baking process is a new and innovative technology designed initially for the pharmaceutical industry. Pioneer is working with Myriad Genetics, Inc., a Salt Lake City-based biopharmaceutical company that develops healthcare products. Myriad scientists are applying their technology to Pioneer germplasm.

Mapping the gene
Myriad researchers working with elite Pioneer corn inbreds are determining the DNA sequence diversity at thousands of locations on the corn chromosome. Pioneer researchers are using this information to "positionally clone" genes of agronomic importance. Positional cloning involves the use of molecular markers to map a gene on the chromosome.

The collaboration has produced a dense, high-resolution, corn genome map. Researchers will use the map to see more precisely where specific genes controlling specific traits are located in the genome. They also will be better able to gauge how much genetic diversity there is in those genes.

Data from Myriad will help Pioneer researchers assign functions to genes - a task that could take years longer without the Myriad technology. It's like knowing the exact location of the ideal apples for the pie before you head into the orchard.

The critical objectives "Until just recently, corn-purchase decisions for most growers were based on yield … period … exclamation point," emphasizes Scott Tingey, Ph.D., yield enhancement director for DuPont Crop Genetics. "Today, traits are more important than ever before. Yield, of course, is still a requirement, but other traits are valuable, too. That's why high-resolution mapping of corn germplasm is so important to new product development."

The information learned through the Myriad collaboration - coupled with the pedigree knowledge Pioneer has collected on each parent line from the 1930s to today - is allowing Pioneer to trace and locate DNA segments for useful traits, says Dean Christensen, Ph.D., director of complex traits for Pioneer.

"This is called association genetics - identifying associations between DNA segments and our trait selection efforts from past years," Christensen says. "We can understand better the diversity in our germplasm pool. This makes association genetics particularly useful for some of the more-complex traits such as drought tolerance and plant response to nitrogen."

A detailed road map
The corn genome is composed of more than 2.5 billion segments. One gene represents about one millionth of the space in the genome.

"If you stretched the corn genome from Washington, D.C., to San Francisco, you would encounter one gene on average every 100 yards. A single gene could be six yards long. The rest of the DNA is of unknown function," Tingey says. "With current molecular marker technology, the highest resolution genetic map can mark sections of the map one-third of a mile long.

"Using positional cloning, we can pinpoint the location of a specific gene within a third of a mile very easily," Tingey explains. "We could say a gene is located somewhere between mile marker 332.1 and 332.4."

By checking this location on the genome for key genes, researchers are doing the equivalent of sorting good and great apples. A road map of this detail is extremely useful to plant breeders. Identifying the exact gene position helps researchers better understand which areas affect complex traits such as drought tolerance and nitrogen-use efficiency.

Replicating drought genes
Tingey cites the Pioneer drought-tolerance program as an example of the potential genetic gains possible through positional cloning.

"We can take two parents - one that's drought tolerant, one that's drought sensitive," Tingey says. "We cross them to create an F1 generation. Then we cross the F1 with itself to make an F2. Some of the resulting plants will have the drought-tolerant genes, some will not."

Pioneer uses molecular markers to know which region of the genome is carrying those genes. "We map those genes finely enough so we're down to a reasonable-sized piece of DNA," Tingey continues. "We can sequence this piece of DNA and identify the exact genes responsible for drought tolerance or drought sensitivity."

Pioneer compares the DNA of tolerant and susceptible parents to the DNA of the offspring to learn which offspring have inherited the tolerance.

What's this mean to Pioneer customers? "This technology will allow us to create superior products and get them to the marketplace faster," Christensen says. "We can select for the best possible traits for yield, disease resistance and sustainability because we know exactly where those traits reside within our elite germplasm."

The information harvested from the relationship with Myriad is already changing the way Pioneer breeds, manages germplasm and develops products.

"These benefits will continue well into the future," Christensen says.

As Pioneer continues to identify the best apples in the orchard, it can experiment with recipes, looking for blue-ribbon winners that bring value to the customer.

(Click on the image for larger view.)

Pioneer uses technology to find the best combination of genes to improve plant performance. The process in many ways is similar to finding the best recipe to take to the state fair. Researchers draw from a vast cupboard of ingredients - genes with various attributes. Pioneer brings the genes with the attributes needed for the specific product to the kitchen - or research facilities - for experiments.

Pioneer researchers draw on years of crop breeding experience to select the ingredients most likely to result in a valuable new product. It's like an experienced cook choosing flour, eggs, milk, sugar, cinnamon and apples to make an apple pie. The idea is to start with the ingredients past efforts tell us will result in the best pie- or corn hybrid.

Researchers see what combination produces the best offspring. This involves trying a lot of different alternatives to weed out the less effective options. Think in terms of a cook creating new recipes and tasting them to find the most mouth-watering dessert.

Finally, the best products go into the field for real-world testing. This is sort of like entering the state fair. If the panel of Pioneer judges decides the new plant performs well, they may award it the blue ribbon - in the case of a hybrid, advance it to commercialization.