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Corn Genome: Mapping a “Maize” of Possibilities


“We’ve all heard the seed companies talk about 300-bu. average yield,” says Larry Hasheider, the Illinois corn grower who chairs the National Corn Growers Association (NCGA) research committee. “I see the recent corn-genome sequencing as part of the farmer’s toolbox to get those yields.” Sequencing the corn plant’s genome, “is where, as a farmer, I really excited.”

Farmers will start seeing yield results from the corn-plant genome sequencing within the next several years, says Edward Buckler, a USDA Agricultural Research Service (ARS) scientist at Cornell University.

It’s been a little more than a year since the National Science Foundation (NSF) announced the breakthrough of sequencing the corn plant’s genome, which will “accelerate the rate of breeding by two or three times,” says Buckler.

In the past, breeders could only evaluate whether a seed line had yield potential by growing it to maturity, limiting them to evaluating one corn generation per year. Now breeders can use gene markers for known qualities to evaluate a generation every four months, then check their progress by growing out every third generation.

“Genomics [the study of an organism’s entire gene sequence] allows us to select the 1% of test plants we want to keep much more effectively. We can breed year ’round and get much better varieties even with non-biotech lines,” Buckler says.

NCGA’s work to promote corn genetics research hasn’t ended with the successful sequencing. Since then, Congress provided an additional $100 million to the NSF for genetics research. The result will be an even higher-quality database of corn traits (the MaizeGDB operated by ARS), which will “take the corn genome from the gold to the platinum standard,” according to Nathan Fields, NCGA director of biotechnology.

Hasheider notes that while corn will reap big rewards from this research, the technology can be applied to any plant species.At the NSF, Rebecca Boston, program director for the Plant Genome Research program, points to another research area of special interest to corn growers: “No one has ever really understood how hybrid vigor (heterosis) works. We offered a heterosis challenge for researchers to study it. It’s not limited to corn, but at least three of the seven grants we funded in 2009 were from corn researchers.”

She likens the corn genome map as a scaffold that speeds scientific progress. “Now researchers can use faster techniques to look for molecular markers. When you find a sequence that’s different, you can look for nearby genes to get a clue to the marker’s function. It’s made genetic selection more powerful.”

One of the most pressing questions for corn researchers now is identifying the new traits that are most needed, according to Anne Sylvester, a corn geneticist at the University of Wyoming and member of the sequencing project’s advisory board.

Over thousands of years, corn has been bred for very specific traits that led to our modern crop, she says. “Now we have new ways to identify traits hidden in the genome. We’ve selected for size of ear, color, sweetness and the ability to grow in many environments. But there are potentially other traits such as better efficiency in water use, improved photosynthesis, pathogen resistance and plant structure we can now explore.”

That will involve comparing the genomes of many types of corn plants from many parts of the world, a process made possible by the availability of the sequenced genome, explains Carolyn Lawrence, an ARS geneticist at Iowa State University.

Corn’s exceptional diversity is an important contributing factor. Corn is one of the most diverse species in the world, according to Buckler, who says that at the molecular level, there’s more diversity among corn plants than between humans and chimpanzees.

“We’re starting to find potentially useful variations we haven’t seen before,” he says.

Much corn research is currently focusing on three challenges: disease resistance, nitrogen use efficiency and drought tolerance.

He speculates that sequences to improve corn’s drought tolerance will have evolved in “a little dry valley somewhere in Mexico,” while better disease resistance will come from a wet environment in the subtropics.

 “We’re at the starting block, and the technique to sequence is maybe 1,000 times less expensive than it was,” he says. “It’s now cheaper to sequence a portion of a genome than to do field trials.”

So scientists can focus on the 10% with the most potential, which makes everything more cost productive.

Institutions and scientists around the world are collaborating at Iowa State; Purdue; the Universities of Missouri, Illinois, Georgia, Wyoming, California (Berkeley and Davis) and Arizona; Cornell University; North Carolina State; the Cold Spring Harbor Laboratory and Stanford University.

Internationally, U.S. and Chinese scientists are coordinating efforts on sequencing projects; an international non-governmental organization is funding diversity research with Mexico and the U.S.; and the Center for Maize and Wheat Improvement (CIMMYT) is leading a major diversity effort.

“We’re at a point where the advances are concrete,” says Sylvester, who agrees with Buckler on a word of caution: “These [research projects] don’t get solved in a year, but we can now tap into corn’s full genetic potential.”


January 2011

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