ARS plant geneticist Edward S. Buckler and N.C. State professor of crop sciences Major Goodman are two of the scientists involved.
"Our group is among the first to associate natural allelic [base] diversity with trait variation in plants by using statistical methods," says Buckler
adapting statistics developed for human genetic research to the world of corn and creating some new equations in the process.
Once developed, "the statistical methodology will be useful to study any type of plant or fungi, and of course humans," says Buckler
predecessors have earmarked so many genes which could possibly control traits of interest that, without statistics, "we may select the right gene only 10 percent of the time.
These statistical approaches will allow us to find the right one 95 percent of the time."
Busy as Bees
Now in his
second year on this project, Buckler
is surveying 19 genes from 100 inbred lines of maize to test for statistical associations.
The genes are known to contribute to traits like stalk length and plant height; flowering time; disease resistance; and the protein, carbohydrate, and oil content of the kernel.
group will probably end up working with 30 genes.
laboratory looks a bit like a beehive, with seven technicians and students and a postdoctoral molecular biologist busily working at automated gene sequencers.
can apply any statistics, each of those 30 genes has to be sequenced-or spelled out base by base-for each of the 100 core lines.
When the work is finished, the group will have sequenced some 10 million bases, he
Then, after he
makes the statistical associations and zeros in on the mutations most likely to affect the traits he
is interested in, he
has to prove the associations.
So Buckler, Goodman, and co-workers are making hundreds of crosses between corn lines with the promising mutations and growing them to see if they really do make the plant flower earlier or shorten its stalk or change the nutritional profile of the kernels.
Complicating things further is the fact that "the corn genome is much more diverse than the human genome," according to Buckler
, who notes that an average of 2.5 percent of the bases differ between any two corn lines.
"That's 25 times more diversity than in the human genome.
In fact, "corn and its wild relatives make up one of the most diverse plant genera in the world," he
Thanks to groundwork laid by corn geneticists, particularly ARS' Charles W. Stuber, who led corn genetics research at Raleigh until his
retirement in 1998, "we have a good map of markers," says Buckler
And we don't know how the subtle changes affect traits," says Buckler
and Goodman are looking for those bases-the specific addresses-on the streets mapped by Stuber and others.
For example, explains Buckler
, take the human population of any large city.
If you associate people's traits with their genotypes, you may get false positives if you assume that the population mated randomly.
There are ethnic groups in any city, and people in those groups are more likely to marry and bear children within their group than outside it.
So, too, corn has lots of little "ethnic" groups.
"If you ignore ancestry, you may get a lot of associations that aren't real," says Buckler
, noting that this happened in research on the human genome.
Fortunately, the science of statistics is always evolving.
Oxford University statistician Jonathan Pritchard recently published new equations that improve accuracy in identifying the mutations behind human diseases across different populations. v "Disease is a yes-or-no situation-you either have it or you don't," says Buckler.
Edward S. Buckler is in the USDA-ARS Plant Science Research Unit, Gardner Hall, Room 2523, P.O. Box 7614, North Carolina State University, Raleigh, NC 27695-7614; phone (919) 513-1475, fax (919) 856-4816.