By Cat Holmes
University of Georgia

The ability to create artificial chromosomes would provide crop geneticists a quantum leap in their ability to create corn varieties adapted to specific production needs.

"Right now we work with one trait at a time instead of the whole shebang," said Wayne Parrott, a UGA crop geneticist and co-investigator of the new grant. "It's a very time-consuming process."

And while simple traits, such as drought tolerance or insect resistance, are time-consuming enough, many of the traits, such as pigmentation or oil expression, are complex traits.

"The greatly limiting step is getting (multiple traits) to work together," Parrott said.

Artificial chromosomes would allow scientists to compile a "package" of desired traits in a test tube and then put it in the corn. "It's the difference between having access to a book or an entire library," said Parrott.

And once artificial chromosomes are developed for corn, Parrott said, the lion's share of the work is done for other crops as well.

"Once you have this package for corn, with very little modification you should be able to put it in soybeans, cotton or peanuts," he said.

The current focus of the work is centromeres, the middle part of a cell's chromosomes.

"We know that chromosomes have ends and a middle," Parrott explained. "The ends are highly conserved. That means there is no difference between the ends of your chromosomes and that of a plant.

"However, in the middle of the chromosomes, the centromere, very little is conserved, even between very related species. That has made it tough to elucidate."

Scientists do know that the centromere is very important in keeping the chromosome stable in the cell, a quality that's critical for plant breeding.

To study the centromere, "we had to ramp up the industry standard," Parrott said. Typically, scientists engineer little snippets of DNA, only about 20,000 base pairs.

For this study, the scientists studied and engineered 150,000 base pairs at once. "That's the difference between a little Cesna aircraft and a 747 jumbo jet in terms of complexity and effort," Parrott said.

The scientists, who include James Birchler of the University of Missouri, Jiming Jiang of the University of Wisconsin, Gernot Prestling of the University of Hawaii and the grant's principal investigator, Kelly Dawe of UGA, now have a good grasp of the sequence of the corn centromere.

"Part of the key is (that) centromeres have an off and on switch to make them work," Parrott said. "It's not so much the sequence of the centromere as the shape, how it's folded, that determines this off and on switch."

Part of the work now is to determine how to turn that off-and- on switch better, Parrott said. It sounds simple but will involve a tremendous amount of research and work.

(Cat Holmes is a news editor for the University of Georgia College of Agricultural and Environmental Sciences.)