By Cat Holmes

University of Georgia

The University of Georgia was recently awarded a $5.6 million
grant for work that could one day lead to the development of
artificial chromosomes in corn.

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.)