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Discovering plants' master genes.

In every plant, genes orchestrate the late of each cell. Genes determine, for instance, whether a cell will help form a new leaf, stem, or root.

But science hasn't yet discovered what genes are the key players in this process, known as cell differentiation. "If we knew which genes control a cell's fate, or how those genes work," says geneticist Sarah C. Hake, "we could change those genes and improve tomorrow's plants."

Hake's studies of corn plants have yielded an important new clue to solving the puzzle of how genes dictate a cell's future. In experiments at the ARS/University of California Plant Gene Expression Center at Albany, Hake discovered the first-ever homeobox in plants.

A homeobox is a region of a gene that enables it to control other genes crucial to a plant's final form and function. "A gene with a homeobox," says Hake, "may control a cascade of events in a plant's growth."

Hake's finding, reported in a cover article of the international scientific journal Nature in 1991, added plants to the list of organism--fruit flies, beetles, worms, mice, frogs, and humans, for instance--already known to contain influential homeobox regions.

She found the plant homeobox in her investigations of Knotted, a mutation of a corn gene that changes the way leaves develop.

For the past 7 years, she has focused her research on Knotted, in part because the mutations are easy to detect.

The mutations aren't of commercial value; they cause cells to differentiate abnormally so that leaves, instead of being smooth, have strange knots, bumps, or fingerlike projections.

Knotted's scientific appeal lies in what it can reveal about normal cell differentiation. Says Hake, "We can use Knotted, a gene that we at least partially understand, to give us clues to the activity of other genes that we don't understand, that we want to know more about--such as those that control reproduction."

Hake and others have now used the Knotted homeobox as a probe to identify more than a dozen other homeobox genes in corn, plus some in tomatoes, barley, peas, and rice. The aspects of growth that these homeobox genes control, however, remain unknown.

"Hake's work is remarkable," says Gerald G. Still, director of the Plant Gene Expression Center. "It has not only pinpointed a region of a corn gene that may profoundly influence that plant's growth, but has also helped other scientists in their search for similar master genes in other crops."

The research, says Still, may provide new, unprecedented options for science to revise the architecture of crops in the next century.

Tall, slender corn plants, for example, might be replaced by thick, squat ones that outproduce even today's best hybrids. The same could happen with fruit or vegetable crops.

"This redesign would exceed anything that's currently possible with conventional breeding," says Still. He admits that these stocky, powerhouse plants are--for now--in the realm of science fiction. "But," he says, "they are definitely going to happen."--By Marcia Wood, ARS.

Sarah Hake is with the USDA-ARS/ University of California Plant Gene Expression Center, 800 Buchanan St., Albany, CA 94710. Phone (510) 559-5900, fax number (510) 559-5678.
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Author:Wood, Marcia
Publication:Agricultural Research
Date:Jun 1, 1993
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