June 2001

From University of North Carolina at Chapel Hill

UNC, Penn State scientists find gene that controls water retention in plants

(Embargoed) CHAPEL HILL - Scientists at the University of North Carolina at Chapel Hill, working with colleagues at Pennsylvania State University, have identified a gene responsible for controlling water retention and cell division in plants.

Their discoveries, announced in two papers appearing in the June 15 issue of the journal Science, raise the possibility of making crop plants more resistant to drought, a goal agronomists have pursued for decades.

"When I was born in 1957, there were 4 billion people on Earth, and if I die a natural death sometime around 2030, there will be about 10 billion," said Dr. Alan M. Jones, professor of biology at UNC. "That's an enormous increase in just one lifetime. If we are going to be able to feed all these people, we're going to figure out ways of improving and increasing the food supply by nontraditional means. We think this work is an important step toward doing that because researchers should be able to modify this gene to make crops hardier."

Besides Jones, UNC authors of the papers are biology graduate student Hemayet Ullah, research associate Jin-Gui Chen and former UNC postdoctoral fellow Kyung-Hoan Im. Penn State authors are postdoctoral fellow Xi-Qing Wang and Dr. Sarah M. Assmann, professor of biology.

In Chapel Hill, Jones' team, as part of a new multidisciplinary genome sciences initiative, created a mutation in a gene from a common laboratory plant, Arabidopsis, that rendered the gene nonfunctional. Mutant plants wilted more readily than normal plants because they were unable to retain water as well.

The UNC scientists suspected that the gene they targeted encodes a critically important molecule called a G protein that plays a central role in regulating the various signals such as light and hormones that control plant development. Their experiments showed they were right. But because the mutant plants wilted, they thought the gene probably also controlled water retention.

Since Assmann specialized in that area of biology, Jones sent seeds to her and Wang, who analyzed the resulting plants. The Pennsylvania researchers found that plants with the gene knocked out could not respond to the natural hormone abscisic acid as well as normal plants do. That hormone controls the size of openings in leaves known as stomatal pores. Surrounding guard cells regulate the opening and closing of the pores.

Normally, when the soil becomes drier through lack of rainfall, guard cells increase in size to close down the openings and reduce the amount of water plants lose to the atmosphere, Jones said. "The pores serve as conduits through which plants exchange the oxygen they produce with the carbon dioxide they use for photosynthesis," he said. "Of course, this gas exchange occurs at the cost of losing water so that plants regulate pore openings carefully via internal signals like abscisic acid."

In other experiments published in Science, the UNC team showed that the G protein controls cell division in the plant they studied. Modifications in the gene responsible for G protein theoretically could affect crop plants in useful ways beyond just water retention, Jones said.

"Plants use many signals, including light, nutrients and hormones, to decide when their cells should divide, and these multiple signals utilize this G protein," he said. "Animals use many different types of G proteins, but plants have only this one, which must play a central role in how various signals shape plant development and behavior."

In a Science commentary, Dr. Brian E. Ellis and graduate student Godfrey P. Miles of the University of British Columbia said that further systematic studies incapacitating genes in Arabidopsis and other plants, combined with detailed analyses of the plants themselves, likely will reveal molecular signaling networks specific to plants. "These will have evolved to meet the unique challenges faced by that large part of the biosphere that must deal with its daily environmental challenges without running away," they wrote.

Drs. Jeff C. Young and Michael R. Sussman of Western Washington University and the University of Wisconsin, respectively, also helped with the investigation. The gene the researchers worked on, known as GPA1, had already been sequenced, but its roles were unknown. Sussman directs a facility at Wisconsin that maintains a library of uncatalogued plant mutants that researchers can sort through.

Note: Jones and Ullah can be reached at 919-962-6932 or alan_jones@unc.edu. Assmann and Wang can be reached at 814-863-9579 or sma3@psu.edu. UNC











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