A molecule already present in soybeans could hold the key to drought resistance in this valuable crop.

"Our research shows that all soybeans have trigonelline, regardless of their variety or maturity group," says Andrew Wood, a molecular physiologist and associate professor of plant biology.

"Some have a little, some have a lot, but they all have it. Since soybeans have been cultivated for so many thousands of years, the implication is that this molecule has to have agronomical importance. We think that importance is drought tolerance."

Drought tolerance is a field ripe for research. "Scientists haven't studied it extensively because drought is so difficult to control," Wood says. "Much more emphasis has been placed on pests or diseases because those are more-defined problems. But if you look at total crop losses, limited water accounts for about 50 percent of the loss, while diseases and insects account for only about 20 percent each."

Wood, who earlier studied drought resistance in sorghum and corn, has focused on soybeans since coming to SIUC in 1996. Work with those other crops had suggested a link between drought tolerance and a particular group of molecules that let water-moving cells survive water loss.

"When we first started here, the obvious question was, 'Do these molecules exist in soybeans?' " Wood says. 

The answer is yes—and no. While the soybean's genetic makeup includes this sort of molecule, the molecules themselves are different from those found in corn and sorghum. Among those found in soybeans: trigonelline.

"It's a really interesting molecule," Wood says. "It has been shown in other plants to help with drought resistance, but it's also been shown to help reduce oxidative stress, and it helps control cell division." Oxidative stress, he explains, is cell damage caused as part of the regular give-and-take of metabolism.

Wood and his research team, who have published several research articles in the past couple of years on trigonelline accumulation in soybean plants, have determined which tissues in the plant contain the enzyme. In addition, greenhouse and field studies have shown them that soybean plants under drought stress produce more trigonelline than well-watered soybean plants do.

"The enzyme that makes this molecule is a central point of metabolism," says Wood. "We know it is important, but we don't know yet if you need more of it or less of it to alter the metabolic pathway [to improve drought tolerance]."

To get a handle on that, his team worked to identify the soybean enzyme that produces trigonelline. They purified this protein and are in the process of determining its composition—that is, what amino acids make up the enzyme. 

With the help of biotechnologist David Lightfoot, professor of plant, soil, and agricultural systems, they're also working to find the gene responsible for the trigonelline-producing enzyme. The gene is the "blueprint" the cell follows to assemble the protein from amino acids; knowing the amino acid sequence will make it much easier for the researchers to find the gene.

Genetic engineering techniques will then allow Wood's team to manipulate the amount of trigonelline that soybean plants make to see what happens when that amount changes.

But they won't be done once they crack the drought resistance problem.

"In the strictest sense, drought tolerance is a plant surviving, but if it doesn't rain for a month, yields are decreased by 5 percent--that's the farmer's profit margin," Wood says.

"If a farmer has a 10 percent yield loss, he might as well plow the whole crop under because he hasn't made any money. Our goal is to have high-yielding plants under drought conditions."

Wood's research has been funded by the Illinois Soybean Program Operating Board and the Illinois Council on Food and Agricultural Research.

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