01/09/1996

Drought Tolerance Gene May Protect and Sweeten Farmers' Yields

AUBURN, Ala.- It may not be nice to fool Mother Nature, but Auburn University researchers have found that genetic engineering is helping us use natural processes to protect our crops from some of Mother Nature's toughest challenges -- with some possibly sweet results.

Robert Locy and Narendra Singh, both faculty members in Auburn University's Department of Botany and Microbiology, have isolated and cloned a gene that helps protect plants from drought conditions. The gene was isolated from corn kernels, but has potential for transfer in many different crops and may actually increase the sweetness of certain crops. The research is being conducted through the Alabama Agricultural Experiment Station (AAES).

"Almost any crop in any year will have some period of time during its growing season where it will not have sufficient water," said Locy. "We began the study with an interest in looking at responses plants have to a lack of water and how we can manipulate those responses to make all plants better at responding to a lack of water."

Locy noted that some responses are obvious, such as the wilting and curling of leaves. Wilting, he explained, allows the plant to reduce the amount of surface area that is exposed to the sun, thus lowering the heat load on the plant and allowing the plant to conserve existing water. However, there are other processes underway in plants that are less obvious, occurring at the cellular or molecular level. That's the level that is of interest to Locy and Singh.

"One response plants have on a cellular level is that the plants tend to make chemicals that help them deal with the stress," said Locy, who is associate professor in Auburn's Department of Botany and Microbiology. "We refer to these chemicals as osmoprotectants." Osmoprotectants protect plant cells from damage caused by drought and other kinds of environmental stresses, such as heat and cold.

"Different plants use different chemicals as osmoprotectants," said Locy. "For example, some plants may use amino acids, while others use glycine betaine and still others use carbohydrates.

Locy and Singh, who is professor of botany and microbiology at Auburn, have been studying a carbohydrate-type osmoprotectant known as sorbitol, which is found in corn kernels and also in many fruit trees. Sorbitol also is made by many other life forms, including humans, insects, algae and fungi.

"We don't fully understand the way sorbitol functions, but we know that many seeds make osmoprotective compounds as they develop," Locy said. "The seeds make osmoprotectants so they can dry down and become dormant, a process referred to as desiccation."

"We wanted to find out how sorbitol was made with the hope that if we could identify the protein that leads to sorbitol production," continued Locy, "we could identify the gene that codes for this protein and possibly engineer plant tissue that could make more sorbitol when it was under drought."

What they found was an enzyme called sorbitol dehydrogenase that appears to be the enzyme responsible for making sorbitol. To verify that this was the right substance, the scientists purified the enzyme and later were able to clone the gene that makes this enzyme.

Now they want to incorporate that gene into other plants and plant tissues to see if it will provide drought tolerance to plants that may not naturally manufacture this chemical. Preliminary results suggest that this gene may be most helpful in protecting the fruiting bodies of plants, rather than the leaves.

Locy explained that different cells within a plant have different functions. Some, such as seeds and fruits, collect carbohydrates made from photosynthesis in the leaf tissue. The tissues that collect carbohydrates are called sink tissues, and Locy believes that the gene they have cloned will lead to sorbitol accumulation in these sink tissues rather than in leaf tissue.

"It's going to be best used for engineering drought stress tolerance in the tissues of the plant that are accumulating carbohydrates," Locy said. "There are other genes that other people have worked with that may work better in leaf tissue and other tissues that are making carbohydrates."

If the gene can be incorporated into the sink tissues of other plants, this may protect the fruits and seeds of plants, which are often the economically important parts of crops, during times of drought. "Yields can be dramatically affected if these sink tissues do not get water at the right time, so if this gene can help protect seeds and fruit from drought stress, we think it could be a very valuable tool for ensuring farmers yields," said Locy.

Another benefit of sorbitol is that it might enhance the sweetness of certain crops. "Sorbitol itself is a sweet compound and can be used as a sugar substitute," he explained. "If you are causing tissue to accumulate sorbitol for drought protection, you may simultaneously be causing the fruiting tissue to be sweeter."

"I'm not sure there is any advantage of having some crops be sweeter -- cotton fibers, for example -- but in crops such as sweet corn and tomatoes this may be an advantage," he added.

Singh said the next step is to see how this gene will function in other plants, and their first attempt will be with tobacco, which is a common plant used for genetic engineering studies because it can be easily genetically altered. If that test is successful, the scientists will then try other crops.

The result may be that dry weather is less of a threat to farmers and gardeners and may even sweeten their harvest.

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News from:

Office of Ag Communications & Marketing

Auburn University College of Agriculture
Alabama Agricultural Experiment Station
3 Comer Hall, Auburn University
Auburn, AL 36849
334-844-4877 (PHONE) 334-844-5892 (FAX)

Contact Jamie Creamer, 334-844-2783 or jcreamer@auburn.edu
Contact Katie Jackson, 334-844-5886 or smithcl@auburn.edu

January 9, 1996