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Media Contacts:
Dr. Eric L. Davis, 919/515-6692 or [email protected]
Tim Lucas, News Services, 919/515-3470 or [email protected]
Steve Hanson, Iowa State Univ., 515/294-2475
June 11, 1998
Study Identifies Gene That Promotes Nematode Infection in Soybeans
FOR IMMEDIATE RELEASE
A team of scientists from four universities, including North Carolina State University, has identified a gene that allows soybean cyst nematodes (SCN) to attack and infect young soybean plants' roots, causing irreversible damage that can drastically reduce yields.
SCN are microscopic parasitic worms that are the leading pathogen of soybeans worldwide, causing hundreds of millions of dollars in damage to crops each year.
"The gene we discovered produces an enzyme, cellulase, that degrades plant cell walls, allowing the nematodes to penetrate the plant's roots," says Dr. Eric L. Davis, assistant professor of plant pathology at NC State and one of the key scientists on the international research team.
"Now that the SCN gene has been identified," he says, "we may be able to develop a way to neutralize the cellulases it produces, giving us a new way to control nematodes in the field."
The discovery was reported in the April 28 issue of the Proceedings of the National Academy of Sciences. It is the first time scientists have been able to isolate a gene that encodes cellulase -- an enzyme that breaks down cellulose, the chief component of plant cell walls -- in an animal. Previously cellulase genes have been identified only in plants and microorganisms such as bacteria and fungi.
Davis' principal co-authors on the Proceedings paper are Dr. Thomas Baum of Iowa State University, Dr. Richard Hussey of the University of Georgia, and Drs. Arjen Schots, Geert Smant and Jaap Bakker of Waginingen Agricultural University in The Netherlands. Research by Davis, Baum and Hussey is funded by the United Soybean Board through a research grant based at Iowa State, and through grants from USDA.
Soybeans are North Carolina's ninth-largest commodity crop. The N.C. Department of Agriculture reports they generated $217 million in cash receipts in 1996, the most recent year for which figures are available.
SCN infestations can be devastating for farmers, Davis says because they're hard to detect. "They're an insidious pathogen. Only if their population is incredibly high will you see yellow, stunted plants. Often, you see only minor symptoms until the end of the season. By then, the damage is done and the nematodes have significantly reduced the harvest."
Currently, farmers have only two primary options to keep infestations from reaching levels where they can cause economic losses. They can plant infested fields with nematode-resistant cultivars or rotate the fields with crops that aren't hosts for SCN. Both methods have drawbacks. "Rotation crops, such as corn, may not be as profitable and the farmer may not be set up mechanically to deal with them," Davis says. "And nematode-resistant soybean cultivars offer only limited protection. There are now 16 different races of SCN; no acceptable cultivar has resistance to them all."
Using the new information from his study and from other studies being conducted through Iowa State's United Soybean Board grant, Davis and his collaborators hope to develop transgenic soybean plants encoded with genes that express a molecule capable of binding and inactivating cellulase -- thus preventing or reducing SCN's ability to penetrate and infect plant roots.
"Soybeans are an increasingly important source of food protein for the world's population, and they are economically vital to agricultural economies worldwide," he says. "The sooner we find alternative ways to control SCN, the better."
-- lucas --
NOTE TO EDITORS: The abstract from Davis' peer-reviewed paper is attached. For copies of the full paper, call Davis at (919) 515-6692 or Tim Lucas at (919) 515-3470. For information about the United Soybean Board research grant at Iowa State, call Steve Hanson at (515) 294-2475.
Endogenous cellulases in animals: Isolation of Beta 1,4-endoglucanase genes from two species of plant-parasitic cyst nematodes
Published April 28, 1998, Proceedings of the National Academy of Sciences
Authors: Geert Smant, Wageningen Agricultural Univ. (WAU); Jack P.W.G. Stokkermans, WAU; Yitang Yan, North Carolina State Univ. (NCSU); Jan M. De Boer, WAU; Thomas J. Baum, Iowa State Univ.; Xiaohong Wang, NCSU; Richard S. Hussey, Univ. of Georgia; Fred J. Gommers, WAU; Bernard Henrissat, WAU; Eric L. Davis, NCSU; Johannes Helder, WAU; Arjen Schots, WAU, and Jaap Bakker, WAU.
ABSTRACT: Beta-1,4-Endoglucanases (EGases, EC 3.2.1.4) degrade polysaccharides possessing Beta-1,4-glucan backbones such as cellulose and xyloglucan and have been found among extremely variegated taxonomic groups. Although many animal species depend on cellulose as their main energy source, most omnivores and herbivores are unable to produce EGases endogenously. So far, all previously identified EGase genes involved in the digestive system of animals originate from symbiotic microorganisms. Here we report on the synthesis of EGases in the esophageal glands of the cyst nematodes Globodora rosiochiensis and Heterodera glycines. From each of the nematodic species, two cDNAs were characterized and hydrophobic cluster analysis revealed that the four catalytic domains belong to family 5 of the glycosyl hydrolases (EC 3.2.1., 3.2.2. and 3.2.3). These domains show 37-44 percent overall amino acid identity with EGases from the bacteria Erwinia chrysanthemi. Clostridium acetobutylicum a! nd Bacilus subtilis. One EGase with a bacterial type of cellulose-binding domain was identified for each nematode species. The leucine-rich hydrophobic core of the signal peptide and the presence of a polyadenylated 3' end precluded the EGases from being of bacterial origin. Cyst nematodes are obligatory plant parasites and the identified EGases presumably facilitate the intracellular migration through plant roots by partial cell wall degradation.
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