High-Tech Research Spells Trouble for Soybean Nematodes

Equipped with computer imaging, DNA slides and a robotic arm, Agricultural Research Service scientists are closing in on soybean genes that could improve the legume’s resistance to soybean cyst nematodes (SCN).

ARS plant physiologist Benjamin Matthews credits the “microarray” technology with granting his lab a first-ever look at thousands of soybean genes working in concert to mobilize the plant’s defenses against SCN attacks. One interest, for example, is tying gene activity to a biochemical process--the phenylopropanoid pathway--that produces lignin, a substance that some resistant soybeans may use to cordon off SCN feeding sites, called syncytia.

Currently, few commercially grown soybean cultivars resist all 14 known SCN races, which cause $1 billion in annual losses. Eventually, plant breeders may be able to use genes identified from microarray studies to develop new cultivars that have broader resistance to these races, according to Matthews, at ARS’s Soybean Genomics and Improvement Laboratory, Beltsville, Maryland.

There, his team is using the microarray to screen 1200 genes from six different soybeans for activity against SCN. In the lab, a robotic arm prints soybean DNA as tiny spots on a glass slide. Each spot is a DNA fragment harboring one gene.

Next, the slides are bathed with fluorescent probes made of complementary material called messenger RNA (mRNA). The mRNA comes from the roots of plants attacked by nematodes, and from nematode-free plants.

Applied to the slides, the mRNA probes bind only to matching genes, illuminating them when exposed to laser light. Computer software calculates the degree to which these genes fluoresce so that scientists can see differences among all 1,200 genes in both nematode-free and nematode-challenged plants.

A medical research speaker at a San Francisco meeting two years ago inspired Matthews to adapt the microarray to his soybean studies, some of which the United Soybean Board now funds.

ARS is the U.S. Department of Agriculture’s principal scientific research agency.

Scientific contact: Benjamin Matthews, ARS Soybean and Alfalfa Research Lab, Beltsville, Md., phone (301) 504-5730, fax (301) 504-5728, matthewb@ba.ars.usda.gov.