Researchers Bioengineer Plants Resistant to Devastating Pathogen

September 26th, 2006

AMES, Iowa — Researchers at three universities, including Iowa State University, have designed a new way to make plants resistant to the root-knot nematode, a microscopic, parasitic worm that is one of the world?s most destructive plant pathogens.

In a decade-long collaboration, Thomas Baum, professor and chair of the Department of Plant Pathology at Iowa State, worked with lead investigators Richard Hussey and Guozhong Huang of the University of Georgia and Eric Davis of North Carolina State University to study nematode parasitism genes and how the gene products affect plants.

Results of the research were published today (Sept. 26) in the journal Proceedings of the National Academy of Sciences.

Root-knot nematodes attack nearly every food and fiber plant grown, including many common vegetables, fruit trees and ornamentals. They induce damaging galls on roots, impacting the quality and quantity of yields. Four major species are responsible for about 95 percent of agricultural infestations. Although they can be a serious problem for soybeans grown in the South, root-knot nematodes do not feed on or damage soybeans in the northern United States, including Iowa.

In their research, the scientists effectively turned the nematode?s biology against itself. They fed the gluttonous worm a piece of double-stranded RNA to knock out a specific parasitism gene in the nematode. Knocking out this gene disrupted the nematode?s ability to infect plants.

The researchers say the resistance technique works for all four major species of root-knot nematode and appears to have no harmful effects on plants.

In the study, the researchers targeted a root-knot nematode parasitism gene called 16D10 that produces a small peptide that the nematode secretes into plant root cells. The invading peptide makes the cells grow precipitously. The nematode then feeds on the bulked-up cells — known as ?giant cells,? which are up to 100 times larger than normal plant cells.

?The nematode turns plant cells into factories that will feed it for the rest of its life,? Baum said. ?When the nematode infects a plant and feeds on giant cells, it becomes swollen and immobile, so it depends on these giant cells to complete its life cycle.?

Utilizing a technique called RNA interference, the researchers found that when root-knot nematodes ingested pieces of double-stranded RNA — 16D10 dsRNA — the targeted nematode gene was silenced, resulting in a dramatic decrease in nematode infection.

?If you introduce double-stranded RNA into an organism, it can specifically disrupt the expression of the targeted gene,? Baum said.

In this project, Guozhong Huang of the University of Georgia bioengineered Arabidopsis, a model plant species, to make its own snippets of double-stranded RNA. The Arabidopsis was able to feed 16D10 dsRNA to the nematodes when they infected the roots. This effectively knocked out the 16D10 gene in the nematode and disrupted the parasitic process, making the plants resistant to the four major species of root-knot nematode.

?This represents a promising, target-specific and durable way of knocking out the mechanism by which root-knot nematodes infect multiple crop species,? said Baum. "We?ve been able to uncover how the nematode infects plants and identify weak points in the nematode life cycle that we can exploit. This work shows that we can successfully interfere with nematode infection.?

The research, Baum said, should lead to new strategies to make host plants resistant to nematode attack and damage.

And it also may be a promising sign for Iowa soybean growers. Baum and his colleagues in Georgia and North Carolina also have been making progress in a similar project to disrupt parasitism by the soybean cyst nematode, the nation?s most damaging soybean pathogen and a constant threat to soybean yields in Iowa, the nation?s number-one soybean producing state.

Greg Tylka, extension nematologist and coordinator of ISU?s Corn and Soybean Initiative, said soybean cyst nematode and root-knot nematode appear to share similar biological strategies in latching on to a host plant. ?So this research also may pay dividends in novel soybean cyst nematode resistance. This is important because there are concerns that current soybean varieties bred for resistance to soybean cyst nematode are becoming less effective.?

Baum said research over the next year or two should reveal whether comparable strategies may work for soybean cyst nematode.

Funding for the root-knot nematode research came from the U.S. Department of Agriculture?s National Research Initiative. Baum also acknowledged the support of soybean grower checkoff funds for the research linked to soybean cyst nematode.


Thomas Baum, Plant Pathology, (515) 294-1741,
Brian Meyer, Agriculture Communications, (515) 294-5616,