Spring 2009

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Baum Battles Nefarious Nematodes Lurking in Soil

Thomas Baum and colleagues are working to make plants more resistant to cyst nematodes, including soybeans, which suffer tens to hundreds of millions of dollars a year in yield losses in Iowa due to the pest.

The more you know about cyst nematodes, the easier it is to characterize them.

Villainous.

The microscopic cyst nematodes are devastating plant parasites that transform plant cells into elaborate feeding machines. They infect many cultivated plants.

In Iowa, the soybean cyst nematode is the bane of the nation’s leading soybean producing state, with tens to hundreds of millions of dollars a year in yield losses.

Worldwide, plant-parasitic nematodes are blamed for an estimated $125 billion in annual yield losses to crops. Most hurtful is how the parasite impacts people who depend on a good harvest just to survive.

Heinous.

Thomas Baum, professor and chair of ISU’s plant pathology department, was a fungi man before being introduced to nematodes 20 years ago. After two decades, he has grudging admiration for their biology, but few kind words.

“The worm has a needle in its head like a hollow syringe. It sticks this stylet into a plant cell and the cell changes. Something’s secreted from the syringe into the cell,” he says.

Discovering that “something” has been slow, tedious work over more than a decade by a team of scientists at Iowa State, University of Georgia and North Carolina State University. “Our biggest hurdle was to understand those secretions,” Baum says. “We now know that more than 60 proteins are part of that piercing.”

Baum and colleagues now have a better understanding of how the nematodes change the cell wall. They’re writing up new findings on the way nematodes suppress a plant’s immune system.

Some of the proteins in the secretions work like sledgehammers to get into a plant’s roots. Once inside, the proteins change tactics and become a “gentle giant,” says Baum.

There’s good reason why scientists call these parasitism proteins “effectors.”

Underhanded.

“Plants have defenses, but the nematode’s tricky. It turns off the plant’s defenses. The plant tries to fight back, but the nematode whispers sweet lies. It’s telling the plant, ‘Relax. Nothing’s happening.’”

Deceitful.

“The cyst nematode is considered one of the highest evolved kinds of plant parasitism. It doesn’t kill the host plant. It needs living cells. It learns how to speak the plant’s language and, subsequently, leads it down the wrong path.”

The nematode can effectively counter most defensive moves the plant throws at it. Baum says the worm can alter signal transduction in the plant — the chemical language that communicates actions in plant development. The nematode makes those events faster, slower or turns them off — all to its advantage.

Nefarious.

Baum and his colleagues are working on the next front — how to make plants more resistant to those sweet lies.

One technique they’re studying is RNA interference. RNA, present in all living things, is key in producing proteins and transmitting genetic information. In lab studies, they’ve found it’s possible to make nematodes ingest plant RNA that turns the tables on the parasite disarming a key nematode gene.

“It’s not perfect, but our studies show this technology is promising in reducing infection,” Baum says. “It’s a good start for plant resistance.”

The research, which has been supported by Iowa’s and the nation’s soybean growers, the National Science Foundation and the USDA, may translate into a very different kind of vocabulary to describe the nematode. Like:

Ineffectual.