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Newswise — AMES, Iowa – Targeting a newly discovered vulnerability in the signals that cyst nematodes use to infect plant roots could be a powerful method for reducing the damage the parasitic worms cause in crops such as soybeans, according to a study co-authored by an Iowa State University professor.

Researchers identified a single protein in cyst nematodes that triggers dozens of the chemical signals called effectors that the microscopic roundworms release inside roots to hijack plant cells and make themselves a home, said Thomas Baum, a distinguished professor of plant pathology, entomology and microbiology at Iowa State University.

Though the protein – a transcription factor that binds to genes, turning them on or off – is likely one of several that regulate effector production, researchers found that without it the nematode infection is severely reduced, according to the recently published in Proceedings of the National Academy of Sciences. That could lead to major progress in reducing the destructiveness of soybean cyst nematodes, which cost U.S. farmers nearly in production last year – by far the crop’s most damaging pest.

“Now we have a validated target, a tangible molecular event involving a single transcription factor. It’s a proof of concept that opens the door to various new ways of thinking about nematode management,” said Baum, a co-author of the study.

A chemical conversation

For years, nematologists like Baum have been studying effectors in hope that targeting them could reduce infections by cyst nematodes, which also are prevalent in other crops such as sugar beets and potatoes. Those efforts have been a bit of a whack-a-mole game, Baum said. Nematodes produce hundreds of distinct effectors, providing redundancy and a capacity for rapid adaptation.

“You take one effector away and a nematode laughs and says, ‘I’ve got 10 more,’” he said. 

Yet effectors are the key molecular mechanism for nematode invasions in plant roots. The worms are sophisticated pathogens that after hatching in soil burrow their way into a root. Once inside, they look for a single cell to take over. When they find what they’re looking for, they start not by feeding but by communicating.

“The language they use is chemicals, not words,” Baum said. “Effectors deliver a message to a plant cell and it changes, turning into a cell type not usually found in a soybean root. Then all the neighboring cells change, and they fuse together to form a huge new organ whose sole function is feeding the worm.”

Finding SUGR-1

Since individual efforts to target individual effectors have little effect, researchers have had to dig deeper. Cyst nematodes produce their effectors in their esophageal glands. In prior research, Baum’s lab sequenced both the of the soybean cyst nematode and the transcriptome of its gland cells, which documents RNA expression over time. Comparing the two sets of data, researchers can identify the genes responsible for nematode effectors and their production. 

Baum generated the same sort of data for a close collaborator from the University of Cambridge in the United Kingdom who studies the sugar beet cyst nematode, which is nearly identical to the soybean cyst nematode. The collaborating research group, run by Sebastian Eves-van den Akker, built on the data, using a method of gene network analysis to identify a transcription factor in the nematode’s glands that becomes active when effectors are produced. Their analysis showed 58 effector genes are triggered by this transcription factor, which they call the Subventral-Gland Regulator (SUGR-1).

But what activates SUGR-1? Based on experiments by Eves-van den Akker’s group, that’s due to signals from the roots the researchers have termed effectostimulins. That explains why SUGR-1 activated when the Cambridge research team exposed it to root extracts from plants that are known nematode hosts.

"The most exciting thing for me about this paper is the picture it paints of a self-reinforcing cycle driving nematode infection of plants,” Eves-van den Akker said. “They break plant cells, sense some signals released and respond in a way which increases their ability to break host cells."

How it could work in fields

Currently, crop rotation and cultivars bred to have some nematode resistance are the main control measures for managing soybean cyst nematodes. The improved understanding of how nematodes trick plants into becoming willing hosts should eventually expand that toolbox, Baum said.

Breeding companies could develop soybean varieties genetically engineered to produce RNA that once consumed by nematodes, prevents SUGR-1 from activating. Blocking effectostimulins with chemical treatments, gene editing or breeding is another option. Methods wouldn’t need to be comprehensive, as merely reducing virulence would be significant. 

“With nematodes, you don’t necessarily have to kill off every worm. If I reduce infection by 40%, that’s a big deal. It would make a real dent in crop damages,” Baum said.  

The findings also hold potential for veterinary medicine and human medical treatment, as different types of nematodes are damaging parasites in animals.

‘Just the beginning’

Baum and Eves-van den Akker plan to continue working together on cyst nematode research, as it has been a fruitful partnership for years, Baum said.

“If you were to draw up the way you want to interact with a scientific collaborator, it would be just like this. You build on each other and freely share to make advances that help both camps,” he said.

Baum said he expects future studies will uncover more about the genetic and molecular mechanics of effector production, which should offer additional ways to disrupt the crucial signaling between cyst nematodes and their plant hosts.

“SUGR-1 is just the first one that jumped off the page. But we know there are others. This is only the beginning. There will be many targets,” he said.