AMES, Iowa – A long-time research collaboration between the University of Cambridge, United Kingdom, and Iowa State University is bringing scientists one step closer to combatting field infections of soybean cyst nematodes (SCN).

SCN are worm-shaped animals that are responsible for over a billion dollars in losses annually in the US and Canada, with estimated yield losses exceeding 125 million bushels each year. Best management practices to combat SCN include using resistant soybean varieties and rotating to non-host crops. However, SCN have been able to adapt and thrive on resistant crops, and it’s impossible to eliminate SCN from a field once it’s been infected.

“(SCN) is a very successful pathogen that has evolved over hundreds of millions of years, and it’s ready for problems coming its way,” Thomas Baum, professor in the Department of Plant Pathology, Entomology and Microbiology at Iowa State University, said. “Under the microscope, they look like a boring little animal. No, these things are very sophisticated and have developed mechanisms of interactions with hosts that are exceedingly complex and fascinating.”

Baum said that what makes the nematode interesting biologically is that it doesn’t just go into the root of the plant and start feeding – it crawls through the root in search of a suitable place to start feeding and does “major remodeling” of the root area.

“The way that parasites or pathogens do that is by communicating with their hosts, and they use chemicals to do so,” he said. “The nematode, like most or maybe all pathogens, delivers certain molecules into the host, and the ones we are dealing with are proteins.”

The proteins are known as effectors. Effectors are delivered from the nematodes to the plant to achieve a variety of outcomes, like altering plant cell structure and function to facilitate feeding. Baum and his collaborators became interested in understanding how SCN knew when to produce and deploy effectors, especially because effectors are critical to the nematode’s success.

“We study all this kind of stuff because we want to find weak points in the nematode life cycle,” Baum said. “When we think of the tools nematodes use to infect plants, we want to know what happens when we take those tools away.”

However, SCN make about a thousand or more effectors. Taking just one away from the worms wouldn’t do much, Baum said, because the nematode has many other proteins available to perform similar functions. Instead, the group focused on understanding the molecular mechanism that turns on the production of effectors in SCNs, recently discovering a molecule that activates the production of effectors called SUGR-1.

“We now know the switch that turns on effector production, and we also have an idea of what flips the switch, and it turns out to be signals from the plant,” Baum said. “We’re talking about the nematode sending proteins to the plant, but the plant also sends signals to the nematode. The nematode uses those compounds released by the plant to switch over to effector synthesis.”

SUGR-1 triggers 58 effector genes. Researchers can focus on SUGR-1 as a target to take away a large number of effectors from SCN all at once.

“If we take that switch away (SUGR-1), the nematode is not happy anymore. We have identified and validated a target that can be exploited,” Baum said.

For example, chemicals could be applied to plants that are designed to switch on SUGR-1 at the wrong time or block the switch, preventing SCN from feeding on and remodeling plant roots and structures. Additionally, plants can be modified to block the molecular mechanism that signals to the nematodes to start producing effectors. While field applications are years off, the discovery is a breakthrough in creating new ways to manage SCN.

Baum added that the research may also be applicable to other nematodes, such as the Root-Knot Nematode. Moving forward, the group will perform experiments to observe what happens when SUGR-1 is knocked out in SCN. The group is also ready to explore other regulatory proteins like SUGR-1 to find even better candidates.

 “Other regulatory proteins may have a more pronounced effect when we knock them out, or they may be easier to knock out. This is just the first discovery of this molecular mechanism in the regulation of the effector repertoire of the worm, and we’ll explore the whole arsenal and see which ones we should focus on,” Baum said.

Finding a way to control SCN would have a huge impact on the profitability of soybean production. Baum extended his thanks to soybean farmers who have been instrumental in funding research projects.