Research Highlights

Fighting the 'Invasion of the Body Snatchers' in Soybeans

By Laura Temple

Soybean cyst nematodes, or SCN, are microscopic parasitic worms found in the soil of many soybean fields. They attack soybean roots and significantly reduce yields. 

Thomas Baum, professor of plant pathology at Iowa State University, studies how SCN interact with soybean roots at a molecular level. The basic research done in his laboratory uncovers knowledge he and others can use to develop new tools to control this pest. 

He leads one current research project focused on understanding how specific biochemicals secreted by SCN suppress natural defenses in soybean plants. The Iowa Soybean Research Center is supporting this study, matching a checkoff investment from the Iowa Soybean Association with research funds from the ISRC partnership. 

Understanding Invasion Tactics 

Baum likens how SCN works at the molecular level to an alien invasion.

“SCN eggs hatch in the soil and each worm penetrates soybean roots looking for a place to become sedentary and feed,” he explains. “Each nematode targets one root cell and starts ‘talking’ to it through molecular protein messages secreted from its mouth that we call effectors. Those biochemical messages tell the targeted cell to completely change its behavior, so that it willingly transforms into a place to feed the worm.”

Baum further describes the SCN takeover: the targeted cell responds to the nematode, and then it starts communicating with the cells around it. Those cells also change their function. All those cells dissolve their walls to become one huge cell that feeds the nematode, stealing water and nutrients from the soybean plant.

SCN have become very good at this method of attack, he says. The nematodes send hundreds of protein effectors into the infected cell with instructions about how to change. Many of these messages turn off natural defense mechanisms in the plant.

“Normally when something goes wrong in a cell, plants use a defense mechanism that kills that cell, known as programmed cell death,” Baum continues. “SCN needs its initial targeted cell to stay alive to feed it, so it sends messages that suppress this natural defense mechanism. We are studying the nematode messages that keep the soybean plant from killing the feeding cells.”

Intercepting Messages

With Baum’s current ISRC research, his team is doing detailed work to understand how two effectors, or proteins carrying messages, suppress the programmed cell death defense mechanism. Specifics about that process will provide knowledge researchers can draw on to figure out how best to reinforce or strengthen defenses in soybeans.

“We need to understand specific communication between the worm and the soybean cell so that we can disrupt it,” he says. “We are focusing on pathways in the plant we know the nematodes are afraid of and have developed ways to attack. Once we understand what their effectors do, we can use our tools to find ways to help soybean cells not respond to the nematodes or ensure the programmed cell death mechanism kills the targeted cell, which will also kill the nematode.”

Using one of the effectors in this study, Baum’s team has figured out what regions of the effector protein are responsible for a specific message. Through this process, they developed an effective technique to discover how the protein messages bind to plant proteins to relay instructions. They can now apply this technique to the other effector protein to more quickly understand what these nematode proteins do.

“We are making progress in understanding what happens at the molecular level, but nematodes are very complex,” Baum explains. “We expect that they have redundant mechanisms, or protein messages, that disarm the soybean defense mechanisms that pose the most threat to their survival.”

Developing Anti-Nematode Strategies

Baum believes the results of this work will arm translational research projects to focus on strategies most likely to either control SCN or enable soybeans to resist them. Translational research is the bridge between basic research like this project and the practical application of that research to solve problems. 

He says that farmers need new ways to manage SCN. Baum notes that some soybeans have resistance to some SCN. However, SCN genetics vary as much as they do among soybeans or people, so that genetic plant resistance isn’t effective against the entire SCN population. Over time, the SCN immune to that type of resistance increase in population, eroding the effectiveness of those specific resistant genes in soybeans.

Baum says that this research project builds on knowledge collected through years of research funded by the soy checkoff through the Iowa Soybean Association, the North Central Soybean Research Program and the United Soybean Board. He credits soybean farmers for having the foresight to invest in creating strong partnerships with researchers at land-grand universities to find solutions to SCN pressure. 

“The soybean checkoff system can take full credit for the tremendous progress made in the fight against SCN,” he says. “Though I focus on lab work, I am proud to be a part of a partnership tackling a complex challenge for farmers.”

Additional Resources:

Soybean cyst nematode: https://soybeanresearchinfo.com/soybean-disease/soybean-cyst-nematode-scn/  

Other SCN articles on SRIN: https://soybeanresearchinfo.com/?s=SCN

Published: Oct 31, 2022