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New Discovery to Fight Billion-Dollar Threat

Researchers discover a new link to fight billion-dollar threat to soybean production.

University of Missouri researchers are trying to stop soybean cyst nematodes (SCN) from causing $1.2 billion in damage annually. SCN can cause 30% yield loss in soybeans without visual symptoms, which has resulted in a lack of awareness for this pest.

Invisible to the naked eye, the microscopic roundworm is the industry’s biggest yield robber. A group of plant scientists led by University of Missouri researchers recently found one of the mechanisms cyst nematodes use to invade and drain life-sustaining nutrients from soybean plants. Researchers wanted to understand the molecular basis of interactions between plants and nematodes. The hope was that the research could lead to the development of new strategies to control these pests.

SCN jeopardizes the healthy production of soybeans by hijacking the soybean plants’ biology.

“Cyst nematodes are one of the most economically devastating groups of plant-parasitic nematodes worldwide,” said Melissa Goellner Mitchum, a researcher in the Bond Life Sciences Center and an associate professor in the division of plant sciences at MU. “These parasites damage root systems by creating a unique feeding cell within the roots of their hosts and leeching nutrients out of the soybean plant. This can lead to stunting, wilting, and yield loss for the plant. We wanted to explore the pathways and mechanisms cyst nematodes use to commandeer soybean plants.”

About 15 years ago, Mitchum and colleagues unlocked clues into how nematodes use small chains of amino acids, or peptides, to feed on soybean roots.

Using next-generation sequencing technologies that were previously unavailable, Michael Gardner, a graduate research assistant, and Jianying Wang, a senior research associate in Mitchum’s lab, made a remarkable new discovery: Nematodes possess the ability to produce a second type of peptide that can effectively take over plant stem cells that are used to create vital pathways for the delivery of nutrients throughout the plant. Researchers compared these peptides to those produced by plants and found that they were identical to the ones the plants use to maintain vascular stem cells, known as CLE-B peptides, according to the University of Missouri report.

“Plants send out these chemical signals to their stem cells to begin various functions of growth, including the vascular pathway that plants use to transport nutrients,” Mitchum said. “Advanced sequencing showed us that nematodes use identical peptides to activate the same process. This molecular mimicry helps nematodes produce the feeding sites from which they drain plant nutrients.”

To test their theory, Xiaoli Guo, a postdoctoral researcher in Mitchum’s lab and first author of the study, synthesized the CLE-B nematode peptide and applied it to the vascular cells of Arabidopsis, a model plant system used in plant research. They found that the nematode peptides triggered a growth response in Arabidopsis much in the same way the plants’ own peptides affected development.

Next, the team knocked out the genes that Arabidopsis plants use to signal to their own stem cells. Here, the nematodes didn’t do as well because the parasites were unable to signal to the plant and the nematode’s feeding site was compromised, Guo says.

“When a nematode attacks the root, it selects vascular stem cells that are located along the root,” Mitchum said. “By knocking out that pathway, we reduced the size of the feeding site that nematodes use to control the plant. This is the first time we’ve been able to show that the nematode is modulating or controlling the vascular plant pathway. Understanding how plant-parasitic nematodes modulate host plants to their own benefit is a crucial step in helping to create pest-resistant plants. If we can block those peptides and the pathways nematodes use to overtake the soybean plant, then we can enhance resistance for this very valuable global food source.”

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