Research Highlights

Tools of Biotechnology: Complementing Soybean Breeding Programs Through Adding Novel Genetic Variation Into the Germplasm

By Sarah Hill

Faster, higher, stronger. These three words might be the Olympic motto, but soybean researchers are working to make soybean plants reach these goals, too. When evaluating soybean varieties, there are three traits that breeders focus on improving—yield, protection of yield, and quality of the harvest. 

“Protecting yield implies protection against a pathogen or cold stress, heat stress or water stress,” says Tom Clemente, professor of biotechnology in the Department of Agronomy and Horticulture at the University of Nebraska. “Anything caused by a pathogen results in that plant experiencing biotic stress. The biggest biotic stress is weed management, and there aren’t enough herbicides to overcome all of the types of weeds out there.”

Soybeans, like all crops, get exposed to stressors that can chip away at their overall yield potential over the course of a growing season. Soybean breeding programs strive to continue to add genetic gains that mitigate these losses due to biotic or abiotic challenges. The challenge plant breeding programs have is that genetic variation is limited to what already exists in the crop’s germplasm. The tools of biotechnology provide a route for breeding programs to access novel genetic variation not found in the soybean germplasm. 

Approximately 44 years ago, plant scientists figured out exactly how a plant pathogen, Agrobacterium tumefaciens, introduces a segment of DNA from its own cell into a plant cell to induce a disease state. Understanding this disease-triggering mechanism allowed plant scientists to exploit the process to add novel genetic variation into plant cells.  

Research is making it more apparent that pathogens and their hosts evolve together. The host gains genetic resistance, while the pathogen develops a strategy to overcome the resistance, creating a constant need for breeders to keep up with the evolution of harmful pathogens.

A strategy many pathogens use to overcome host resistance is through the ‘injection’ into the host of proteins called ‘effectors.’ Effectors perturb the biological processes of the host, allowing a disease state to progress. Understanding how an effector triggers this susceptibility allows plant scientists to design genetic strategies to combat it. The pathogen Pseudomonas syringae carries a cache of effectors to circumvent resistance, such as ‘HopE1’, which destabilizes the hollow structures that support the plant’s cells called microtubules, leading to susceptibility. This knowledge set the stage to test the hypothesis: can producing more proteins that HopE1 targets in the plant provide resistance when challenged with the pathogen? 

To answer this question, researchers created transgenic soybeans with extra copies of the target protein and evaluated their resistance when challenged with the pathogens P. syringae pv. glycinea, Phytophthora sojae and Heterodera glycines. The results revealed that boosting the target protein in soybeans boosted the resistance towards the P. syringae pv. glycinea and P. sojae, but not H. glycines. The research team also sprayed the transgenic soybeans with the herbicide oryzalin, which also destabilizes microtubules, and observed a herbicide tolerance response. 

“Once you understand how a pathogen overcomes resistance, then you can reinforce the plant’s immune system,” Clemente says. “If you understand mechanisms underlying the host microbe’s interaction, one can use what has been learned to design and build genetic strategies to combat the pathogen.”

Clemente notes that technologies and scientific processes like these may initially seem obscure to stakeholders, but they are addressing fundamental questions that can in turn be translated to applied technologies to protect soybean yield and benefit agriculture as a whole. 

Published: Sep 25, 2024