Plant pathologists develop method to study plant defense against viruses

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A group of plant pathologists within Texas A&M AgriLife Research has created a surprisingly simple approach to studying the complex interactions between plants and viruses. They hope the breakthrough will make improving plant resilience quicker and easier, as well as shed light on the evolutionary arms race between plants and their viruses.

Viral infections make up almost half of the known plant pathogens and cost producers about $30 billion globally each year. For decades, scientists have explored the ways plants defend themselves against viruses and how to enhance the plant's defense system.

To clarify key components in this system, Texas A&M AgriLife researchers developed an innovative approach that uses a modified plant virus to simulate an infection and simultaneously act as a sensor for the plant's resistance response.

Herman Scholthof, Ph.D., professor emeritus of the Texas A&M College of Agriculture and Life Sciences Department of Plant Pathology and Microbiology, led the study published in PNAS Nexus showcasing their novel approach—the final study in his career as a plant virology researcher.

The three-part approach to identifying crucial genes in plant defense

The researchers took a three-step approach in their new technique: infect, knock out, detect.

First, they simulated an infection in plants using a modified virus that expresses a green fluorescent protein. The fluorescent protein is important because it provides a way for scientists to easily see if the virus was able to replicate unchecked.

Next, specific parts of the plant's RNA-silencing pathway, its defense system against viral infection, were targeted and inactivated by gene-editing materials delivered by the same virus. Finally, the researchers checked for a buildup of the virus in the plant, which informed the team whether the targeted, inactivated genes were critical in preventing the virus's replication or not.

By observing where and how much green fluorescence was produced—a visual cue easy for scientists to measure—the researchers could tell whether the plant's defense mechanism was working or not.

If the plant's defense was active and responding to the viral infection, there would be little viral accumulation or green fluorescence. But if the plant's defense is not active because one or more of the crucial genes needed to stop a virus is targeted and silenced, the plant leaf lights up fluorescent green as the virus replicates.

Using this approach, Scholthof said the team was able to target several key genes in the RNA-silencing pathway and identify those essential for preventing viral replication. They were also able to confirm their previous findings that some commonly overlooked genes are crucial in the plant's viral defense.

Scholthof said he considers their study to be proof of concept, showcasing a new method to quickly screen plant genes involved in antiviral defense. By delivering the gene-editing system directly into the plant cells using a viral vector, the process avoids time-consuming aspects of other methods.

"This represents a significant step forward in unraveling the complexities of plant-virus interactions and may eventually support more resilient agriculture," he said.

The final chapter in a research career

Scholthof has served as a professor and researcher at Texas A&M AgriLife for almost 30 years. He said this last research study was the perfect way to close the book on his career, as it brought together many of the focus areas he's returned to over the years, such as RNA silencing and viral gene vectors.

A significant amount of the research was done by April DeMell, first author of the study and previous graduate student in Scholthof's lab.

"I've been surrounded by very talented people—technicians, undergraduate and graduate students, postdoctoral researchers, and visiting scientists—who were responsible for carrying out much of the work in the lab," he said. "Training people who then move on to become successful is one of the most rewarding aspects of this profession."

Scholthof and his wife, Karen-Beth Scholthof, professor emerita of the plant pathology department, both retired in July and recently relocated to Colorado. But neither has given up on educating the world about plant pathology.

Instead, Scholthof is starting a new chapter—both literally and figuratively—in the form of a book aiming to shed light on the fascinating world of virology to draw the next generation into its wonders and applications.

"After teaching plant virology for over 30 years, it's more than just the subject matter that you teach," he said. "You find examples, analogies, explanations that other people don't. So, who knows? Maybe other people will find it interesting too. I'm looking forward to sharing what we've learned from viruses and seeing what's ahead for the field I've dedicated my career to."

More information: April DeMell et al, A tomato bushy stunt virus–based vector for simultaneous editing and sensing to survey the host antiviral RNA silencing machinery, PNAS Nexus (2023). DOI: 10.1093/pnasnexus/pgad436

Journal information: PNAS Nexus

Provided by Texas A&M University