Have you ever opened your fridge to discover that those strawberries you bought last week are now coated with an unappetizing layer of gray fuzz?

Those unlucky berries were probably infected with gray mold, a disease caused by the fungus Botrytis cinerea. This fungal pathogen can wreak havoc not only in your fridge or kitchen, but also in high-humidity environments like commercial greenhouses.

Fungal diseases threaten crop production, food security, and human health worldwide. Gray mold alone afflicts more than 200 plant species, including agricultural crops, and results in more than $10 billion in losses annually.

Unfortunately, the problem isn’t going away—in fact, it’s growing. Many fungal pathogens have flourished with shifting weather and precipitation patterns. At the same time, heavy use of conventional fungicides has resulted in widespread fungicide resistance.

“The rise of fungicide-resistant fungal pathogens poses a significant threat to human health and agriculture,” says Seungmee Jung, who graduated from UW in 2024 with a PhD in molecular biology. “The risk of a potential fungal pandemic is a pressing concern.”

But, thanks to Jung’s lab group, future fungicides may be safer, more effective, and much less vulnerable to the development of resistance.

A “self-eating” process

The new fungicide candidates discovered by Jung’s team target a cellular process known as autophagy, which recycles old, faulty, or unnecessary cell components and helps cells maintain homeostasis. Broken down to its Greek roots, the term translates to “self eating.”

Autophagy occurs in all eukaryotic organisms (those whose cells contain a nucleus), from baker’s yeast to human beings. “It’s a nutrient-recycling process in the cell that allows the cell to maintain their healthy status,” Jung explains. “Autophagy processes are boosted under stressful conditions like starvation or infection.”

In fungi, autophagy also affects pathogenicity. Previous studies have shown that many fungal pathogens lose their ability to cause disease when genes related to autophagy are deleted.

Many fungi are known for swiftly adapting to environmental conditions and nimbly evolving resistance to existing fungicides. But even these seemingly invincible pathogens would struggle to dodge a chemical treatment that blocked autophagy.

“Autophagy is a very basic process on a cellular level, so that means it’s really hard to change as time goes on,” Jung explains. “Autophagy is not only important for their pathogenicity but also very important for their life cycle. So it would be really hard for them to just ‘delete.’”

Disrupting the fungal life cycle

In a fungal cell, the first step in autophagy is the formation of an autophagosome, a cellular “container” that forms a membrane around unnecessary cell materials and hauls them away to be digested and recycled.

The enzyme ATG4 plays a pivotal role in this process by cleaving apart a specific protein, ATG8, which then facilitates the formation of a lipid membrane around the materials to be recycled. Without ATG4 to activate the process, ATG8 cannot form this membrane and autophagy cannot be completed.

To identify chemical compounds that might disrupt autophagy, Jung and her colleagues first developed a molecular “sensor” to indirectly monitor ATG4 activity. To deploy the sensor, the researchers attached two proteins to ATG8, then measured changes in energy transfer between the two proteins when a potential fungicide compound was introduced.

In this BRET (bioluminescent resonance energy transfer) system, one of the proteins acts as an energy donor, while the other functions as an energy receptor. Energy transfer depends on the distance between the two proteins, Jung explains. If the proteins are close to each other—as they are before ATG4 cleaves ATG8 apart—the energy donor can transfer more energy to the receptor. If the proteins are farther away from one another—as they are after ATG4 cleaves ATG8—the energy donor transfers less energy to the receptor.

If the potential fungicide compound didn’t interfere with ATG4 splitting ATG8, the proteins affixed to ATG8 would wind up farther apart, resulting in a lower BRET ratio. But if the chemical inhibited ATG4’s ability to cleave ATG8, the proteins would remain close together and the BRET ratio would be higher.

The researchers’ goal was to identify compounds with high BRET ratios, as they were likely blocking autophagy in the cell. “These compounds bind directly to fungal ATG4 enzymes, disrupting their activity and impairing pathogen development and infection structures,” Jung explains.

Identifying antifungal compounds

In their search for an effective autophagy inhibitor, Jung’s team screened more than 2,400 chemical compounds using the BRET system. Ultimately, they identified several compounds that inhibit autophagy in fungi that cause diseases like gray mold, rice blast fungus, white mold, and brown rot.

One of the chemicals Jung’s team tested has been under clinical trial for potential use in human medicine. Hopefully, this will allow for the development of fungicides that are less harmful to human health than existing options.

The chemicals that most effectively blocked autophagy included a molecule known as ebselen and several closely related compounds.

Initial experiments occurred “in vitro,” meaning that the researchers tested the process using lab-grown proteins found in fungi cells. Successful candidates were then tested in actual fungi cells. Lastly, to mimic fungicide application, the researchers sprayed the finalists onto host plants, then exposed those plants to fungal pathogens.

Autophagy was completely blocked in the fungal pathogens when the compounds were applied, Jung reports—a promising sign for potential use as a fungicide. Ebselen, for example, effectively prevented fungal infection in grapes, strawberries, tomatoes, rice, and roses.

“By targeting the autophagy process in fungal pathogens, we not only reduce crop loses but also protect human health…while minimizing environmental impact,” Jung concludes.

After nearly a decade of work developing, testing, and using this BRET sensor, she’s already busy designing a second-generation sensor to study autophagy in animals, including humans. She hopes her work will ultimately benefit human health as well as crop production.

This article was originally published in the 2025 issue of Reflections, the annual research magazine published by the UW College of Agriculture, Life Sciences and Natural Resources.