New research provides insight into how plant pathogens trigger plant diseases that threaten the global food supply

Interdisciplinary team identifies a small molecule that behaves differently from other bacterial toxins by suppressing plant immune responses.

The graphic shows pseudomonas syringae and arrows pointing to phevamine A and a plant with the words "Suppresses Plant immunity."A UNC-Chapel Hill interdisciplinary research team of chemists and biologists has unlocked an important clue in understanding how plant pathogens cause diseases that can create significant crop damage worldwide.

The bacterial species Pseudomonas syringae can infect a wide range of plants (over 50 different species) including bean, wheat, rice, cabbage, tomato, beet and more. The study utilized two model plants, Arabidopsis thaliana (thale cress) and Nicotiana benthamiana (a tobacco relative) that can also be infected by this bacterial pathogen.

Bo Li (right). (photo by Steve Exum)
Bo Li (right). (photo by Steve Exum)

The team, led by Bo Li, assistant professor of chemistry, and Jeff Dangl, HHMI Investigator and John N. Couch Professor of Biology in UNC’s College of Arts & Sciences, wanted to understand how pathogenic bacteria can impair plant defense and promote infection.

They identified a new small molecule called phevamine A that has a very different structure from other known bacterial toxins. Rather than damaging the plant cell, it suppresses several tested plant defense mechanisms, which gives the pathogen the opportunity to grow and cause infection.

Small molecules are organic compounds produced by bacteria using designated enzymes for a specific function. For example, some small molecules help defend the bacteria against competitors, i.e. antibiotics. Other small molecules enable the bacteria to mount attack on host cells, like phevamine A, according to Li.

The research appears in the journal PNAS.

“Our approach to identify phevamine A was very different from past approaches to identify bacterial toxins,” Li said. The team drew on expertise from multiple disciplines, including organic chemistry, biochemistry, microbiology, genomics and plant biology. “This approach is powerful and can be broadly applied to identify other small molecules essential for bacteria–host interactions.”

Inhibiting this bacterial pathway could help control plant infections, Li added.

Jeff Dangl (photo courtesy of HHMI /Jim R. Bounds)
Jeff Dangl (photo courtesy of HHMI /Jim R. Bounds)

“In the future we will be identifying the plant proteins with which phevamine A interacts. This will help us develop ways to disrupt the interaction and identify versions of the protein that are resistant to the action of phevamine A,” she said.

Are there applications for this research in fighting human diseases?

Li said researchers are exploring that trajectory as well. Her lab is dedicated to decoding the hidden chemistry of bacterial genomes and discovering small molecules that could treat human diseases.

“The structure of phevamine A resembles certain neuroactive molecules produced by insects. We are also exploring the potential of phevamine A and related compounds to inhibit human proteins that are involved in neurological disorders,” she said.

The work, conducted with colleagues at Cornell University, was supported by the Rita Allen Foundation, the David and Lucile Packard Foundation, the National Institutes of Health, the National Science Foundation and the Howard Hughes Medical Institute.

By Kim Weaver Spurr ’88