UNC Study Uncovers Key Chemical Signal Behind Devastating Crop Disease
Researchers uncovered how Pseudomonas syringae, a common bacterial pathogen responsible for diseases in crops across the globe, uses a chemical signal to bolster its virulence and survival.
February 11, 2025 I By Dave DeFusco
In the fight against plant diseases that devastate global food crops, understanding the mechanisms of bacterial virulence is critical. A UNC study published in Molecular Plant-Microbe Interactions, sheds light on how Pseudomonas syringae, a common bacterial pathogen responsible for diseases in crops across the globe, uses a chemical signal to bolster its virulence and survival.
Co-authored by Dr. Bo Li, a professor in the Department of Chemistry, postdoc fellow Qiang Guo and graduate students Caitlin Vitro and Drake Crawford, the research, “A Diazeniumdiolate Signal in Pseudomonas syringae Upregulates Virulence Factors and Promotes Survival in Plants,” characterizes a diazeniumdiolate-based molecule, leudiazen, which is a key player in the bacterium’s ability to infect and thrive within plant hosts.
With over 50 identified pathovars, P. syringae poses a significant threat to agriculture worldwide. This bacterium infects a wide range of crops, from tomatoes to kiwifruit, causing diseases that lead to massive economic losses. For example, the kiwifruit canker outbreak in Europe and New Zealand in the early 2010s devastated orchards, underscoring the need for effective management strategies.
A specific strain, Pseudomonas syringae pv. syringae (Pss) UMAF0158, is known for producing mangotoxin, a substance that disrupts plant metabolism. While the chemical structure of mangotoxin remains elusive, production of this toxin is controlled by a signaling molecule called leudiazen, which plays a critical role in the bacterium’s ability to infect plants. Leudiazen is made by the protein products of a group of genes called the mangotoxin-generating operon (mgo) in the same bacterium.
The research made several key insights:
- Gene Deletion Reduces Disease Symptoms: When scientists deleted the mgo genes in Pss UMAF0158, the bacterium caused less damage to tomato plants. This finding suggests that mgo is essential for the bacterium’s virulence.
- Leudiazen Restores Activity: In mutant bacteria lacking mgo, adding leudiazen restored their ability to produce mangotoxin. This result shows that leudiazen is a powerful signal for bacterial virulence, effective at extremely low concentrations.
- Survival and Spread: The mgo genes also help the bacteria survive within plants. Without these genes, the bacterial population in infected plants dropped significantly.
- New Gene Cluster Identified: The study discovered a group of genes (RS17235–RS17245) that are regulated by mgo. These genes help the bacteria survive inside plants and are found in many strains of P. syringae.
“Understanding how P. syringae uses mgo and leudiazen to regulate plant infection opens new doors for controlling bacterial diseases,” said Dr. Li. “By targeting these genes or the signaling pathway, we could develop treatments to protect crops without relying on traditional pesticides.”
Leudiazen contains two key features: a diazeniumdiolate group and an isobutyl side chain. Both are essential for its signaling power. This molecule acts like a messenger. When there is a large enough bacterial population, it tells the bacterium to activate genes that produce toxins and other factors needed to infect plants.
The mgo system is not unique to Pss UMAF0158. Similar gene clusters exist in other bacteria, where they regulate various behaviors, including toxin production and disease suppression. This suggests that the findings could apply to a wide range of bacteria, helping researchers understand how microbes interact with their environments.
The study raises several questions: How does the bacterium sense leudiazen? How do other bacteria use mgo-like signaling systems? Can disrupting these signals prevent infections?
“By answering these questions, we hope to turn this knowledge into practical solutions for agriculture,” said Dr. Li. “The ultimate goal is to protect crops and ensure food security in a world facing increasing challenges from plant diseases.”