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ChnagG Plays the Role of 5-Salicylate Hydroxylase in the Gentisic Acid Pathway of Salicylic Acid Metabolism in Cochliobolus heterostrophus

Summary

A common corn fungus called Cochliobolus heterostrophus has evolved a clever strategy to infect maize plants by producing an enzyme that breaks down salicylic acid, a key plant defense hormone. When scientists removed the gene encoding this enzyme, the fungus became less effective at causing disease and plants mounted stronger immune responses. This discovery helps explain how this fungal pathogen overcomes plant defenses and could lead to new ways to protect corn crops.

Background

Salicylic acid (SA) is a crucial plant defense hormone against fungal pathogens. Pathogenic fungi have evolved mechanisms to degrade SA and evade plant immunity. The SA metabolic pathways in Cochliobolus heterostrophus, a major maize pathogen causing southern corn leaf blight, have not been previously characterized.

Objective

To identify and characterize the gene ChnagG encoding 5-salicylate hydroxylase in C. heterostrophus and determine its role in SA metabolism and fungal pathogenicity. The study aimed to elucidate how this fungal pathogen overcomes plant defense mechanisms through SA degradation.

Results

ChnagG encodes a 5-salicylate hydroxylase that converts SA to gentisic acid via the gentisic acid pathway. The ChnagG deletion mutant showed reduced melanin synthesis and decreased pathogenicity. Plants infected with the knockout mutant accumulated higher SA levels and exhibited increased expression of SA-responsive defense genes compared to wild-type infection.

Conclusion

C. heterostrophus uses ChnagG to degrade plant SA through the gentisic acid pathway, thereby suppressing host immune signaling and enhancing fungal pathogenicity. This discovery reveals a novel SA metabolic pathway in fungi and provides insights into the mechanisms of plant-pathogen interactions.
  • Published in:Molecular Plant Pathology,
  • Study Type:Experimental Research,
  • Source: PMC12130555; PMID: 40457709; doi: 10.1111/mpp.70090
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