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A Toxin of Valsa mali Determines Virulence and Host Preference

Lin Tang¹, Liangliang Zhu¹, Xinyun Wu¹

¹State Key Laboratory for Crop Stress Resistance and High-Efficiency Production, College of Plant Protection, Northwest A&F University, Yangling, Shaanxi, China.

Molecular Plant Pathology

|June 17, 2025

Abstract:

Through co-evolutionary adaptation, phytopathogenic fungi have evolved specialised host preference mechanisms to optimise infection efficacy. Fungi of the Valsa genus infect various Rosaceae fruit trees, with Valsa mali exhibiting a marked host preference for apple trees, while Valsa pyri preferentially colonises pear trees. The divergent secondary metabolite biosynthetic gene clusters (SMBGCs) between these two species may serve as key determinants of their distinct host preferences. In this study, VmPKS5, a polyketide synthase, was identified as a key factor influencing the host preference of V. mali, which is the main pathogen of apple Valsa canker (AVC). Deletion of VmPKS5 greatly reduced the virulence of V. mali in apple trees, but not in pear trees. Deletion of VmPKS5 completely abolished the production of the toxin p-coumaric acid ethyl ester (p-CAEE). Exogenous p-CAEE application partly restored the virulence of ΔVmPKS5 and enhanced the virulence of the wild-type strain of V. mali. Crucially, heterologous expression of VmPKS5 in V. pyri increased its virulence towards apple trees by production of p-CAEE during infection. Notably, V. mali can uptake double-stranded RNA (dsRNA), and exogenous spray of VmPKS5-dsRNA significantly inhibited the infection by V. mali. This study provides new perspectives on host preference mechanisms of fungal pathogens and green disease control of tree disease by dsRNA fungicides.

Insights

A key fungal gene, VmPKS5, dictates Valsa mali

Area of Science:

Plant Pathology
Molecular Mycology
Biochemistry

Background:

Phytopathogenic fungi exhibit host specificity driven by co-evolutionary adaptations.
The Valsa genus, including Valsa mali (apple) and Valsa pyri (pear), shows distinct host preferences within Rosaceae fruit trees.
Divergent secondary metabolite biosynthetic gene clusters (SMBGCs) are hypothesized to underlie these host preferences.

Purpose of the Study:

To investigate the role of VmPKS5 in Valsa mali's host preference for apple trees.
To explore the involvement of p-coumaric acid ethyl ester (p-CAEE) in Valsa mali virulence.
To assess the potential of dsRNA technology for controlling apple Valsa canker (AVC).

Main Methods:

Gene deletion and heterologous expression of VmPKS5 in Valsa species.
Analysis of p-coumaric acid ethyl ester (p-CAEE) production and virulence assays.
Application of VmPKS5-specific double-stranded RNA (dsRNA) to inhibit fungal infection.

Main Results:

Deletion of VmPKS5 significantly reduced V. mali virulence on apple trees and abolished p-CAEE production.
Exogenous p-CAEE partially restored virulence in VmPKS5-deleted strains and enhanced wild-type virulence.
Heterologous expression of VmPKS5 in V. pyri increased its virulence on apple trees via p-CAEE production.
Exogenous VmPKS5-dsRNA effectively inhibited V. mali infection, demonstrating its potential as a fungicide.

Conclusions:

VmPKS5 is a critical determinant of Valsa mali's host preference and virulence on apple trees.
The toxin p-CAEE, produced by VmPKS5, plays a significant role in Valsa mali pathogenesis.
VmPKS5-dsRNA represents a promising novel strategy for the green control of tree diseases caused by Valsa pathogens.

Read full analysis

Keywords:

Valsa mali VmPKS5 dsRNA host preference p‐CAEE

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