Mycoviral gene integration converts a plant pathogenic fungus into a biocontrol agent

Area of Science:

• Plant Pathology
• Mycology
• Virology

Background:

• Mycoviruses can induce hypovirulence in fungi, but molecular mechanisms are unclear.
• Stemphylium lycopersici alternavirus 1 (SlAV1) is a mycovirus found in the plant pathogen *Stemphylium lycopersici*.
• Altersolanol A is a polyketide phytotoxin crucial for *S. lycopersici* pathogenicity.

Purpose of the Study:

• To elucidate the molecular mechanism of SlAV1-induced hypovirulence.
• To investigate SlAV1's effect on Altersolanol A biosynthesis.
• To explore the potential of SlAV1-gene integrated fungi as biocontrol agents.

Main Methods:

• Isolation and characterization of SlAV1 from *S. lycopersici*.
• Analysis of SlAV1's impact on the expression of fungal polyketide synthase (PKS1).
• Generation of transgenic *S. lycopersici* strains expressing SlAV1 open-reading frame 3 (ORF3).
• Pathogenicity assays and biocontrol efficacy tests on various plant species.

Main Results:

• SlAV1 significantly down-regulates *PKS1*, inhibiting Altersolanol A biosynthesis.
• *PKS1* deletion mutants exhibited reduced pathogenicity.
• Transgenic expression of SlAV1 ORF3 mimicked SlAV1 infection, reducing virulence.
• Fungi engineered with SlAV1 ORF3 demonstrated biocontrol potential against virulent strains.

Conclusions:

• SlAV1-mediated hypovirulence results from the inhibition of host phytotoxin biosynthesis via PKS1 down-regulation.
• Mycovirus-gene integrated fungi can be developed as effective biocontrol agents for plant disease management.
• This study provides a novel mechanism for mycovirus-induced virulence attenuation and a new strategy for biological control.