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Transformation of Alternaria dauci demonstrates the involvement of two polyketide synthase genes in aldaulactone production and fungal pathogenicity

Summary

A fungus that causes leaf spots on carrots produces a toxic chemical that helps it infect plants. Scientists identified two genes responsible for making this toxin and used genetic engineering to create mutant fungi unable to produce it. When these mutant fungi tried to infect carrot plants, they were much less damaging than the normal fungus, proving the toxin is crucial for the fungus to cause disease.

Background

Alternaria dauci causes Alternaria Leaf Blight (ALB) on carrots and produces the phytotoxin aldaulactone, which plays a key role in fungal pathogenicity and plant resistance. The involvement of polyketide synthase genes in aldaulactone biosynthesis has been hypothesized based on bioinformatic analyses identifying two PKS genes (AdPKS7 and AdPKS8) in secondary metabolism gene cluster 8.

Objective

To provide functional validation of AdPKS7 and AdPKS8 genes as responsible for aldaulactone production in A. dauci through generation of knock-out mutants. To assess the roles of these genes in aldaulactone biosynthesis and their contribution to fungal pathogenicity on carrot plants.

Results

All PKS mutants failed to produce aldaulactone as confirmed by HPLC-UV analysis, while wild-type and non-coding control strains retained aldaulactone production. Mutant strains exhibited significantly reduced pathogenicity on H1-susceptible carrot leaves but showed no significant difference on I2-partially resistant leaves, demonstrating aldaulactone’s central role in fungal pathogenicity.

Conclusion

AdPKS7 and AdPKS8 are essential genes for aldaulactone biosynthesis in A. dauci, and aldaulactone is the primary phytotoxin determining fungal pathogenicity on susceptible carrot genotypes. The study establishes an efficient genetic transformation method for A. dauci and provides a foundation for understanding toxin-mediated pathogenicity and plant resistance mechanisms.
  • Published in:Scientific Reports,
  • Study Type:Functional Genomics Study,
  • Source: PMID: 41038945, DOI: 10.1038/s41598-025-17441-z
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