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

Chemical warfare between the host and the pathogen plays a crucial role in plant-necrotrophic pathogen interactions, but examples of its involvement in quantitative disease resistance in plants are poorly documented. In the Daucus carota-Alternaria dauci pathosystem, the novel toxin aldaulactone has been identified as a key factor in both fungal pathogenicity and the carrot’s partial resistance to the pathogen. Bioinformatic analyses have pinpointed a secondary metabolism gene cluster that harbors two polyketide synthase genes, AdPKS7 and AdPKS8 , that are likely responsible for the biosynthesis of aldaulactone. Here, we present the functional validation of AdPKS7 and AdPKS8 as genes responsible for aldaulactone production in A. dauci . We generated knock-out A. dauci mutants for AdPKS7 and AdPKS8 by replacing essential domains with a hygromycin resistance gene, marking the first reported case of genetic manipulation in A. dauci . Following transformation, the mutants were analyzed for toxin production via HPLC-UV and assessed for pathogenicity in planta . Aldaulactone production was abolished in all PKS mutants, which also exhibited significantly reduced pathogenicity on H1-susceptible carrot leaves. These findings confirm the roles of AdPKS7 and AdPKS8 in aldaulactone biosynthesis and their contribution to fungal pathogenicity.