Polyketide synthase gene clusters in the ericoid mycorrhizal fungus Oidiodendron maius: genome-wide prediction, expression profiling, and functional characterization of knockout mutants

Abstract

Introduction Fungal polyketides constitute a structurally diverse class of secondary metabolites involved in ecological adaptation, stress responses, antagonistic interactions, and host-associated processes. However, their roles in mycorrhizal fungi remain poorly understood. In this study, we investigated the repertoire and potential functions of polyketide synthases (PKSs) in the ericoid mycorrhizal fungus Oidiodendron maius. Methods and Results Genome-wide analyses identified 45 PKS-coding genes and 59 predicted biosynthetic gene clusters associated with secondary metabolite production. Transcriptomic analyses revealed that several PKS genes were differentially regulated during symbiosis with Vaccinium myrtillus and under cadmium exposure. Among these, the gene OmPKS197601 was strongly upregulated under both conditions and was selected for functional characterization through Agrobacterium tumefaciens-mediated gene disruption. Three independent OmPKS197601 knockout mutants were generated and evaluated for their ability to establish mycorrhizal symbiosis and tolerate cadmium and zinc stress. Knock-out mutants were also tested for their ability to antagonize the growth of selected fungal species. No significant differences were observed between the wild-type strain and the three OmPKS197601 knock-out mutants in either mycorrhization efficiency or metal tolerance. In contrast, dual-culture assays with the M2 knock-out mutant demonstrated reduced antagonistic activity against both plant pathogenic and saprotrophic fungi, including Heterobasidion annosum, Pythium sp., Kuehneromyces mutabilis, and Stereum hirsutum. Conclusions Overall, these findings reveal the extensive genetic potential of O. maius for polyketide biosynthesis and suggest that regulated expression of PKS genes may contribute to the ecological fitness and biocontrol potential of ericoid mycorrhizal fungi.