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Fusarium avenaceum is an aggressive pathogen of pulse crops and a causal agent in root rot disease that negatively impacts Canadian agriculture. This study reports the results of a targeted metabolomics-based profiling of secondary metabolism in an 18-strain panel of Fusarium avenaceum cultured axenically in multiple media conditions, in addition to an in planta infection assay involving four strains inoculated on two pea cultivars. Multiple secondary metabolites with known roles as virulence factors were detected which have not been previously associated with F. avenaceum, including fungal decalin-containing diterpenoid pyrones (FDDPs), fusaoctaxins, sambutoxin and fusahexin, in addition to confirmation of previously reported secondary metabolites including enniatins, fusarins, chlamydosporols, JM-47 and others. Targeted genomic analysis of secondary metabolite biosynthetic gene clusters was used to confirm the presence/absence of the profiled secondary metabolites. The detection of secondary metabolites with diverse bioactivities is discussed in the context of virulence factor networks potentially coordinating the disruption of plant defenses during disease onset by this generalist plant pathogen.

Fusarium graminearum is a causal organism of Fusarium head blight in cereals and maize. Although a few secondary metabolites produced by F. graminearum are considered disease virulence factors, many molecular products of biosynthetic gene clusters expressed by F. graminearum during infection and their associated role in the disease are unknown. In particular, the predicted meroterpenoid products of the biosynthetic gene cluster historically designated as “C16” are likely associated with pathogenicity. Presented here are the results of CRISPR-Cas9 gene-editing experiments disrupting the polyketide synthase and terpene synthase genes associated with the C16 biosynthetic gene cluster in F. graminearum. Culture medium screening experiments using transformant strains were profiled by UHPLC-HRMS and targeted MS2 experiments to confirm the associated secondary metabolite products of the C16 biosynthetic gene cluster as the decalin-containing diterpenoid pyrones, FDDP-D and FDDP-E. Both decalin-containing diterpenoid pyrones were confirmed to be produced in wheat heads challenged with F. graminearum in growth chamber trials. The extent to which the F. graminearum C16 biosynthetic gene cluster is dispersed within the genus Fusarium is discussed along with a proposed role of the FDDPs as pathogen virulence factors.

Research into ergot alkaloid production in major cereal cash crops is crucial for furthering our understanding of the potential toxicological impacts of Claviceps purpurea upon Canadian agriculture and to ensure consumer safety. An untargeted metabolomics approach profiling extracts of C. purpurea sclerotia from four different grain crops separated the C. purpurea strains into two distinct metabolomic classes based on ergot alkaloid content. Variances in C. purpurea alkaloid profiles were correlated to genetic differences within the lpsA gene of the ergot alkaloid biosynthetic gene cluster from previously published genomes and from newly sequenced, long-read genome assemblies of Canadian strains. Based on gene cluster composition and unique polymorphisms, we hypothesize that the alkaloid content of C. purpurea sclerotia is currently undergoing adaptation. The patterns of lpsA gene diversity described in this small subset of Canadian strains provides a remarkable framework for understanding accelerated evolution of ergot alkaloid production in Claviceps purpurea.