Genome mining reveals the distribution of biosynthetic gene clusters in Alternaria and related fungal taxa within the family Pleosporaceae.

BACKGROUND

The advancement of whole genome sequencing techniques has led to the development of genome mining strategies that enable high-resolution research into fungal secondary metabolite (SM) biosynthesis. Alternaria species are producers of prominent SMs including virulence factors and mycotoxins that affect phytosanitation, food safety, and the economy. Here, we apply genome mining to identify a total of 6,323 biosynthetic gene clusters (BGCs) from 187 genomes: 123 Alternaria and 64 from seven other closely related genera in the family Pleosporaceae.

RESULTS

An average of 34 BGCs were detected per genome, with 29 on average for Alternaria genomes. The distribution of different BGC classes (e.g. polyketide synthases, non-ribosomal peptide synthetases) across taxa was investigated. BGCs were grouped into 548 gene cluster families (GCFs) revealing that while individuals within the same species may differ in their toxicological potential, the overall patterns of GCF presence/absence were also generally well correlated with phylogenomic patterns at higher taxonomic levels. Comparative genome analyses revealed that the divergent Alternaria sections Infectoriae and Pseudoalternaria possessed highly unique GCF profiles compared to other Alternaria sections, providing nine ideal candidates for diagnostic or chemotaxonomic marker development. However, none of these GCFs were associated with known compounds, prompting further research into the genetic characterization of Alternaria SMs. The GCF for the most prominent Alternaria mycotoxin alternariol (AOH) was found in Alternaria sections Alternaria and Porri, suggesting that food safety monitoring efforts should prioritize these two sections. Findings supported phytosanitary regulations regarding Alternaria gaisen, associated with Asian pear host-specific AK-toxin I.

CONCLUSIONS

Our analyses are of unprecedented scale and resolution, allowing the identification of SM BGCs that are shared among multiple genera, or restricted to certain groups of focal taxa. Our study highlights the challenges associated with exploratory genome mining as a launching point for further research, and informs Alternaria disease management and regulation, food safety practices, and natural product discovery.