Apiospora arundinis, a panoply of carbohydrate-active enzymes and secondary metabolites.

The Apiospora genus comprises filamentous fungi with promising potential, though its full capabilities remain undiscovered. In this study, we present the first genome assembly of an Apiospora arundinis isolate, demonstrating a highly complete and contiguous assembly estimated to 48.8 Mb, with an N99 of 3.0 Mb. Our analysis predicted a total of 15,725 genes, with functional annotations for 13,619 of them, revealing a fungus capable of producing very high amounts of carbohydrate-active enzymes (CAZymes) and secondary metabolites. Through transcriptomic analysis, we observed differential gene expression in response to varying growth media, with several genes related to carbohydrate metabolism showing significant upregulation when the fungus was cultivated on a hay-based medium. Finally, our metabolomic analysis unveiled a fungus capable of producing a diverse array of metabolites.

Cyclic, Hydrophobic Hexapeptide Fusahexin Is the Product of a Nonribosomal Peptide Synthetase in Fusarium graminearum.

The plant pathogenic fungus Fusarium graminearum is known to produce a wide array of secondary metabolites during plant infection. This includes several nonribosomal peptides. Recently, the fusaoctaxin (NRPS5/9) and gramilin (NRPS8) gene clusters were shown to be induced by host interactions. To widen our understanding of this important pathogen, we investigated the involvement of the NRPS4 gene cluster during infection and oxidative and osmotic stress. Overexpression of NRPS4 led to the discovery of a new cyclic hexapeptide, fusahexin (1), with the amino acid sequence cyclo-(d-Ala-l-Leu-d-allo-Thr-l-Pro-d-Leu-l-Leu). The structural analyses revealed an unusual ether bond between a proline Cδ to Cß of the preceding threonine resulting in an oxazine ring system. The comparative genomic analyses showed that the small gene cluster only encodes an ABC transporter in addition to the five-module nonribosomal peptide synthetase (NRPS). Based on the structure of fusahexin and the domain architecture of NRPS4, we propose a biosynthetic model in which the terminal module is used to incorporate two leucine units. So far, iterative use of NRPS modules has primarily been described for siderophore synthetases, which makes NRPS4 a rare example of a fungal nonsiderophore NRPS with distinct iterative module usage.