Genomic and transcriptomic survey of an endophytic fungus Calcarisporium arbuscula NRRL 3705 and potential overview of its secondary metabolites

Abstract

Background: Endophytic fungi can produce many active secondary metabolites, which are important resources of natural medicines. However, there is currently little understanding of endophytic fungi at the omics levels. Calcarisporium arbuscula, an endophytic fungus from the healthy fruit of Russulaceae, can produce a variety of secondary metabolites with anti-cancer, anti-nematode and antibiotic bioactivities. Comprehensive survey of the endophytic fungi genome and transcriptome will help to understand their capacity to biosynthesize secondary metabolites and lay the foundation for the development of these precious resources.Results: In this study，we reported the high-quality genome sequence of a strain C. arbuscula NRRL 3705 based on Single Molecule Real-Time sequencing technology. The genome of this fungus is over 45 Mb in size, relatively larger than other typical filamentous fungi, and comprises 10,001 predictable genes, encoding at least 762 secretory-proteins, 386 carbohydrate-active enzymes and 177 P450 enzymes. 398 virulence factors and 228 genes related to pathogen-host interactions were also predicted in this fungus. Moreover, 65 secondary metabolite biosynthetic gene clusters were revealed, including the gene cluster for mycotoxins aurovertins. In addition, several gene clusters were predicted to produce various mycotoxins, including aflatoxin, alternariol, destruxin, citrinin and isoflavipucine. Notably, two independent gene clusters were shown possibly involved in the biosynthesis of alternariol. Furthermore, RNA-Seq assay showed that only the expression of aurovertin gene cluster is much stronger than the housekeeping genes under laboratory conditions, consistent with that aurovertins are the predominant metabolites. The gene expression of the remaining 64 gene clusters for compound backbone biosynthesis was all lower than the housekeeping genes, which might partially explain poor production of other secondary metabolites in this fungus.Conclusions: Our omics data along with bioinformatics analysis indicated that C. arbuscula NRRL 3705 contains a large number of biosynthetic gene clusters and has a huge potential to produce profound secondary metabolites. This work also provides the basis for development of endophytic fungi as a new resource of natural products with promising biological activities.