A new vector system for targeted integration and overexpression of genes in the crop pathogen Fusarium solani

Final piece to the Fusarium pigmentation puzzle - Unraveling of the phenalenone biosynthetic pathway responsible for perithecial pigmentation in the Fusarium solani species complex

The Fusarium solani species complex (FSSC) is comprised of important pathogens of plants and humans. A distinctive feature of FSSC species is perithecial pigmentation. While the dark perithecial pigments of other Fusarium species are derived from fusarubins synthesized by polyketide synthase 3 (PKS3), the perithecial pigments of FSSC are derived from an unknown metabolite synthesized by PKS35. Here, we confirm in FSSC species Fusarium vanettenii that PKS35 (fsnI) is required for perithecial pigment synthesis by deletion analysis and that fsnI is closely related to phnA from Penicillium herquei, as well as duxI from Talaromyces stipentatus, which produce prephenalenone as an early intermediate in herqueinone and duclauxin synthesis respectively. The production of prephenalenone by expression of fsnI in Saccharomyces cerevisiae indicates that it is also an early intermediate in perithecial pigment synthesis. We next identified a conserved cluster of 10 genes flanking fsnI in F. vanettenii that when expressed in F. graminearum led to the production of a novel corymbiferan lactone F as a likely end product of the phenalenone biosynthetic pathway in FSSC.

Transcriptional Divergence Underpinning Sexual Development in the Fungal Class Sordariomycetes

Gene expression divergence through evolutionary processes is thought to be important for achieving programmed development in multicellular organisms. To test this premise in filamentous fungi, we investigated transcriptional profiles of 3,942 single-copy orthologous genes (SCOGs) in five related sordariomycete species that have morphologically diverged in the formation of their flask-shaped perithecia. We compared expression of the SCOGs to inferred gene expression levels of the most recent common ancestor of the five species, ranking genes from their largest increases to smallest increases in expression during perithecial development in each of the five species. We found that a large proportion of the genes that exhibited evolved increases in gene expression were important for normal perithecial development in Fusarium graminearum. Many of these genes were previously uncharacterized, encoding hypothetical proteins without any known functional protein domains. Interestingly, the developmental stages during which aberrant knockout phenotypes appeared largely coincided with the elevated expression of the deleted genes. In addition, we identified novel genes that affected normal perithecial development in Magnaporthe oryzae and Neurospora crassa, which were functionally and transcriptionally diverged from the orthologous counterparts in F. graminearum. Furthermore, comparative analysis of developmental transcriptomes and phylostratigraphic analysis suggested that genes encoding hypothetical proteins are generally young and transcriptionally divergent between related species. This study provides tangible evidence of shifts in gene expression that led to acquisition of novel function of orthologous genes in each lineage and demonstrates that several genes with hypothetical function are crucial for shaping multicellular fruiting bodies. IMPORTANCE The fungal class Sordariomycetes includes numerous important plant and animal pathogens. It also provides model systems for studying fungal fruiting body development, as its members develop fruiting bodies with a few well-characterized tissue types on common growth media and have rich genomic resources that enable comparative and functional analyses. To understand transcriptional divergence of key developmental genes between five related sordariomycete fungi, we performed targeted knockouts of genes inferred to have evolved significant upward shifts in expression. We found that many previously uncharacterized genes play indispensable roles at different stages of fruiting body development, which have undergone transcriptional activation in specific lineages. These novel genes are predicted to be phylogenetically young and tend to be involved in lineage- or species-specific function. Transcriptional activation of genes with unknown function seems to be more frequent than ever thought, which may be crucial for rapid adaption to changing environments for successful sexual reproduction.

Speed dating for enzymes! Finding the perfect phosphopantetheinyl transferase partner for your polyketide synthase

The biosynthetic pathways for the fungal polyketides bikaverin and bostrycoidin, from Fusarium verticillioides and Fusarium solani respectively, were reconstructed and heterologously expressed in S. cerevisiae alongside seven different phosphopantetheinyl transferases (PPTases) from a variety of origins spanning bacterial, yeast and fungal origins. In order to gauge the efficiency of the interaction between the ACP-domains of the polyketide synthases (PKS) and PPTases, each were co-expressed individually and the resulting production of target polyketides were determined after 48 h of growth. In co-expression with both biosynthetic pathways, the PPTase from Fusarium verticillioides (FvPPT1) proved most efficient at producing both bikaverin and bostrycoidin, at 1.4 mg/L and 5.9 mg/L respectively. Furthermore, the remaining PPTases showed the ability to interact with both PKS's, except for a single PKS-PPTase combination. The results indicate that it is possible to boost the production of a target polyketide, simply by utilizing a more optimal PPTase partner, instead of the commonly used PPTases; NpgA, Gsp and Sfp, from Aspergillus nidulans, Brevibacillus brevis and Bacillus subtilis respectively.

Targeted Genetic Engineering via Agrobacterium-Mediated Transformation in Fusarium solani

Members of the Fusarium solani species complex are filamentous fungi that can act as pathogens to many crops and animals. Although relevant, a robust molecular toolbox is missing for the investigation of gene function and metabolism. In this chapter, we describe how Agrobacterium-mediated transformation can be used to facilitate gene targeting. A flexible vector system, based on in vivo recombination in Saccharomyces cerevisiae, is utilized to achieve overexpression and gene deletion of targeted biosynthetic genes in F. solani f. sp. pisi.

Production and Selectivity of Key Fusarubins from Fusarium solani due to Media Composition

Natural products display a large structural variation and different uses within a broad spectrum of industries. In this study, we investigate the influence of carbohydrates and nitrogen sources on the production and selectivity of production of four different polyketides produced by Fusarium solani, fusarubin, javanicin, bostrycoidin and anhydrofusarubin. We introduce four different carbohydrates and two types of nitrogen sources. Hereafter, a full factorial design was applied using combinations of three levels of sucrose and three levels of the two types of nitrogen. Each combination displayed different selectivity and production yields for all the compounds of interest. Response surface design was utilized to investigate possible maximum yields for the surrounding combinations of media. It was also shown that the maximum yields were not always the ones illustrating high selectivity, which is an important factor for making purification steps easier. We visualized the production over time for one of the media types, illustrating high yields and selectivity.

The effects of different potato dextrose agar media on secondary metabolite production in Fusarium

Potatoes contain several nutrients essential for fungal growth, making them an excellent component of media such as the popular Potato Dextrose Agar (PDA) medium. Commercially, PDA is available from multiple retailers offering virtually the same product. These media, however, could contain small differences in composition of nutrients affecting the expression of secondary metabolites. This study aims to investigate the use of four PDA media from different manufacturers (Fluka, Oxoid, Sigma, and VWR) and their effect on the metabolite profile of four species of Fusarium (F. fujikuroi, F. graminearum, F. pseudograminearum and F. avenaceum). Secondary metabolites were analysed using HPLC-HRMS, from which statistically significant differences in intensities were observed for 9 out of 10 metabolites.

Heterologous Expression of the Core Genes in the Complex Fusarubin Gene Cluster of Fusarium Solani

Through stepwise recreation of the biosynthetic gene cluster containing PKS3 from Fusarium solani, it was possible to produce the core scaffold compound of bostrycoidin, a red aza-anthraquinone pigment in Saccharomyces cerevisiae. This was achieved through sequential transformation associated recombination (TAR) cloning of FvPPT, fsr1, fsr2, and fsr3 into the pESC-vector system, utilizing the inducible bidirectional galactose promoter for heterologous expression in S. cerevisiae. The production of the core metabolite bostrycoidin was investigated through triplicate growth cultures for 1-4 days, where the maximum titer of bostrycoidin was achieved after 2 days of induction, yielding 2.2 mg/L.