siRNA mediated gene silencing in Fusarium sp. HKF15 for overproduction of bikaverin

Annotating Multiple Prebiotic Synthesizing Capabilities Through Whole Genome Sequencing of Fusarium Strain HFK-74

In the present study, seven fungal isolates from effluent treatment plants were screened for the production of prebiotic fructooligosaccharide synthesizing enzymes with the highest activity of fructofuranosidase (17.52 U/mL) and fructosyl transferase (18.92 U/mL) in strain HKF-74. Mining of genome sequence of strain revealed the annotation of genes providing multiple carbohydrate metabolizing capacities, such as amylases (AMY1), beta-galactosidase (BGAL), beta-xylosidase (Xyl), β-fructofuranosidase (ScrB), fructosyltransferase (FTF), and maltose hydrolases (malH). The annotated genes were further supported by β-galactosidase (15.90 U/mL), xylanase (17.91 U/mL), and α-amylase (14.05 U/mL) activities for synthesis of galactooligosaccharides, xylooligosaccarides, and maltooligosaccharides, respectively. In addition to genes encoding prebiotic synthesizing enzymes, four biosynthetic gene clusters (BGCs) including Type I polyketide synthase (PKS), non-ribosomal peptide synthetase (NRPS), NRPS-like, and terpene were also predicted in strain HKF-74. This was significant considering their potential role in pharmaceutical and therapeutic applications as well as in virulence. Accurate taxonomic assignment of strain HKF-74 by in silico genomic comparison indicated its closest identity to type strains Fusarium verticillioides NRRL 20984, and 7600. The average nucleotide identity (ANI) of strain HKF-74 with these strains was 92.5% which was close to the species threshold cut-off value (95-96%) while the DNA-DNA hybridization (DDH) value was 83-84% which was greater than both, species delineating (79-80%), and also sub-species delineating (70%) boundaries. Our findings provide a foundation for further research into the use of Fusarium strains and their prebiotic synthesizing enzymes for the development of novel prebiotic supplements.

Strategies for the Development of Industrial Fungal Producing Strains

The use of microorganisms in industry has enabled the (over)production of various compounds (e.g., primary and secondary metabolites, proteins and enzymes) that are relevant for the production of antibiotics, food, beverages, cosmetics, chemicals and biofuels, among others. Industrial strains are commonly obtained by conventional (non-GMO) strain improvement strategies and random screening and selection. However, recombinant DNA technology has made it possible to improve microbial strains by adding, deleting or modifying specific genes. Techniques such as genetic engineering and genome editing are contributing to the development of industrial production strains. Nevertheless, there is still significant room for further strain improvement. In this review, we will focus on classical and recent methods, tools and technologies used for the development of fungal production strains with the potential to be applied at an industrial scale. Additionally, the use of functional genomics, transcriptomics, proteomics and metabolomics together with the implementation of genetic manipulation techniques and expression tools will be discussed.

FvatfA regulates growth, stress tolerance as well as mycotoxin and pigment productions in Fusarium verticillioides

FvatfA from the maize pathogen Fusarium verticillioides putatively encodes the Aspergillus nidulans AtfA and Schizasaccharomyces pombe Atf1 orthologous bZIP-type transcription factor, FvAtfA. In this study, a ΔFvatfA deletion mutant was constructed and then genetically complemented with the fully functional FvatfA gene. Comparing phenotypic features of the wild-type parental, the deletion mutant and the restored strains shed light on the versatile regulatory functions played by FvAtfA in (i) the maintenance of vegetative growth on Czapek-Dox and Potato Dextrose agars and invasive growth on unwounded tomato fruits, (ii) the preservation of conidiospore yield and size, (iii) the orchestration of oxidative (H₂O₂, menadione sodium bisulphite) and cell wall integrity (Congo Red) stress defences and (iv) the regulation of mycotoxin (fumonisins) and pigment (bikaverin, carotenoid) productions. Expression of selected biosynthetic genes both in the fumonisin (fum1, fum8) and the carotenoid (carRA, carB) pathways were down-regulated in the ΔFvatfA strain resulting in defected fumonisin production and considerably decreased carotenoid yields. The expression of bik1, encoding the polyketide synthase needed in bikaverin biosynthesis, was not up-regulated by the deletion of FvatfA meanwhile the ΔFvatfA strain produced approximately ten times more bikaverin than the wild-type or the genetically complemented strains. The abolishment of fumonisin production of the ΔFvatfA strain may lead to the development of new-type, biology-based mycotoxin control strategies. The novel information gained on the regulation of pigment production by this fungus can be interesting for experts working on new, Fusarium-based biomass and pigment production technologies.

Key points • FvatfA regulates vegetative and invasive growths of F. verticillioides. • FvatfA also orchestrates oxidative and cell wall integrity stress defenses. • The ΔFvatfA mutant was deficient in fumonisin production. • FvatfA deletion resulted in decreased carotenoid and increased bikaverin yields.

In Vitro and in Silico Evaluation of Bikaverin as a Potent Inhibitor of Human Protein Kinase CK2

Protein kinase CK2 is an emerging target for therapeutic intervention in human diseases, particularly in cancer. Inhibitors of this enzyme are currently in clinical trials, indicating the druggability of human CK2. By virtual screening of the ZINC database, we found that the natural compound bikaverin can fit well in the ATP binding site of the target enzyme CK2. By further in vitro evaluation using CK2 holoenzyme, bikaverin turned to be a potent inhibitor with an IC₅₀ value of 1.24 µM. In this work, the cell permeability of bikaverin was determined using a Caco-2 cell permeability assay as a prerequisite for cellular evaluation and the compound turned out to be cell permeable with a P_app- value of 4.46 × 10^-6 cm/s. Bikaverin was tested for its effect on cell viability using a MTT assay and cell proliferation using an EdU assay in different cancer cell lines (MCF7, A427 and A431 cells). Cell viability and cell proliferation were reduced dramatically after treatment with 10 µM bikaverin for 24 h. Additionally the IncuCyte^® live-cell imaging system was applied for monitoring the cytotoxicity of bikaverin in the three tested cancer cell lines. Finally, molecular dynamic studies were performed to clarify the ligand binding mode of bikaverin at the ATP binding site of CK2 and to identify the amino acids involved.

AAC as a Potential Target Gene to Control Verticillium dahliae

Verticillium dahliae invades the roots of host plants and causes vascular wilt, which seriously diminishes the yield of cotton and other important crops. The protein AAC (ADP, ATP carrier) is responsible for transferring ATP from the mitochondria into the cytoplasm. When V. dahliae protoplasts were transformed with short interfering RNAs (siRNAs) targeting the VdAAC gene, fungal growth and sporulation were significantly inhibited. To further confirm a role for VdAAC in fungal development, we generated knockout mutants (ΔVdACC). Compared with wild-type V. dahliae (Vd wt), ΔVdAAC was impaired in germination and virulence; these impairments were rescued in the complementary strains (ΔVdAAC-C). Moreover, when an RNAi construct of VdAAC under the control of the 35S promoter was used to transform Nicotiana benthamiana, the expression of VdAAC was downregulated in the transgenic seedlings, and they had elevated resistance against V. dahliae. The results of this study suggest that VdAAC contributes to fungal development, virulence and is a promising candidate gene to control V. dahliae. In addition, RNAi is a highly efficient way to silence fungal genes and provides a novel strategy to improve disease resistance in plants.

Protoplast transformation as a potential platform for exploring gene function in Verticillium dahliae

BACKGROUND

Large efforts have focused on screening for genes involved in the virulence and pathogenicity of Verticillium dahliae, a destructive fungal pathogen of numerous plant species that is difficult to control once the plant is infected. Although Agrobacterium tumefaciens-mediated transformation (ATMT) has been widely used for gene screening, a quick and easy method has been needed to facilitate transformation.

RESULTS

High-quality protoplasts, with excellent regeneration efficiency (65 %) in TB3 broth (yeast extract 30 g, casamino acids 30 g and 200g sucrose in 1L H20), were generated using driselase (Sigma D-9515) and transformed with the GFP plasmid or linear GFP cassette using PEG or electroporation. PEG-mediated transformation yielded 600 transformants per microgram DNA for the linear GFP cassette and 250 for the GFP plasmid; electroporation resulted in 29 transformants per microgram DNA for the linear GFP cassette and 24 for the GFP plasmid. To determine whether short interfering RNAs (siRNAs) can be delivered to the protoplasts and used for silencing genes, we targeted the GFP gene of Vd-GFP (V. dahliae GFP strain obtained in this study) by delivering one of four different siRNAs-19-nt duplex with 2-nt 3' overhangs (siRNA-gfp1, siRNA-gfp2, siRNA-gfp3 and siRNA-gfp4)-into the Vd-GFP protoplasts using PEG-mediated transformation. Up to 100 % silencing of GFP was obtained with siRNA-gfp4; the other siRNAs were less effective (up to 10 % silencing). Verticillium transcription activator of adhesion (Vta2) gene of V. dahliae was also silenced with four siRNAs (siRNA-vta1, siRNA-vta2, siRNA-vta3 and siRNA-vta4) independently and together using the same approach; siRNA-vta1 had the highest silencing efficiency as assessed by colony diameter and quantitative real time PCR (qRT-PCR) analysis.

CONCLUSION

Our quick, easy transformation method can be used to investigate the function of genes involved in growth, virulence and pathogenicity of V. dahliae.