Fosp9, a Novel Secreted Protein, Is Essential for the Full Virulence of Fusarium oxysporum f. sp. cubense on Banana (Musa spp.).

The banana vascular wilt pathogen, Fusarium oxysporum f. sp. cubense, delivers a number of different secreted proteins into host plant tissues during infection. Until now, only a few of the secreted proteins from this fungus have been shown to be virulence effectors. Here, the product of fosp9, which is a gene in this pathogen, was found to be a novel virulence effector. The fosp9 gene encodes a hypothetical 185-amino-acid protein which has a functional signal peptide but contains no known motifs or domains. The fosp9 disruptants displayed a significant reduction in producing wilt symptoms on bananas, indicating that fosp9 is essential for the full virulence of this pathogen for banana. These disruptants did not exhibit a change in either saprophytic growth or conidiation on potato dextrose agar medium, but their invasive growth in the rhizomes of banana was markedly compromised, suggesting a pivotal role for fosp9 in the colonization of banana rhizome tissues by this fungus. Live-cell imaging revealed that the Fosp9-GFP fusion protein accumulated in the apoplast of the plant cells. Moreover, transcriptome profiling revealed that a number of virulence-associated genes were differentially expressed in the fosp9 disruptant relative to the wild type. Taken together, these findings suggest that Fosp9 is a genuine effector of F. oxysporum f. sp. cubense. IMPORTANCE Fusarium wilt of bananas (also known as Panama disease), caused by the fungus F. oxysporum f. sp. cubense, is one of the most devastating banana diseases worldwide. The understanding of the molecular mechanism of its pathogenicity is very limited so far. We demonstrated that the secreted protein Fosp9 from this fungus contributes to its virulence against banana hosts and is essential for colonization of banana rhizome tissues by this fungus. In particular, Fosp9 contains no known domains or motifs and has no functionally characterized homologs, implying that it is a novel secreted effector involved in F. oxysporum f. sp. cubense-banana interactions. This work provides insight into molecular mechanisms of F. oxysporum f. sp. cubense pathogenicity, and the characterization of the fosp9 gene will facilitate development of transgenic banana and plantain strains resistant to this disease by silencing this effector gene through host-induced gene silencing or other strategies.

Genome and transcriptome analysis of the fungal pathogen Fusarium oxysporum f. sp. cubense causing banana vascular wilt disease.

BACKGROUND: The asexual fungus Fusarium oxysporum f. sp. cubense (Foc) causing vascular wilt disease is one of the most devastating pathogens of banana (Musa spp.). To understand the molecular underpinning of pathogenicity in Foc, the genomes and transcriptomes of two Foc isolates were sequenced. METHODOLOGY/PRINCIPAL FINDINGS: Genome analysis revealed that the genome structures of race 1 and race 4 isolates were highly syntenic with those of F. oxysporum f. sp. lycopersici strain Fol4287. A large number of putative virulence associated genes were identified in both Foc genomes, including genes putatively involved in root attachment, cell degradation, detoxification of toxin, transport, secondary metabolites biosynthesis and signal transductions. Importantly, relative to the Foc race 1 isolate (Foc1), the Foc race 4 isolate (Foc4) has evolved with some expanded gene families of transporters and transcription factors for transport of toxins and nutrients that may facilitate its ability to adapt to host environments and contribute to pathogenicity to banana. Transcriptome analysis disclosed a significant difference in transcriptional responses between Foc1 and Foc4 at 48 h post inoculation to the banana 'Brazil' in comparison with the vegetative growth stage. Of particular note, more virulence-associated genes were up regulated in Foc4 than in Foc1. Several signaling pathways like the mitogen-activated protein kinase Fmk1 mediated invasion growth pathway, the FGA1-mediated G protein signaling pathway and a pathogenicity associated two-component system were activated in Foc4 rather than in Foc1. Together, these differences in gene content and transcription response between Foc1 and Foc4 might account for variation in their virulence during infection of the banana variety 'Brazil'. CONCLUSIONS/SIGNIFICANCE: Foc genome sequences will facilitate us to identify pathogenicity mechanism involved in the banana vascular wilt disease development. These will thus advance us develop effective methods for managing the banana vascular wilt disease, including improvement of disease resistance in banana.

[Biological characteristics of an Hog1 MAPK homologous gene FoHog1 knock-out mutant of Fusarium oxysporum f. sp. cubense].

OBJECTIVE: This study was aimed to obtain a mitogen-activated protein kinase (MAPK) gene namely FoHog1 from Fusarium oxysporum f. sp. cubense and to verify its function. METHODS: We amplified FoHog1 gene by PCR and RT-PCR methods and analyzed it through bioinformatics method. PEG-mediated protoplast transformation was used to create the deletion mutants of FoHog1 gene. We analyzed different biological characteristics between knock-out strain and wild-type strain. RESULTS: FoHog1 gene encoding a putative protein of 357 amino acids and its genetic relationship with different Fusarium' s protein. Compared with the wild-type strain, FoHog1 deletion mutants have loose hyphae colony, less spores production, lower dry weight of hyphae and more sensitive to temperature, pH and osmotic stress. FoHog1 deletion mutants also have reduced colonization ability compared with the wild-type strain. CONCLUSION: FoHog1 gene participated in mycelial growth, sporulation, catabolism of sodium acetate and ammonium chloride, osmotic stress response and pathogenic process with Fusarium oxysporum f. sp. cubense Race 4.