| Summary: | Effectors are small, secreted proteins produced by a pathogen that manipulate the host to aid colonisation. The effector repertoire of plant pathogens is a key determinant of the success of pathogen-host interactions and could mean the difference between a compromised or a successful crop harvest. One notorious pathogen, the fungus Fusarium graminearum is the causal agent of Fusarium head blight (FHB), one of the most destructive diseases threatening wheat production worldwide.
We have adopted in silico bioinformatic pipelines that consider a multifaceted approach to effector discovery such as transcriptional analysis (RNA-seq and microarray), proteomics, taxonomic distribution analysis and the genomic location of candidates.
By taking a two-pronged approach for the functional characterisation of candidates, I have identified a paralogous pair of effectors that are expressed during the early symptomless stage of F. graminearum infection. These effectors, FgSSP34 and FgSSP53 are adjacent to each other on the F. graminearum chromosome and divergently orientated. Both effectors, in this orientation, are highly conserved within the wider F. graminearum species complex (FGSC), closely related Fusaria sp. and homologues are present in distantly related grass infecting Ascomycetes. Of the pair, FgSSP53 induces cell death in the non-host Nicotiana benthamiana, however, the second isoform of FgSSP53 found within FGSC does not. Within the host system, viral overexpression of FgSSP53 using BSMV-VOX in wheat, reduces disease severity of FHB. Both FgSSP53 and FgSSP34 deletion mutants have reduced virulence in wheat coleoptiles and wheat spikes. Complementations of ΔFgSSP53 fungal strains with both isoforms of FgSSP53 restored virulence, indicating both are functional effectors despite inducing different responses in planta. Interestingly, the double ΔFgSSP34ΔFgSSP53 strains have reduced virulence in wheat coleoptiles but wildtype pathogenicity when infecting wheat spikes.
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