Exploring the function of two paralogous F. graminearum effectors reveals an alternative genetic pathway required for virulence on wheat spikes.

IS-MPMI XIV Congress Abstract of Poster Presentations

The fungus Fusarium graminearum (Fg) is the causal agent of fusarium head blight, a destructive disease threatening global wheat production. We used an in silico bioinformatic discovery pipeline incorporating transcriptional analysis (RNA-seq and microarray), proteomics, taxonomic distribution and genomic location of ~ 300 candidate sequences. We identified a paralogous pair of candidate effectors FgSSP34 and FgSSP53 expressed during the early symptomless (latent) stage of wheat infection. The genes are adjacent and divergently orientated. Both effectors, and their orientation, are highly conserved within the Fg species complex and in other grass infecting fungi. Of the pair, FgSSP53 induces cell death in the non-host Nicotiana benthamiana, independent of the cell-surface co-receptors NbBAK1 and NbSOBIR1, whereas FgSSP34 fails to induce a detectable response. In wheat coleoptiles, ΔFgSSP53, ΔFgSSP34, and ΔFgSSP34ΔFgSSP53 fungal deletion strains produced smaller lesions compared to wild-type, indicating a reduction in virulence. Whereas, in wheat spikes, both the single ΔFgSSP34 and ΔFgSSP53 strains have reduced virulence, however the double ΔFgSSP34ΔFgSSP53 mutants unexpectedly restored wild-type pathogenicity. These results reveal that the simultaneous loss of two crucial effector paralogs leads to the abandonment of the preferred primary genetic pathway controlling spike infection and the adoption of an alternative genetic pathway to ensure successful colonization.