Fusarium graminearum regulates kp4l genes, encoding killer toxins, during competitive interaction with other plant...

Fusarium graminearum (Fg) is one of the most virulent causal agents of Fusarium head blight (FHB) in Central Europe. The disease is also caused by other Fusarium species within the FHB Species Complex (FHBSC). Some Fusarium species secrete killer proteins (KPs) during host plant infection. Fg produces KP4-L killer toxins (FgKP4L), of which the clustered Fgkp4l-1, -2, -3 genes and Fgkp4l-4 (encoding for the heterodimeric KP4L-4 protein) are expressed in competitive interactions against the biocontrol agent Trichoderma gamsii T6085. We investigated the involvement of the four Fgkp4l genes in the competition with other plant-pathogenic Fusarium species either lacking KP4L proteins or carrying different combinations of them. Fusarium sporotrichioides (Fs) and Fusarium langsethiae (Fl) belonging to the FHBSC, and the outgroup Fusarium verticillioides (Fv), were used for both in vitro and in vivo tests. To monitor mycotoxin production, relative expression of Tri4 gene included within the trichothecene biosynthetic pathway was also evaluated. In dual cultures, modulation of KP4L-encoding genes was tailored according to the facing species and the distance between fungi. Against Fs, the three clustered Fgkp4l genes were up-regulated but no changes on gene expression occurred with Fl. Fgkp4l-2 was up-regulated facing Fv during the two contact independent stages (Early sensing and Sensing) of the interaction. The Tri4 gene was expressed only during the in vitro interaction with Fv, but not on spikes. Fgkp4l-2 and -3 were up-regulated at 3 days post-inoculation on wheat heads inoculated with a mix of the four Fusarium species. Competition against the other Fusarium did not influence Fg growth rate on spikes.