Fusarium graminearum arabinanase (Arb93B) enhances wheat head blight susceptibility by suppressing plant immunity

Fusarium head blight (FHB) of wheat and barley caused by the fungus Fusarium graminearum reduces crop yield and contaminates grain with mycotoxins. In this study, we investigated two exo-1, 5-α-L-arabinanases (Arb93A and Arb93B) secreted by F. graminearum, and their effect on wheat head blight development. Arabinan is an important component of plant cell walls, but it was not known if these arabinanases play a role in FHB. Both ARB93A and ARB93B were induced during the early stages of infection. arb93A mutants did not exhibit a detectable change in ability to cause FHB, whereas, arb93B mutants caused lower levels of FHB symptoms and deoxynivalenol contamination compared to the wild type. Furthermore, virulence and deoxynivalenol contamination were restored to wild-type levels in ARB93B complemented mutants. Fusion proteins of GFP with the predicted chloroplast peptide or the mature protein of Arb93B were not observed in the chloroplast. Reactive oxygen species production was reduced in the infiltrated zones of N. benthamiana leaves expressing ARB93B-GFP. Co-expression of ARB93B-GFP and Bax in N. benthamiana leaves significantly suppressed Bax-programmed cell death. Our results indicate that Arb93B enhances plant disease susceptibility by suppressing ROS associated plant defense responses.