fusarium graminearum 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 exo15larabinanases 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 whether 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 with the wild type furthermore virulence and deoxynivalenol contamination were restored to wildtype levels in arb93b complemented mutants fusion proteins of green fluorescent protein gfp with the predicted chloroplast peptide or the mature protein of arb93b were not observed in the chloroplast reactive oxygen species ros production was reduced in the infiltrated zones of nicotiana benthamiana leaves expressing arb93bgfp coexpression of arb93bgfp and bax in n benthamiana leaves significantly suppressed baxprogrammed cell death our results indicate that arb93b enhances plant disease susceptibility by suppressing rosassociated plant defense responses