Oral: Plant Resistance
Antifungal mechanisms of a plant defensin MtDef4 are not conserved between ascomycete fungi, Neurospora crassa and Fusarium graminearum
K. ISLAM (1), K. El-Mounadi (2), D. Shah (3) (1) Donald Danforth Center, U.S.A.; (2) Kutztown University of Pennsylvania, U.S.A.; (3) Donald Danforth Center, Bangladesh
Small cysteine-rich defensins are ubiquitous antifungal plant peptides which contribute to the innate immunity of plants. The plant defensin, MtDef4, inhibits the growth of the ascomycete fungi, Neurospora crassa and Fusarium graminearum, at micromolar concentrations. Previous studies have suggested that MtDef4 is transported into the cytoplasm of these fungi and exerts its antifungal activity on various intracellular targets. Here, we have investigated whether the antifungal mechanisms of MtDef4 are conserved in these fungi. We show that N. crassa and F. graminearum respond very differently to MtDef4 challenge. Membrane permeabilization is required for the antifungal activity of MtDef4 against F. graminearum but not against N. crassa. We find that MtDef4 is targeted to different subcellular compartments in each fungus. Internalization of MtDef4 in N. crassa is energy-dependent and involves endocytosis. By contrast, MtDef4 appears to translocate into F. graminearum autonomously using partially energy-dependent pathway. MtDef4 has been previously shown to bind to the phospholipid phosphatidic acid (PA). We provide evidence that the plasma membrane localized phospholipase D (PLD1), involved in the biosynthesis of PA, is needed for entry of this defensin in N. crassa, but not in F. graminearum. To our knowledge, this is the first example of a plant defensin which inhibits the growth of two ascomycete fungi via different mechanisms.