Characterization of the molecular pathways that direct development and pathogenicity in the vascular wilt fungus Verticillium dahliae

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Verticillium dahliae is a filamentous fungus that causes vascular wilt of a broad range of economically important annual and perennial crops. During infection the fungus is confined to the plant's water-conducting (vascular) system, growing dimorphically (in two forms), as hyphal and yeast-like cells. In the late stages of disease V. dahliae escapes from the vascular system into the surrounding tissues where it produces its survival structures. These hardy, pigmented clusters of cells are dispersed into the soil with plant debris, can survive for at least a decade in the soil, and are the primary source of disease inoculum. The molecular pathways involved in development of these structures, and in planta dimorphic growth offer attractive potential targets for disease control. In previous studies in my lab we showed that both a hydrophobic protein (hydrophobin VDH1) and the process of autophagy (the cells' intracellular recycling system) are essential for survival structure development. The other important discovery was that VDH1 is recognized by the plant during the early phase of infection to induce plant defence responses, but that the plant is unable to sustain those defences. Molecular strategies will be used to address two major objectives in of the proposed research. The first will be to better define the survival structure developmental pathway, and to identify steps in the pathway that could potentially be blocked to prevent survival structure formation and/or pathogen colonization of the plant. The second objective will be to determine the roles of as-yet uncharacterized V. dahliae hydrophobins during survival structure development and in plant recognition to induce plant defences. Studies will be initiated to determine what molecular mechanism(s) the pathogen uses to thwart the plant defence responses that are triggered by recognition of the pathogen. The results of the proposed research would provide knowledge for future development of new, and badly needed disease control strategies to manage verticillium wilt. The resulting data are also anticipated to be relevant to studies of other pathogenic fungi for which the plant vascular system is the preferred environmental niche.