Dimorphic growth and resting structure development in plant pathogenic verticillium species

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Verticillium dahliae, V. albo-atrum, and V. longisporum are soilborne fungi that cause vascular wilt disease in a variety of annual crops and perennials that are grown commercially in Canada and worldwide, including tomato, potato, oilseed rape, and other brassica crops.  The soil habitat of these pathogens, their inaccessibility during infection, and their ability to survive for many years in the soil, pose formidable challenges to disease control.  Few verticillium wilt-resistant cultivars are available, and chemical fumigants, which reduce levels of V. dahliae in the soil, are environmentally harmful, and destroy beneficial soil microorganisms.  Given the present and potential economic impact of the pathogen, new approaches to disease control must be considered.    One approach with much potential for disease control is to specifically target, and interfere with, the molecular processes which are critical for the growth of Verticillum in the plant, and/or its survival in the soil.  The proposed research program will focus on molecular and genetic studies of: 1) the development of the long-lived resting structures, microsclerotia or melanized mycelia, which are produced in dying plant tissues, and provide the primary source of disease inoculum, and 2) dimorphic growth (production of both yeast-like spores and mycelia), which occurs in liquid culture, and in the plant vascular system during infection.  Previous studies have shown that V. dahliae carries a gene that encodes a hydrophobin protein which is required for microsclerotia production.  The same gene has been identified in V. albo-atrum, which does not produce microsclerotia; the role of this gene in V. albo-atrum is therefore unknown.  A comparison of expression in V. albo-atrum and V. dahliae of these genes, and their respective proteins, will be carried out using reporter genes, mutational, and biochemical analysis.  In addition, DNA microarray analyses will be used to identify additional genes that are highly expressed during resting structure development and/or dimorphic growth.  Such genes will be candidates for further characterization.