Insect pathogenic fungi and the plant rhizosphere

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The commercially important ascomycetous insect pathogenic fungus, Metarhizium anisopliae has an extremely wide distribution and can be easily recovered from soils of different climates and ecological settings such as forested or agricultural habitats (Roberts & St. Leger, 2004). Recently, M. anisopliae has been shown to be plant rhizosphere competent, with evidence that it can adhere to, and colonize, plant roots strongly suggesting an alternate role in the plant rhizosphere. M. anisopliae upregulates a specific subset of genes when grown in the presence of bean root exudate. The best studies of these is Mad2, which encodes a plant adhesin. In the presence of insect cuticle it upregulates a different subset of genes, including Mad1, which encodes for an insect cuticle adhesin. This fungus appears to have, at least, a bifunctional lifestyle. The objective of this proposal is to further investigate the association of this insect pathogenic fungus with plant roots. What types of associations does it have as a rhizoplane fungus? Do different genotypes of M. anisopliae show differing abilities to form associations with different plant species? Is this a mutualistic association where the fungus provides insect nitrogen to the plant in exchange for carbon? Does M. anisopliae afford plant protection from root feeding insects? This proposal represents a shift in the wider understanding of the role these fungi play in the soil ecosystem, particularly the role they play in the plant rhizosphere. Elucidating the association of this fungus with plants could generate alternate ideas of nutrient cycling in plants, particularly nitrogen cycling. This fungal-insect-plant association could also contribute to the utility of fungi as insect pathogens particularly for insect pests that destroy plant roots. The overall objective of this proposal is to increase our understanding of the association of insect pathogenic fungi with host plants and the mechanisms of these associations. This is a particularly novel proposal since it investigates the tripartite interaction of fungus-insect-plant, which could be of significance since certain insect pathogenic fungi could have a role in plant protection.