Using the fungus Metarhizium anisopliae as a model system to study the role of gene duplication, divergence and expression in adapting to pathogenicity.

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2005-04-20

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Fungal pathogens have been recorded for virtually all groups of multicellular organisms. They are the major cause of disease in insects in nature, sometimes causing devastating epizootics. Entomopathogenic fungi are applied in the field as biological control agents world-wide. However, there remain many gaps in our knowledge concerning pathogenicity of fungi towards insects (St. Leger and Screen 2001).

This study focuses on the entomopathogenic fungus Metarhizium anisopliae. In particular, it focuses on the evolutionary significance and biocontrol potential of gene duplication and loss events among its plethora of serine proteases. The serine proteases produced by M. anisopliae and other pathogenic fungi currently provide the best-understood model of fungal determinants of pathogenicity (St. Leger and Screen 2001). The importance of subtilase Pr1A during the progress of infection by M. anisopliae was first identified through its high concentration at the site of penetration, and its considerable ability to degrade the cuticular integument (St. Leger et al 1987, 1989). Here a phylogenomic approach is adopted with fungi of very different virulence and habitat to survey and characterize their serine proteinases with the goal of providing a framework of information on these important enzymes, as well as improving understanding of general processes in fungal gene family evolution.

Serine proteases became candidate for gene manipulation due to their critical role in the infection process. A strain of M. anisopliae was genetically modified so it overexpressed Pr1A and kills insects faster than the wild type does in laboratory tests (St. Leger et al. 1996). This technology has potential for pest control (St. Leger 2001), but there is an uncertainty about the efficacy, survivability, and environmental risk posed by any introduced or engineered fungus because of our lack of knowledge about the fate of fungal genotypes at the population and ecosystem levels (Bidochka 2001, Hajek et al. 1997). So a planned release (approved by EPA) was conducted in a field of cabbage plants. The release established the technology required to monitor the fate of genetically enhanced M. anisopliae. This technology was used to determine the potential of engineered strains to establish and disperse over 1-year test period.

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