38th Annual Meeting of the Society for Invertebrate Pathology

Host pathogen interactions are an important force shaping organismal diversity, yet little is known about the evolution of genes responsible for virulence in pathogens. The tremendous amount of genetic variation, distinct disease phenotypes and host ranges of strains of the insect pathogen Metarhizium anisopliae have made it an excellent model to study the role of gene duplication/divergence in generating the functional diversification of enzymes and toxins necessary for adaptation to different hosts. To illustrate this, we present examples where strains with broad host ranges and strains with very narrow host ranges have diverged through changes in gene regulation, gene duplication/loss, and gene divergence. In addition, like many other fungal pathogens M. anisopliae is a facultative saprophyte with both soil-dwelling and insect pathogenic life-stages. As M. anisopliae traverses the cuticle and enters the hemolymph it must also adapt to several different host environments. We shall present studies employing cDNA microarray analyses that identify different subsets of genes allowing physiological adaptation to insect cuticle, insect hemolymph and bean root exudate (a model for life in the soil). Overall, most differences in gene expression involved perception mechanisms, carbon metabolism, proteolysis, cell surface properties and synthesis of toxic metabolites. These differences suggest many previously unsuspected stratagems of fungal pathogenicity that we are currently testing.