Horizontal and Vertical Gene Transmission in Ascomycete Fungi

University Of Maryland, College Park, College Park MD

Investigators

Abstract

This project is concerned with the mechanisms generating genetic diversity among ascomycete fungi enabling them to adapt to a broad array of habitats as saprophytes and pathogens. While gene duplication and divergence are presumed to play an important role in evolving an array of chemical weaponry for this purpose, the hypothesis is that many toxins, enzymes and antibiotics are of bacterial, specifically streptomycete origin, and have been acquired by horizontal gene transfer. An expressed sequence tag project (http://TEGR.umd.edu) on the ascomycete insect pathogen Metarhizium anisopliae identified 15 genes encoding enzymes and toxins that have counterparts in various streptomycetes. Some of these genes have so far been found only in M. anisopliae among eukaryotes, while others have also been found in some related plant and insect pathogens. To date, available sequence data derives from a small number of species, insufficient to conduct a comparative analysis on the evolution of gene diversity. This project will employ PCR techniques to sample representative fungal lineages to confirm the origin and identify recipients of these streptomycete-like sequences. Phylogenetic modeling will be used to deduce the number and timing of any transfer events, the direction in which they occurred and the extent to which genes have been lost from different fungal lineages. To investigate the role of gene duplication and divergence in a large family of pathogenicity-related genes, a comparison of subtilisin-like protease sequences among genotypic classes of M. anisopliae to elucidate the relationships of these genes and determine how orthologs have diverged through recent selection on different hosts will be conducted. By calculating rates of mutations the extent to which the subtilisins comprise a rapidly duplicating multigene family and whether they are diversifying by strong selective pressure (positive Darwinian evolution) or random fixation of neutral mutations will be determined. Together, these experiments will provide important new information on fungal genes that contribute to ecological diversification and could lead to reinterpretation of ascomycete gene diversity in the context of streptomycete gene diversity and gene transfer.