Horizontal and Vertical Gene Transmission in Ascomycete Fungi

该项目关注子囊菌中产生遗传多样性的机制，使它们能够适应广泛的栖息地，如卫星和病原体。虽然基因复制和趋异被认为在为此目的进化一系列化学武器方面发挥着重要作用，但假设许多毒素、酶和抗生素都是细菌来源的，特别是链霉菌，并且是通过水平基因转移获得的。一个关于子囊菌昆虫病原体金龟子绿僵菌的表达序列标签项目（TEGR.umd.edu）鉴定了15个编码酶和毒素的基因，这些基因在各种链霉菌中具有对应物。 这些基因中的一些至今只在M.在真核生物中发现了绿僵菌，而在一些相关的植物和昆虫病原体中也发现了其他病原体。迄今为止，现有的序列数据来自少数物种，不足以对基因多样性的进化进行比较分析。该项目将采用PCR技术对代表性真菌谱系进行采样，以确认这些链霉菌样序列的来源并确定其接受者。系统发育模型将用于推断任何转移事件的数量和时间，它们发生的方向以及不同真菌谱系中基因丢失的程度。为了研究致病性相关基因大家族中基因重复和趋异的作用，比较了不同基因型M。绿僵菌，以阐明这些基因的关系，并确定直系同源物如何通过最近的选择不同的主机分歧将进行。通过计算突变率，将确定枯草杆菌蛋白酶组成快速复制的多基因家族的程度，以及它们是否通过强选择压力（正达尔文进化）或中性突变的随机固定而多样化。总之，这些实验将提供重要的新信息，真菌基因，有助于生态多样化，并可能导致重新解释子囊菌基因多样性的背景下，链霉菌基因多样性和基因转移。

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.