Horizontal and Vertical Gene Transmission in Ascomycete Fungi

该项目涉及产生子囊菌真菌遗传多样性的机制，使它们能够适应腐生植物和病原体等广泛的栖息地。虽然基因复制和分化被认为在为此目的进化一系列化学武器方面发挥了重要作用，但假设许多毒素、酶和抗生素来自细菌，特别是链霉菌，并通过水平基因转移获得。一个子囊菌昆虫病原菌绿僵菌的表达序列标签项目(http://TEGR.umd.edu))确定了15个编码酶和毒素的基因，这些基因在各种链霉菌中都有对应的基因。其中一些基因到目前为止只在真核生物中的金龟子绿僵菌中发现，而另一些基因也在一些相关的植物和昆虫病原体中发现。到目前为止，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。该项目将使用聚合酶链式反应技术对具有代表性的真菌谱系进行采样，以确认这些链霉菌样序列的来源和识别接受者。系统发育模型将被用来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的基因丢失的程度。为了研究基因复制和差异在致病相关基因大家族中的作用，将对不同类型的金龟子绿僵菌进行类枯草杆菌蛋白水解酶序列的比较，以阐明这些基因之间的关系，并确定通过最近在不同宿主上的选择，同源基因是如何差异的。通过计算突变率，将确定枯草杆菌毒素组成快速复制的多基因家族的程度，以及它们是通过强大的选择压力(积极的达尔文进化)还是随机固定的中性突变而多样化。总之，这些实验将提供有助于生态多样性的真菌基因的重要新信息，并可能导致在链霉菌基因多样性和基因转移的背景下重新解释子囊菌基因多样性。

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.