Collaborative Research: Characterization of a Fungal Pathogenicity Island

植物病理学中的一个主要问题是什么使病原体成为病原体。这项研究将描述一组真菌基因的特征，这些基因的特性类似于细菌中所谓的“致病岛”。 该簇在真菌赤壳菌（Nectria haematococca）的菌株中被鉴定，该菌株对豌豆具有致病性，并且被称为豌豆致病性或PEP基因簇，因为它含有对豌豆具有致病性的基因。 PEP簇位于1.6 Mb“条件性染色体”（CD）上。 CD染色体在培养基中正常生长，但含有独特的基因，似乎允许含有染色体的菌株生活在特定的栖息地，在这种情况下豌豆组织。PEP基因簇包含在豌豆组织感染期间表达的六个基因，但是仅确定地知道其中一个基因的生化功能。 这个基因，PDA 1，编码一种特殊的细胞色素P450，赋予抗pisatin，豌豆植物产生的抗生素。三个PEP基因，除了PDA 1，可以独立地赋予一定程度的毒力缺乏CD染色体的分离株，这三个基因中的两个的功能是假设的基础上预测的氨基酸序列。PEP簇的另一个转录部分的推导的氨基酸序列，以及在该25 kb区域中的三个明显非转录的开放阅读框，与已知的真菌转座酶具有高度的相似性。 PEP簇中6个基因的G+C含量和密码子使用与染色体DNA之间的差异表明PEP簇和可能的CD染色体可能是水平获得的。 PEP簇的几个特征-致病基因簇、转座因子的存在和外源来源的指示-在动物和植物病原菌中的致病岛共享。 本研究的目的是：1）定位PEP基因簇的物理边界，2）评价单个PEP基因对N.红球菌属，3）PEP同源物分布的表征，4）PEP基因表达的分析和5）它们的生化功能的测定。 这些研究结果将有助于阐明植物病原真菌致病的新机制，并有助于更好地理解植物病原真菌的寄主专化、进化和变异。导致植物病害的真菌菌株通常与无害的自由生活的真菌非常密切相关。 这项研究已经确定了在植物病原真菌中发现的一组基因，这些基因在相关但非病原性菌株中缺失或改变。 对这些基因的功能及其遗传的研究可以更好地了解致病微生物如何从其无害的近亲发展而来。

AbstractVanEttenMCB-9910624 A primary question in plant pathology has been what makes a pathogen a pathogen. This research will characterize a cluster of fungal genes with properties similar to what have been called "pathogenicity islands" in bacteria. This cluster was identified in a strain of the fungus Nectria haematococca which is pathogenic on pea and is called the Pea Pathogenicity or PEP gene cluster because it contains genes for pathogenicity on pea. The PEP cluster is located on a 1.6 Mb "conditionally dispensable" (CD) chromosome. CD chromosomes are dispensable for normal growth in culture but contain unique genes that appear to allow strains containing the chromosomes to live in specific habitats; in this case pea tissue. The PEP gene cluster contains six genes that are expressed during infection of pea tissue but the biochemical function of only one of the genes is known with certainty. This gene, PDA1, encodes a specific cytochrome P450 that confers resistance to pisatin, an antibiotic produced by pea plants. Three of the PEP genes, in addition to PDA1, can independently confer some level of virulence to an isolate lacking the CD chromosome; functions for two of these three genes are hypothesized based on predicted amino acid sequences. The deduced amino acid sequence of another transcribed portion of the PEP cluster, as well as three apparently non-transcribed open reading frames in this 25 kb region, have a high degree of similarity to known fungal transposases. Differences between the G+C content and codon usage of the six genes in the PEP cluster and chromosomal DNA suggest that the PEP cluster and possibly the CD chromosome might have been acquired horizontally. Several of the features of the PEP cluster - a cluster of pathogenicity genes, the presence of transposable elements and the indication of an exogenous origin - are shared by pathogenicity islands in animal and plant pathogenic bacteria. The objectives of this research are 1) localization of the physical borders of the PEP gene cluster, 2) evaluation of the relative contributions of the individual PEP genes to the lesion-causing ability of N. haematococca, 3) characterization of the distribution of PEP homologues, 4) analysis of the expression of PEP genes and 5) determination of their biochemical function(s). The results of the proposed research may define new mechanisms of pathogenicity as well as contribute to a better understanding of host specialization, evolution and variation in plant pathogenic fungi.Most diseases of plants, including economically important crop plants, are caused by fungi. The strains of fungi that cause plant disease are often very closely related to harmless, free-living fungi. This research has identified a cluster of genes found in a plant pathogenic fungus that is missing or altered in related but nonpathogenic strains. This research into the function of these genes and their inheritance can lead to a greater understanding of how pathogenic microbes develop from their harmless nearest relatives.