Collaborative Research: Characterization of a Fungal Pathogenicity Island

合作研究：真菌致病岛的表征

• 批准号: 9910624
• 负责人: Hans. VanEtten
• 金额: $ 19.25万
• 依托单位: University of Arizona
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-10-01 至 2002-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9910624&HistoricalAwards=false
• 关键词: Collaborative; Research; Characterization; Fungal; Pathogenicity

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.

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，这些基因具有类似于细菌中所谓的“致病性岛屿”的特性。这一基因簇是在一株对豌豆有致病性的真菌血Nectria haematococca中鉴定出来的，由于它含有对豌豆有致病性的基因，因此被称为豌豆致病性或PEP基因簇。PEP集群位于一条1.6 Mb的“有条件可有可无”（conditional dispensable， CD）染色体上。CD染色体对于培养物的正常生长是必不可少的，但它含有独特的基因，似乎允许含有这些染色体的菌株在特定的栖息地生活；在这个例子中是豌豆组织。PEP基因簇包含6个在豌豆组织感染过程中表达的基因，但其中只有一个基因的生化功能是确定的。这个名为PDA1的基因编码了一种特殊的细胞色素P450，这种细胞色素赋予了豌豆素（一种由豌豆植物产生的抗生素）的抗性。除PDA1外，PEP中的三个基因可以独立地赋予缺乏CD染色体的分离物一定程度的毒力；这三个基因中的两个的功能是基于预测的氨基酸序列假设的。PEP簇的另一个转录部分的氨基酸序列，以及在这个25kb区域的三个明显未转录的开放阅读框，与已知的真菌转座酶具有高度的相似性。PEP集群和染色体DNA中6个基因的G+C含量和密码子使用的差异表明PEP集群和CD染色体可能是水平获得的。PEP簇的一些特征——致病性基因簇、转座因子的存在和外源起源的迹象——是动植物致病菌中的致病性岛所共有的。本研究的目的是：1)定位PEP基因簇的物理边界；2)评估PEP基因对血链球菌致伤能力的相对贡献；3)表征PEP同源物的分布；4)分析PEP基因的表达；5)测定PEP基因的生化功能。本研究的结果可能定义新的致病性机制，并有助于更好地了解植物病原真菌的寄主特化、进化和变异。植物的大多数疾病，包括经济上重要的农作物，都是由真菌引起的。引起植物疾病的真菌菌株通常与无害的、自由生活的真菌密切相关。这项研究已经确定了在一种植物致病性真菌中发现的一组基因，这些基因在相关但非致病性菌株中缺失或改变。这项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是如何从它们无害的近亲发展而来的。