VanEtten H, Funnell-Baerg D, Wasmann C, McCluskey K
Department of Plant Pathology, University of Arizona, Tucson 85721.
Antonie Van Leeuwenhoek. 1994;65(3):263-7. doi: 10.1007/BF00871955.
Nectria haematococca MPVI can be found in many different biological habitats but has been most studied as a pathogen of pea (Pisum sativum). Genetic analyses of isolates obtained from a variety of biological sources has indicated that a number of genes control pathogenicity on pea but that one important PEa Pathogenicity (PEP) gene is PDA, which confers the ability to detoxify the pea phytoalexin pisatin. In these studies, all naturally occurring isolates that lacked PDA (i.e. Pda- isolates) and all Pda- progeny were essentially non-pathogenic on pea. However, we have demonstrated recently that Pda- mutants created by transformation-mediated gene disruptions, while having a modest reduction in virulence, and more virulent than any naturally occurring Pda- isolates. In addition we know that PDA genes are on dispensable (DS) chromosomes in this fungus. We believed that the gene disruption mutants have allowed the detection of other PEP genes that are present on the DS chromosomes along with PDA and that naturally occurring Pda- isolates usually lack this DS chromosome. This would explain why naturally occurring Pda- isolates are always low in virulence. We propose that the DS chromosomes in fungi are analogous to bacterial plasmids which allow those microorganisms to colonise different habitats, i.e. the DS chromosomes of Nectria haematococca contain genes that allow individual isolates of this broad host range pathogen to occupy different biological niches.
血座壳菌MPVI可在许多不同的生物栖息地中发现，但作为豌豆（Pisum sativum）的病原体受到的研究最多。对从多种生物来源获得的分离株进行的遗传分析表明，多个基因控制对豌豆的致病性，但一个重要的豌豆致病性（PEP）基因是PDA，它赋予了对豌豆植保素豌豆素解毒的能力。在这些研究中，所有天然存在的缺乏PDA的分离株（即Pda-分离株）和所有Pda-后代在豌豆上基本无致病性。然而，我们最近证明，通过转化介导的基因破坏产生的Pda-突变体，虽然毒力略有降低，但比任何天然存在的Pda-分离株更具毒力。此外，我们知道PDA基因位于这种真菌的可 dispensable（DS）染色体上。我们认为，基因破坏突变体使得能够检测到与PDA一起存在于DS染色体上的其他PEP基因，并且天然存在的Pda-分离株通常缺乏这条DS染色体。这可以解释为什么天然存在的Pda-分离株毒力总是很低。我们提出，真菌中的DS染色体类似于细菌质粒，使这些微生物能够定殖于不同的栖息地，即血座壳菌的DS染色体包含一些基因，使这种广寄主范围病原体的单个分离株能够占据不同的生态位。
