Murillo J, Shen H, Gerhold D, Sharma A, Cooksey D A, Keen N T
Department of Plant Pathology, University of California, Riverside 92521.
Plasmid. 1994 May;31(3):275-87. doi: 10.1006/plas.1994.1029.
Avirulence gene D (avrD) in strain PT23 of Pseudomonas syringae pv. tomato (Pst) specifies the production of syringolides, which are elicitors of plant defense reactions. An 83-kb indigenous plasmid (pPT23B) that carries avrD has been mapped and characterized and a putative par region was identified. pPT23B contains a large amount of DNA that is repeated in other native plasmids in PT23. A putative mobile insertion element that occurs on plasmid pPT23A as well as on the chromosome was also identified in strain PT23. New broad-host-range expression vectors that functioned in Pst were constructed for overexpression of the cloned avrD gene and high-level production of the syringolides. Introduction of an avrD overexpression plasmid into PT23 or plasmid-cured strains led to identical syringolide peaks on HPLC with no new peaks observed. These results suggested that neither pPT23B nor other indigenous plasmids in Pst carry additional genes required for syringolide production or metabolism. Pst strains lacking pPT23B were not impaired in virulence on tomato plants.
丁香假单胞菌番茄致病变种（Pst）PT23菌株中的无毒基因D（avrD）决定丁香酚类化合物的产生，而丁香酚类化合物是植物防御反应的激发子。携带avrD的一个83kb的内源质粒（pPT23B）已被定位和表征，并且鉴定出一个假定的par区域。pPT23B含有大量在PT23的其他天然质粒中重复的DNA。在PT23菌株中还鉴定出一个假定的移动插入元件，它存在于质粒pPT23A以及染色体上。构建了在Pst中起作用的新型广宿主范围表达载体，用于克隆的avrD基因的过表达和丁香酚类化合物的高水平产生。将avrD过表达质粒导入PT23或质粒消除菌株后，在高效液相色谱（HPLC）上产生相同的丁香酚类化合物峰，未观察到新峰。这些结果表明，Pst中的pPT23B和其他内源质粒均不携带丁香酚类化合物产生或代谢所需的其他基因。缺乏pPT23B的Pst菌株对番茄植株的毒力没有受损。
