Lorang J M, Keen N T
Department of Plant Pathology, University of California, Riverside 92521.
Mol Plant Microbe Interact. 1995 Jan-Feb;8(1):49-57. doi: 10.1094/mpmi-8-0049.
Cosmid clone pPT10E9 from Pseudomonas syringae pv. tomato caused P. s pv. glycinea to elicit the HR on leaves of all tested soybean cultivars. The avirulence function of pPT10E9, called avrE, occurred on an 11.3-kb DNA fragment located immediately adjacent to the P. s. pv. tomato hrp gene cluster. Tn3-gus saturation mutagenesis of the avrE locus and adjacent DNA revealed at least four transcriptional units occurring immediately adjacent to the hrpRS locus that were all regulated in a manner similar to hrp genes (induced only in minimal induction media or in planta and required the hrpL and hrpRS loci for expression). Transcriptional units III and IV, but not II or V, were required for avrE function. P. s. pv. tomato DC3000 carrying mutations in each of the four transcripts retained full virulence on tomato leaves and elicited the HR on tobacco and soybean plants. This was unlike strain PT23, where mutation of avrE greatly decreased virulence on tomato leaves. The promoter regions for three of the investigated transcriptional units contained a consensus sequence occurring in the promoter regions of several other P. syringae avirulence and hrp genes. The promoter region of transcriptional unit IV, required for avrE function, did not contain such a sequence, but included an element which may function as a sigma-54 promoter. Introduction of the cloned P. s. pv. tomato avrE locus into five other P. syringae pathovars did not cause them to elicit the HR on their normal host plants.
来自丁香假单胞菌番茄致病变种的黏粒克隆pPT10E9能使大豆致病变种在所有测试的大豆品种叶片上引发过敏反应。pPT10E9的无毒功能基因avrE位于一个11.3 kb的DNA片段上，该片段紧邻丁香假单胞菌番茄致病变种的hrp基因簇。对avrE基因座及相邻DNA进行Tn3 - gus饱和诱变，结果显示至少有四个转录单元紧邻hrpRS基因座，它们的调控方式与hrp基因相似（仅在最低诱导培养基或植物体内诱导表达，且表达需要hrpL和hrpRS基因座）。转录单元III和IV对avrE功能是必需的，而II和V则不是。携带这四个转录本中每个转录本突变的丁香假单胞菌番茄致病变种DC3000在番茄叶片上仍保持完全毒性，并能在烟草和大豆植株上引发过敏反应。这与PT23菌株不同，在PT23中avrE突变会大大降低其在番茄叶片上的毒性。所研究的三个转录单元的启动子区域含有一个在其他几种丁香假单胞菌无毒和hrp基因启动子区域中出现的共有序列。avrE功能所需的转录单元IV的启动子区域不包含这样的序列，但包含一个可能作为σ-54启动子发挥作用的元件。将克隆的丁香假单胞菌番茄致病变种avrE基因座导入其他五个丁香假单胞菌致病型中，并未使它们在其正常寄主植物上引发过敏反应。
