Wei Z M, Sneath B J, Beer S V
Department of Plant Pathology, Cornell University, Ithaca, New York 14853.
J Bacteriol. 1992 Mar;174(6):1875-82. doi: 10.1128/jb.174.6.1875-1882.1992.
Seven hrp loci that are essential for the hypersensitive reaction elicited by Erwinia amylovora were transcriptionally fused with a derivative of transposon Tn5, containing the promoterless Escherichia coli beta-glucuronidase reporter gene. The seven hrp fusions were used to monitor expression of the hrp loci in vitro and in planta. No significant expression was detected in rich medium for any of the fusions. However, five of them were expressed highly in planta and in inducing medium that contains mannitol, salts, and 5 mM (NH4)2SO4. Expression of these five hrp loci is regulated by ammonium, nicotinic acid, complex-nitrogen sources, certain carbon sources, temperature, and pH. Under well-defined conditions, i.e., in inducing medium, no specific plant components were required for transcriptional activation of the hrp loci. The high levels of expression detected in vitro were comparable to those determined during the development of the hypersensitive reaction in tobacco. Differential levels of expression of the hrp loci occurred in host and nonhost plants. In pear, a host plant, expression of the hrp loci was delayed and greatly reduced compared with expression in tobacco leaves, a nonhost.
七个对解淀粉欧文氏菌引发的过敏反应至关重要的hrp基因座与转座子Tn5的一个衍生物进行转录融合，该衍生物含有无启动子的大肠杆菌β-葡萄糖醛酸酶报告基因。这七个hrp融合基因用于监测hrp基因座在体外和植物体内的表达。在丰富培养基中，未检测到任何融合基因的显著表达。然而，其中五个在植物体内以及含有甘露醇、盐和5 mM硫酸铵的诱导培养基中高度表达。这五个hrp基因座的表达受铵、烟酸、复合氮源、某些碳源、温度和pH的调节。在明确的条件下，即在诱导培养基中，hrp基因座的转录激活不需要特定的植物成分。在体外检测到的高水平表达与烟草过敏反应发生过程中测定的水平相当。hrp基因座在寄主植物和非寄主植物中表达水平存在差异。在寄主植物梨中，与非寄主烟草叶相比，hrp基因座的表达延迟且大幅降低。
