US-Switzerland Cooperative Research: Molecular Analysis of Host Range in Several Rhizobium Species

美国密苏里大学哥伦比亚分校的Steven G. Pueppke博士和瑞士Chambesy/Geneva高等植物生物分子实验室的William J. Broughton博士共同提出的“几种根瘤菌寄主范围的分子分析”提案。是美国国家科学基金会在美瑞合作科学计划下批准的。研究人员建议了解大豆，豇豆和其他豆类是如何被广泛的宿主根瘤菌结瘤的。模式微生物是弗雷迪根瘤菌257（哥伦比亚大学研究）和根瘤菌sp. NGR234（日内瓦研究）。利用Tn5诱变技术，研究人员已经从菌株257中分离出两种不同寻常的突变体，这两种突变体使大豆品种不受亲本菌株的影响而结瘤。我们打算将这两个突变体与根瘤菌NGR234的突变体进行分析，以找出它们之间的区别，从而帮助阐明宿主特异性的基础。菌株257的一个突变体在染色体上有Tn5，而另一个突变体在同质粒上有转座子。研究人员已经分离出含有Tn5插入位点两侧DNA的宇宙体，亚克隆了感兴趣的片段，并绘制了它们的地图。本研究希望明确这些克隆中包含的负作用宿主范围基因，并在NGR234中寻找对应的基因。布劳顿博士分离出了一系列具有积极作用的宿主范围基因并从生理和基因上定义了它们。合作的第二个目标是在菌株257中寻找类似的基因。这些目标的实现将有助于确定正向和负向作用基因在确定广域根瘤菌宿主范围方面的相对贡献。

This proposal on "Molecular Analysis of Host Range in Several Rhizo- bium Species" between Dr. Steven G. Pueppke of the University of Missouri, Columbia, and Dr. William J. Broughton of the Laboratoire de Biologie Moleculaire des Plantes Superieures, Chambesy/Geneva, Switzerland, is approved by NSF under the US-Switzerland Cooperative Science Program. The researchers propose to understand how soybean, cowpea, and other legumes are nodulated by broad host-range rhizobia. The model microor- ganisms are rhizobium fredii 257 (researched at Columbia) and rhizo- bium sp. NGR234 (researched at Geneva). Using Tn5 mutagenesis, the investigators already have isolated two unusual mutants of strain 257 that nodulate soybean cultivars not nodulated by the parental strain. The intend to coordinate analysis of these two mutants with that of Rhizobium sp. NGR234 to exploit distinctions which can be exploited to help elucidate the basis of host specificity. One mutant of strain 257 has Tn5 in the chromosome while the other has the transposon in the sym plasmid. The investigators have isolated cosmids containing DNA flanking the sites of the Tn5 insertion, subcloned the fragments of interest, and are mapping them. This proposal hopes to define the negatively-acting host range genes contained in these clones and search for counterparts in NGR234. Dr. Broughton has isolated a series of positively-acting host range genes and is defining them physically and genetically. A second objective of the collaboration is to seek analogous genes in strain 257. Achievement of these objectives will help determine the relative contributions of positively and negatively acting genes in specifying host range in broad host-range rhizobia.