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

美国国家科学基金会批准了密苏里大学哥伦比亚分校的Steven G.Pueppke博士和瑞士香贝西/日内瓦植物分子高级实验室的William J.Broughton博士关于“几种根生真菌寄主范围的分子分析”的建议。研究人员建议了解大豆、豌豆和其他豆类是如何被广泛寄主范围的根瘤菌节化的。模式微生物是哥伦比亚大学研究的费氏根瘤菌257和根瘤菌sp.NGR234(在日内瓦研究)。利用Tn5突变，研究人员已经分离出257菌株的两个不寻常的突变株，它们使未被亲本菌株结瘤的大豆品种结瘤。本研究拟将这两个突变体与根瘤菌的突变体进行协同分析。NGR234利用可用来帮助阐明宿主特异性的基础的差异。菌株257的一个突变株在染色体上含有Tn5，另一个突变株在sym质粒中含有转座子。研究人员已经分离出了含有Tn5插入位点两侧DNA的宇宙体，亚克隆了感兴趣的片段，并正在绘制它们的图谱。这项提议希望定义这些克隆中包含的负性作用宿主范围基因，并寻找NGR234中的对应基因。布劳顿博士分离出了一系列积极作用的寄主范围基因，并正在从物理和基因上对它们进行定义。合作的第二个目标是在257菌株中寻找相似的基因。这些目标的实现将有助于确定正负作用基因在指定寄主范围广泛的根瘤菌中的相对贡献。

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.