Philip-Hollingsworth S, Hollingsworth R I, Dazzo F B, Djordjevic M A, Rolfe B G
Department of Microbiology, Michigan State University, East Lansing 48824.
J Biol Chem. 1989 Apr 5;264(10):5710-4.
Host specificity in the Rhizobium-legume symbiosis is controlled in the bacterium by host specific nodulation (hsn) genes residing on its symbiotic plasmid. We have examined the structure of the major acidic heteropolysaccharide produced by recombinant hybrid strains of Rhizobium leguminosarum carrying cloned R. trifolii hsn genes with those produced by the parent donor and recipient strains. Alteration of the nod gene composition of R. leguminosarum strain 300 by introduction of an 8-kilobase set of hsn genes (nodFERL and nodMN) from R. trifolii strain ANU843, resulted in a hybrid strain which conferred efficient white clover infection and nodulation, production of the R. trifolii-type acidic polysaccharide, and an increased proportion of bacterial cells which bound to the white clover lectin, trifoliin A, in the external root environment. 1H NMR studies indicated that the structure of the polysaccharide from the hybrid recombinant differed from that of the R. leguminosarum strain 300 recipient in site and stoichiometry of acetate and stoichiometry of 3-hydroxybutyrate substituents. In contrast, the polysaccharide from a different hybrid recombinant strain containing only R. trifolii nodFERL genes had the acetylation pattern of the R. leguminosarum recipient but was substituted with 3-hydroxybutyrate at a level between that made by R. trifolii and R. leguminosarum. This latter recombinant strain displays sparse infection and nodulation of white clover roots. Immunofluorescence studies indicated that the R. leguminosarum recombinant strain containing the full complement of R. trifolii hsn genes (nodFERL and nodMN) gained the ability to interact with the excreted lectin, trifoliin A, in the white clover root environment, whereas the recombinant strain containing R. trifolii nodFERL only, was significantly attenuated in this cell-lectin interaction. These results indicate that the acylation pattern of the acidic polysaccharide synthesized by these hybrid recombinants of R. leguminosarum is influenced by the introduced hsn genes of R. trifolii and suggest that the acidic polysaccharide of R. trifolii and the interaction of these bacteria with the host lectin may contribute to host specificity in the white clover-R. trifolii symbiosis.
根瘤菌与豆科植物共生中的宿主特异性在细菌中由位于其共生质粒上的宿主特异性结瘤（hsn）基因控制。我们研究了携带克隆的三叶草根瘤菌hsn基因的豌豆根瘤菌重组杂交菌株产生的主要酸性杂多糖的结构，以及亲本供体和受体菌株产生的酸性杂多糖的结构。通过引入来自三叶草根瘤菌菌株ANU843的一组8千碱基的hsn基因（nodFERL和nodMN）来改变豌豆根瘤菌菌株300的结瘤基因组成，产生了一种杂交菌株，该菌株能高效感染和结瘤白三叶草，产生三叶草根瘤菌型酸性多糖，并且在根外部环境中与白三叶草凝集素三叶草素A结合的细菌细胞比例增加。1H NMR研究表明，杂交重组体的多糖结构在乙酸酯的位点和化学计量以及3-羟基丁酸酯取代基的化学计量方面与豌豆根瘤菌菌株300受体的不同。相比之下，来自另一种仅含有三叶草根瘤菌nodFERL基因的杂交重组菌株的多糖具有豌豆根瘤菌受体的乙酰化模式，但3-羟基丁酸酯的取代水平介于三叶草根瘤菌和豌豆根瘤菌之间。后一种重组菌株对白三叶草根系的感染和结瘤较少。免疫荧光研究表明，含有完整三叶草根瘤菌hsn基因（nodFERL和nodMN）的豌豆根瘤菌重组菌株在白三叶草根系环境中获得了与分泌的凝集素三叶草素A相互作用的能力，而仅含有三叶草根瘤菌nodFERL的重组菌株在这种细胞与凝集素的相互作用中明显减弱。这些结果表明，这些豌豆根瘤菌杂交重组体合成的酸性多糖的酰化模式受引入的三叶草根瘤菌hsn基因的影响，并表明三叶草根瘤菌的酸性多糖以及这些细菌与宿主凝集素的相互作用可能对白三叶草 - 三叶草根瘤菌共生中的宿主特异性有贡献。
