影响紫云英根瘤菌入侵和根瘤发育的exo基因的克隆及分析

紫云英根瘤菌菌株107的3个胞外多糖缺陷突变株NA－01、02、04不具备诱导宿主植物紫云英结瘤的能力。以NA-01突变位点的DNA片段为探针，从可互补这3个变种的exoR′－11质粒上亚克隆到2．6kb的DNA片段。互补试验表明，2．6kb的片段不仅可纠正突变株的胞外多糖缺陷表型，而且使变种恢复诱导宿主植物形成有效根瘤的能力。2．6kb片段经Tn5定位突变后丧失这种恢复能力，表明该片段带有对应于3个变种的野生型基因。

Cloning and Analysis of exo Gene Required for Nodule Invasion and Development of Rhizobium astragali

Three exopolysaccharide (EPS )deficient mutants NA-01, 02, 04(Exo- ) isolated from wild Rhizobium as-tragali strains 107 showed no ability toinduce nodule formation on the roots ofAstagalus sinicus L. From plasmid exoR'-11 which could complement thesethree mutants, a 2. 6 kb DNA fragmentwas cloned (Fig. 2) using 3. 1 kb fragment from mutant site of NA-01 asprobe (Figs. 1, 3). It was shown thatthe 2. 6 kb fragment did not only fullycomplemented the EPS phenotype ofeach of the three mutunts, but also restored its ability to induce Fix- noduleformation as did the wild-type strain107 (Fig. 4 ). After Tns site--directedmutugenesis, the 2. 6 kb DNA withTn5 insertion lost such complementationability. Therefore, we could concludethat 2. 6 kb DNA fragment containedthe exo gene which complements thethree mutants.