紫云英根瘤菌寄主专性结瘤基因和固氮基因的鉴定

IDENTIFICATION OF hsn AND nif HDK GENES ON pRaZ15 INCORPORATED TO RHIZOBIUM ASTRAGALI

Previous work showed that the recombinatant plasmid pRaZ15 construed in this laboratory contained the common nod genes of Rhizobium astragali. Incorporation of pRaZ15 into R. astragali Nod~- mutant 7653R+1 (a nod~- mutant of 7653R devoid of Sym-plasmid) recovered its nodulation ability. In this report, evidances presented showed that the host-specific nod genes (hsn) and nitrogenase structural gencs(nifHDK) were also carried by pRaZ15. Transconjugants were obtained by thihyhridization incorporated pRaZ15 into Rhizobium leguminosarum strain T83K3 and Rhizobium phaseoli strain 3622-15, of which the original recipents were unable to nodulate Astragalus sinicus. Both transconjugants were found to nodulate A. sinicus. The experiments prove that the pRaZ15 contains the hsn genes specific to A. sinicus nodulation. The pRaZ15 was again transfered to the Sym-plasmid cured mutant R. astragali strain 7653R+1 and used to inoculate A. sinicus. Nodules were formed and its nitrogenase activities were detected by the aectylene-reduction method. ~(32)P--dCTP labeled pSA30 cloned with K. p. nifHDK genes was hybridized with Sall fragments and EcoRI fragments of pRaZ15. Radioactivity exposure suggested that pRaZ15 contained nif genes.Evidences gather so far indicate that pRaZ15 contains all the necessry genes for symbiotic nitrogen fixation as contained in the sym-plasmid of R. astragli.