[A study of the effects on the symbiotic nitrogen fixation of Sinorhizobium fredii with the introduction of dctABD and nifA genes].

A recombinant plasmid pHN307 containing C4-dicarboxylic acid transport genes (dctABD) from Sinorhizobium meliloti, nifA genes from Klebsiella pneumoniae and reporter genes luxAB from pDB30 was constructed by using pTR102 as the vector. The pHN307 was then introduced into the S. fredii HN01, YC4 and GR3 by tri-parental mating, and the stability of pHN307 in the transconjugants under free-living and symbiotic condition was also investigated. The results of plant pot experiment indicated that the introduction of pHN307 in the transconjugants could significantly increase the nodule fresh weight, shoot dry weight (biomass) and total nitrogen content of the symbiotic plants with soybean variety of Heilong 33. When the transconjugants were in symbiotic with soybean variety of Chuanzao No. 1, HN01 (pHN307) could significantly increase its root nodule number and fresh weight; GR3 (pHN307) could significantly increase its root nodule number, nodule fresh weight, shoot dry weight and total nitrogen content, but YC4(pHN307) demonstrated negative effect under the same condition. The results of this study suggested that the introduction of dctABD and nifA could improve the symbiotic nitrogen fixation efficiency and nodulation ability of the rhizobia tested, respectively, and its effect was relevant to the characteristics of recipient rhizobia and soybean variety.