【摘要】 根瘤菌的ｎｏｄＡＢＣ和ｎｏｄＤ在结构和功能上保守，在不同的菌种之间能够互换［１］，是目前所有供试的豆科植物结瘤所必不可少的，称为共同结瘤基因。另一类是寄生专一性结瘤基因，如苜蓿中华根瘤菌（Ｓｉｎｏｒｈｉｚｏｂｉｕｍｍｅｌｉｌｏｔｉ）的ｎｏｄＰＱ等［２...更多还原

【Abstract】 Genomic DNA of S.meliloti 042B was partially digested to 20～30 kb by restriction endonuclease Sau 3AI ,and the gene library was constructed with cosmid pLAFR3.Using S.meliloti nodABC probe and Southern blot analysis,three clones were found to harbor nodABC genes.Cosmids carried by these colonies were named pXCA,pXCB and pXCC,respectively.By triparental mating with the helper plasmid pRK2013,these recombinant cosmids were transferred into S.meliloti nodC mutant AK 1657.In this way,it was found that AK1657 containing pXCB restored its nodulation ability on alfalfa.By double enzyme digesting following by Southern blot analysis,a physical map of 25 kb insert of pXCB was made.A sequencing plasmid pXCB1 was constructed by cloning 2.8 kb sized nodABC fragment from pXCB into vector pUC18.The DNA sequencing results showed that 042B nodABC are highly homologous to S.meliloti nodABC ,and homologous to nodABC of Rhizobium sp. NGR234,and to nodABC of S.fredii, respectively,but have low homologies to nodABC gene of the other rhizobia.This might explain the reason why strain 042B can nodulate on both soybean and alfalfa.更多还原