摘要
总结了紫云英根瘤菌分子遗传学研究进展。这类根瘤菌的寄主范围较窄 ,早先根据互接种族概念将其定名为Rhizobiumastragali,后来定名为Rhizobiumhuakuii,最近并入Mesorhizobium属。对大量菌株进行的 16S和2 3SrDNAPCR RFLP分析和代表菌株的部分 16SrDNA碱基测序 ,揭示了 7个不同基因型 ,表明这类菌具有遗传多样性 ,可以认为存在不同的种。它们都有质粒 ,数量 1～ 5个 ,因菌株而异 ,可分为不同质粒型 ,共生基因常定位在最大的一个质粒上 ,即共生质粒。它们的结瘤基因具有独特结构。采用包括nodA ,nodB ,nodC ,nodD的苜蓿根瘤菌突变株进行基因互补 ,从紫云英根瘤菌基因文库中获得了相应的转移接合子。这类根瘤菌的nodA与nodBC分隔约 2 2kb距离 ,不同于多数根瘤菌nodABC为一个操纵元的结构。紫云英根瘤菌结瘤基因的这种结构在 7个基因型的菌株中都是一致的 ,说明结瘤基因的保守性。
Advances on molecular genetics of Astragalus sinicus rhizobia, which were achieved mainly by researchers in Huazhong Agricultural University, are summarized in this paper. Astragalus sincus rhizobia have very narrow host range and they were firstly assigned as Rhizobium astragali according to the 'cross inoculation'concept. They were also called Bradyrhizoium by some researchers in late 1980s. A new species of Rhizobium huakuii was proposed for A. sinicus rhizobia by using numerical taxonomy and DNA-DNA hybridization in 1991. It was transferred into the new established genus Mesorhizobium in 1997.In order to evaluate the genetic diversity of rhizobia associated with A. sinicus, a great number of strains were isolated and characterized by PCR-RFLP analysis of 16S rDNA, 23S rDNA and their intergenic spacers (IGS). Results indicated that the A. sinicus rhizobia belongs to two distinct groups. The minor group contains 7 isolates and could be a new species in Mesorhizobium. Strains generally harbor 1～5 plasmids and the symbiotic genes locate on the largest one, pSym. Common nod genes nodD, nodA, nodBC of strain 7653R, were cloned by functional complementation and subsequent sequence analysis. The nodA was found to be separated from nodBC by approximately 22 kb and was divergently transcribed. This unique nod gene organization and nodA gene sequences are highly conserved among all types of A. sinicus rhizobia. Therefore, the rhizobial genetic diversity was caused by horizontal gene transfer (HGT).
出处
《华中农业大学学报》
CAS
CSCD
北大核心
2003年第1期77-83,共7页
Journal of Huazhong Agricultural University
基金
国家自然科学基金
欧盟STD3与RTD4计划资助项目
关键词
紫云英
根瘤菌
中慢根瘤菌
分子遗传学
Astragalus sinicus, rhizobia, Mesorhizobium, molecular genetics
