title: Genetic divergence and gene flow among Mesorhizobium strains nodulating the shrub legume Caragana.
abstract: Although the biogeography of rhizobia has been investigated extensively, little is known about the adaptive molecular evolution of rhizobia influenced by soil environments and selected by legumes. In this study, microevolution of Mesorhizobium strains nodulating Caragana in a semi-fixing desert belt in northern China was investigated. Five core genes-atpD, glnII, gyrB, recA, and rpoB, six heat-shock factor genes-clpA, clpB, dnaK, dnaJ, grpE, and hlsU, and five nodulation genes-nodA, nodC, nodD, nodG, and nodP, of 72 representative mesorhizobia were studied in order to determine their genetic variations. A total of 21 genospecies were defined based on the average nucleotide identity (ANI) of concatenated core genes using a threshold of 96% similarity, and by the phylogenetic analyses of the core/heat-shock factor genes. Significant genetic divergence was observed among the genospecies in the semi-fixing desert belt (areas A-E) and Yunnan province (area F), which was closely related to the environmental conditions and geographic distance. Gene flow occurred more frequently among the genospecies in areas A-E, and three sites in area B, than between area F and the other five areas. Recombination occurred among strains more frequently for heat-shock factor genes than the other genes. The results conclusively showed that the Caragana-associated mesorhizobia had divergently evolved according to their geographic distribution, and have been selected not only by the environmental conditions but also by the host plants.
authors: State Key Laboratory of Agrobiotechnology, Beijing 100193, China; College of Biological Sciences and Rhizobia Research Center, China Agricultural University, Beijing 100193, China.
authors: Zhaojun
authors: Z
authors: Ji
authors: State Key Laboratory of Agrobiotechnology, Beijing 100193, China; College of Biological Sciences and Rhizobia Research Center, China Agricultural University, Beijing 100193, China.
authors: Hui
authors: H
authors: Yan
authors: State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.
authors: Qingguo
authors: Q
authors: Cui
authors: State Key Laboratory of Agrobiotechnology, Beijing 100193, China; Departamento de Microbiología, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, México D. F. 11340, Mexico.
authors: Entao
authors: E
authors: Wang
authors: State Key Laboratory of Agrobiotechnology, Beijing 100193, China; College of Biological Sciences and Rhizobia Research Center, China Agricultural University, Beijing 100193, China.
authors: Wenxin
authors: W
authors: Chen
authors: State Key Laboratory of Agrobiotechnology, Beijing 100193, China; College of Biological Sciences and Rhizobia Research Center, China Agricultural University, Beijing 100193, China. Electronic address: chenwf@cau.edu.cn.
authors: Wenfeng
authors: W
authors: Chen
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics; D032602:Caragana / Q000382:microbiology*; D002681:China; D016000:Cluster Analysis; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D003889:Desert Climate; D051456:Gene Flow; D005798:Genes, Bacterial; D014644:Genetic Variation; D005838:Genotype; D059128:Mesorhizobium / Q000145:classification* / Q000235:genetics* / Q000302:isolation & purification; D008969:Molecular Sequence Data; D058974:Phylogeography; D011995:Recombination, Genetic; D053204:Root Nodules, Plant / Q000382:microbiology; D017422:Sequence Analysis, DNA; D012689:Sequence Homology, Nucleic Acid
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial
keywords: Caragana; Mesorhizobium; Microevolution; Mutation; Phylogeny; Recombination