Gao Mengzhe, Yuan Xiaoxia, Ji Zhaojun, Yang Bingjie, Li Hua, Zhang Bo
College of Life Science and Food Engineering, Inner Mongolia Minzu University, Tongliao, China.
Inner Mongolia Autonomous Region Engineering Technology Research Center for Prevention and Control of Pathogenic Bacteria in Milk, Tongliao, China.
Front Microbiol. 2024 Dec 13;15:1507637. doi: 10.3389/fmicb.2024.1507637. eCollection 2024.
Bunge is an important medicinal legume species widely cultivated in northeastern China (NEC) and northwestern China (NWC) and can establish a symbiotic relationship with nitrogen-fixing rhizobial strains. However, there are limited reports comparing the genetic diversity, differentiation, and gene flow of rhizobial strains associated with this plant in different geographic regions.
We used multilocus sequence analysis (MLSA) to investigate the phylogeny and genetic diversity of rhizobia and to estimate their intra- and inter-regional gene flow and genetic differentiation based on the analysis of concatenated core genes (, , and ) and the critical symbiotic gene .
We isolated eight known and three novel genospecies representing four genera, among which was the most predominant microsymbiont. Phylogenetic analysis revealed a highly diverse rhizobial community nodulating in NEC, consisting of the four genera , , , and . This community differed markedly from the rhizobial community found in NWC. Various rhizobial genospecies with different symbiotic gene sequences were capable of nodulating in NEC. Therefore, exhibits promiscuity in its association with symbionts in the natural environment, showing no strong preference for either the species-defining core genes or the symbiotic genes of rhizobia. We also found that the Glyco_tranf_GTA_type superfamily (Glycosyltransferase family A) is the most highly conserved and essential domain in the NodC protein, which is encoded by the symbiotic gene, across nodulating rhizobia. In addition, we found independent genetic differentiation among rhizobial communities geographically, and the frequency of gene flow among microsymbionts between NEC and NWC was low. We speculate that the formation of the highly diverse rhizobial community in NEC resulted from the independent evolution of each ancestral lineage. This diversity likely arose from intraregional genetic differentiation driven by mutations rather than recombination.
Ecogeographical isolation between NEC and NWC restricted inter-regional genetic drift and gene flow. Therefore, intraregional genetic differentiation is the major evolutionary force underlying the genetic diversity of rhizobia.
草木樨是一种重要的药用豆科植物，在中国东北（NEC）和西北（NWC）广泛种植，并且能够与固氮根瘤菌菌株建立共生关系。然而，关于比较不同地理区域与该植物相关的根瘤菌菌株的遗传多样性、分化和基因流的报道有限。
我们使用多位点序列分析（MLSA）来研究根瘤菌的系统发育和遗传多样性，并基于串联核心基因（、和）以及关键共生基因的分析，估计它们的区域内和区域间基因流以及遗传分化。
我们分离出代表四个属的八个已知基因型和三个新基因型，其中是最主要的微共生体。系统发育分析表明，NEC中与草木樨共生的根瘤菌群落高度多样，由、、和四个属组成。该群落与NWC中发现的根瘤菌群落明显不同。在NEC中，具有不同共生基因序列的各种根瘤菌基因型都能够与草木樨结瘤。因此，草木樨在自然环境中与共生体的关联表现出混杂性，对根瘤菌的物种定义核心基因或共生基因均无强烈偏好。我们还发现，在结瘤根瘤菌中，由共生基因编码的NodC蛋白中，糖基转移酶_GTA_类型超家族（糖基转移酶A家族）是最保守且必不可少的结构域。此外，我们发现根瘤菌群落在地理上存在独立的遗传分化，并且NEC和NWC之间微共生体之间的基因流频率较低。我们推测，NEC中高度多样的根瘤菌群落的形成是由于每个祖先谱系的独立进化。这种多样性可能源于由突变而非重组驱动的区域内遗传分化。
NEC和NWC之间的生态地理隔离限制了区域间的遗传漂变和基因流。因此，区域内遗传分化是根瘤菌遗传多样性的主要进化驱动力。
