Plants establish symbioses with mutualistic fungi, such as arbuscular mycorrhizal (AM) fungi, and bacteria, such as rhizobia, to exchange key nutrients and thrive. Plants and symbionts have coevolved and represent vital components of terrestrial ecosystems. Plants employ an ancestral AM signaling pathway to establish intracellular symbioses, including the legume–rhizobia symbiosis, in their roots. Nevertheless, the relationship between the AM and rhizobial symbioses in native soil is poorly understood. Here, we examined how these distinct symbioses affect root-associated bacterial communities in Medicago truncatula by performing quantitative microbiota profiling (QMP) of 16S rRNA genes. We found that M. truncatula mutants that cannot establish AM or rhizobia symbiosis have an altered microbial load (quantitative abundance) in the rhizosphere and roots, and in particular that AM symbiosis is required to assemble a normal quantitative root-associated microbiota in native soil. Moreover, quantitative microbial co-abundance network analyses revealed that AM symbiosis affects Rhizobiales hubs among plant microbiota and benefits the plant holobiont. Through QMP of rhizobial rpoB and AM fungal SSU rRNA genes, we revealed a new layer of interaction whereby AM symbiosis promotes rhizobia accumulation in the rhizosphere of M. truncatula. We further showed that AM symbiosis-conditioned microbial communities within the M. truncatula rhizosphere could promote nodulation in different legume plants in native soil. Given that the AM and rhizobial symbioses are critical for crop growth, our findings might inform strategies to improve agricultural management. Moreover, our work sheds light on the co-evolution of these intracellular symbioses during plant adaptation to native soil conditions.

植物与共生真菌（如丛枝菌根 (AM) 真菌）和细菌（如根瘤菌）建立共生关系，以交换关键营养物质并茁壮成长。植物和共生体共同进化并代表了陆地生态系统的重要组成部分。植物利用祖先的 AM 信号通路在其根部建立细胞内共生，包括豆科植物 - 根瘤菌共生。然而，对原生土壤中 AM 与根瘤菌共生之间的关系知之甚少。在这里，我们 通过对 16S rRNA基因进行定量微生物群分析 (QMP)，研究了这些不同的共生如何影响蒺藜苜蓿根相关细菌群落。我们发现M . 截形不能建立 AM 或根瘤菌共生的突变体在根际和根中具有改变的微生物负荷（定量丰度），特别是 AM 共生需要在天然土壤中组装正常的定量根相关微生物群。此外，定量微生物共丰度网络分析表明，AM 共生影响植物微生物群中的根瘤菌中心，并使植物全息生物受益。通过根瘤菌的QMP的rpoB和AM真菌SSU rRNA的基因，我们揭示相互作用的新层，由此AM共生促进根际根瘤菌积累中号。截形。我们进一步表明，AM 共生条件下的微生物群落米。truncatula根际可以促进原生土壤中不同豆科植物的结瘤。鉴于 AM 和根瘤菌共生对作物生长至关重要，我们的研究结果可能会为改善农业管理的策略提供信息。此外，我们的工作揭示了植物适应原生土壤条件期间这些细胞内共生体的共同进化。