Understanding how plants respond to nitrogen in their environment is crucial for determining how they use it and how the nitrogen use affects other processes related to plant growth and development. Under nitrogen limitation the activity and affinity of uptake systems is increased in roots, and lateral root formation is regulated in order to adapt to low nitrogen levels and scavenge from the soil. Plants in the legume family can form associations with rhizobial nitrogen-fixing bacteria, and this association is tightly regulated by nitrogen levels. The effect of nitrogen on nodulation has been extensively investigated, but the effects of nodulation on plant nitrogen responses remain largely unclear. In this study, we integrated molecular and phenotypic data in the legume Medicago truncatula and determined that genes controlling nitrogen influx are differently expressed depending on whether plants are mock or rhizobia inoculated. We found that a functional autoregulation of nodulation pathway is required for roots to perceive, take up, and mobilize nitrogen as well as for normal root development. Our results together revealed that autoregulation of nodulation, root development, and the location of nitrogen are processes balanced by the whole plant system as part of a resource-partitioning mechanism.

了解植物如何对环境中的氮作出反应对于确定其使用方式以及氮的使用如何影响与植物生长和发育相关的其他过程至关重要。在氮限制下，根系吸收系统的活性和亲和力增加，侧根的形成受到调节，以适应低氮水平并从土壤中清除。豆科植物可以与根瘤菌固氮细菌形成关联，并且该关联受氮水平的严格调控。氮对根瘤的影响已得到广泛研究，但根瘤对植物氮响应的影响仍不清楚。在这项研究中，我们整合了豆科植物紫花苜蓿的分子和表型数据并确定控制氮流入的基因是根据接种的是假植株还是根瘤菌而不同表达的。我们发现，根部感知，吸收和调动氮素以及正常的根部发育都需要功能调节结瘤途径。我们的研究结果共同表明，根瘤形成，根系发育和氮素定位的自动调节是整个植物系统平衡的过程，这是资源分配机制的一部分。