Root nodule symbiosis enables nitrogen fixation in legumes and, therefore, improves crop production for sustainable agriculture^1,2. Environmental nitrate levels affect nodulation and nitrogen fixation, but the mechanisms by which legume plants modulate nitrate uptake to regulate nodule symbiosis remain unclear¹. Here, we identify a member of the Medicago truncatula nitrate peptide family (NPF), NPF7.6, which is expressed specifically in the nodule vasculature. NPF7.6 localizes to the plasma membrane of nodule transfer cells (NTCs), where it functions as a high-affinity nitrate transporter. Transfer cells show characteristic wall ingrowths that enhance the capacity for membrane transport at the apoplasmic–symplasmic interface between the vasculature and surrounding tissues³. Importantly, knockout of NPF7.6 using CRISPR–Cas9 resulted in developmental defects of the nodule vasculature, with excessive expansion of NTC plasma membranes. npf7.6 nodules showed severely compromised nitrate responsiveness caused by an attenuated ability to transport nitrate. Moreover, npf7.6 nodules exhibited disturbed nitric oxide homeostasis and a notable decrease in nitrogenase activity. Our findings indicate that NPF7.6 has been co-opted into a regulatory role in nodulation, functioning in nitrate uptake through NTCs to fine-tune nodule symbiosis in response to fluctuating environmental nitrate status. These observations will inform efforts to optimize nitrogen fixation in legume crops.

根瘤共生能使豆类固氮，因此提高了可持续农业^1,2的作物产量。环境中的硝酸盐水平会影响结瘤和固氮，但豆科植物调节硝酸盐吸收以调节结节共生的机制尚不清楚¹。在这里，我们确定了苜蓿苜蓿硝酸盐肽家族（NPF）NPF7.6的成员，具体在结节脉管系统中表达。NPF7.6定位于结节转移细胞（NTC）的质膜，在其中它起着高亲和力硝酸盐转运蛋白的作用。转移细胞显示出特征性的壁向内生长，从而增强了脉管系统与周围组织之间的无质-对称界面上的膜运输能力³。重要的是，使用CRISPR–Cas9敲除NPF7.6会导致结节脉管系统的发育缺陷，以及NTC质膜的过度膨胀。npf7.6结节显示出严重的硝酸盐反应能力受损，这是由于硝酸盐转运能力减弱所致。而且，npf7.6结核显示出一氧化氮的稳态紊乱，并且固氮酶活性显着下降。我们的发现表明，NPF7.6在结瘤过程中已被选为调节角色，可通过NTC吸收硝酸盐，从而微调结节共生，以适应不断变化的环境硝酸盐状态。这些观察将有助于优化豆类作物固氮的努力。