Polar auxin transport (PAT) is unique to plants and coordinates their growth and development^1,2. The PIN-FORMED (PIN) auxin transporters with remarkable asymmetrical localizations at the plasma membrane drive PAT^3,4, however, their structures and transport mechanisms remain largely unknown. Here, we report three inward-facing conformation structures of the major member of the PIN family, PIN1 in Arabidopsis thaliana (AtPIN1): (i) in the apo state, (ii) in the natural auxin, indole-3-acetic acid (IAA)-bound state, and (iii) in complex with the PAT inhibitor N-1-naphthylphthalamic acid (NPA). The transmembrane domain of AtPIN1 shares a conserved NhaA-fold⁵. In the substrate-bound structure, IAA is coordinated through both hydrophobic stacking and hydrogen bonding. The inhibitor NPA competes with IAA for the same site of the intracellular pocket with a much higher affinity. These findings facilitate our understanding of the substrate recognition and transport mechanisms of PINs, and set up a framework for future research on the directional auxin movement, one of the most crucial processes underlying plant development.

极地生长素运输 (PAT) 是植物独有的，可协调它们的生长和发育^1,2。在质膜上具有显着不对称定位的 PIN 形成 (PIN) 生长素转运蛋白驱动 PAT ^3,4，然而，它们的结构和转运机制仍然很大程度上未知。在这里，我们报告了 PIN 家族主要成员的三个面向内的构象结构，即拟南芥中的 PIN1 （在PIN1）：（i）在 apo 状态，（ii）在天然生长素中，吲哚-3-乙酸(IAA) 结合状态，和(iii)与 PAT 抑制剂N -1-萘基邻苯二甲酸 (NPA) 复合。跨膜结构域在PIN1 共享一个保守的 NhaA 折叠⁵。在底物结合结构中，IAA 通过疏水堆积和氢键进行配位。抑制剂 NPA 与 IAA 以更高的亲和力竞争细胞内袋的同一位点。这些发现有助于我们理解 PIN 的底物识别和转运机制，并为未来研究定向生长素运动（植物发育的最关键过程之一）建立了框架。