Structural insights into auxin recognition and efflux by Arabidopsis PIN1

Polar auxin transport is unique to plants and coordinates their growth and development(1,2). The PIN-FORMED (PIN) auxin transporters exhibit highly asymmetrical localizations at the plasma membrane and drive polar auxin transport(3,4); however, their structures and transport mechanisms remain largely unknown. Here, we report three inward-facing conformation structures of Arabidopsis thaliana PIN1: the apo state, bound to the natural auxin indole-3-acetic acid (IAA), and in complex with the polar auxin transport inhibitor N-1-naphthylphthalamic acid (NPA). The transmembrane domain of PIN1 shares a conserved NhaA fold(5). In the substrate-bound structure, IAA is coordinated by both hydrophobic stacking and hydrogen bonding. NPA competes with IAA for the same site at the intracellular pocket, but with a much higher affinity. These findings inform our understanding of the substrate recognition and transport mechanisms of PINs and set up a framework for future research on directional auxin transport, one of the most crucial processes underlying plant development.

Automated summary

This study reports different conformational structures of Arabidopsis thaliana PIN1, revealing the substrate recognition and transport mechanisms of PIN proteins. These findings are of great significance for understanding the directional auxin transport process in plant development.