eLife publishes the study of Melina Zourelidou from the laboratory of C. Schwechheimer (TUM-WZW) and Birgit Absmanner from the laboratory of U. Hammes (Regensburg), where they demonstrate for the first time the direct activation of PINs by D6PK and PINOID.

Auxin efflux by PIN-FORMED proteins is activated by two different protein kinases, D6 PROTEIN KINASE and PINOID.

Melina Zourelidou, Birgit Absmanner, Benjamin Weller, Inês CR Barbosa, Björn C Willige, Astrid Fastner, Verena Streit, Sarah A Port, Jean Colcombet, Sergio de la Fuente van Bentem, Heribert Hirt, Bernhard Kuster, Waltraud X Schulze, Ulrich Z Hammes, Claus Schwechheimer

The development and morphology of vascular plants is critically determined by synthesis and proper distribution of the phytohormone auxin. The directed cell-to-cell distribution of auxin is achieved through a system of auxin influx and efflux transporters. PIN-FORMED (PIN) proteins are proposed auxin efflux transporters, and auxin fluxes can seemingly be predicted based on the - in many cells - asymmetric plasma membrane distribution of PINs. Here, we show in a heterologous Xenopus oocyte system as well as in Arabidopsis thaliana inflorescence stems that PIN-mediated auxin transport is directly activated by D6 PROTEIN KINASE (D6PK) and PINOID (PID)/WAG kinases of the Arabidopsis AGCVIII kinase family. At the same time, we reveal that D6PKs and PID have differential phosphosite preferences. Our study suggests that PIN activation by protein kinases is a crucial component of auxin transport control that must be taken into account to understand auxin distribution within the plant.