Plants, are sessile organisms, have developed strategies to adapt to changes in their environment, in part by altering their growth and development. One of the central regulators of this adaptive plant growth and development is the plant hormone auxin. Auxin is transported by the PIN class of proteins. PIN proteins are membrane localized proteins that transport auxin through the membrane. Plasma membrane localized PIN proteins often show a polarized localization that is regulated by the the AGC kinase PINOID. We investigated the regulation of the PINOID kinase by phosphoinositide-dependent protein kinase 1 (PDK1), a central upstream regulator of AGC kinases. Here we show in arabidopsis protoplasts that PDK1 phosphorylation induces a switch in PINOID subcellular localization from the plasma membrane to endomembrane compartments and the microtubule cytoskeleton (MT). Our results in planta suggest a new role for dynamic PDK1-mediated activation of PINOID in plant development. We reveal a regulatory complex that on the one hand links PINOID to a dynamic process in young tissues that requires high protein turnover and the MT. On the other hand, the complex is not essential for survival and allows much variability within the involved kinesin sequences between plant species.
