Biochemical and physiological characterization of PIN-FORMED auxin efflux carriers

• Applicant: Privatdozent Dr. Ulrich Hammes
• Subject Area: Plant Physiology ; Plant Cell and Developmental Biology
• Term: since 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 283873977

The phytohormone auxin controls virtually all aspects of plant growth and development. Many of the effects of auxin are due to the polar transport of the compound. The PIN-FORMED (PIN) family of auxin exporters is crucial in this process. The biochemical properties of PINs were for a long time poorly understood. We have established an auxin efflux assay from Xenopus oocytes that allowed us to comprehensively characterize the transport properties of this transporter family. We were able to show that the kinetics of auxin transport differ between different PINs and that the kinetic parameters of the so-called canonical PINs are dependent on the kinase. We were also able to show that the loop domain of canonical PINs is not merely regulatory, but it contributes to the transport properties. Finally, we could show that complementation of the agravitropic pin2 mutant depends not only on the localization of PINs but also on their transport properties. In the present proposal we wish to take advantage of the Xenopus expression system to further characterize PIN proteins and extend our efforts to the so-called non-canonical PINs in which the loop domain is significantly reduced. We will determine which loop domains bring about unique properties of PIN proteins and identify loop domains which are required for the differential response to kinases. We will further characterize the interaction between loop and kinases using yeast two hybrid assays and several different biochemical approaches with the aim to understand the interplay between transporter and kinase in more detail. We will then verify predictions derived from the biochemical analyses in planta using the complementation of pin mutant phenotypes. Finally, we will characterize the interaction of PINs as well as physiologically relevant PIN-kinase pairs in planta. The results of these studies will substantially increase our understanding of the mode-of-action by which PIN-mediated auxin transport occurs.

• DFG Programme: Research Grants