| The plasticity of plant development allows plants to adapt to sudden changes in their environment. This plasticity is nicely illustrated by a plant?s growth toward the direction of light or gravity, and also by the unique ability of plant tissues or even single cells to regenerate into a new plant. A major determinant of plant development is the polar intercellular transport of the plant hormone auxin (indole-3-acetic acid), which regulates cell division and cell expansion by establishing dynamic auxin maxima and -gradients. Polar auxin transport is driven by the PIN transporter-like membrane proteins, whose asymmetric sub-cellular localization determine the direction of transport. My group, with a team of international collaborators, has shown that the PINOID (PID) protein kinase determines the cellular polarity of the PIN auxin transporters. Further research in my group has uncovered interacting/regulatory (KIR) proteins of PID and of the related PID-like kinases. I hypothesize that the combined action of PID, the PID-like kinases and the KIR proteins provides plants with a compass that integrates both external and internal signals to direct auxin transport, thereby determining plant growth orientation and architecture. Here I propose a multi-disciplinary mix of molecular genetic, biochemical and phospho-proteomics approaches, using the unique tools that are available in my group, to unravel the molecular mechanisms of action of PID and PID-like signaling complexes in the model plant Arabidopsis thaliana. Polar targeting of PIN proteins through PIN phosphorylation provides a unique model system for examining how protein kinases alter the phosphorylation state and thereby the polar targeting of membrane proteins. The proposed research will allow me to test the plant compass hypothesis and, in a broader sense, to examine potential paradigms underlying the molecular mechanisms governing cell polarity in both plants and animals. |
