Recent developments in the understanding of PIN polarity.

Polar localization of PIN-FORMED proteins (PINs) at the plasma membrane is essential for plant development as they direct the transport of phytohormone auxin between cells. PIN polar localization to certain sides of a given cell is dynamic, strictly regulated and provides directionality to auxin flow. Signals that act upstream to control subcellular PIN localization modulate auxin distribution, thereby regulating diverse aspects of plant development. Here I summarize the current understanding of mechanisms by which PIN polarity is established, maintained and rearranged to provide a glimpse into the complexity of PIN polarity.