Auxin distribution and plant pattern formation: How many angels can dance on the point of PIN?

The plant hormone auxin is central in patterning diverse plant tissues. The direction of auxin flow and the distribution of auxin within tissues are regulated by auxin efflux transporters that are polarly localized in cells. Feedback regulation between auxin and its transporters establishes homeostatic patterns of auxin accumulation but allows dynamic repatterning in response to developmental or environmental cues.