Growing with the flow: Plant patterning through auxin transport
Plant multicellularity evolved independently and is subject to unique constraints. Plant cells are physically constrained by cell walls, by cytoplasmic connections that are maintained after cell division, and by the inability to simply move in response to environmental stimuli. Against these constraints plants have evolved a distributed mechanism of developmental patterning based on the active transport of a signaling molecule, the hormone auxin. While auxin can passively enter plant cells, triggering a vast array of developmental responses, it cannot easily exit without active transport. Thus active auxin efflux mediated by the membrane-localized and polarized PIN proteins provides directionality to auxin movement. In developing tissues polarized PIN proteins create auxin concentration maxima that act as organizing foci for development. PINs also mediate bulk transport throughout the mature tissues which facilitates long-range communication between the growing parts of the plant. Because auxin feeds back to control its own transport by regulating the polarization, abundance and activity of PIN proteins, the transport system has self-organizing properties. Much like water flowing across a landscape can create a myriad of emergent patterns, from narrow canyons to broad deltas, so too can minor variations in the auxin transport system result in diverse and adaptive patterning outputs. I will describe how my lab uses comparative genetics, imaging and computer modeling to understand the nature of auxin transport mediated patterning.