Regulation of auxin transport polarity by AGC kinases

The plant hormone auxin controls plant development through gradients and maxima that are generated by PIN efflux carrier driven polar auxin transport. PIN proteins direct this cell-to-cell auxin transport, and thus orient plant development through their asymmetric subcellular distribution. PIN polarity is regulated by PINOID and the phototropins, members of the AGC protein serine/threonine kinase family. Here we review the signaling pathways of these kinases and the role of calcium and BTB proteins in translating both internal and external signals into developmental responses via PIN relocalization, to adapt plant development to changing environmental conditions.