A new perspective on auxin perception

An important question in modern plant biology concerns the mechanisms of auxin perception. Despite the recently discovered soluble receptor, the F-box protein TIR1, there is no doubt that another type of signal perception exists, and is linked to the plasma membrane. Two models for the receptor have been suggested: either the receptor includes a protein kinase, or it is coupled with a G-protein. We propose a third model, acting through Ca2+-channels in the plasma membrane. The model is based on the revealed rapid auxin-induced reactions, including changes in the membrane potential, shifts in cytosol concentration of Ca2+ and H+ and modulation of cell sensitivity to hormones by the external Ca2+ concentration. Detailed inhibitor analysis with both living cells and isolated plasma membranes show that auxin might directly stimulate Ca2+ transport through the plasma membrane. A hypothetical scheme of auxin perception at the plasma membrane is suggested together with further transduction events. In addition, comparative analyses of auxin and serotonin perceptions are provided. (C) 2010 Elsevier GmbH. All rights reserved.