Marcelo Kemel Zago • Carlos S. Galvan-Ampudia • Remko Offringa (K)
Institute of Biology Leiden, Leiden University, Wassenaarseweg 64, 2333 AL Leiden, The Netherlands [email protected]
Abstract Plants are versatile organisms that, in order to compensate for their sessile life style, employ significant developmental plasticity to respond to environmental changes. To support this flexibility, plants have developed a plethora of signaling pathways that, in comparison to other organisms, involve a relatively large number of molecular switches, e.g. the protein kinases and phosphoprotein phosphatases. The plant hormone auxin plays a central role in these adaptation processes, and its action is not only determined by the perception and signal transduction of this signaling molecule, but also by its polar transport-mediated differential distribution. Herein we will review the role of the main signaling components in auxin-dependent plant development. Interestingly, auxin signaling is very unusual, as it does not involve a canonical signaling pathway comprising a receptor and a downstream kinase cascade. Instead, auxin employs the TIR1/AFB F-box proteins as receptors to initiate targeted proteolysis of Aux/IAA repressors leading to an increase in auxin-responsive gene expression. However, protein kinases play a crucial role in regulating and directing differential auxin distribution. Of particular interest is a group of serine/threonine kinases belonging to the plant specific AGCVIII subfamily. Of this group, the PINOID kinase has been shown to direct polar auxin transport by controlling the basal-to-apical deployment of the PIN auxin efflux carriers, a process that is reversible by PP2A phosphatases.
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