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As sessile organisms, plants have acquired a plethora of mechanisms to adapt and optimize their development and growth to changes in their environment. In this regulatory network, the plant hormone auxin, or indole-3-acetic acid (IAA), plays a central role, as it controls many aspects of plant growth and development through dynamic polar cell-to-cell transport-generated maxima and minima. The polarity of auxin transport is determined by the asymmetric subcellular distribution of the PIN1-type auxin efflux carriers. Reversible phosphorylation of these PIN proteins in their central hydrophilic loop through the antagonistic action of PINOID (PID) and related AGC3 kinases and PP2A phosphatases is sufficient to direct their proper localization during embryogenesis, tropic growth, and the initiation of flowers and floral organs.
Detailed functional analysis of the Arabidopsis AGC3 kinases shows that they act both redundantly and differentially in regulating auxin transport, and that their subcellular localization is a key aspect of their functionality. All four Arabidopsis AGC3 kinases are peripheral membrane proteins, but they also show differential subcellular localization, in part determined by interacting proteins. I will provide an update on what we know now on the action of the AGC3 kinase, with an outlook on how PIN phosphorylation may direct the subcellular distribution of these efflux carriers. |
