Polar transport in plants mediated by membrane transporters: focus on mechanisms of polar auxin transport

- PIN polarity regulator GNOM localizes to both Golgi and PMs instead of endosomes.
- NPH3-like proteins inhibit endocytosis of PINs at polar domains.
- Phosphorylation of PINs mediated by AGCVIII kinase and MAP kinase regulates auxin efflux activity.
- Membrane trafficking regulates lateral localization of nutrient transporters.

Directional cell-to-cell transport of functional molecules, called polar transport, enables plants to sense and respond to developmental and environmental signals. Transporters that localize to plasma membranes (PMs) in a polar manner are key components of these systems. PIN-FORMED (PIN) auxin efflux carriers, which are the most studied polar-localized PM proteins, are implicated in the polar transport of auxin that in turn regulates plant development and tropic growth. In this review, the regulatory mechanisms underlying polar localization of PINs, control of auxin efflux activity, and PIN abundance at PMs are considered. Up to date information on polar-localized nutrient transporters that regulate directional nutrient movement from soil into the root vasculature is also discussed.