Actin, Myosin VIII and ABP1 as Central Organizers of Auxin-Secreting Synapses

In the root apex transition zone, large portion of the polar auxin transport (PAT) is accomplished via endocytic vesicular recycling at F-actin and myosin VIII-enriched cell–cell adhesion domains which are characterized as plant synapses. In these cells, PINs act as vesicular transporters that enrich recycling vesicles and endosomes with auxin, which is then secreted out of cells in a neurotransmitter-like mode. Besides F-actin and myosin VIII, auxin receptor auxin binding protein 1 (ABP1) emerges as critical organizing molecule not only for the plant synapses but also for the whole transition zone. Synaptic auxin transport in root apices is directly linked for sensing environment, and also central for translating these perceptions, via sensory-motoric circuits, into adaptive root tropisms. Finally, PINs acting also as vesicular transportes are suggested to represent transceptors, and the synaptic activity is proposed act as flux sensor for the polar transport of auxin