Intercellular transport of auxin

Abstract

Auxin is an essential hormone that regulates both programmed and plastic plant development. The mechanisms that regulate auxin metabolism, transport and signal transduction are well characterized, although important unresolved questions remain. A unique feature of auxin-regulated plant development is that it involves a combination of cellular perception with polarized auxin gradients across groups of cells, tissues, and organs. Plants achieve these polarized auxin gradients via site-specific synthesis followed by directed and polar patterning of transport components in individual cells. These streams are primarily mediated by three functionally distinct plasma membrane transporter families. Apical-basal and organogenic patterning is largely defined by the polar efflux activities of full-length PIN-FORMED (PIN) facilitators. Dynamic auxin uptake into directed streams is mediated by the AUXIN RESISTANT 1 (AUX1) and LIKE AUX1 (LAX) symporters. Finally, long-distance transport streams are motivated by the ATP-BINDING CASSETTE subfamily B (ABCB) active transporters that continually pump across the plasma membrane and prevent reuptake of exported auxin. Multiple accessory proteins regulate auxin transporter activity and interactions with subcellular environments. The current understanding of cellular transport of auxin will be reviewed in this chapter.