How Does Auxin Enhance Cell Elongation? Roles of Auxin-Binding Proteins and Potassium Channels in Growth Control

Abstract

Elongation growth and a several other phenomena in plant development are controlled by the plant hormone auxin. A number of recent discoveries shed light on one of the classical problems of plant physiology: the perception of the auxin signal. Two types of auxin receptors are currently known: the AFB/TIR family of F box proteins and ABP1. ABP1 appears to control membrane transport processes (H+ secretion, osmotic adjustment) while the TIR/AFBs have a role in auxin-induced gene expression. Models are proposed to explain how membrane transport (e.g., K+ and H+ fluxes) can act as a cross-linker for the control of more complex auxin responses such as the classical stimulation of cell elongation.

A Major Facilitator Superfamily Transporter Plays a Dual Role in Polar Auxin Transport and Drought Stress Tolerance inArabidopsis

“…In support of this notion, complementation experiments with the Δqdr2 yeast mutant indicate high-affinity K + transport activity for both ZIFL1 splice isoforms. Indeed, potassium fluxes, in particular those mediated by K + channels, have been previously shown to modulate auxininduced cell elongation growth (Christian et al, 2006;Fuchs et al, 2006). Moreover, deletion of the Arabidopsis plasma membrane K + transporter Tiny Root Hair 1 (TRH1) leads to auxin-related phenotypes similar to those reported here for the zifl1 mutants (Vicente-Agullo et al, 2004).…”

Apoplast Acidification in Growing Barley (Hordeum vulgare L.) Leaves

“…Cell expansion is generally considered to be caused by wall loosening and driven by turgor pressure (Christian et al, 2006).…”

AUXIN BINDING PROTEIN1 Links Cell Wall Remodeling, Auxin Signaling, and Cell Expansion in Arabidopsis

“…This theory states that auxin promotes the excretion of protons at the apoplast resulting in cell wall loosening and increased growth rate (Rayle and Cleland, 1992). Binding of auxin to ABP1 and increased amount of ABP1 at the plasma membrane promote protoplast swelling and enhance expansion of leaf cells (Jones et al, 1998;Steffens et al, 2001;Christian et al, 2006). Conversely, the functional inactivation of ABP1 severely impairs cell expansion in shoot tissues irrespective of their DNA content (Braun et al, 2008;Xu et al, 2010) but does not affect root cell elongation (Tromas et al, 2009).…”