High impact information on AUX1

• Previous studies have implicated the ubiquitin-ligase SCF(TIR1) and the AUX/IAA proteins in auxin response [1].
• Dominant mutations in several AUX/IAA genes confer pleiotropic auxin-related phenotypes, whereas recessive mutations affecting the function of SCF(TIR1) decrease auxin response [1].
• Arabidopsis AUX1 gene: a permease-like regulator of root gravitropism [2].
• Indole-3-acetic acid, the major form of auxin in higher plants, is structurally similar to tryptophan and is a likely substrate for the AUX1 gene product [2].
• We show that mutations in the MAX4 gene of Arabidopsis result in increased and auxin-resistant bud growth [3].

Biological context of AUX1

• Mutations within the permease-like AUX1 protein significantly reduce the rate of carrier-mediated auxin uptake within Arabidopsis roots, conferring an agravitropic phenotype [4].
• Among them, the ARG1 gene encodes a DnaJ-like protein involved in gravity signal transduction, whereas the AUX1 and AGR1 genes encode proteins involved in polar auxin transport [5].
• The ease of identification of new mutant alleles in the AUX1 gene of Arabidopsis thaliana has provided a useful system to study novel mutations affecting mRNA stability and pre-mRNA splicing [6].
• Mutational approaches in the model plant, Arabidopsis thaliana, have led to the molecular genetic characterization of putative auxin influx and efflux carrier components, AUX1 and AtPIN1 [7].
• The AUX1 and PIN auxin influx and efflux facilitators are key regulators of root growth and development [8].

Anatomical context of AUX1

• Real-time live cell analysis along with subcellular markers revealed that AUX1 resides at the apical plasma membrane of protophloem cells and at highly dynamic subpopulations of Golgi apparatus and endosomes in all cell types [9].
• Here we show that Arabidopsis thaliana SORTING NEXIN 1 (AtSNX1) is involved in the auxin pathway and that PIN2, but not PIN1 or AUX1, is transported through AtSNX1-containing endosomes [10].
• Upon expression of AUX1 in Xenopus oocytes, saturable, pH-dependent uptake of 3H-IAA was measured [11].
• Here we show that AXR4 is a previously unidentified accessory protein of the endoplasmic reticulum (ER) that regulates localization of AUX1 but not of PIN proteins [8].
• Here we report that the presumptive auxin influx carrier AUX1 contributes to apical-basal hair cell polarity [12].

Associations of AUX1 with chemical compounds

• Hence, AUX1 uses a novel trafficking pathway in plants that is distinct from PIN trafficking, providing an additional mechanism for the fine regulation of auxin transport [9].
• Plasma membrane and intracellular pools of AUX1 are interconnected by actin-dependent constitutive trafficking, which is not sensitive to the vesicle trafficking inhibitor brefeldin A [9].
• Furthermore, auxin transport inhibitors and interference with the sterol composition of membranes disrupt polar AUX1 distribution at the plasma membrane [9].
• The measured Km for AUX1-mediated uptake of 3H-IAA was at concentrations at which physiological responses are observed for exogenously added IAA and 2,4-D [11].
• Our results identify AUX1 as one component of a novel BFA-sensitive auxin transport pathway polarizing cells toward a hormone maximum [12].

Other interactions of AUX1

• Apical and basal plasma membrane localization of AUXIN-RESISTANT1 (AUX1) and PIN-FORMED1 (PIN1) auxin transport components underpins the directionality of intercellular auxin flow in Arabidopsis thaliana roots [9].
• Vectorial Information for Arabidopsis Planar Polarity Is Mediated by Combined AUX1, EIN2, and GNOM Activity [13].
• Consistently, the membrane localization of the PIN1 and PIN3 proteins was disturbed in smt1(orc), whereas polar positioning of the influx carrier AUX1 appeared normal [14].
• However, the morphology of double mutant plants indicates that there is an inter-action between the AXR1 and AUX1 genes [15].
• Expression studies using an auxin-regulated reporter suggest that AUX1 is necessary for root gravitropism by facilitating basipetal auxin transport to distal elongation zone tissues [16].

Analytical, diagnostic and therapeutic context of AUX1

• Complementation tests indicate that rgr1 is not allelic to previously characterized agravitropic or auxin-resistant mutants [17].

References