title: The Arabidopsis concentration-dependent influx/efflux transporter ABCB4 regulates cellular auxin levels in the root epidermis.
abstract: Arabidopsis ATP-binding cassette B4 (ABCB4) is a root-localised auxin efflux transporter with reported auxin uptake activity in low auxin concentrations. Results reported here demonstrate that ABCB4 is a substrate-activated regulator of cellular auxin levels. The contribution of ABCB4 to shootward auxin movement at the root apex increases with auxin concentration, but in root hair elongation assays ABCB4-mediated uptake is evident at low concentrations as well. Uptake kinetics of ABCB4 heterologously expressed in Schizosaccharomyces pombe differed from the saturation kinetics of AUX1 as uptake converted to efflux at threshold indole-3-acetic acid (IAA) concentrations. The concentration dependence of ABCB4 appears to be a direct effect on transporter activity, as ABCB4 expression and ABCB4 plasma membrane (PM) localisation at the root apex are relatively insensitive to changes in auxin concentration. However, PM localization of ABCB4 decreases with 1-naphthylphthalamic acid (NPA) treatment. Unlike other plant ABCBs studied to date, and consistent with decreased detergent solubility, ABCB4(pro) :ABCB4-GFP is partially internalised in all cell types by 0.05% DMSO, but not 0.1% ethanol. In trichoblasts, ABCB4(pro) :ABCB4-GFP PM signals are reduced by >200 nm IAA and 2,4-dichlorophenoxyacetic acid (2,4-D). In heterologous systems and in planta, ABCB4 transports benzoic acid with weak affinity, but not the oxidative catabolism products 2-oxindole-3-acetic-acid and 2-oxindole-3-acetyl-β-D-glucose. ABCB4 mediates uptake, but not efflux, of the synthetic auxin 2,4-D in cells lacking AUX1 activity. Results presented here suggest that 2,4-D is a non-competitive inhibitor of IAA transport by ABCB4 and indicate that ABCB4 is a target of 2,4-D herbicidal activity.
authors: Institute of Experimental Botany, the Academy of Sciences of the Czech Republic, Rozvojová 263, CZ-165 02 Prague 6, Czech Republic.
authors: Martin
authors: M
authors: Kubeš
authors: Haibing
authors: H
authors: Yang
authors: Gregory L
authors: GL
authors: Richter
authors: Yan
authors: Y
authors: Cheng
authors: Ewa
authors: E
authors: Młodzińska
authors: Xia
authors: X
authors: Wang
authors: Joshua J
authors: JJ
authors: Blakeslee
authors: Nicola
authors: N
authors: Carraro
authors: Jan
authors: J
authors: Petrášek
authors: Eva
authors: E
authors: Zažímalová
authors: Klára
authors: K
authors: Hoyerová
authors: Wendy Ann
authors: WA
authors: Peer
authors: Angus S
authors: AS
authors: Murphy
mesh_terms: D015084:2,4-Dichlorophenoxyacetic Acid / Q000378:metabolism; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis / Q000166:cytology / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D007210:Indoleacetic Acids / Q000378:metabolism*; D007211:Indoles / Q000378:metabolism; D009154:Mutation; D000078183:Oxindoles; D019441:Plant Epidermis / Q000166:cytology / Q000378:metabolism; D018517:Plant Roots / Q000166:cytology / Q000378:metabolism; D012568:Schizosaccharomyces / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism; D000097202:ATP-Binding Cassette Sub-Family B Member 4
chemical_list: D015084:2,4-Dichlorophenoxyacetic Acid; D018528:ATP-Binding Cassette Transporters; D029681:Arabidopsis Proteins; D007210:Indoleacetic Acids; D007211:Indoles; D000078183:Oxindoles; C000589476:ABCB4 protein, Arabidopsis; D000097202:ATP-Binding Cassette Sub-Family B Member 4; C022960:2-oxindole; C030737:indoleacetic acid