title: Cellular efflux of auxin catalyzed by the Arabidopsis MDR/PGP transporter AtPGP1.
abstract: Directional transport of the phytohormone auxin is required for the establishment and maintenance of plant polarity, but the underlying molecular mechanisms have not been fully elucidated. Plant homologs of human multiple drug resistance/P-glycoproteins (MDR/PGPs) have been implicated in auxin transport, as defects in MDR1 (AtPGP19) and AtPGP1 result in reductions of growth and auxin transport in Arabidopsis (atpgp1, atpgp19), maize (brachytic2) and sorghum (dwarf3). Here we examine the localization, activity, substrate specificity and inhibitor sensitivity of AtPGP1. AtPGP1 exhibits non-polar plasma membrane localization at the shoot and root apices, as well as polar localization above the root apex. Protoplasts from Arabidopsis pgp1 leaf mesophyll cells exhibit reduced efflux of natural and synthetic auxins with reduced sensitivity to auxin efflux inhibitors. Expression of AtPGP1 in yeast and in the standard mammalian expression system used to analyze human MDR-type proteins results in enhanced efflux of indole-3-acetic acid (IAA) and the synthetic auxin 1-naphthalene acetic acid (1-NAA), but not the inactive auxin 2-NAA. AtPGP1-mediated efflux is sensitive to auxin efflux and ABC transporter inhibitors. As is seen in planta, AtPGP1 also appears to mediate some efflux of IAA oxidative breakdown products associated with apical sites of high auxin accumulation. However, unlike what is seen in planta, some additional transport of the benzoic acid is observed in yeast and mammalian cells expressing AtPGP1, suggesting that other factors present in plant tissues confer enhanced auxin specificity to PGP-mediated transport.
authors.affiliation: Basel-Zurich Plant Science Center, University of Zurich, Institute of Plant Biology, CH-8007 Zurich, Switzerland.
authors.forename: Markus
authors.initials: M
authors.lastname: Geisler
authors.forename: Joshua J
authors.initials: JJ
authors.lastname: Blakeslee
authors.forename: Rodolphe
authors.initials: R
authors.lastname: Bouchard
authors.forename: Ok Ran
authors.initials: OR
authors.lastname: Lee
authors.forename: Vincent
authors.initials: V
authors.lastname: Vincenzetti
authors.forename: Anindita
authors.initials: A
authors.lastname: Bandyopadhyay
authors.forename: Boosaree
authors.initials: B
authors.lastname: Titapiwatanakun
authors.forename: Wendy Ann
authors.initials: WA
authors.lastname: Peer
authors.forename: Aurèlien
authors.initials: A
authors.lastname: Bailly
authors.forename: Elizabeth L
authors.initials: EL
authors.lastname: Richards
authors.forename: Karin F K
authors.initials: KF
authors.lastname: Ejendal
authors.forename: Aaron P
authors.initials: AP
authors.lastname: Smith
authors.forename: Célia
authors.initials: C
authors.lastname: Baroux
authors.forename: Ueli
authors.initials: U
authors.lastname: Grossniklaus
authors.forename: Axel
authors.initials: A
authors.lastname: Müller
authors.forename: Christine A
authors.initials: CA
authors.lastname: Hrycyna
authors.forename: Robert
authors.initials: R
authors.lastname: Dudler
authors.forename: Angus S
authors.initials: AS
authors.lastname: Murphy
authors.forename: Enrico
authors.initials: E
authors.lastname: Martinoia
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D001693:Biological Transport, Active; D018506:Gene Expression Regulation, Plant / Q000502:physiology; D006367:HeLa Cells; D006801:Humans; D007210:Indoleacetic Acids / Q000378:metabolism*; D009154:Mutation; D009280:Naphthaleneacetic Acids / Q000378:metabolism; D010641:Phenotype; D010937:Plant Growth Regulators / Q000378:metabolism*; D018517:Plant Roots / Q000378:metabolism; D018520:Plant Shoots / Q000378:metabolism; D012441:Saccharomyces cerevisiae; D013379:Substrate Specificity
chemical_list: D018528:ATP-Binding Cassette Transporters; C114215:ATPGP1 protein, Arabidopsis; D029681:Arabidopsis Proteins; D007210:Indoleacetic Acids; D009280:Naphthaleneacetic Acids; D010937:Plant Growth Regulators; C034182:1-naphthaleneacetic acid; C030737:indoleacetic acid