Cellular efflux of auxin catalyzed by the Arabidopsis MDR/PGP transporter AtPGP1.
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.
Geisler
Markus
M
Basel-Zurich Plant Science Center, University of Zurich, Institute of Plant Biology, CH-8007 Zurich, Switzerland.
Blakeslee
Joshua J
JJ
Bouchard
Rodolphe
R
Lee
Ok Ran
OR
Vincenzetti
Vincent
V
Bandyopadhyay
Anindita
A
Titapiwatanakun
Boosaree
B
Peer
Wendy Ann
WA
Bailly
Aurèlien
A
Richards
Elizabeth L
EL
Ejendal
Karin F K
KF
Smith
Aaron P
AP
Baroux
Célia
C
Grossniklaus
Ueli
U
Müller
Axel
A
Hrycyna
Christine A
CA
Dudler
Robert
R
Murphy
Angus S
AS
Martinoia
Enrico
E
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
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