title: Block of ATP-binding cassette B19 ion channel activity by 5-nitro-2-(3-phenylpropylamino)-benzoic acid impairs polar auxin transport and root gravitropism.
abstract: Polar transport of the hormone auxin through tissues and organs depends on membrane proteins, including some B-subgroup members of the ATP-binding cassette (ABC) transporter family. The messenger RNA level of at least one B-subgroup ABCB gene in Arabidopsis (Arabidopsis thaliana), ABCB19, increases upon treatment with the anion channel blocker 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB), possibly to compensate for an inhibitory effect of the drug on ABCB19 activity. Consistent with this hypothesis, NPPB blocked ion channel activity associated with ABCB19 expressed in human embryonic kidney cells as measured by patch-clamp electrophysiology. NPPB inhibited polar auxin transport through Arabidopsis seedling roots similarly to abcb19 mutations. NPPB also inhibited shootward auxin transport, which depends on the related ABCB4 protein. NPPB substantially decreased ABCB4 and ABCB19 protein levels when cycloheximide concomitantly inhibited new protein synthesis, indicating that blockage by NPPB enhances the degradation of ABCB transporters. Impairing the principal auxin transport streams in roots with NPPB caused aberrant patterns of auxin signaling reporters in root apices. Formation of the auxin-signaling gradient across the tips of gravity-stimulated roots, and its developmental consequence (gravitropism), were inhibited by micromolar concentrations of NPPB that did not affect growth rate. These results identify ion channel activity of ABCB19 that is blocked by NPPB, a compound that can now be considered an inhibitor of polar auxin transport with a defined molecular target.
authors.affiliation: Department of Botany, University of Wisconsin, Madison, Wisconsin 53706 (M.C., E.M.H., G.W., E.P.S.); andDepartment of Biology, Wake Forest University, Winston-Salem, North Carolina 27109 (D.R.L., G.K.M.).
authors.forename: Misuk
authors.initials: M
authors.lastname: Cho
authors.affiliation: Department of Botany, University of Wisconsin, Madison, Wisconsin 53706 (M.C., E.M.H., G.W., E.P.S.); andDepartment of Biology, Wake Forest University, Winston-Salem, North Carolina 27109 (D.R.L., G.K.M.).
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Henry
authors.affiliation: Department of Botany, University of Wisconsin, Madison, Wisconsin 53706 (M.C., E.M.H., G.W., E.P.S.); andDepartment of Biology, Wake Forest University, Winston-Salem, North Carolina 27109 (D.R.L., G.K.M.).
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Lewis
authors.affiliation: Department of Botany, University of Wisconsin, Madison, Wisconsin 53706 (M.C., E.M.H., G.W., E.P.S.); andDepartment of Biology, Wake Forest University, Winston-Salem, North Carolina 27109 (D.R.L., G.K.M.).
authors.forename: Guosheng
authors.initials: G
authors.lastname: Wu
authors.affiliation: Department of Botany, University of Wisconsin, Madison, Wisconsin 53706 (M.C., E.M.H., G.W., E.P.S.); andDepartment of Biology, Wake Forest University, Winston-Salem, North Carolina 27109 (D.R.L., G.K.M.).
authors.forename: Gloria K
authors.initials: GK
authors.lastname: Muday
authors.affiliation: Department of Botany, University of Wisconsin, Madison, Wisconsin 53706 (M.C., E.M.H., G.W., E.P.S.); andDepartment of Biology, Wake Forest University, Winston-Salem, North Carolina 27109 (D.R.L., G.K.M.) spalding@wisc.edu.
authors.forename: Edgar P
authors.identifier: http://orcid.org/0000-0002-8690-4765
authors.initials: EP
authors.lastname: Spalding
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects; D018506:Gene Expression Regulation, Plant; D018522:Gravitropism / Q000187:drug effects; D007210:Indoleacetic Acids / Q000378:metabolism*; D007473:Ion Channels; D009154:Mutation; D009579:Nitrobenzoates / Q000494:pharmacology*; D018517:Plant Roots / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D036226:Seedlings / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D015398:Signal Transduction
chemical_list: C532604:ABCB19 protein, Arabidopsis; D018528:ATP-Binding Cassette Transporters; D029681:Arabidopsis Proteins; D007210:Indoleacetic Acids; D007473:Ion Channels; D009579:Nitrobenzoates; C058176:5-nitro-2-(3-phenylpropylamino)benzoic acid