title: Auxin Influx Carrier AUX1 Confers Acid Resistance for Arabidopsis Root Elongation Through the Regulation of Plasma Membrane H+-ATPase.
abstract: The plant plasma membrane (PM) H+-ATPase regulates pH homeostasis and cell elongation in roots through the formation of an electrochemical H+gradient across the PM and a decrease in apoplastic pH; however, the detailed signaling for the regulation of PM H+-ATPases remains unclear. Here, we show that an auxin influx carrier, AUXIN RESISTANT1 (AUX1), is required for the maintenance of PM H+-ATPase activity and proper root elongation. We isolated a low pH-hypersensitive 1 (loph1) mutant by a genetic screen of Arabidopsis thaliana on low pH agar plates. The loph1 mutant is a loss-of-function mutant of the AUX1 gene and exhibits a root growth retardation restricted to the low pH condition. The ATP hydrolysis and H+extrusion activities of the PM H+-ATPase were reduced in loph1 roots. Furthermore, the phosphorylation of the penultimate threonine of the PM H+-ATPase was reduced in loph1 roots under both normal and low pH conditions without reduction of the amount of PM H+-ATPase. Expression of the DR5:GUS reporter gene and auxin-responsive genes suggested that endogenous auxin levels were lower in loph1 roots than in the wild type. The aux1-7 mutant roots also exhibited root growth retardation in the low pH condition like the loph1 roots. These results indicate that AUX1 positively regulates the PM H+-ATPase activity through maintenance of the auxin accumulation in root tips, and this process may serve to maintain root elongation especially under low pH conditions.
authors: Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa, Nagoya, 464-8602 Japan.
authors: Shin-Ichiro
authors: SI
authors: Inoue
authors: Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa, Nagoya, 464-8602 Japan.
authors: Koji
authors: K
authors: Takahashi
authors: Department of Biology, Graduate School of Science, Kyushu University, Hakozaki, Fukuoka, 812-8581 Japan.
authors: Hiromi
authors: H
authors: Okumura-Noda
authors: Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa, Nagoya, 464-8602 Japan kinoshita@bio.nagoya-u.ac.jp.|Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Chikusa, Nagoya, 464-8602 Japan.
authors: Toshinori
authors: T
authors: Kinoshita
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism* / Q000502:physiology; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D001692:Biological Transport; D002462:Cell Membrane / Q000201:enzymology*; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D006706:Homeostasis; D006863:Hydrogen-Ion Concentration; D007210:Indoleacetic Acids / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D010766:Phosphorylation; D018517:Plant Roots / Q000201:enzymology / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D006180:Proton-Translocating ATPases / Q000378:metabolism*
chemical_list: C100794:AUX1 protein, Arabidopsis; D029681:Arabidopsis Proteins; D007210:Indoleacetic Acids; D006180:Proton-Translocating ATPases
keywords: 
  Arabidopsis thaliana
  ; AUX1; Auxin; PM H+-ATPase; Phosphorylation; Root