title: The Arabidopsis cax1 mutant exhibits impaired ion homeostasis, development, and hormonal responses and reveals interplay among vacuolar transporters.
abstract: The Arabidopsis Ca(2+)/H(+) transporter CAX1 (Cation Exchanger1) may be an important regulator of intracellular Ca(2+) levels. Here, we describe the preliminary localization of CAX1 to the tonoplast and the molecular and biochemical characterization of cax1 mutants. We show that these mutants exhibit a 50% reduction in tonoplast Ca(2+)/H(+) antiport activity, a 40% reduction in tonoplast V-type H(+)-translocating ATPase activity, a 36% increase in tonoplast Ca(2+)-ATPase activity, and increased expression of the putative vacuolar Ca(2+)/H(+) antiporters CAX3 and CAX4. Enhanced growth was displayed by the cax1 lines under Mn(2+) and Mg(2+) stress conditions. The mutants exhibited altered plant development, perturbed hormone sensitivities, and altered expression of an auxin-regulated promoter-reporter gene fusion. We propose that CAX1 regulates myriad plant processes and discuss the observed phenotypes with regard to the compensatory alterations in other transporters.
authors.affiliation: United States Department of Agriculture/Agricultural Research Service Children's Nutrition Research Center, Baylor College of Medicine, Houston, Texas 77030, USA.
authors.forename: Ning-Hui
authors.initials: NH
authors.lastname: Cheng
authors.forename: Jon K
authors.initials: JK
authors.lastname: Pittman
authors.forename: Bronwyn J
authors.initials: BJ
authors.lastname: Barkla
authors.forename: Toshiro
authors.initials: T
authors.lastname: Shigaki
authors.forename: Kendal D
authors.initials: KD
authors.lastname: Hirschi
mesh_terms: D000483:Alleles; D017920:Antiporters / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D027682:Cation Transport Proteins / Q000378:metabolism; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D006706:Homeostasis / Q000187:drug effects; D017136:Ion Transport / Q000187:drug effects; D009154:Mutation; D010641:Phenotype; D010937:Plant Growth Regulators / Q000494:pharmacology*; D025262:Vacuolar Proton-Translocating ATPases / Q000378:metabolism; D014617:Vacuoles / Q000378:metabolism
chemical_list: D017920:Antiporters; D002135:Calcium-Binding Proteins; D027682:Cation Transport Proteins; D010937:Plant Growth Regulators; C027614:calcium-hydrogen antiporters; D025262:Vacuolar Proton-Translocating ATPases; D002118:Calcium