title: AtNHX8, a member of the monovalent cation: proton antiporter-1 family in Arabidopsis thaliana, encodes a putative Li/H antiporter.
abstract: The Arabidopsis monovalent cation:proton antiporter-1 (CPA1) family includes eight members, AtNHX1-8. AtNHX1 and AtNHX7/SOS1 have been well characterized as tonoplast and plasma membrane Na+/H+ antiporters, respectively. The proteins AtNHX2-6 have been phylogenetically linked to AtNHX1, while AtNHX8 appears to be related to AtNHX7/SOS1. Here we report functional characterization of AtNHX8. AtNHX8 T-DNA insertion mutants are hypersensitive to lithium ions (Li+) relative to wild-type plants, but not to the other metal ions such as sodium (Na+), potassium (K+) and caesium (Cs+). AtNHX8 overexpression in a triple-deletion yeast mutant AXT3 that exhibits defective Na+/Li+ transport specifically suppresses sensitivity to Li+, but does not affect Na+ sensitivity. Likewise, AtNHX8 overexpression complemented sensitivity to Li+, but not Na+, in sos1-1 mutant seedlings, and increased Li+ tolerance of both the sos1-1 mutant and wild-type seedlings. Results of Li+ and K+ measurement of loss-of-function and gain-of-function mutants indicate that AtNHX8 may be responsible for Li+ extrusion, and may be able to maintain K+ acquisition and intracellular ion homeostasis. Subcellular localization of the AtNHX8-enhanced green fluorescent protein (EGFP) fusion protein suggested that AtNHX8 protein is targeted to the plasma membrane. Taken together, our findings suggest that AtNHX8 encodes a putative plasma membrane Li+/H+ antiporter that functions in Li detoxification and ion homeostasis in Arabidopsis.
authors.affiliation: State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing 100094, China.
authors.forename: Rui
authors.initials: R
authors.lastname: An
authors.forename: Qi-Jun
authors.initials: QJ
authors.lastname: Chen
authors.forename: Mao-Feng
authors.initials: MF
authors.lastname: Chai
authors.forename: Ping-Li
authors.initials: PL
authors.lastname: Lu
authors.forename: Zhao
authors.initials: Z
authors.lastname: Su
authors.forename: Zhi-Xiang
authors.initials: ZX
authors.lastname: Qin
authors.forename: Jia
authors.initials: J
authors.lastname: Chen
authors.forename: Xue-Chen
authors.initials: XC
authors.lastname: Wang
mesh_terms: D017920:Antiporters / Q000235:genetics* / Q000502:physiology; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000502:physiology; D001692:Biological Transport / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D008094:Lithium / Q000378:metabolism; D018021:Lithium Chloride / Q000494:pharmacology; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D009154:Mutation; D011188:Potassium / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics; D011522:Protons; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000502:physiology
chemical_list: D017920:Antiporters; D029681:Arabidopsis Proteins; C520771:NHX8 protein, Arabidopsis; D011522:Protons; D011993:Recombinant Fusion Proteins; D017923:Sodium-Hydrogen Exchangers; D049452:Green Fluorescent Proteins; D008094:Lithium; D018021:Lithium Chloride; D011188:Potassium