title: Functional analysis of the three HMA4 copies of the metal hyperaccumulator Arabidopsis halleri.
abstract: In Arabidopsis halleri, the HMA4 gene has an essential function in Zn/Cd hypertolerance and hyperaccumulation by mediating root-to-shoot translocation of metals. Constitutive high expression of AhHMA4 results from a tandem triplication and cis-activation of the promoter of all three copies. The three AhHMA4 copies possess divergent promoter sequences, but highly conserved coding sequences, and display identical expression profiles in the root and shoot vascular system. Here, an AhHMA4::GFP fusion was expressed under the control of each of the three A. halleri HMA4 promoters in a hma2hma4 double mutant of A. thaliana to individually examine the function of each AhHMA4 copy. The protein showed non-polar localization at the plasma membrane of the root pericycle cells of both A. thaliana and A. halleri. The expression of each AhHMA4::GFP copy complemented the severe Zn-deficiency phenotype of the hma2hma4 mutant by restoring root-to-shoot translocation of Zn. However, each copy had a different impact on metal homeostasis in the A. thaliana genetic background: AhHMA4 copies 2 and 3 were more highly expressed and provided higher Zn tolerance in roots and accumulation in shoots than copy 1, and AhHMA4 copy 3 also increased Cd tolerance in roots. These data suggest a certain extent of functional differentiation among the three A. halleri HMA4 copies, stemming from differences in expression levels rather than in expression profile. HMA4 is a key node of the Zn homeostasis network and small changes in expression level can have a major impact on Zn allocation to root or shoot tissues.
authors.affiliation: Functional Genomics and Plant Molecular Imaging, Center for Protein Engineering (CIP), Department of Life Sciences, University of Liège, B-4000 Liège, Belgium.
authors.forename: Cécile
authors.initials: C
authors.lastname: Nouet
authors.affiliation: Functional Genomics and Plant Molecular Imaging, Center for Protein Engineering (CIP), Department of Life Sciences, University of Liège, B-4000 Liège, Belgium.
authors.forename: Jean-Benoit
authors.initials: JB
authors.lastname: Charlier
authors.affiliation: Laboratory of Plant and Microbial Ecology, Department of Biology, Ecology, Evolution, University of Liège, B-4000 Liège, Belgium.
authors.forename: Monique
authors.initials: M
authors.lastname: Carnol
authors.affiliation: Laboratory of Plant and Microbial Ecology, Department of Biology, Ecology, Evolution, University of Liège, B-4000 Liège, Belgium.
authors.forename: Bernard
authors.initials: B
authors.lastname: Bosman
authors.affiliation: Biostatistics and Bioinformatics, FARAH, Faculty of Veterinary Medicine, University of Liège, B-4000 Liège, Belgium.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Farnir
authors.affiliation: Functional Genomics and Plant Molecular Imaging, Center for Protein Engineering (CIP), Department of Life Sciences, University of Liège, B-4000 Liège, Belgium PhytoSYSTEMS, University of Liège, B-4000 Liège, Belgium.
authors.forename: Patrick
authors.initials: P
authors.lastname: Motte
authors.affiliation: Functional Genomics and Plant Molecular Imaging, Center for Protein Engineering (CIP), Department of Life Sciences, University of Liège, B-4000 Liège, Belgium PhytoSYSTEMS, University of Liège, B-4000 Liège, Belgium marc.hanikenne@ulg.ac.be.
authors.forename: Marc
authors.initials: M
authors.lastname: Hanikenne
mesh_terms: D000251:Adenosine Triphosphatases / Q000235:genetics* / Q000378:metabolism; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D018076:DNA, Complementary / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006706:Homeostasis; D008670:Metals / Q000378:metabolism; D009154:Mutation; D011401:Promoter Regions, Genetic; D017422:Sequence Analysis, DNA
chemical_list: D029681:Arabidopsis Proteins; D018076:DNA, Complementary; D008670:Metals; D049452:Green Fluorescent Proteins; D000251:Adenosine Triphosphatases; C477864:HMA4 protein, Arabidopsis
keywords: Arabidopsis relative; P-type ATPase; cadmium; metal homeostasis; metal hyperaccumulation; metal hypertolerance; zinc.