title: HvHMA2, a P(1B)-ATPase from barley, is highly conserved among cereals and functions in Zn and Cd transport.
abstract: Manipulation of crops to improve their nutritional value (biofortification) and optimisation of plants for removal of toxic metals from contaminated soils (phytoremediation) are major goals. Identification of membrane transporters with roles in zinc and cadmium transport would be useful for both aspects. The P(1B)-ATPases play important roles in heavy metal allocation and detoxification in Arabidopsis and it is now important to elucidate their roles in monocots. We identified nine P(1B)-ATPases in barley and this study focuses on the functional characterization of HvHMA2, providing evidence for its role in heavy metal transport. HvHMA2 was cloned using information from EST analysis and 5' RACE. It possesses the conserved aspartate that is phosphorylated during the reaction cycle of P-type pumps and has motifs and key residues characteristic of P(1B)-ATPases, falling into the P(1B-2) subclass. Homologous sequences occur in three major sub-families of the Poaceae (Gramineae). Heterologous expression in Saccharomyces cerevisiae demonstrates that HvHMA2 functions as a Zn and Cd pump. Mutagenesis studies show that proposed cation coordination sites of the P(1B-2) pumps are crucial for the metal responses conferred by HvHMA2 in yeast. HvHMA2 expression suppresses the Zn-deficient phenotype of the Arabidopsis hma2hma4 mutant indicating that HvHMA2 functions as a Zn pump in planta and could play a role in root to shoot Zn transport. When expressed in Arabidopsis, HvHMA2 localises predominantly to the plasma membrane.
authors.affiliation: Centre for Biological Sciences, University of Southampton, Highfield Campus, Southampton, United Kingdom.
authors.forename: Rebecca F
authors.initials: RF
authors.lastname: Mills
authors.forename: Kerry A
authors.initials: KA
authors.lastname: Peaston
authors.forename: John
authors.initials: J
authors.lastname: Runions
authors.forename: Lorraine E
authors.initials: LE
authors.lastname: Williams
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry* / Q000235:genetics; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development; D001692:Biological Transport; D002104:Cadmium / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D017124:Conserved Sequence / Q000235:genetics*; D002523:Edible Grain / Q000201:enzymology*; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D001467:Hordeum / Q000201:enzymology* / Q000235:genetics* / Q000254:growth & development; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D010802:Phylogeny; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D012639:Seeds / Q000235:genetics / Q000254:growth & development; D016415:Sequence Alignment; D015032:Zinc / Q000378:metabolism*
chemical_list: D010940:Plant Proteins; D002104:Cadmium; D000251:Adenosine Triphosphatases; D015032:Zinc