P-type ATPase heavy metal transporters with roles in essential zinc homeostasis in Arabidopsis.
Arabidopsis thaliana has eight genes encoding members of the type 1(B) heavy metal-transporting subfamily of the P-type ATPases. Three of these transporters, HMA2, HMA3, and HMA4, are closely related to each other and are most similar in sequence to the divalent heavy metal cation transporters of prokaryotes. To determine the function of these transporters in metal homeostasis, we have identified and characterized mutants affected in each. Whereas the individual mutants exhibited no apparent phenotype, hma2 hma4 double mutants had a nutritional deficiency phenotype that could be compensated for by increasing the level of Zn, but not Cu or Co, in the growth medium. Levels of Zn, but not other essential elements, in the shoot tissues of a hma2 hma4 double mutant and, to a lesser extent, of a hma4 single mutant were decreased compared with the wild type. Together, these observations indicate a primary role for HMA2 and HMA4 in essential Zn homeostasis. HMA2promoter- and HMA4promoter-reporter gene constructs provide evidence that HMA2 and HMA4 expression is predominantly in the vascular tissues of roots, stems, and leaves. In addition, expression of the genes in developing anthers was confirmed by RT-PCR and was consistent with a male-sterile phenotype in the double mutant. HMA2 appears to be localized to the plasma membrane, as indicated by protein gel blot analysis of membrane fractions using isoform-specific antibodies and by the visualization of an HMA2-green fluorescent protein fusion by confocal microscopy. These observations are consistent with a role for HMA2 and HMA4 in Zn translocation. hma2 and hma4 mutations both conferred increased sensitivity to Cd in a phytochelatin-deficient mutant background, suggesting that they may also influence Cd detoxification.
Hussain
Dawar
D
Department of Genetics, University of Melbourne, Australia 3010.
Haydon
Michael J
MJ
Wang
Yuwen
Y
Wong
Edwin
E
Sherson
Sarah M
SM
Young
Jeff
J
Camakaris
James
J
Harper
Jeffrey F
JF
Cobbett
Christopher S
CS
D000251:Adenosine Triphosphatases / Q000235:genetics* / Q000378:metabolism*; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D027682:Cation Transport Proteins / Q000235:genetics* / Q000378:metabolism; D035264:Flowers / Q000235:genetics; D005838:Genotype; D049452:Green Fluorescent Proteins; D006706:Homeostasis; D008164:Luminescent Proteins / Q000235:genetics; D008969:Molecular Sequence Data; D010641:Phenotype; D030821:Plants, Genetically Modified; D012333:RNA, Messenger / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015032:Zinc / Q000378:metabolism*
D029681:Arabidopsis Proteins; D027682:Cation Transport Proteins; D008164:Luminescent Proteins; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D000251:Adenosine Triphosphatases; D015032:Zinc