Expression of the cation transporter McHKT1 in a halophyte.
From the ice plant, Mesembryanthemum crystallinum, McHKT1 was isolated encoding a protein 41-61% identical to other plant HKT1-like sequences previously described as potassium or sodium/potassium transporters. McHKT1 acts as a potassium transporter in yeast with specificity similar to that of wheat HKT1. In Xenopus oocytes it transports cations with a specificity Rb+ > Cs+ > [K+ = Na+ = Li+]. McHKT1 is exclusively localized to the plasma membrane. The isoform isolated is most highly expressed in leaves and is present in stems, flowers and seed pods but absent from the root where, according to immunological data, a second isoform exists which does not cross-hybridize with the leaf form in RNA blots at high stringency. McHKT1 transcript amounts increase during the first 6-10 h of stress and then decline to pre-stress levels with kinetics reminiscent of the initial influx of sodium into this halophyte. Immunocytological localization showed strong signals in the leaf vasculature and surrounding mesophyll cells but low-intensity signals are also detected in other cell types. In roots, McHKT is mainly confined to endodermis and stele. Possible functions of McHKT1 in ion homeostasis in the halophytic ice plant are discussed.
Su
Hua
H
Department of Plant Sciences, University of Arizona, Tucson, AZ 85721, USA.
Balderas
Enrique
E
Vera-Estrella
Rosario
R
Golldack
Dortje
D
Quigley
Francoise
F
Zhao
Chengsong
C
Pantoja
Omar
O
Bohnert
Hans J
HJ
D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport; D015152:Blotting, Northern; D027682:Cation Transport Proteins / Q000235:genetics* / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D018506:Gene Expression Regulation, Plant; D005816:Genetic Complementation Test; D035723:Mesembryanthemum / Q000235:genetics*; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D009154:Mutation; D009865:Oocytes / Q000378:metabolism; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics; D011188:Potassium / Q000378:metabolism; D020033:Protein Isoforms / Q000235:genetics; D018749:RNA, Plant / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D012964:Sodium / Q000378:metabolism; D027981:Symporters / Q000235:genetics* / Q000378:metabolism; D014981:Xenopus
D027682:Cation Transport Proteins; D018076:DNA, Complementary; C088864:HKT1 protein, plant; D010940:Plant Proteins; D020033:Protein Isoforms; D018749:RNA, Plant; D027981:Symporters; D012964:Sodium; D011188:Potassium