A plasma membrane zinc transporter from Medicago truncatula is up-regulated in roots by Zn fertilization, yet down-regulated by arbuscular mycorrhizal colonization.
Here we present a Zn transporter cDNA named MtZIP2 from the model legume Medicago truncatula. MtZIP2 encodes a putative 37 kDa protein with 8-membrane spanning domains and has moderate amino acid identity with the Arabidopsis thaliana Zn transporter AtZIP2p. MtZIP2 complemented a Zn-uptake mutant of yeast implying that the protein encoded by this gene can transport Zn across the yeast's plasma membrane. The product of a MtZIP2-GFP fusion construct introduced into onion cells by particle bombardment likewise localized to the plasma membrane. The MtZIP2 gene was expressed in roots and stems, but not in leaves of M. truncatula and, in contrast to all other plant Zn transporters characterized thus far, MtZIP2 was up-regulated in roots by Zn fertilization. Expression was highest in roots exposed to a toxic level of Zn. MtZIP2 expression was also examined in the roots of M. truncatula when colonized by the obligate plant symbiont, arbuscular mycorrhizal (AM) fungi, since AM fungi are renowned for their ability to supply plants with mineral nutrients, including Zn. Expression was down-regulated in the roots of the mycorrhizal plants and was associated with a reduced level of Zn within the host plant tissues.
Burleigh
Stephen H
SH
Plant Research Department, Riø National Laboratory, 4000 Roskilde, Denmark. stephen.burleigh@mbioekol.lu.se
Kristensen
Brian K
BK
Bechmann
Iben Ellegaard
IE
D000595:Amino Acid Sequence; D001692:Biological Transport / Q000235:genetics; D002462:Cell Membrane / Q000378:metabolism; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification; D015536:Down-Regulation; D005308:Fertilizers; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D005816:Genetic Complementation Test; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D029902:Medicago / Q000187:drug effects / Q000235:genetics* / Q000382:microbiology; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D009154:Mutation; D038821:Mycorrhizae / Q000254:growth & development*; D010802:Phylogeny; D018517:Plant Roots / Q000187:drug effects / Q000235:genetics* / Q000382:microbiology; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013559:Symbiosis / Q000235:genetics; D015854:Up-Regulation; D015032:Zinc / Q000378:metabolism / Q000494:pharmacology*
D018076:DNA, Complementary; D005308:Fertilizers; D008164:Luminescent Proteins; D026901:Membrane Transport Proteins; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D015032:Zinc