Mutation of the Arabidopsis NRT1.5 nitrate transporter causes defective root-to-shoot nitrate transport.
Little is known about the molecular and regulatory mechanisms of long-distance nitrate transport in higher plants. NRT1.5 is one of the 53 Arabidopsis thaliana nitrate transporter NRT1 (Peptide Transporter PTR) genes, of which two members, NRT1.1 (CHL1 for Chlorate resistant 1) and NRT1.2, have been shown to be involved in nitrate uptake. Functional analysis of cRNA-injected Xenopus laevis oocytes showed that NRT1.5 is a low-affinity, pH-dependent bidirectional nitrate transporter. Subcellular localization in plant protoplasts and in planta promoter-beta-glucuronidase analysis, as well as in situ hybridization, showed that NRT1.5 is located in the plasma membrane and is expressed in root pericycle cells close to the xylem. Knockdown or knockout mutations of NRT1.5 reduced the amount of nitrate transported from the root to the shoot, suggesting that NRT1.5 participates in root xylem loading of nitrate. However, root-to-shoot nitrate transport was not completely eliminated in the NRT1.5 knockout mutant, and reduction of NRT1.5 in the nrt1.1 background did not affect root-to-shoot nitrate transport. These data suggest that, in addition to that involving NRT1.5, another mechanism is responsible for xylem loading of nitrate. Further analyses of the nrt1.5 mutants revealed a regulatory loop between nitrate and potassium at the xylem transport step.
Lin
Shan-Hua
SH
Institute of Molecular Biology, Academia Sinica, Taipei 11529, Taiwan.
Kuo
Hui-Fen
HF
Canivenc
Geneviève
G
Lin
Choun-Sea
CS
Lepetit
Marc
M
Hsu
Po-Kai
PK
Tillard
Pascal
P
Lin
Huey-Ling
HL
Wang
Ya-Yun
YY
Tsai
Chyn-Bey
CB
Gojon
Alain
A
Tsay
Yi-Fang
YF
D000595:Amino Acid Sequence; D027321:Anion Transport Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D002462:Cell Membrane / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D003001:Cloning, Molecular; D017403:In Situ Hybridization; D017136:Ion Transport; D008969:Molecular Sequence Data; D009154:Mutation; D000091285:Nitrate Transporters; D009566:Nitrates / Q000378:metabolism*; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism; D018520:Plant Shoots / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
D027321:Anion Transport Proteins; D029681:Arabidopsis Proteins; C539716:NRT1.5 protein, Arabidopsis; D000091285:Nitrate Transporters; D009566:Nitrates
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