Regulation of GmNRT2 expression and nitrate transport activity in roots of soybean (Glycine max).
A full-length cDNA, GmNRT2, encoding a putative high-affinity nitrate transporter was isolated from a Glycine max (L.) root cDNA library and sequenced. The deduced GmNRT2 protein is 530 amino acids in length and contains 12 putative membrane-spanning domains and a long, hydrophilic C-terminal domain. GmNRT2 is related to high-affinity nitrate transporters in the eukaryotes Chlamydomonas reinhardtii and Aspergillus nidulans, and to putative high-affinity nitrate transporters in barley and tobacco. Southern blot analysis indicated that GmNRT2 is part of a small, multigene family in soybean. Expression of GmNRT2 in roots was regulated by the type of nitrogen source provided to plants: GmNRT2 mRNA levels were barely detectable in ammonium-grown plants, higher in nitrogen-deprived plants, and highest in nitrate-grown plants. Induction of GmNRT2 mRNA levels in roots occurred within 1 h after exposure of plants to nitrate. Nitrate induction of GmNRT2 mRNA levels was accompanied by a fourfold increase in net nitrate uptake by soybean roots at 100 microM external nitrate. The molecular and physiological evidence indicates that GmNRT2 is probably a high-affinity nitrate transporter involved in nitrate uptake by soybean roots.
Amarasinghe
B H
BH
Division of Biochemistry and Molecular Biology, Faculty of Science, Australian National University, Canberra, Australia.
de Bruxelles
G L
GL
Braddon
M
M
Onyeocha
I
I
Forde
B G
BG
Udvardi
M K
MK
D000595:Amino Acid Sequence; D027321:Anion Transport Proteins; D001483:Base Sequence; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D018076:DNA, Complementary; D018744:DNA, Plant; D018506:Gene Expression Regulation, Plant; D008969:Molecular Sequence Data; D005810:Multigene Family; D000091285:Nitrate Transporters; D009566:Nitrates / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism; D012333:RNA, Messenger; D017386:Sequence Homology, Amino Acid; D030262:Soybean Proteins; D013025:Glycine max / Q000235:genetics*
D027321:Anion Transport Proteins; D002352:Carrier Proteins; D018076:DNA, Complementary; D018744:DNA, Plant; D000091285:Nitrate Transporters; D009566:Nitrates; D010940:Plant Proteins; D012333:RNA, Messenger; D030262:Soybean Proteins