Regulation of GmNRT2 expression and nitrate transport activity in roots of soybean (Glycine max)

Ranamalie Amarasinghe, B. H.R. and De Bruxelles, Guy L. and Braddon, Marysha and Onyeocha, Ignatius and Forde, Brian G. and Udvardi, Michael K. (1998) Regulation of GmNRT2 expression and nitrate transport activity in roots of soybean (Glycine max). Planta, 206 (1). pp. 44-52. ISSN 0032-0935

Abstract

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 μM external nitrate. The molecular and physiological evidence indicates that GmNRT2 is probably a high-affinity nitrate transporter involved in nitrate uptake by soybean roots.