Characterization and expression of a high-affinity nitrate system transporter gene (TaNRT2.1) from wheat roots, and its evolutionary relationship to other NTR2 genes

Higher plants have two nitrate uptake systems, designated as the high- and low-affinity transporter systems (HATS and LATS, respectively). Here we report the isolation and characterization of a new nitrate transporter gene (TaNRT2.1) from wheat. Alignment and comparative analyses of the deduced amino acid sequence from TaNRT2.1 cDNA with known higher plant nitrate transport proteins indicated that this gene encodes a member of the HATS family. Genomic Southern analysis illustrated that TaNRT2.1 is present as a single copy in the wheat genome. Northern analysis demonstrated that TaNRT2.1 mRNA accumulated in roots, but was not present in leaves. Accumulation of TaNRT2.1 mRNA was transiently induced by nitrate, showing a rapid increase by 1 h following NO3− treatment, reaching a maximum at 4 h after treatment, and then decreased to the original level by 24 h. Transcript levels did not increase with NH4+ induction. TaNRT2.1 also showed increased levels of expression under 0.05 mM as well as 10 mM NO3− concentrations, relative to untreated control or NO3− starved plants. TaNRT2.1 expression patterns suggest it may be a candidate gene of the inducible HATS (iHATS) gene family. Phylogenic analysis indicated that known plant NRT2 genes occur within a single monophylic group, with three subgroups. These subgroups, two showing preferential expression in roots and one in shoots, appear to have differentiated before the split of monocots from other flowering plants. TaNRT2.1 is the orthologue of AtNRT2.1 in the NRT2 phylogenic tree.