Molecular identification of tobacco NtAMT1.3 that mediated ammonium root-influx with high affinity and improved plant growth on ammonium when overexpressed in Arabidopsis and tobacco.

Although biological functions of ammonium (NH4 + ) transporters (AMTs) have been intensively studied in many plant species, little is known about molecular bases responsible for NH4 + movement in tobacco. Here, we reported the identification and functional characterization of a putative NH4 + transporter NtAMT1.3 from tobacco (Nicotiana tabacum). Analysis in silico showed that NtAMT1.3 encoded an integral membrane protein containing 464 amino acid residues and exhibiting 10 predicted transmembrane α-helices. Heterologous functionality study demonstrated that NtAMT1.3 expression facilitated NH4 + entry across plasma membrane of NH4 + -uptake defective yeast and Arabidopsis qko mutant, allowing a restored growth of both yeast and Arabidopsis mutant on low NH4 + . qPCR assay revealed that NtAMT1.3 was expressed in both roots and leaves and significantly up-regulated by nitrogen starvation and resupply of its putative substrate NH4 + and even nitrate, suggesting that NtAMT1.3 should represent a nitrogen-responsive gene. Critically, constitutive overexpression of NtAMT1.3 in tobacco per se improved obviously the growth of transgenic plants on NH4 + and enhanced leaf nitrogen (15% more) accumulation, consistent with observation of 35% more NH4 + uptake by the roots of transgenic lines in 20min root-influx test. Together with data showing its plasma membrane localization and saturated transport nature with Km of about 50μM for NH4 + , we suggest that NtAMT1.3 acts an active NH4 + transporter that plays a significant role in NH4 + acquisition and utilization in tobacco.