Functional characterization of PsAMT1.1 from Populus simonii in ammonium transport and its role in nitrogen uptake and metabolism

Abstract

Ammonium (NH4+) is an important inorganic nitrogen (N) form essential for plant growth. The role of ammonium transporters (AMTs) in plant growth and how AMTs mediate NH4+ uptake and regulate N metabolism remain vague. To explore the role of AMT1.1 in poplar, PsAMT1.1 was cloned from Populus simonii and was functionally characterized in NH4+ uptake, metabolism and poplar growth. PsAMT1.1 was highly expressed in fine roots and old leaves of P. simonii and PsAMT1.1 protein was located on the plasma membrane. PsAMT1.1 mediates NH4+ uptake in yeast mutants and restores growth with a high-affinity ammonium transporter for NH4+ (Km=79.27 ± 9.5 μM). Transgenic poplar overexpressing PsAMT1.1 showed higher plant height, increased stem diameter, net photosynthetic rate and total biomass than the wild type (WT) (Populus tremula × Populus alba INRA 717-IB4 genotype) after 96 days' of low nitrogen stress. The NH4+ concentration, glutamine concentration, total amino acid and total N content were markedly raised in the roots of PsAMT1.1 overexpression poplar in comparison to WT under low N stress. At the same time, compared with WT, the activities of NR, NiR, GS and GOGAT in both roots and leaves of transgenic poplar overexpressing PsAMT1.1 were significantly increased when the external N was very low. Most of the investigated N-metabolism related genes were upregulated in the roots and leaves of PsAMT1.1-overexpression poplar when N-limitation conditions. In short, PsAMT1.1 has a vital role on nitrogen absorption and metabolism and could increase poplar growth.