Overexpression of PsAMT1.2 in poplar enhances nitrogen utilization and resistance to drought stress

Ammonium is an important form of inorganic nitrogen, which is essential for plant growth and development, and the uptake of ammonium is mediated by different members of ammonium transporters (AMTs). It is reported that PsAMT1.2 is specially expressed in the root of poplar, and the overexpression of PsAMT1.2 could improve plant growth and the salt tolerance of poplar. However, the role of AMTs in plant drought and low nitrogen (LN) resistance remains unclear. To understand the role of PsAMT1.2 in drought and LN tolerance, the response of PsAMT1.2-overexpression poplar to polyethylene glycol (PEG)-simulated drought stress (5% PEG) under LN (0.001 mM NH4NO3) and moderate nitrogen (0.5 mM NH4NO3) conditions was investigated. The PsAMT1.2-overexpression poplar showed better growth with increased stem increment, net photosynthetic rate, chlorophyll content, root length, root area, average root diameter and root volume under drought and/or LN stress compared with the wild type (WT). Meanwhile, the content of malondialdehyde significantly decreased, and the activities of superoxide dismutase and catalase significantly increased in the roots and leaves of PsAMT1.2-overexpression poplar compared with WT. The content of NH4+ and NO2- in the roots and leaves of PsAMT1.2-overexpression poplar was increased, and nitrogen metabolism-related genes, such as GS1.3, GS2, Fd-GOGAT and NADH-GOGAT, were significantly upregulated in the roots and/or leaves of PsAMT1.2-overexpression poplar compared with WT under drought and LN stress. The result of this study would be helpful for understanding the function of PsAMT1.2 in plant drought and LN tolerance and also provides a new insight into improving the drought and LN tolerance of Populus at the molecular level.