Functional Identification and Genetic Transformation of the Ammonium Transporter PtrAMT1;6 in Populus

The ammonium transporter (AMT) family gene is an important transporter involved in ammonium uptake and transfer in plants and is mainly engaged in the uptake and transport of ammonium from the environment by roots and the reabsorption of ammonium in the aboveground parts. In this study, the expression pattern, functional identification, and genetic transformation of the PtrAMT1;6 gene, a member of the ammonium transporter protein family in P. trichocarpa, were investigated as follows: (1) Fluorescence quantitative PCR demonstrated that the PtrAMT1;6 gene was preferentially expressed in the leaves, with both dark-induced and light-inhibited expression patterns. (2) A functional restoration assay using the yeast ammonium transporter protein mutant strain indicated that the PtrAMT1;6 gene restored the ability of the mutant to transport ammonium with high affinity. (3) Arabidopsis was transformed with pCAMBIA-PtrAMT1;6P, and the transformed lines were stained with GUS, which showed that the rootstock junction, cotyledon petioles, and the leaf veins and pulp near the petioles of the transformed plants could be stained blue, indicating that the promoter of the PtrAMT1;6 gene had promoter activity. (4) The overexpression of the PtrAMT1;6 gene caused an imbalance in carbon and nitrogen metabolism and reduced nitrogen assimilation ability in ‘84K’ poplar and ultimately reduced biomass. The above results suggest that PtrAMT1;6 may be involved in ammonia recycling during nitrogen metabolism in aboveground parts, and overexpression of PtrAMT1;6 may affect the process of carbon and nitrogen metabolism, as well as nitrogen assimilation in plants, resulting in stunted growth of overexpression plants.