VcAMT14 Enhances Ammonium Uptake in Blueberries During Mycorrhizal Symbiosis

ABSTRACT Ammonium (NH 4 + ) is a crucial nitrogen (N) form for plant growth. The functions of ammonium transporters (AMTs) in mycorrhizal plants and their role in mediating ammonium uptake and regulating N metabolism in blueberry are not fully understood. In this study, 19 VcAMT genes were identified in blueberry. Tissue‐specific expression analysis revealed that nine VcAMT members exhibited root‐predominant expression patterns, with significant upregulation following inoculation with the O. maius BL01. Notably, VcAMT14 was specifically upregulated during mycorrhizal symbiosis and under N regulation, and subcellular localisation analysis confirmed its protein is located at the plasma membrane. Functional analysis in yeast demonstrated that VcAMT14 mediates NH₄⁺ transport activity. Furthermore, inoculation with O. maius BL01 enhanced rhizosphere soil sucrase activity, soil urease activity, soil phosphatase activity, N content, GS/GOGAT enzyme activity, and the expression levels of related genes in blueberry plants, while simultaneously reducing soil pH. Conversely, VcAMT14 silencing resulted in significantly reduced NH₄⁺ content, GS/GOGAT enzyme activities, and the expression of related genes, along with an increase in the pH of the hydroponic nutrient solution. These findings suggest that VcAMT14 plays a crucial role in regulating N response in blueberry under ERMF symbiosis, providing important insights into the mycorrhiza‐mediated N uptake mechanism.