Genome-Wide Analysis of Ammonium Transporter Genes in Flowering Chinese Cabbage and Functional Insights into BcAMT1.1 Under Low-Nitrogen Conditions

As a primary macronutrient, nitrogen is integral to plant growth and regulates their development; ammonium transporters (AMTs) mediate nitrogen absorption and its involvement in metabolism. In this study, nine <i>BcAMT</i> genes were identified in flowering Chinese cabbage (<i>Brassica campestris</i>) and were systematically categorized into two subfamilies. Their evolutionary relationships, conserved motifs, chromosomal distribution, cis-regulatory elements, and expression profiling were systematically characterized. RNA sequencing and quantitative real-time PCR (qRT-PCR) analyses demonstrated that <i>BcAMT1.1</i> was abundantly expressed in roots, leaves, and stems of flowering Chinese cabbage and was markedly upregulated under nitrogen deficiency. Assessing subcellular location using GFP fusion demonstrated that BcAMT1.1 localized to the plasma membrane. Functional assays identified heterologous expression in the yeast mutant strain 31019b, and transgenic <i>Arabidopsis</i> validated that BcAMT1.1 acted as a functional ammonium transporter. Compared with the wildtype, overexpressing <i>BcAMT1.1</i> promoted seedling growth, enhanced NH₄⁺ influxes and NO₃^- effluxes under low-nitrogen conditions, and significantly increased the transcription levels of key nitrogen assimilation genes (i.e., <i>AtGLN1.1</i>, <i>AtGLN2</i>, <i>AtGDH2</i>). Collectively, our findings enhance the fundamental understanding of <i>BcAMT</i> gene functions and highlight BcAMT1.1 as a crucial component in nitrogen uptake and assimilation under low-nitrogen conditions, providing valuable genetic resources for improving nitrogen efficiency in vegetable crops.