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 developmental reg-ulation; ammonium transporters (AMTs) mediate its absorption and involvement in ni-trogen metabolism. In this study, nine BcAMT genes were identified from flowering Chi-nese cabbage (Brassica campestris), which were systematically categorized into two sub-families. Their evolutionary relationships, conserved motifs, chromosomal distribution, cis-regulatory elements, and expression profiling were systematically characterized. RNA-sequencing and RT-PCR analyses demonstrated that BcAMT1.1 was abundantly expressed in roots, leaves, and stems of flowering Chinese cabbage, and was markedly up-regulated under nitrogen deficiency or low-nitrogen conditions. Subcellular location using GFP-fusion demonstrated that BcAMT1.1 localized to the plasma membrane. Func-tional assays through heterologous expression in the yeast mutant strain 31019b and transgenic Arabidopsis validated that BcAMT1.1 acted as a functional ammonium trans-porter. Compared with wildtype, overexpressing BcAMT1.1 promoted seedling growth, enhanced NH4+ influxes and NO3- effluxes under low nitrogen conditions, and signifi-cantly increased the transcription levels of key nitrogen assimilation genes (i.e., AtGLN1.1, AtGLN2, AtGDH2). Collectively, our findings enhance the fundamental understanding of BcAMT gene functions, and highlighting of BcAMT1.1 as a crucial component in nitrogen uptake and assimilation under low nitrogen conditions, and providing valuable genetic resources for improving nitrogen efficiency in vegetable crops.