Characterization and expression analysis of BcAMT1;4, an ammonium transporter gene in flowering Chinese cabbage

Abstract

Ammonium (NH4+) is generated during many endogenous metabolic processes in the leaves of plants, and there is increasing evidence that ammonium transporters (AMTs) play important roles in NH4+ transmembrane transport and distribution. However, the expression of different AMT genes is tissue-type specific and their functions differ. Information about AMT genes and their expression under different environmental conditions in flowering Chinese cabbage (Brassica campestris L.) is currently limited. Here, we isolated and characterized an AMT gene, BcAMT1;4, in flowering Chinese cabbage. BcAMT1;4 was localized to the plasma membrane and complemented NH4+ transport in NH4+ uptake-deficient yeast. The highest expression levels of BcAMT1;4 were detected in the flowers and leaves of flowering Chinese cabbage. The expression of BcAMT1;4 was induced by nitrogen deficiency and significantly inhibited by the reapplication of NH4+ (NH4Cl or NH4NO3). In contrast, when plants pre-cultured in nitrate were transferred to an NH4+ nutrient solution, BcAMT1;4 expression was significantly enhanced. BcAMT1;4 exhibited a diurnal expression pattern, with higher expression levels during the light period than during the dark period, and a peak expression at the later stage of the light period. Knowledge of AMT genes in flowering Chinese cabbage will lay a foundation for enhancing our understanding of the functional roles of different AMT members in the regulation of its growth by NH4+, as BcAMT1;4 seems to play an important role in leaf NH4+ transport.