BcAMT1;2 interacts with BcLBD41 and BcMAMYB transcription factors during nitrogen metabolism in flowering Chinese...

Chinese cabbage is an important vegetable in southern China. Excessive nitrogen fertilizer application can lead to the accumulation of nitrate in edible organs, which affects food value. Hence, the cultivation of varieties with high nitrogen utilization efficiency (NUE) and low nitrate accumulation is essential for molecular breeding. In flowering Chinese cabbage, Ammonium transporter 1;2 (AMT1;2,XM_009113156.2) significantly promotes plant growth, while reducing the nitrate content and ultimately improving the nutritional value of the crop; however, the exact underlying regulatory mechanisms remain unclear. Here, we aimed to investigate the response pattern of BcAMT1;2 to nitrogen (N) deficiency and mixed ammonium-nitrate nutrition and the potential roles played by its interacting proteins, Lateral organ boundaries domain 41 (LBD41,XM_009120072.3) and Membrane-anchored MYB (MAMYB,XM_009103351.3), in N metabolism. We found that transient silencing and overexpression of BcAMT1;2 regulated the absorption and accumulation of ammonium (NH₄⁺) and nitrate (NO₃^-) in flowering Chinese cabbage. BcLBD41 may directly induce BcAMT1;2 expression, thereby regulating NH₄⁺ accumulation in flowering Chinese cabbages. The expression of BcLBD41 and BcAMT1;2 were downregulated during N-deficiency and upregulated after NH₄⁺ supply restoration. Overexpression of BcLBD41 in Arabidopsis improved root and shoot growth under both LA (low-ammonium; 0.25 mM NH₄⁺) and A/Ni (ammonium [NH₄⁺]: nitrate [NO₃^-]; 0.25 mM:0.75 mM) conditions by facilitating the expression of AtAMT1;2 in transgenic plants, leading to enhanced NH₄⁺ uptake and accumulation. The BcMAMYB protein serves as a transmembrane protein and has a strong interaction with the BcAMT1;2 protein, as well as inducing the expression of the BcAMT1;2 promoter. In the OE-BcMAMYB strain, the expression of both BcMAMYB and BcAMT1;2 were repressed under N-deficiency conditions, whereas after silencing BcMAMYB, the expression of BcAMT1;2 was not induced by ammonium. Our findings contribute to a more profound understanding of the regulatory mechanisms responsible for nitrogen absorption and accumulation in relation to BcAMT1;2.