Cloning and characterization of the nitrate transporter gene BraNRT2.1 in non-heading Chinese cabbage

Abstract

To improve the efficiency of nitrogen use and to reduce the accumulation of nitrates in vegetables, an improved understanding of the mechanisms that regulate nitrate uptake and signaling is essential. Nitrogen use is regulated largely by the nitrate transporter genes, but few studies have examined the nitrate transporter genes in non-heading Chinese cabbage (Brassica rapa ssp. Chinensis Makino), one of the most important leafy vegetables in East Asia. In this study, the nitrate transporter gene BraNRT2.1 was isolated from non-heading Chinese cabbage. The cDNA for this gene contains an open reading frame of 1593 base pairs and encodes a predicted protein of 530 amino acid residues. Analysis of the BraNRT2.1 showed that BraNRT2.1 was expressed mainly in the roots and that the transcription of the gene was induced following exposure to 250 μM and 25 mM nitrate. In addition, GUS staining revealed that the BraNRT2.1 promoter directed expression to the roots. The BraNRT2.1-YFP fusion protein was observed to be localized to the plasma membrane. Finally, we observed that BraNRT2.1 could restore nitrate uptake in the presence of 200 μM nitrate in Arabidopsis thaliana plants lacking AtNRT2.1 function. Together, these results demonstrate that BraNRT2.1 encodes a high-affinity nitrate transporter that participates in nitrate uptake. These findings provide a foundation for future studies and plant breeding to improve the efficiency of nitrogen use and to reduce the accumulation of nitrates in vegetables.