Abstract:

Based on the OsNrt2.1 cDNA sequence of rice (Oryza sativa) cultivar Nipponbare, a nitrate transporter gene OsTNrt2.1 with high similarity with OsNrt2.1 was cloned from TP309, a rice cultivar with high nitrogen use efficiency. The open reading frame of OsTNrt2.1 is 1 602 bp and encodes 533 amino acids. OsTNrt2.1 had the conserved motif and domains to be found in nitrate transporters. It had high similarities with other nitrate transporters in plant species, such as Arabidopsis (Arabidopsis thaliana), maize (Zea mays), wheat (Triticum aestivum), Barley (Hordeum vulgare) and tobacco (Nicotiana plumbaginifolia). The results indicated that the expression level of OsTNrt2.1 was higher in root than in leaf. Otherwise, the expression of OsTNrt2.1 was inhibited by NH₄⁺ and induced by NO₃^- in the medium. The expression pattern of OsTNrt2.1 was affected by photoperiod, showing a typical diurnal regulation with high expression level in the light period. The transcripts of OsTNrt2.1 were similar under different NO₃^- concentrations, suggesting that OsTNrt2.1 is possibly a dual-affinity nitrate transporter. Under the conditions of different nitrogen sources and concentrations in the medium, there were always much more transcripts in roots, suggesting that OsTNrt2.1 has important functions in NO₃^- uptake for roots at different nitrogen levels in the growth medium.

Key words: Rice (Oryza sativa), Nitrate transporter gene, OsTNrt2.1, Gene characterization, Gene expression