根据Nipponbare的OsNrt2.1 cDNA序列，从氮效率较高的水稻品种TP309中克隆了与OsNrt2.1高度同源的硝酸盐转运蛋白（NRT）基因OsTNrt2.1。其开放阅读框为1 602 bp，编码533个氨基酸残基。OsTNrt2.1具有NRT共有的结构特征，与拟南芥、玉米、小麦、大麦和烟草的NRT基因高度同源。OsTNrt2.1的表达表现器官特异性，在根中高于在叶中。此外，OsTNrt2.1的表达受NH4+的抑制和NO3-的诱导，并具典型的昼夜节律特征。在不同NO3-浓度下，OsTNrt2.1的表达水平相近，表明OsTNrt2.1可能是具有双亲和特征的NRT基因。在不同氮源及不同介质氮浓度条件下，OsTNrt2.1在根中的表达均高于在叶中，表明OsTNrt2.1对于根系吸收NO3-可能具有重要作用。
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.
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