Nitrogen is an essential nutrient for plant growth and development, and plays vital roles in crop yield. Assimilation of nitrogen is thus fine-tuned in response to heterogeneous environments. However, the regulatory mechanism underlying this essential process remains largely unknown. Here, we report that a zinc-finger transcription factor, drought and salt tolerance (DST), controls nitrate assimilation in rice by regulating the expression of OsNR1.2. We found that loss of function of DST results in a significant decrease of nitrogen use efficiency (NUE) in the presence of nitrate. Further study revealed that DST is required for full nitrate reductase activity in rice and directly regulates the expression of OsNR1.2, a gene showing sequence similarity to nitrate reductase. Reverse genetics and biochemistry studies revealed that OsNR1.2 encodes an NADH-dependent nitrate reductase that is required for high NUE of rice. Interestingly, the DST-OsNR1.2 regulatory module is involved in the suppression of nitrate assimilation under drought stress, which contributes to drought tolerance. Considering the negative role of DST in stomata closure, as revealed previously, the positive role of DST in nitrogen assimilation suggests a mechanism coupling nitrogen metabolism and stomata movement. The discovery of this coupling mechanism will aid the engineering of drought-tolerant crops with high NUE in the future.

氮是植物生长发育的必需营养素，对作物产量起着至关重要的作用。因此，氮的同化可以根据异质环境进行微调。然而，这一基本过程背后的调控机制在很大程度上仍然未知。在这里，我们报告了一种锌指转录因子，干旱和耐盐性 (DST)，通过调节OsNR1.2的表达来控制水稻中的硝酸盐同化。我们发现，在硝酸盐存在的情况下， DST功能的丧失导致氮利用效率 (NUE) 显着降低。进一步的研究表明，DST 是水稻中完全硝酸还原酶活性所必需的，并直接调节OsNR1.2的表达，一个显示与硝酸还原酶序列相似性的基因。反向遗传学和生物化学研究表明，OsNR1.2编码水稻高 NUE 所需的 NADH 依赖性硝酸还原酶。有趣的是，DST-OsNR1.2 调节模块参与抑制干旱胁迫下的硝酸盐同化，这有助于提高耐旱性。考虑到 DST 在气孔关闭中的负面作用，如前所述，DST 在氮同化中的积极作用表明了一种耦合氮代谢和气孔运动的机制。这种耦合机制的发现将有助于未来高NUE的耐旱作物的工程化。