Increasing nitrogen use efficiency (NUE) is critical to improve crop yield, reduce N fertilizer demand and alleviate environmental pollution. N remobilization is a key component of NUE. The nitrate transporter NRT1.7 is responsible for loading excess nitrate stored in source leaves into phloem and facilitates nitrate allocation to sink leaves. Under N starvation, the nrt1.7 mutant exhibits growth retardation, indicating that NRT1.7-mediated source-to-sink remobilization of stored nitrate is important for sustaining growth in plants. To energize NRT1.7-mediated nitrate recycling, we introduced a hyperactive chimeric nitrate transporter NC4N driven by the NRT1.7 promoter into the nrt1.7 mutant. NRT1.7p::NC4N::3′ transgenic plants accumulated more nitrate in younger leaves, and ¹⁵NO₃⁻ tracing analysis revealed that more ¹⁵N was remobilized into sink tissues. Consistently, transgenic Arabidopsis, tobacco and rice plants showed improved growth or yield. Our study suggests that enhancing source-to-sink nitrate remobilization represents a new strategy for enhancing NUE and crop production.

提高氮利用效率（NUE）对于提高作物产量、减少氮肥需求和减轻环境污染至关重要。N再动员是NUE的关键组成部分。硝酸盐转运蛋白 NRT1.7 负责将储存在源叶中的过量硝酸盐加载到韧皮部，并促进硝酸盐分配到下沉叶。在 N 饥饿下，nrt1.7突变体表现出生长迟缓，表明 NRT1.7 介导的储存硝酸盐的源到汇再动员对于维持植物的生长很重要。为了激发 NRT1.7 介导的硝酸盐再循环，我们将由NRT1.7启动子驱动的高活性嵌合硝酸盐转运蛋白 NC4N引入到nrt1.7突变体中。NRT1.7p::NC4N::3' 转基因植物在幼叶中积累了更多的硝酸盐，¹⁵ NO ₃ ^-示踪分析表明更多的¹⁵ N 被重新动员到水槽组织中。一致地，转基因拟南芥、烟草和水稻植物表现出改善的生长或产量。我们的研究表明，加强硝酸盐源到汇的再动员是提高 NUE 和作物产量的新策略。