黄瓜是我国设施栽培第一大蔬菜，在生产中氮素过度施用的现象非常普遍。这导致蔬菜成本增加，品质降低，地下水污染等一系列严重的问题。因此黄瓜高效获取和利用氮营养的生理和分子机制是重要研究课题。植物氮响应的局部信号通路已经基本确定，但是长距离运输的系统信号通路还不清楚。黄瓜是研究长距离信号运输的模式系统，韧皮部运输的RNA在植物系统信号中有重要作用。前期研究发现，调控根系形态建成的miR167低氮下在黄瓜的韧皮部液中显著富集，推测RNA系统信号在氮响应中发挥了重要作用。本项目拟基于分根实验系统（split-root system）鉴定韧皮部液中的RNA信号分子，通过嫁接技术鉴定其中未知的从叶芽到根（shoot-to-root）的RNA氮响应系统信号，并通过RNAi确证部分系统信号的功能。本研究有助于将为解析黄瓜氮响应系统信号的遗传调控网络，为在栽培和育种上提高黄瓜和其它作物的氮利用率提供理论依据。

Cucumber is one of the major vegetable in protected cultivation in China, and excessive application of nitrogen on cucumber production is very common, which results in a series of serious problems, such as cost increase, quality decrease, and groundwater pollution. Therefore, research on the molecular mechanism of high-efficiency nitrogen acquisition and utilization in cucumber is an important field. The local signal pathway of plant nitrogen response has been basically determined, however, the long-distance systemic signal pathway is still not clear. Cucumber is the model plant for studying long-distance signal transduction, while phloem-mobile RNAs play vital roles in systemic signaling in plant. Our previous studies showed that miR167, which can regulate root morphogenesis, was enriched in cucumber phloem sap under low nitrogen treatment, indicating RNA systemic signals are important in nitrogen response. Base on split-root system, RNA-seq, small RNA-seq and grafting technology, the current project plan to identify the nitrogen responsive RNA systemic signals in cucumber phloem sap, and to demonstrate the function of some key RNA systemic signals by RNAi. This study will help to uncover genetic regulatory networks of cucumber systemic nitrogen response, and to provide theoretical basis for the utilization rate of nitrogen in cultivation and breeding.