氮是植物从土壤中吸收最多的元素之一，它不仅作为植物必须的营养元素调控植物的生长发育，还能作为一种信号物质调控植物生长来适应周围多变的土壤环境。近年来随着氮肥的不合理利用引发的环境问题越发严重，改良作物品种，提高作物的氮利用率是目前迫切需要解决的问题。油菜素内酯是一种重要的植物激素，调控众多的植物学发育过程。申请人前期的研究工作显示油菜素内酯对植物硝态氮的信号转导有显著的调控作用。为解析油菜素内酯调控植物氮信号转导的分子机理，申请人系统分析了油菜素内脂信号转导各个组份在氮信号转导中的功能，并将对其中的一个bHLH转录因子HBI1及其互做蛋白HITs进行深入研究，以期阐明油菜素内酯在植物氮信号转导中的功能，并为我们下一步利用油菜素内酯培育氮高效作物新品种和农业合理施肥提供理论指导和技术支持。

Nitrogen is an essential mineral element that affects plant growth and development, and is also an important signal molecular to regulate plant to adapt to the changing soil environment conditions. Nitrogen fertilizers are the major driving force for improvement of crop yield. However, application of nitrogen fertilizers leads to quite a number of problems including soil acidification, water eutrophication and increased production cost. The best solution to these problems is improving nitrogen use efficiency of crops. Our previous study indicated that brassinosteroid, a key phytohormone for plant growth and development, play an important role for nitrogen signal transduction. Here in this proposal, we will take advantage of the genetic and genomic tools to gain a deep insight into the mechanism of brassinosteroid regulation of nitrogen signaling pathway. The specific aims in this proposal are to (1) elucidate the molecular network for BR regulation of nitrogen signal transduction using genetic analysis of interactions between BR-related mutants and known nitrogen signaling mutants, (2) genomic analysis of nitrogen regulate transcription network controlled by HBI1 and HBI1-interacting transcription factor HITs, and (3) elucidate the functions of HBI1 and HITs in nitrogen signal transduction. Our long-time goal is to define the molecular mechanisms by which BR regulates nitrogen signaling pathway, and provides some new tools for breeding high nitrogen use efficiency crops and farmland rational fertilization.