水稻对硝铵混合氮源响应的分子机制研究

Nitrate and ammonium are two major inorganic nitrogen (N) sources for plants, and they behave largely different in utilization and signaling as well as have different effects in plants growth and development. It is shown that rice displays much better growth performance and higher N use efficiency (NUE) under nitrate and ammonium mixed condition than the only nitrate or ammonium condition. Thus, unveiling the mechanism of how plants respond to nitrate and ammonium mixed condition holds great promise to improve the NUE. However, the work on this aspect is still very limited. To study the underlying mechanism of plants in response to nitrate-ammonium N source, we carried out large-scale transcriptome analysis with rice seedlings cultured with nitrate, ammonium, or nitrate-ammonium mixture by using RNA-sequencing. We found that an N responsive WRKY transcription factor (NRW) and NRT1.1B, the important regulator of nitrate signaling, locate at the key nodes in the interacting network from RNA-sequencing analysis. We further found that NRW displays relative higher expression under nitrate-ammonium mixed condition, and it is induced by both nitrate and ammonium and responds to nitrate induction more intensively. Based on these results, this project attempts to explore the key regulatory genes from RNA-sequencing by more comprehensive methods and, more importantly, to study the detailed function of NRT1.1B-NRW (and other candidate genes) in nitrate-ammonium interaction and investigate the potential application of NRW (and other candidate genes) in NUE improvement.

硝酸盐与铵盐是最主要的无机氮源，对植物的生长发育却表现出不同的效果。硝铵混合条件下，水稻表现出较单一氮源更高的氮利用能力。解析水稻对硝铵混合氮源的响应机制对提高氮利用效率具有重要意义，而相关研究却非常有限。我们利用RNA-seq对不同氮源培养的水稻进行大规模转录组分析以鉴定硝铵响应的关键调控基因。初步分析发现，硝酸盐信号通路的重要组分NRT1.1B及一个氮响应WRKY类转录因子（NRW）分别处于互作网络的重要节点位置。研究发现，NRW在硝铵混合氮源下具有更高的表达，且受铵盐及硝酸盐的诱导。此项申请拟在前期研究基础上，对RNA-seq数据进行深入挖掘，以获得硝铵响应关键调控基因；此外，对NRW及NRT1.1B（其它候选基因）在硝铵混合氮源的响应中的功能进行深入研究，构建NRT1.1B—NRW为核心的硝铵互作调控通路，并探索NRW及相关候选基因对提高氮利用效率的应用价值。

硝酸盐与铵盐是最主要的无机氮源，对植物的生长发育却表现出不同的效果。硝铵混合条件下，水稻表现出较单一氮源更高的氮利用能力。解析水稻对硝铵混合氮源的响应机制对提高氮利用效率具有重要意义，而相关分子机制研究却非常有限。在本项目资助下，我们鉴定了水稻中参与硝铵混合氮源信号响应的重要调控因子—NRT1.1B、NRW及AR1。NRT1.1B和NRW可以介导硝酸盐信号对铵利用的调控，而且NRW作为转录因子有可能直接结合铵利用相关基因的启动子从而调控其表达。本项目还发现铵盐可作为重要的信号分子触发一系列氮利用相关基因的表达变化，而且NRT1.1B和NRW参与了铵信号对下游基因的调控。进一步研究表明AR1可能作为铵信号的受体介导信号的传导过程。AR1可以与NRT1.1B及SPX4互作，而且在铵盐处理下它们的互作会得到显著加强。此外，SPX4蛋白会在铵盐诱导条件下发生快速降解，进一步表明了AR1-NRT1.1B-SPX4对实现铵盐信号传导的重要作用。通过对NRW自然变异分析，鉴定了NRW的优异等位NRW-indica，其导入粳稻品种可以显著提高在不同氮供应下的产量，表明NRW对水稻氮高效改良具有重要应用价值。