NO3-转运蛋白NRT1.5在霸王适应干旱逆境中的作用研究

The uptake and transport of nitrogen plays a vital role in drought resistance in plants. The nitrate transporter NRT1.5, a protein responsible for nitrate transport from roots to shoots, is involved in regulating the transport and spatial distribution of Na+ and K+, and thus modulating the drought resistance in plants. However, plant used in previous researches was the salt-sensitive glycophyte Arabidopsis thaliana, which has a weak capacity to sequester Na+ into vacuoles and a decreased K+ concentration under drought stress. In this project, taking the xerophyte Zygophyllum xanthoxylum which could absorb a great quantity of Na+ and maintain the stability of K+ concentration under drought stress as material, the following experiments would be done: cloning the full-length gene encoding the nitrate transporter ZxNRT1.5 from Z. xanthoxylum and quantitative analyzing its transcript abundance under osmotic stress (simulating the drought stress); analyzing NO3-, Na+, K+ concentrations and the expression level of genes encoding important Na+, K+ transporters/channels in different tissues, and evaluating drought tolerance of plants, after gene silencing of ZxNRT1.5 using RNA interference (RNAi) technique. The results would contribute to clarifying the function of ZxNRT1.5 in the transport and spatial distribution of Na+ and K+ under drought stress, and therefore, reveal the important role of ZxNRT1.5 in the drought resistance in Z. xanthoxylum.

植物对氮素的吸收转运在植物适应干旱逆境中发挥着重要作用。NO3-转运蛋白NRT1.5除介导NO3-从植株根向地上部的长距离运输外，亦可影响植株体内Na+、K+的转运和空间分配，进而影响植物的耐盐抗旱性。但关于NRT1.5上述功能的研究仅以Na+区域化能力很弱、干旱胁迫下体内K+浓度显著下降的植物拟南芥为对象。本项目拟以干旱逆境下能大量吸收积累Na+并维持体内K+浓度稳定的旱生植物霸王为材料，克隆其NO3-转运蛋白ZxNRT1.5基因，并系统分析其在渗透胁迫(模拟干旱胁迫)下的表达模式；采用RNAi技术沉默ZxNRT1.5基因的表达，分析渗透胁迫下RNAi株系不同组织中NO3-、Na+和K+含量及重要Na+、K+转运蛋白编码基因表达的变化，并对其抗旱性进行评价。以期解析ZxNRT1.5调节干旱逆境下霸王体内Na+、K+转运和空间分布的作用机制及其在植株抗旱性中的功能。

本项目取得了以下主要进展和成果：(1) 从荒漠旱生植物霸王中克隆并鉴定了NO3-转运蛋白基因ZxNRT1.5，发现其主要表达于霸王根部，且表达量受盐处理和渗透胁迫的显著诱导，该表达模式与盐敏感模式植物拟南芥中NRT1.5同源基因的表达模式相反；(2) 发现ZxNRT1.5主要表达于霸王根系木质部导管周围的维管束鞘，编码蛋白定位于细胞质膜；(3) 构建了ZxNRT1.5的RNAi 植物表达载体并完成了其对霸王的遗传转化；(4) 在模式植物拟南芥中分析了ZxNRT1.5对植株抗逆性的影响，发现ZxNRT1.5不仅参与NO3-从根向地上部的转运，还可通过影响Na+转运相关基因的表达或影响细胞质膜的超极化，进而调控植株体内Na+、Cl-的转运和积累，从而影响植株耐盐性。(5) 发现ZxNRT1.5超表达能显著提高拟南芥幼苗抵御渗透胁迫的能力；(6) 发现NRT1.5可通过影响低磷胁迫下PO43-吸收转运相关基因的表达，进而影响植株体内PO43-含量，从而参与调控植株对低磷胁迫的响应。本项目发表SCI论文4篇，其中SCI一区论文1篇、2区论文1篇；发表国内核心CSCD 1篇、会议论文4篇和学位论文2部。