盐生植物四翅滨藜盐囊泡Na+积累机制及其分子基础研究

Excluding excessive Na+ from epidermal cell and sequestering it into salt bladder is an important strategy for many halophyte species in response to saline environments. However, it is not yet clear about the mechanisms underlying this process. Previous studies have demonstrated that the plasma membrane Na+/H+ antiporter (SOS1) mediates the Na+ efflux from cell, and the high affinity potassium transporter (HKT) is involved in the Na+ influx into cell, respectively. In recent study, we found that both AcSOS1 and AcHKT1;1 showed predominant expression in leaves of Atriplex canescens, an excellent halophyte with salt bladder, and were significantly induced by NaCl treatment. In this project, therefore, we will try to analyze the expression patterns of AcSOS1 and AcHKT1;1 among the mesophyll tissue and the salt bladders of A. canescens under NaCl treatments. After that, the subcellular location and the ion transport characteristics of AcSOS1 and AcHKT1;1 will be confirmed, respectively. Finally, the RNAi lines with down-regulated expression of AcSOS1 or AcHKT1;1 will be developed, respectively. The salt tolerance, Na+ contents and distribution from mesophyll tissue to salt bladders, and the Na+ flux rate in EC–SC–EBC complex will be comparatively analyzed between RNAi lines and wild-type under NaCl treatment. The aim of this project is to reveal the roles of AcSOS1 and AcHKT1;1 in salt bladder Na+ sequestration as well as the salt tolerance of A. canescens, which will lay a theoretical basis for elucidating salt-resistant mechanisms of halophytes with salt bladder.

将体内大量Na+从表皮细胞排出并积累至盐囊泡，是众多盐生植物适应盐渍生境的重要策略，但有关该过程的机制尚无报道。已有研究表明，质膜Na+/H+逆向转运蛋白(SOS1)介导植物细胞Na+的外排，而高亲和性钾转运蛋白(HKT)则参与Na+向细胞内的装载。我们近期发现，AcSOS1和AcHKT1;1在盐囊泡类盐生植物四翅滨藜的叶中高丰度表达，且受盐处理强烈诱导。因此，本项目拟系统分析盐处理下AcSOS1和AcHKT1;1在四翅滨藜叶肉组织和盐囊泡中的表达模式，并检测其亚细胞定位和离子转运特性；通过RNAi技术分别沉默其表达，评价RNAi 株系的抗盐性，分析盐处理下其叶肉组织和盐囊泡中Na+的含量与分布、并测定叶表皮细胞-柄细胞-盐囊泡复合体中Na+的实时流速。以期揭示AcSOS1和AcHKT1;1在四翅滨藜盐囊泡Na+积累及其抗盐性中的作用，为阐明盐囊泡类盐生植物的抗盐机制奠定理论基础。

将体内大量Na+从表皮细胞排出并积累至盐囊泡，是众多盐生植物适应盐渍生境的重要策略，但有关该过程的机制尚无报道。我们前期研究发现，AcSOS1和AcHKT1;2在盐囊泡类盐生植物四翅滨藜的叶中高丰度表达，且受盐处理强烈诱导。在此基础上，本项目经过4年的努力，取得如下主要成果：(1) 四翅滨藜盐囊泡是由囊泡细胞、柄细胞以及基部的表皮细胞共同构成盐囊泡复合体，具有再生性，NaCl处理能够显著加快其再生速度、促使其体积增大。(2) 盐囊泡能够直接调控盐渍环境下四翅滨藜体内离子稳态平衡，从而维持其耐盐性。(3) AcSOS1定位于质膜，介导细胞Na+外排，在四翅滨藜成熟叶中的表达受盐处理的显著诱导，且刷除盐囊泡刺激其表达丰度在短时间内大幅度上调，表明其可能通过介导Na+由叶表皮细胞排出而直接参与四翅滨藜盐囊泡Na+积累过程。(4) AcHKT1;2为特异性介导Na+吸收的质膜定位蛋白，主要在四翅滨藜成熟叶中高丰度表达，且刷除盐囊泡显著降低其在四翅滨藜成熟叶中的表达水平，表明AcHKT1;2可能在盐囊泡复合体中优先表达，介导Na+进入盐囊泡。(5) 转录组分析发现，100 mmol/L NaCl处理下四翅滨藜根和叶中众多必需元素、Na+转运蛋白以及水通道蛋白编码基因的表达丰度显著上调，在此基础上，筛选出多个与四翅滨藜耐盐性密切相关的重要候选基因。项目执行期间，发表SCI论文7篇，中文核心期刊论文7篇，培养毕业博士研究生1名、毕业硕士研究生4名。项目研究成果为系统阐明盐囊泡类泌盐植物的抗盐机制奠定了理论基础。