多浆旱生植物霸王叶中Na+装载机制及其分子基础研究

积盐型植物霸王能通过ZxSOS1将根系吸收的大量Na+长距离上运至叶、并由ZxNHX将其区域化于液泡中作为有益的渗透调节剂以抵御逆境胁迫，但运至叶脉中的Na+如何装载至叶肉组织的机制尚未见报道。目前学术界对植物体内Na+转运的研究主要以根系Na+吸收能力有限且叶中Na+区域化能力很弱的拒盐型植物为材料，并不是研究叶中Na+装载机制的理想材料。我们近期研究发现，霸王ZxHKT1;3特异性地在叶中高丰度表达，并受盐处理的强烈诱导。在此基础上，本项目拟采用异源表达系统分析ZxHKT1;3的离子选择性；利用原位PCR和烟草瞬时表达明确其组织与亚细胞定位；通过RNA干扰和在拟南芥中的超表达，分析渗透胁迫与盐处理下转基因植株不同组织中Na+、K+等含量及抗逆性的变化；比较霸王RNAi及野生型植株基因表达谱的差异。以期揭示ZxHKT1;3在霸王抗逆性中的作用，并填补高等植物叶中Na+装载机制研究的空白。

As a typical salt-accumulating xerophyte, Zygophyllum xanthoxylum could transport a large quantity of Na+ efficiently from roots to leaves mediated by ZxSOS1, and eventually, compartmentalize them by ZxNHX into the vacuoles in order to cope with environmental stresses by using Na+ as an important osmoregulatory substance. However, the mechanisms of Na+ loading into mesophyll tissue from the vein have not been explored. To date, the molecular mechanisms of Na+ transport in higher plants has only been reported in salt-excluding plants, but these species might not be the ideal materials to understand the pathway of Na+ loading into leaves, since they have a weak ability of Na+ uptake and compartmentalization. Our recent studies showed that ZxHKT1;3 was predominantly expressed in leaves and intensely induced by 50 mmol/L NaCl. Based on our previous results, in this project, in order to reveal the function of ZxHKT1;3 in Na+ loading into mesophyll tissue and the stress tolerance in Z. xanthoxylum, the following experiments would be done: analyzing the ion selective characteristics by using heterologous expression systems; revealing the expression patterns in plant tissues and the subcellular location by in situ PCR and transient expression of fluorescent fusion protein in tobacco, respectively; analyzing the changes in the concentrations of Na+, K+ and other ions in different tissues and evaluating stress tolerance of plants, after gene silencing using RNA interference technique and overexpression in Arabidopsis thaliana; comparing the gene expression profiles of ZxHKT1;3-silenced plants and wild-type Z. xanthoxylum. The results could also fill the gap in the research field of Na+ loading into leaves in higher plants.