Abstract: A new vacuolar Na +/H + antiporter gene OsNHX2was isolated from rice by RT-PCR. The OsNHX2cDNA with 1726 bp in length encodes a protein of 544 amino acid residues with a calculated molecular mass of 60 kD. Hydrophobicity plot analysis showed the OsNHX2 has 11 putative transmembrane domains. Database searching results revealed the deduced amino acid sequence of OsNHX2 has 78% similarity to vacuolar Na +/H + antiporter (OsNHX1) from rice and 77% similarity to Na +/H + antiporter (AtNHX1) from Arabidopsis thaliana. Phylogenetic analysis showed that OsNHX2 clustered with other plant vacuolar Na +/H + antiporters. Semi-quantitive RT-PCR results revealed that OsNHX1 and OsNHX2expression was continuously up-regulated under NaCl stress in roots and shoots of salt-tolerant variety Jiucaiqing. However, in a salt-sensitive variety IR28, the OsNHX2 transcripts were up-regulated transiently in shoots then down-regulated immediately, and not regulated in roots under salt stress. OsNHX1 was increased transiently in both shoots and roots after exposure to salt stress in IR28. These results suggested the mRNA expression of vacuolar Na +/H + antiporter genes was diverse in rice varieties with different salt-sensitivity, and its transcriptional regulation possibly was an important factor deciding the ability of rice to cope with salt stress.

Key words: rice, salt stress, vacuolar Na +/H + antiporter gene, gene cloning, expression characterization

摘要： 通过RTPCR技术从水稻幼苗组织中克隆了一个新的Na+/H+逆向转运蛋白基因OsNHX2，它编码一条长544氨基酸的多肽。OsNHX2与水稻和拟南芥的液泡膜Na+/H+逆向转运蛋白OsNHX1、AtNHX1氨基酸序列一致性分别为78%和77%。基因结构分析表明OsNHX2与OsNHX1具有类似的外显子和内含子构成，但不同于拟南芥AtNHX1，表明OsNHX2与OsNHX1可能起源于单双子叶植物分化后的水稻染色体复制。半定量RTPCR方法检测了OsNHX2与OsNHX1在水稻耐盐品种韭菜青与盐敏感品种IR28的地上部与根部的表达。结果表明：耐盐品种韭菜青的OsNHX2与OsNHX1基因在盐胁迫下表达持续增强，而在盐敏感品种IR28的地上部，OsNHX2基因在盐胁迫处理后1 h表达增强后立即减弱，根部的表达则基本不变，而IR28地上部与根部OsNHX1则在盐胁迫处理初期表达增强，随后即减弱。研究结果表明水稻两个液泡膜Na+/H+逆向转运蛋白基因OsNHX2、OsNHX1在盐敏感程度不同的水稻品种中表达有所不同，液泡膜Na+/H+逆向转运蛋白基因的转录调控可能是决定水稻耐盐能力的一个重要因素。

关键词: 水稻, 盐胁迫, 液泡膜Na+/H+逆向转运蛋白基因, 基因克隆, 表达特性