红砂响应干旱的泌盐特征及其分子基础研究

Reaumuria soongorica, a super xerophytic salt-secretion plant, is a main forage plant at desert steppe in northwest China, as well as an important species for windbreak and sand-fixation. It is a highlighted academic issue that salt glands participate in the adaptation of R. soongorica to stress environments. Our recent study showed that salt-secreting plays important roles in drought adaptation of R. soongorica. However, very little is known about the mechanisms underlying salt-secretion participating in plant's response to drought. Moreover, previous studies demonstrated that plasma membrane Na+/H+ antiporter (SOS1) plays an important role in mediating cell Na+ efflux, but those studies mainly focused on the non-salt-gland cells. In the present project, the salt-secretion dynamics and real-time Na+ secretion rate will be further analyzed in R. soongorica subjected to osmotic stress. The RsSOS1 gene encoding the plasma membrane Na+/H+ antiporter will be cloned from R. soongorica and its transcript abundance under osmotic stress will be quantitatively analyzed by real-time RT-PCR. The temporal and spatial expression pattern of RsSOS1 in the salt gland will be accurately determined through RNA in situ hybridization assays. The changes of salt-secretion traits and drought resistance will be assayed in RNAi plants using RNA interference. The aims of this project are to determine salt-secreting characteristics in super xerophyte R. soongorica responding to drought and analyze the roles of Na+ secretion mediated by SOS1 in drought adaptation of R. soongorica. The expected results will lay theoretical basis for elucidating the mechanisms of xerophytic salt-secretion plants adapting to stress environments.

泌盐型超旱生植物红砂(R. soongorica)是我国西北荒漠草原的主要牧草，也是防风固沙的重要物种，盐腺在其适应逆境中的功能是学术界关注的重点问题。我们前期研究发现，盐腺泌盐在红砂适应干旱过程中发挥着重要作用，但目前对其参与植物干旱响应的内在机制还不清楚。已有研究表明质膜Na+/H+逆向转运蛋白(SOS1)主要介导细胞的Na+外排，但以往的研究多集中于非盐腺细胞。本项目拟进一步分析渗透胁迫下红砂的泌盐动态及Na+实时分泌速率；克隆红砂RsSOS1基因，通过Real-time RT-PCR分析其在渗透胁迫下的转录丰度，用RNA原位杂交精细分析其在盐腺中的时空表达模式；采用RNA干扰技术沉默RsSOS1的表达，分析干扰植株泌盐特性及抗旱性的变化。以期探明红砂响应干旱的泌盐特征，并解析SOS1在红砂盐腺泌盐及其抗旱性中的作用。预期研究结果可为阐明泌盐型旱生植物的逆境适应机制奠定理论基础。

泌盐型超旱生植物红砂是我国西北荒漠草原的主要牧草，前期研究发现盐腺泌盐在红砂适应干旱过程中发挥着重要作用。经过4年的不懈努力，本项目取得如下主要进展和成果：(1) 红砂盐腺为下陷于表皮的多细胞盐腺，包含2个收集细胞和6个分泌细胞；(2) 发现红砂盐腺Na+分泌受NaCl处理和渗透胁迫的显著诱导，且与胁迫强度和时间存在正相关关系；(3) NaCl处理或渗透胁迫下红砂盐腺的Na+净外排和H+净内流速率的显著增加，且 H+-ATPase抑制剂正钒酸钠处理显著降低了离子流速，表明盐腺泌盐过程存在依赖于代谢能的主动Na+-H+交换；(4) 克隆并鉴定了红砂质膜Na+/H+逆向转运蛋白基因RsSOS1，发现其在地上部优先表达，并受NaCl和渗透胁迫处理的诱导和调节，RNA原位杂交显示RsSOS1在红砂盐腺细胞中大量表达，表明RsSOS1可能介导盐腺分泌细胞的Na+外排过程；(5) 构建了其RsSOS1的RNAi干扰载体并成功转入红砂，获得了RsSOS1-RNAi干扰植株；(6) 克隆并鉴定了红砂液泡膜Na+/H+逆向转运蛋白基因RsNHX1基因片段，发现该基因也主要在红砂地上部表达，并受NaCl和渗透胁迫处理的显著诱导，推测RsNHX1可能参与Na+在叶肉细胞和盐腺收集细胞的积累过程。项目执行期间，发表SCI论文3篇，中文核心期刊论文4篇，授权国家发明专利2项，培养博士研究生2名、硕士研究生5名。项目的研究成果为揭示泌盐型旱生植物的逆境适应机制奠定了理论基础，在植物盐腺泌盐机制研究方面具有重要的理论与实践意义。