AtPGK2介导的叶绿体逆向信号参与拟南芥响应盐胁迫的分子机制

3-Phosphoglycerate kinase (3-PGK) plays a critical role not only in photosynthetic carbon metabolism but also in glycolysis and gluconeogenesis. Although a large number of PGKs have been isolated from a variety of higher plants, their molecular mechanisms involved in plant abiotic stress responses still remain elusive. In the previous studies, we found that over-expression of AtPGK2 conferred salt tolerance in transgenic Arabidopsis plants accompanied by increased expression of stress-responsive nuclear genes. Chloroplast dysfunction causes a significant reduction in the expression levels of AtPGK2 and stress-responsive nuclear genes. GUN1, an important component in chloroplast retrograde signaling, was proved to be a putative AtPGK2-interacting protein by yeast two-hybrid assay. Further studies showed that ABI4 regulates the expression of stress-responsive nuclear genes as a component of the chloroplast retrograde signal pathway. Therefore, we speculated that AtPGK2 is involved in response to salt stress possibly through chloroplast-to-nucleus retrograde signaling in Arabidopsis. Based on these previous experimental data, we will further investigate the molecular mechanisms of AtPGK2-mediated chloroplast retrograde signaling involved in response to salt stress by using biochemical, molecular genetic and molecular biological methods. The results of this study will not only open up new ideas of the research on the roles of chloroplast retrograde signaling involved in plant salt stress responses but also provide the theoretical basis for breeding salt-tolerant crop plants.

3-磷酸甘油酸激酶（3-PGK）在碳固定、糖酵解和糖异生代谢途径中有重要作用。目前，虽然许多高等植物的PGKs被分离，但是对于其参与植物响应逆境胁迫的机制尚不清楚。本项目前期的研究发现过表达AtPGK2使拟南芥细胞核参与胁迫响应的基因上调表达，转基因植株耐盐性提高；叶绿体功能的缺失导致AtPGK2基因和细胞核胁迫响应基因的表达降低；酵母双杂交试验显示AtPGK2与叶绿体逆向信号的重要组分GUN1互作。进一步研究发现ABI4作为逆向信号途径的组分调控细胞核胁迫响应基因的表达。因此，我们推测AtPGK2可能通过介导叶绿体的逆向信号参与拟南芥响应盐胁迫。本项目在前期研究的基础上，利用生化、分子遗传和分子生物学的方法深入探究AtPGK2介导的叶绿体逆向信号参与拟南芥响应盐胁迫的分子机制。其结果不仅为阐明叶绿体逆向信号在植物响应盐胁迫中的作用提供新的思路，而且为提高作物的耐盐性提供重要的理论依据。

土壤盐渍化在全世界十分严重，盐胁迫是影响全球农作物产量的重要非生物胁迫之一。本研究组早期在模式植物拟南芥中鉴定了一个参与盐胁迫响应的基因AtPGK2，盐胁迫显著诱导AtPGK2的表达，超表达该基因显著增强转基因拟南芥对盐胁迫的耐受性。在此基础之上，本项目对拟南芥AtPGK2响应盐胁迫的分子机制进行深入的研究，主要研究结果包括：（1）通过酵母双杂交实验发现，在盐胁迫条件下，拟南芥AtPGK2与AtDPG1互作；AtDPG1主要在拟南芥的绿色叶片组织中表达，但随着叶片发育进程的延长，其表达量逐渐降低；进一步的研究发现，AtDPG1功能缺失导致拟南芥的子叶和莲座叶在早期的发育阶段呈黄白色，但随着叶龄的增加，叶片的颜色逐渐转为浅绿色，透射电镜实验结果表明，AtDPG1突变使拟南芥早期叶绿体的发育受阻，类囊体膜片层丰度降低，并通过叶绿体到细胞核的逆向信号下调细胞核编码光合作用相关基因的表达，表明AtDPG1在拟南芥早期的叶绿体发育中具有重要的作用。（2）AtDPG1与AtPGK2相似，盐胁迫使AtDPG1的启动子活性在绿色叶片组织中特异性增强，其mRNA的积累量在盐胁迫条件下显著增加；AtDPG1功能的缺失导致其突变体dpg1以ABA依赖的方式增强对盐胁迫的敏感性，进一步的研究发现，dpg1/abi4双突变体对盐胁迫的敏感性较dpg1单突变体显著降低，表明拟南芥AtDPG1通过ABI4参与响应盐胁迫。（3）AtDPG1功能缺失使拟南芥幼苗花青素的含量增加，编码花青素合成和调控的关键基因上调表达，进一步的研究发现氧化胁迫可能导致拟南芥dpg1幼苗花青素的含量升高；外源ABA处理显著降低氧化胁迫诱导拟南芥幼苗花青素的积累水平，并且ABI1和ABI3在该过程中起重要的作用。该项目的研究结果不仅为阐明叶绿体逆向信号在植物响应盐胁迫中的作用提供新的思路，而且为提高作物的耐盐性提供重要的理论依据。