染色质重塑因子调控内质网胁迫诱导的PCD的分子机理研究

Environmental stresses, such as heat, salinity and pathogen infection, induce protein misfolding in plants. When unfolded or misfolded proteins accumulate in the endoplasmic reticulumn (ER) in Arabidopsis, a well-conserved response called the unfolded protein response (UPR) is elicited to bring protein folding and degradation capacity in line with demands either by enhancing the protein folding or degradation machinery to ensure cell survial. Two membrane-associated transcriptions factors (MTFs), AtbZIP28 and AtbZIP60, were previously identified as the key regulators for plant UPR to promote cell survival. The UPR also induces programmed cell death (PCD) when the ER stress is severe; however, the underlying molecular mechanisms are less understood, especially in plants. Recently, we have identified another MTF, AtNAC089, as an important regulator of ER stress-induced PCD in plants, which provides more opportunities for further understanding new molecular components involved in plant PCD, especially under ER stress conditions. In the current proposal, we are planning to characterize two chromatin remodeling factors (CHRs) which are downstream genes of AtNAC089. The biological function and underlying molecular mechanisms of two CHRs in ER-stress-induced PCD in plants, and its relationship to environmental stress tolerance will be substantially invesitgated, which should be important for understanding the balance between cell survial and cell death during plant environmental stress responses.

高温、高盐与病原菌侵染等逆境胁迫容易引起蛋白错误折叠。当模式植物拟南芥内质网内错误折叠蛋白大量积累时，细胞启动内质网胁迫应答（未折叠蛋白应答，UPR），通过蛋白裂解和非常规剪切分别活化膜结合转录因子AtbZIP28和AtbZIP60，调节一系列下游基因，增强蛋白折叠能力，加速错误折叠蛋白的降解，促进细胞生存。当内质网胁迫较严重时，细胞激活程序性细胞死亡（PCD）途径，主动杀死部分细胞，但相关分子机理研究较少。本课题组最近发现膜结合转录因AtNAC089调控了植物内质网胁迫诱导的PCD。AtNAC089调控通路的发现为研究植物内质网胁迫下PCD的分子机理提供了新的切入点。本项目拟研究拟南芥AtNAC089下游两个染色质重塑因子AtCHR-A和AtCHR-B在内质网胁迫诱导的PCD中的生物功能、作用机理及其与高温和氧化胁迫等逆境胁迫抗性的关系，为精确调控逆境条件下细胞生存与死亡的平衡奠定基础。

高温、高盐与病原菌侵染等逆境胁迫容易引起蛋白错误折叠。当模式植物拟南芥内质网内错误折叠蛋白大量积累时，细胞启动内质网胁迫应答（未折叠蛋白应答，UPR），调节一系列下游基因，增强蛋白折叠能力，加速错误折叠蛋白的降解，促进细胞生存。.DNA复制是所有生物体中保证遗传信息准确体现和忠实传递的基本生物学过程。许多内源和外源信号在DNA合成过程中可能导致复制叉暂时停顿，诱导DNA复制错误，从而诱导DNA复制胁迫应答/应激反应。染色质重塑因子可导致核小体位置和结构的变化，引起染色质空间变化以及相关组蛋白修饰和DNA甲基化修饰变化，但染色质重塑因子是否参与植物DNA复制胁迫应答之前未见报道。本研究以CHR18为切入点，研究其在植物应答环境胁迫过程中的功能。本研究结果显示，chr18突变体植物对DNA交联剂Mitomycin C (MMC)敏感。MMC会抑制DNA正常合成，造成DNA复制胁迫。在拟南芥植物中，CHR18是染色质重塑因子SNF2的Distant 亚家族的成员。这个亚家族中有CHR18和CHR14两个基因，chr18 chr14 双突变体表现出对MMC试剂更加敏感的表型。通过酵母双杂实验我们发现DNA复制蛋白RPA1A蛋白与CHR18具有强烈的相互作用。进一步，BiFC的结果显示，RPA1A-CHR18复合物是定位到细胞核聚集点的位置。CHR18单独并不定位到细胞核聚集点，而RPA1A自身就能定位到细胞核聚集点的位置。因此， RPA1A-CHR18复合物的定位是依赖于RPA1A的。总之，我们的研究发现：拟南芥的染色质重塑因子CHR18是一种典型的具有ATP酶活性的重塑因子，与单链DNA结合蛋白RPA相互作用，并调控了MMC诱导的DNA损伤和复制胁迫应答，在植物DNA合成胁迫应答过程中可以帮助缓解胁迫，减少DNA复制错误，保障细胞增殖和植物正常生长发育。.此外，也研究了内质网胁迫应答重要调控因子S2P和bZIP17在ABA调控种子萌发中的功能。发现S2P可通过活化bZIP17来调控PP2Cs的表达水平，即存在S2P-bZIP17调控通路负调控ABA信号转导。发现膜结合转录因子bZIP28 和bZIP60 与COMPASS-LIKE成员互作，参与表观遗传调控内质网胁迫应答基因的表达。

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