拟南芥PLATZ1调控内质网胁迫应答的分子机理研究

Environmental stresses such as high temperature are great threat to sustained crop yield production. Plants need to protect themselves from environmental stress damages constantly because of their sessile lifestyle. Environmental stresses cause accumulation of unfolded or misfolded proteins in endoplasmic reticulum (ER), leading to ER stress responses. In the model plant Arabidopsis, there are two main ER stress response pathways--the bZIP28 pathway and bZIP60 pathway, which regulate expression of ER stress responsive genes at transcriptional level. PLATZ family is a novel class of plant-specific zinc finger proteins. An increased mRNA level of PLATZ1 under ER stress have been showed in our previous microarray data. Loss-of-function of PLATZ1 in bzip28bzip60 background enhanced ER stress sensitivity, and over-expression of PLATZ1 in the wild-type background increased ER stress tolerance. Thus, PLATZ1 positively regulates ER stress tolerance in Arabidopsis. Co-IP/MS analysis revealed that PLATZ1 interacts with multiple proteins involved in mRNA degradation, such as XRN4 and XRN3. The project will reveal the biological function of PLATZ1 in plant endoplasmic reticulum stress response and elucidate the biological significance of interaction between PLATZ1 and XRN4. The project will also reveal the new pathway for plant endoplasmic reticulum stress response at post-transcriptional level, and should help us to improve plant abiotic stress resistance and crop yield more effectively.

高温等环境胁迫是农作物产量减少、品质下降的重要原因之一。逆境胁迫会造成内质网上未折叠或错误折叠的蛋白质大量积累，从而引起内质网胁迫应答。拟南芥中bZIP28途径和bZIP60途径是内质网胁迫应答中主要的转录调控途径。PLATZ家族是一类植物特有的锌指蛋白。前期研究发现拟南芥PLATZ1表达水平受内质网胁迫诱导上调，PLATZ1的功能缺失突变增加了bzip28bzip60双突变体对内质网胁迫的敏感性，而过表达PLATZ1可以增强植株对内质网胁迫的耐受性。通过Co-IP/MS分析发现PLATZ1与mRNA降解有关的多个蛋白（比如XRN4和XRN3）相互作用。本项目将揭示PLATZ1在植物内质网胁迫应答中的生物学功能，阐明PLATZ1与XRN4等互作的生物学意义，发现植物内质网胁迫应答转录后调控新途径，增强我们对植物的内质网胁迫应答分子机理的理解，为提高植物的抗逆性奠定基础。

与高等动物相比，植物是不能通过移动来躲避外界环境的侵害的，因而更加需要通过自身调节来适应高温、干旱、虫害等逆境胁迫。高温等环境胁迫使得未折叠或者错误折叠蛋白在内质网大量积累，导致内质网胁迫。在拟南芥中，当细胞遭受到内质网胁迫后，定位在内质网上的膜相关转录因子bZIP28和bZIP60，分别经过不同的剪切机制去掉跨膜结构域，从而进入细胞核中调控内质网胁迫应答基因的转录。PLATZ（plant AT-rich sequence-and zinc-binding protein）家族是一类植物特有的可以结合AT-rich序列的DNA结合蛋白，它们均含有两个保守的锌指结构域。拟南芥PLATZ家族共有12个成员。本项目的研究表明，PLATZ1在内质网胁迫下表达水平会增加，这种增加是依赖于bZIP60的存在的。我们通过CRISPR/Cas9系统获得了在不同遗传背景下PLATZ1功能缺失突变体，发现PLATZ1的功能缺失突变增加了bzip28bzip60双突变体对内质网胁迫的敏感性，而过表达PLATZ1可以增强植株对内质网胁迫的耐受性。通过Co-IP/MS以及体内BiFC实验发现PLATZ1与mRNA降解有关的多个蛋白（比如XRN4、XRN3及mRNA去帽复合体成员VCS、DCP1、DCP2）相互作用，体外pull down实验也证明了PLATZ1与XRN4具有相互作用。本项目揭示了PLATZ1在植物内质网胁迫应答中的重要作用，拓宽了我们对植物应对环境胁迫的调控机制的理解。