Exploration of molecular bases of polyamine's defensive roles against environmental stresses in plants

在植物中，多胺在细胞分裂、生长和分化中起作用，因为在分裂活跃的细胞和生殖器官中发现多胺含量较高。在非生物和生物胁迫条件下，编码多胺生物合成酶的基因表达往往增强。因此，多胺有望起到保护寄主植物免受各种环境胁迫的作用。在开始这个项目之前，申请人在植物多胺研究中做了两个重要的发现：(1)缺乏精胺的突变体拟南芥对高盐和脱水胁迫变得敏感，这表明精胺对这两个胁迫具有防御作用。(2)精胺具有信号功能，可以激发参与病原菌防御的基因子集的表达。2007年12月，一个研究小组报道，以前被认为编码精胺合酶的ACL5基因编码精胺合酶(精胺的异构体)合酶。借助TH…更多的是背景，我们首先建立了一种分离精胺和温敏胺的方法。其次，通过监测β-葡萄糖苷酸酶报告基因在拟南芥中的表达情况，分析了精胺合成酶基因和温度敏合酶基因在拟南芥中的时空表达。在精胺信号转导途径中，多胺氧化酶(S)参与了精胺信号转导。第三，对拟南芥和水稻的多胺氧化酶(PAO)基因进行了鉴定。在拟南芥中，4个PAO基因被克隆到大肠杆菌表达载体中。所有重组PAO都能催化后向转化反应，但不能催化多胺末端分解代谢反应。水稻基因组包含7个PAO基因。其中，至少有3个PAO基因催化了多胺的反向转化反应，有力地表明水稻对多胺有两条分解代谢途径。第四，精胺在热休克反应中具有防御作用(提交，修订准备)。我们还证明了精胺上调了未折叠应激反应(UPR)的主控基因bZIP60。在生理条件下，bZIP60的产物存在于内质网(ER)，而一旦触发UPR，bZIP60的转录本就被IRE1的核糖核酸酶活性剪接。第五，bZIP60转录本被精胺剪接，生成的转录本产生活性的bZIP60蛋白，该蛋白靶向细胞核(手稿正在准备中)。在这个激活过程中，IRE1也参与其中。最后，我们发现热敏素具有与精胺相似的信号活性，可以诱导防御基因并抑制植物病毒粒子的增殖。较少

In plants, polyamines function in cell division, growth and differentiation because the polyamine contents were found to be higher in actively dividing cells and in reproductive organs. Expression of the genes encoding polyamine biosynthesis enzymes is often enhanced in abiotic and biotic stress condition. Thus polyamines are expected to function for defending host plants against various environmental stresses. Before starting this project, the applicant did two important findings in plant polyamine research ; i. e.,(1)spermine-deficient mutant Arabidopsis plant became hypersensitive to high salinity and dehydration stresses, suggesting that spermine has a defensive role against these two stresses.(2)spermine has a signaling role to evoke the expression of a subset of genes involved in pathogen defense. In December, 2007, a research group reported that ACL5 gene which was previously thought to encode a spermine synthase, encodes a thermospermine (an isomer of spermine)synthase. With th … More is background, first we established a method to separate those two tetraamines, spermine and thermospermine. Second we analyzed the spatio-temporal expression of spermine synthase gene and thermospermine synthase gene in Arabidopsis by monitoring β-glucuronidase reporter gene expression under the promoters of these genes in Arabidopsis. In spermine-signaling pathway, the involvement of polyamine oxidase(s)is strongly suggested. Third, therefore, characterization of polyamine oxidase (PAO)genes of Arabidopsis thaliana and Oryza sativa was performed. In Arabidopsis, four of the PAO genes were cloned into Escherichia coli expression vector. All of the recombinat PAOs catalyzed the back-conversion reaction but not the polyamine terminal catabolism reaction. Rice genome contains 7 PAO genes. Of them, at least 3 PAO genes catalyzed the polyamine back-conversion reaction, strongly suggesting that rice plant has two catabolic pathways for polyamines. Fourth, spermine has a defensive role in heat shock response (submitted, revision prepared). We also demonstrated that bZIP60, one of the master genes in the unfolded stress response (UPR), is upregulated by spermine. The product of bZIP60 resides in endoplasmic reticulum (ER)in physiological condition, while, once UPR is triggered, it is shown that bZIP60 transcript is spliced by RNase activity of IRE1. Fifth, bZIP60 transcript is spliced by spermine and the resulting transcript produces the active bZIP60 protein which targets into the nucleus (manuscript in preparation). In this activation process, IRE1 is also involved. Lastly we showed that thermospermine has a similar signaling activity to induce the defense genes and inhibits phytoviral particle multiplication as spermine does. Less