An improvement of rice chilling tolerance by means of over expression of polyamine biosynthesis genes

精氨酸脱羧酶（ADC; EC4.1.1.19）和鸟氨酸脱羧酶（ODC; EC4.1.1.17）在腐胺的生物合成中起关键作用，腐胺是另外两种高级多胺亚精胺和精胺的前体。多胺参与了高等植物的许多发育过程和逆境反应。然而，目前关于植物多胺生物合成与ADC或ODC基因表达在环境胁迫下的调控信息有限。我们从水稻中克隆了ADC和ODC基因，分别命名为osadc1和OsODC1，它们编码假定的ADC和ODC蛋白。据预测，只有OsADC1推断蛋白具有针对叶绿体的n端推测信号肽，这表明OsADC1蛋白的定位可能与OsODC1蛋白不同。Northern-blot分析显示，低温胁迫强烈诱导OsODC1基因表达，而淹没胁迫则使OsODC1基因表达增加。有趣的是，在低温和水下胁迫下，游离腐胺水平的增加与OsADC1和OsODC1mRNA水平的增加同时发生。据我们所知，这是第一个直接证据表明，OsADC1和OsODC1基因分别与水稻幼苗在寒冷胁迫和淹没胁迫下诱导的腐胺水平增加有关。

Arginine decarboxylase (ADC; EC4.1.1.19) and ornithine decarboxylase (ODC; EC4.1.1.17) play pivotal roles in biosynthesis of putrescine, which is the precursor of the other two higher polyamines, spermidine and spermine. The polyamines have been implicated in many developmental processes and stress responses in higher plants. At the present time, however, only limited information is available for the regulation of polyamine biosynthesis in relation to ADC or ODC gene expression in plants in response to environmental stress. We have cloned ADC and ODC genes from rice, designated here as OsADC1and OsODC1, which encode putative ADC and ODC proteins. Only OsADC1 deduced protein is predicted to have an N-terminal putative signal peptide targeting to chloloroplasts, suggesting that the localization of OsADC1protein may differ from that of OsODC1 protein. Northern-blot analysis revealed that gene expression of OsADC1 was strongly induced by chilling stress, while OsODC1 gene expression increased in response to submergence stress. Interestingly, a concomitant increase in the levels of free putrescine coincided with the increase in levels of OsADC1 and OsODC1mRNA in response to chilling and submergence stress, respectively. To our knowledge, this is the first direct evidence to show that OsADC1 and OsODC1 genes are involved with the increase in putrescine levels that is induced in response to chilling stress and submergence stress in rice seedlings, respectively.