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

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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.