Isolation and Characterization of a Salt- and Drought-inducible Gene for S-adenosylmethionine Decarboxylase from Wheat (Triticum aestivum L.)

A full-length cDNA for S-adenosylmethionine decarboxylase (SAMDC), a key enzyme involved in the biosynthesis of spermidine and spermine, was isolated from wheat (Triticum aestivum L.) by using reverse transcription PCR technique. Sequence analysis of the wheat SAMDC cDNA (designated TaSAMDC) revealed that it was significantly homologous to SAMDC genes from both monocot and dicot plant species. Alignment of the deduced polypeptide sequence of TaSAMDCwith those of plant, yeast and human SAMDC genes identified several conserved domains, suggesting the structural and functional similarities of SAMDC proteins in eukaryotes. These conserved regions included a proenzyme cleavage site and a putative PEST domain which is characteristic of the rapid protein turnover. Genomic Southern blot indicated that two or three homologous sequences of TaSAMDC gene were present in the wheat genome. Comparative mapping in rice predicts that this gene locates on the long arm of the homologous group 2 of the wheat genome. The expression of TaSAMDC gene under environmental stress conditions was investigated by Northern blot analysis. It was observed that salinity, drought and exogenous ABA can all induce the expression of TaSAMDC, suggesting that this gene is implicated in response of wheat plants to the adverse circumstances.