Spatio-temporal expression analysis of Arabidopsis thaliana spermine synthase gene promoter

Of the polyamines (PAs), plants contain at least two kinds of tetraamines, spermine (Spm) and thermospermine (T-Spm). They seem to have different functions in plants because the stem growth defect shown by the loss-of-function mutant plant of ACL5 (encoding T-Spm synthase) was partially complemented by T-Spm but not by Spm in Arabidopsis thaliana. Here we examined the localization of Spm synthase (SPMS) gene promoter activity using the SPMS promoter-beta-glucronidase (GUS) gene expressed in transgenic Arabidopsis plants and compared it with that of ACL5 promoter-GUS expression. SPMS promoter activity was detected in almost all organs at all developmental growth stages, while ACL5 promoter activity was only detected in the vascular systems. Upon high salt stress, SPMS promoter activity was highly enhanced in all organs except cotyledons whereas the ACL5 promoter activity was reduced which is consistent with the reduced levels of ACL5 transcripts. The result indicates that SPMS expression is different from that of ACL5 in respect to tissue specificity and stress response, suggesting corresponding differences in functions of Spm and T-Spm.