Abstract
Thermospermine is a structural isomer of spermine and has been shown to play a critical role in stem elongation in Arabidopsis (Arabidopsis thaliana). Loss-of-function mutants of the Arabidopsis ACAULIS5 (ACL5) gene, which encodes thermospermine synthase, exhibit severe dwarfism with excess proliferation of xylem tissues. The phenotype is partially rescued by exogenous thermospermine. To investigate the molecular basis of thermospermine-dependent growth, the genes up- and down-regulated by thermospermine were identified with the use of cDNA microarray and gene chip methods. acl5 spms double mutant seedlings which produce neither thermospermine nor spermine, were grown for 7days in liquid MS media and treated with thermospermine for 24 h. We found that many genes involved in the induction of vascular differentiation are down-regulated by treatment with thermospermine, indicating a repressive role for thermospermine in vascular differentiation. Unexpectedly, only few genes were identified that are up-regulated by thermospermine or are responsive to both thermospermine and spermine.
