title: Thermospermine is required for stem elongation in Arabidopsis thaliana.
abstract: Loss-of-function mutants of the ACAULIS5 (ACL5) gene in Arabidopsis thaliana have severe defects in stem elongation. ACL5 was previously reported as encoding a spermine synthase. A more recent study, however, showed that the bacterial expressed recombinant ACL5 protein catalyzes the conversion of spermidine to thermospermine, a structural isomer of spermine, rather than to spermine. In the present study, we found that thermospermine was detected in wild-type seedlings but was not detectable in the acl5-1 mutant. We further examined the effect of exogenous application of these isomers on the growth of acl5-1. Daily application of 0.1 mM thermospermine onto the shoot apex partially rescued the dwarf phenotype of acl5-1, while that of spermine had no effects on the morphology of the mutant. The acl5-1 transcript level in acl5-1 seedlings, which is much higher than the ACL5 transcript level in wild-type seedlings, was reduced by exogenous thermospermine. Thus we conclude that thermospermine is indeed produced through the action of ACL5 and required for stem elongation in Arabidopsis.
authors.affiliation: Division of Bioscience, Graduate School of Natural Science and Technology, Okayama University, Okayama, 700-8530 Japan.
authors.forename: Jun-ichi
authors.initials: J
authors.lastname: Kakehi
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Kuwashiro
authors.forename: Masaru
authors.initials: M
authors.lastname: Niitsu
authors.forename: Taku
authors.initials: T
authors.lastname: Takahashi
mesh_terms: D017360:Arabidopsis / Q000187:drug effects / Q000201:enzymology / Q000235:genetics / Q000254:growth & development*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002855:Chromatography, Thin Layer; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D010641:Phenotype; D010937:Plant Growth Regulators / Q000378:metabolism / Q000494:pharmacology; D018520:Plant Shoots / Q000187:drug effects / Q000201:enzymology / Q000235:genetics / Q000254:growth & development; D018547:Plant Stems / Q000187:drug effects / Q000201:enzymology / Q000235:genetics / Q000254:growth & development*; D018749:RNA, Plant / Q000235:genetics; D013096:Spermine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D013097:Spermine Synthase / Q000235:genetics / Q000378:metabolism*
chemical_list: C414439:ACAULIS5 protein, Arabidopsis; D029681:Arabidopsis Proteins; D010937:Plant Growth Regulators; D018749:RNA, Plant; D013096:Spermine; C021097:thermospermine; D013097:Spermine Synthase