Journal
PLANT AND CELL PHYSIOLOGY
Volume 49, Issue 9, Pages 1342-1349Publisher
OXFORD UNIV PRESS
DOI: 10.1093/pcp/pcn109
Keywords
acaulis5; Arabidopsis thaliana; polyamine; spermine; stem elongation; thermospermine
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Funding
- Japan Society for the promotion of Science [17370023]
- Toray Science Foundation [06-4705]
- Grants-in-Aid for Scientific Research [17370023] Funding Source: KAKEN
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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.
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