title: Thermospermine enhances translation of SAC51 and SACL1 in Arabidopsis.
abstract: The excessive xylem phenotype of acaulis5 (acl5), an Arabidopsis mutant defective in the synthesis of thermospermine, indicates that thermospermine is required for negative regulation of xylem differentiation. SAC51 was identified from a dominant suppressor of acl5, sac51-d, and encodes a basic helix-loop-helix (bHLH) protein. sac51-d has a premature termination codon in one of upstream open-reading frames (uORFs) of the SAC51 mRNA that is conserved among the SAC51 family members. Thermospermine may act to bypass the inhibitory effect of the uORF on main ORF translation. Another suppressor, sac57-d, also has a mutation in the conserved uORF of SACL3, a member of the SAC51 family. On the other hand, the double knockout of SAC51 and SACL3 is insensitive to thermospermine, suggesting their key role in the response to thermospermine. However, we found that thermospermine enhances mRNA translation of SAC51 and SACL1 but not of SACL2 and SACL3. Taken together with recent findings from other groups, we propose a mechanism by which thermospermine diffused from xylem precursor cells acts non-cell-autonomously to restrict their proliferation.
authors.affiliation: a Graduate School of Natural Science and Technology, Okayama University , Tsushimanaka, Okayama , Japan.
authors.forename: Mai
authors.initials: M
authors.lastname: Yamamoto
authors.affiliation: a Graduate School of Natural Science and Technology, Okayama University , Tsushimanaka, Okayama , Japan.
authors.forename: Taku
authors.initials: T
authors.lastname: Takahashi
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant / Q000235:genetics / Q000502:physiology; D016366:Open Reading Frames / Q000235:genetics; D013096:Spermine / Q000031:analogs & derivatives* / Q000378:metabolism; D052584:Xylem / Q000235:genetics / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D013096:Spermine; C515850:SAC51 protein, Arabidopsis; C021097:thermospermine
keywords: Arabidopsis; thermospermine; translation; uORF; xylem differentiation