title: Mutations in ribosomal proteins, RPL4 and RACK1, suppress the phenotype of a thermospermine-deficient mutant of Arabidopsis thaliana.
abstract: Thermospermine acts in negative regulation of xylem differentiation and its deficient mutant of Arabidopsis thaliana, acaulis5 (acl5), shows excessive xylem formation and severe dwarfism. Studies of two dominant suppressors of acl5, sac51-d and sac52-d, have revealed that SAC51 and SAC52 encode a transcription factor and a ribosomal protein L10 (RPL10), respectively, and these mutations enhance translation of the SAC51 mRNA, which contains conserved upstream open reading frames in the 5' leader. Here we report identification of SAC53 and SAC56 responsible for additional suppressors of acl5. sac53-d is a semi-dominant allele of the gene encoding a receptor for activated C kinase 1 (RACK1) homolog, a component of the 40S ribosomal subunit. sac56-d represents a semi-dominant allele of the gene for RPL4. We show that the GUS reporter activity driven by the CaMV 35S promoter plus the SAC51 5' leader is reduced in acl5 and restored by sac52-d, sac53-d, and sac56-d as well as thermospermine. Furthermore, the SAC51 mRNA, which may be a target of nonsense-mediated mRNA decay, was found to be stabilized in these ribosomal mutants and by thermospermine. These ribosomal proteins are suggested to act in the control of uORF-mediated translation repression of SAC51, which is derepressed by thermospermine.
authors.affiliation: Graduate School of Natural Science and Technology, Okayama University, Okayama, Japan.
authors.forename: Jun-ichi
authors.initials: J
authors.lastname: Kakehi
authors.affiliation: Graduate School of Natural Science and Technology, Okayama University, Okayama, Japan.
authors.forename: Eri
authors.initials: E
authors.lastname: Kawano
authors.affiliation: Graduate School of Natural Science and Technology, Okayama University, Okayama, Japan.
authors.forename: Kaori
authors.initials: K
authors.lastname: Yoshimoto
authors.affiliation: Graduate School of Natural Science and Technology, Okayama University, Okayama, Japan.
authors.forename: Qingqing
authors.initials: Q
authors.lastname: Cai
authors.affiliation: Graduate School of Natural Science and Technology, Okayama University, Okayama, Japan.
authors.forename: Akihiro
authors.initials: A
authors.lastname: Imai
authors.affiliation: Graduate School of Natural Science and Technology, Okayama University, Okayama, Japan.
authors.forename: Taku
authors.initials: T
authors.lastname: Takahashi
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D005799:Genes, Dominant; D008969:Molecular Sequence Data; D009154:Mutation; D010641:Phenotype; D020871:RNA Stability; D000075370:Receptors for Activated C Kinase; D011956:Receptors, Cell Surface / Q000235:genetics* / Q000378:metabolism; D000080882:Ribosomal Protein L10; D012269:Ribosomal Proteins / Q000235:genetics* / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D000075370:Receptors for Activated C Kinase; D011956:Receptors, Cell Surface; D012269:Ribosomal Proteins; C515163:RACK1 protein, Arabidopsis; C515850:SAC51 protein, Arabidopsis; C000630691:ribosomal protein L10, Arabidopsis; C056368:ribosomal protein L4