title: AtObgC, a plant ortholog of bacterial Obg, is a chloroplast-targeting GTPase essential for early embryogenesis.
abstract: Obg is a ribosome-associated GTPase essential for bacterial viability and is conserved in most organisms, from bacteria to eukaryotes. Obg is also expressed in plants, which predicts an important role for this molecule in plant viability; however, the functions of the plant Obg homologs have not been reported. Here, we first identified Arabidopsis AtObgC as a plant chloroplast-targeting Obg and elucidated its molecular biological and physiological properties. AtObgC encodes a plant-specific Obg GTPase that contains an N-terminal region for chloroplast targeting and has intrinsic GTP hydrolysis activity. A targeting assay using a few AtObgC N-terminal truncation mutants revealed that AtObgC localizes to chloroplasts and its transit peptide consists of more than 50 amino acid residues. Interestingly, GFP-fused full-length AtObgC exhibited a punctate staining pattern in chloroplasts of Arabidopsis protoplasts, which suggests a dimerization or multimerization of AtObgC. Moreover, its Obg fold was indispensable for the generation of the punctate staining pattern, and thus, was supposed to be important for such oligomerization of AtObgC by mediating the protein-protein interaction. In addition, the T-DNA insertion AtObgC null mutant exhibited an embryonic lethal phenotype that disturbed the early stage of embryogenesis. Altogether, our results provide a significant implication that AtObgC as a chloroplast targeting GTPase plays an important role at the early embryogenesis by exerting its function in chloroplast protein synthesis.
authors.affiliation: Division of Applied Life Sciences (BK21 and EB-NCRC), Graduate School of Gyeongsang National University, Jinju 660-701, Korea.
authors.forename: Woo Young
authors.initials: WY
authors.lastname: Bang
authors.forename: Akira
authors.initials: A
authors.lastname: Hata
authors.forename: In Sil
authors.initials: IS
authors.lastname: Jeong
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Umeda
authors.forename: Takayuki
authors.initials: T
authors.lastname: Masuda
authors.forename: Ji
authors.initials: J
authors.lastname: Chen
authors.forename: Ishizaki
authors.initials: I
authors.lastname: Yoko
authors.forename: I Nengah
authors.initials: IN
authors.lastname: Suwastika
authors.forename: Dae Won
authors.initials: DW
authors.lastname: Kim
authors.forename: Chak Han
authors.initials: CH
authors.lastname: Im
authors.forename: Byung Hyun
authors.initials: BH
authors.lastname: Lee
authors.forename: Yuno
authors.initials: Y
authors.lastname: Lee
authors.forename: Keun Woo
authors.initials: KW
authors.lastname: Lee
authors.forename: Takashi
authors.initials: T
authors.lastname: Shiina
authors.forename: Jeong Dong
authors.initials: JD
authors.lastname: Bahk
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000196:embryology* / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D001426:Bacterial Proteins / Q000737:chemistry; D002736:Chloroplasts / Q000378:metabolism*; D020558:GTP Phosphohydrolases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D019204:GTP-Binding Proteins / Q000737:chemistry; D018506:Gene Expression Regulation, Plant / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D010802:Phylogeny; D030821:Plants, Genetically Modified; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D029681:Arabidopsis Proteins; D001426:Bacterial Proteins; C090542:Obg GTP-binding protein, Bacteria; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins