AtObgC, a plant ortholog of bacterial Obg, is a chloroplast-targeting GTPase essential for early embryogenesis.
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.
Bang
Woo Young
WY
Division of Applied Life Sciences (BK21 and EB-NCRC), Graduate School of Gyeongsang National University, Jinju 660-701, Korea.
Hata
Akira
A
Jeong
In Sil
IS
Umeda
Tetsuya
T
Masuda
Takayuki
T
Chen
Ji
J
Yoko
Ishizaki
I
Suwastika
I Nengah
IN
Kim
Dae Won
DW
Im
Chak Han
CH
Lee
Byung Hyun
BH
Lee
Yuno
Y
Lee
Keun Woo
KW
Shiina
Takashi
T
Bahk
Jeong Dong
JD
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
D029681:Arabidopsis Proteins; D001426:Bacterial Proteins; C090542:Obg GTP-binding protein, Bacteria; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins