Bang Woo Young, Hata Akira, Jeong In Sil, Umeda Tetsuya, Masuda Takayuki, Chen Ji, Yoko Ishizaki, Suwastika I Nengah, Kim Dae Won, Im Chak Han, Lee Byung Hyun, Lee Yuno, Lee Keun Woo, Shiina Takashi, Bahk Jeong Dong
Division of Applied Life Sciences (BK21 and EB-NCRC), Graduate School of Gyeongsang National University, Jinju 660-701, Korea.
Plant Mol Biol. 2009 Nov;71(4-5):379-90. doi: 10.1007/s11103-009-9529-3. Epub 2009 Jul 28.
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.
Obg是一种与核糖体相关的GTP酶，对细菌的生存能力至关重要，并且在从细菌到真核生物的大多数生物体中都保守存在。Obg在植物中也有表达，这预示着该分子在植物生存能力中具有重要作用；然而，植物Obg同源物的功能尚未见报道。在这里，我们首先将拟南芥AtObgC鉴定为一种靶向植物叶绿体的Obg，并阐明了其分子生物学和生理学特性。AtObgC编码一种植物特异性的Obg GTP酶，它含有一个用于叶绿体靶向的N端区域，并具有内在的GTP水解活性。使用几个AtObgC N端截短突变体进行的靶向分析表明，AtObgC定位于叶绿体，其转运肽由超过50个氨基酸残基组成。有趣的是，绿色荧光蛋白融合的全长AtObgC在拟南芥原生质体的叶绿体中呈现点状染色模式，这表明AtObgC发生了二聚化或多聚化。此外，其Obg折叠对于点状染色模式的形成是不可或缺的，因此，推测它通过介导蛋白质-蛋白质相互作用对于AtObgC的这种寡聚化很重要。另外，T-DNA插入AtObgC缺失突变体表现出胚胎致死表型，扰乱了胚胎发育的早期阶段。总之，我们的结果提供了一个重要启示，即AtObgC作为一种靶向叶绿体的GTP酶，通过在叶绿体蛋白质合成中发挥作用，在胚胎发育早期起着重要作用。
