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AtObgC, a plant ortholog of bacterial Obg, is a chloroplast-targeting GTPase essential for early embryogenesis

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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.

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Abbreviations

G domain:

GTPase domain

GFP:

Green fluorescent protein

OCT:

Obg C-terminal region

PPR:

Pentatrico-peptide repeat

RFP:

Red fluorescent protein

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Acknowledgments

We thank Prof. Hisashi Koiwa at the Texas A&M University for the kind gift of the pENSOTG vector and Prof. Woo Sik Chung and Dr. Sang Min Lee at the Gyeongsang National University in Korea for providing the F 1 -ATPase-RFP clone as a mitochondrial marker. J. Chen, I·S. Jeong, D.W. Kim, C·H. Im, and Y. Lee are graduate students supported by scholarships from the BK21 program at the Gyeongsang National University in Korea. This work was supported by grants from the BK21 program and the EB-NCRC (#R15-2003-012-01002-0) of the Ministry of Education and Science Technology of Korea, and by the New Energy and Industrial Technology Development Organization (the Green Biotechnology Program) and Grants-in-Aid from the Ministry of Education, Culture, Sports, Science and Technology (Nos. 18570048 and 19039030 to T.S.) of Japan.

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Authors and Affiliations

  1. Division of Applied Life Sciences (BK21 and EB-NCRC), Graduate School of Gyeongsang National University, Jinju, 660-701, Korea

    Woo Young Bang, In Sil Jeong, Ji Chen, Dae Won Kim, Chak Han Im, Byung Hyun Lee, Yuno Lee, Keun Woo Lee & Jeong Dong Bahk

  2. Graduate School of Human and Environmental Sciences, Kyoto Prefectural University, Shimogamo, Sakyo-ku, Kyoto, 606-8522, Japan

    Akira Hata, Tetsuya Umeda, Takayuki Masuda, Ishizaki Yoko & Takashi Shiina

  3. Graduate School of Biostudies, Kyoto University, Sakyo-ku, Kyoto, 606-8502, Japan

    I Nengah Suwastika

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  1. Woo Young Bang
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Correspondence to Jeong Dong Bahk.

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Woo Young Bang, Akira Hata and In Sil Jeong contributed equally to this work.

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Bang, W.Y., Hata, A., Jeong, I.S. et al. AtObgC, a plant ortholog of bacterial Obg, is a chloroplast-targeting GTPase essential for early embryogenesis. Plant Mol Biol 71, 379 (2009). https://doi.org/10.1007/s11103-009-9529-3

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