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Arabidopsis OBG-Like GTPase （AtOBGL）Is Localized in Chloroplasts and Has an Essential Function in Embryo Development

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Molecular Plant 2009年第6期2卷 1373-1383页

作者： fatima chigri Claudia Sippel Manuela Kolb Ute C. Vothknecht Center for Integrated Protein Science (Munich) Department of Biology LMU Munich D-81377 Munich Germany Department of Biology I Botany LMU Munich D-82152 Planegg-Martinsried Germany

OBG-like GTPases, a subfamily of P-loop GTPases, have divers and important functions in bacteria, including initiation of sporulation, DNA replication, and protein translation. Homologs of the Bacillus subtilis spo0B GTP-binding protein （OBG） can be found in plants and algae but their specific function in these organisms has not yet been elucidated. Here, it is shown that ATSG18570 encodes an Arabidopsis thaliana OBG-like protein （AtOBGL） that is localized in chlor- oplasts. In contrast to the bacterial members of this protein family, AtOBGL and other OBG-like proteins from green algae and plants possess an additional N-terminal domain, indicating functional adaptation. Disruption of the gene locus of ATOBGL by TDNA insertion resulted in an embryo-lethal phenotype and light microscopy using Normarski optics revealed that embryo maturation in the atobgl mutant is arrested at the late globular stage before development of a green embryo. Expression of 35S：：ATOBGL within the atobgl mutant background could rescue the mutant phenotype, confirming that embryo-lethality is caused by the loss of AtOBGL. Together, the data show that the bacterial-derived OBG-like GTPases have retained an essential role in chloroplasts of plants and algae. They furthermore corroborate the significance of chloroplast functions for embryo development -- an important stage within the Arabidopsis lifecycle.

关键词： GTPase OBG embryo development chloroplast.

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TOM9.2 Is a Calmodulin-Binding Protein Critical for TOM Complex Assembly but Not for Mitochondrial Protein Import in Arabidopsis thaliana

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Molecular Plant 2017年第4期10卷 575-589页

作者： Nargis Parvin Chris Carrie Isabelle Pabst Antonia Laber Debabrata Laha Melanie V. Paul Peter Geigenberger Ralf Heermann Kirsten Jung Ute C. Vothknecht fatima chigri Department Biology I Botany Ludwig-Maximilians-University Munich GroBhaderner Stra6e 2-4 82152 Martinsried Germany Department Biology 1 Microbiology Ludwig-Maximilians-University Munich Grobhaderner Strabe 2-4 82152 Martinsried Germany Department of Biology Center for Integrated Protein Science (Munich) Ludwig-Maximilians-University Munich 81377 Munich Germany Center for Plant Molecular Biology Plant Physiology University of Tuebingen Auf der Morgenstelle 32 72076 Tuebingen Germany present address: Plant Cell Biology IZMB University of Bonn Kirschallee 153115 Bonn Germany Present address: Center for Plant Molecular Biology Developmental Genetics University of Tubingen Auf der Morgenstelle 32 72076 Tubingen Germany

The translocon on the outer membrane of mitochondria （TOM） facilitates the import of nuclear-encoded proteins. The principal machinery of mitochondrial protein transport seems conserved in eukaryotes; however, divergence in the composition and structure of TOM components has been observed between mammals, yeast, and plants. TOM9, the plant homolog of yeast Tom22, is significantly smaller due to a truncation in the cytosolic receptor domain, and its precise function is not understood. Here we provide evidence showing that TOM9.2 from Arabidopsis thaliana is involved in the formation of mature TOM com- plex, most likely by influencing the assembly of the pore-forming subunit TOM40. Dexamethasone- induced RNAi gene silencing of TOM9.2 results in a severe reduction in the mature TOM complex, and the assembly of newly imported TOM40 into the complex is impaired. Nevertheless, mutant plants are fully viable and no obvious downstream effects of the loss of TOM complex, i.e., on mitochondrial import ca- pacity, were observed. Furthermore, we found that TOM9.2 can bind calmodulin （CAM） in vitro and that CaM impairs the assembly of TOM complex in the isolated wild-type mitochondria, suggesting a regula- tory role of TOM9.2 and a possible integration of TOM assembly into the cellular calcium signaling network.

关键词： protein import plant mitochondria TOM complex calmodulin calcium signaling

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