title: TOM9.2 Is a Calmodulin-Binding Protein Critical for TOM Complex Assembly but Not for Mitochondrial Protein Import in Arabidopsis thaliana.
abstract: 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 complex, 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 capacity, 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 regulatory role of TOM9.2 and a possible integration of TOM assembly into the cellular calcium signaling network.
authors.affiliation: Department Biology I, Botany, Ludwig-Maximilians-University Munich, Großhaderner Straße 2-4, 82152 Martinsried, Germany.
authors.forename: Nargis
authors.initials: N
authors.lastname: Parvin
authors.affiliation: Department Biology I, Botany, Ludwig-Maximilians-University Munich, Großhaderner Straße 2-4, 82152 Martinsried, Germany.
authors.forename: Chris
authors.initials: C
authors.lastname: Carrie
authors.affiliation: Department Biology I, Botany, Ludwig-Maximilians-University Munich, Großhaderner Straße 2-4, 82152 Martinsried, Germany.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Pabst
authors.affiliation: Department Biology I, Botany, Ludwig-Maximilians-University Munich, Großhaderner Straße 2-4, 82152 Martinsried, Germany.
authors.forename: Antonia
authors.initials: A
authors.lastname: Läßer
authors.affiliation: Center for Plant Molecular Biology, Plant Physiology, University of Tuebingen, Auf der Morgenstelle 32, 72076 Tuebingen, Germany.
authors.forename: Debabrata
authors.initials: D
authors.lastname: Laha
authors.affiliation: Department Biology I, Botany, Ludwig-Maximilians-University Munich, Großhaderner Straße 2-4, 82152 Martinsried, Germany.
authors.forename: Melanie V
authors.initials: MV
authors.lastname: Paul
authors.affiliation: Department Biology I, Botany, Ludwig-Maximilians-University Munich, Großhaderner Straße 2-4, 82152 Martinsried, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Geigenberger
authors.affiliation: Department Biology I, Microbiology, Ludwig-Maximilians-University Munich, Großhaderner Straße 2-4, 82152 Martinsried, Germany.
authors.forename: Ralf
authors.initials: R
authors.lastname: Heermann
authors.affiliation: Department Biology I, Microbiology, Ludwig-Maximilians-University Munich, Großhaderner Straße 2-4, 82152 Martinsried, Germany; Department of Biology, Center for Integrated Protein Science (Munich), Ludwig-Maximilians-University Munich, 81377 Munich, Germany.
authors.forename: Kirsten
authors.initials: K
authors.lastname: Jung
authors.affiliation: Department Biology I, Botany, Ludwig-Maximilians-University Munich, Großhaderner Straße 2-4, 82152 Martinsried, Germany; Department of Biology, Center for Integrated Protein Science (Munich), Ludwig-Maximilians-University Munich, 81377 Munich, Germany. Electronic address: vothknecht@uni-bonn.de.
authors.forename: Ute C
authors.initials: UC
authors.lastname: Vothknecht
authors.affiliation: Department Biology I, Botany, Ludwig-Maximilians-University Munich, Großhaderner Straße 2-4, 82152 Martinsried, Germany; Department of Biology, Center for Integrated Protein Science (Munich), Ludwig-Maximilians-University Munich, 81377 Munich, Germany. Electronic address: fchigri@uni-bonn.de.
authors.forename: Fatima
authors.initials: F
authors.lastname: Chigri
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D020013:Calcium Signaling / Q000235:genetics / Q000502:physiology; D002148:Calmodulin-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport / Q000235:genetics / Q000502:physiology
chemical_list: D029681:Arabidopsis Proteins; D002148:Calmodulin-Binding Proteins; D002352:Carrier Proteins; D000090622:Mitochondrial Precursor Protein Import Complex Proteins; D024101:Mitochondrial Proteins
keywords: TOM complex; calcium signaling; calmodulin; plant mitochondria; protein import