Abstract
Mitochondrial and plastid biogenesis requires the biosynthesis and assembly of proteins, nucleic acids, and lipids. In Arabidopsis (Arabidopsis thaliana), the mitochondrial outer membrane protein DGD1 SUPPRESSOR1 (DGS1) is part of a large multi-subunit protein complex that contains the mitochondrial contact site and cristae organizing system 60-kD subunit, the translocase of outer mitochondrial membrane 40-kD subunit (TOM40), the TOM20s, and the Rieske FeS protein. A point mutation in DGS1, dgs1-1, altered the stability and protease accessibility of this complex. This altered mitochondrial biogenesis, mitochondrial size, lipid content and composition, protein import, and respiratory capacity. Whole plant physiology was affected in the dgs1-1 mutant as evidenced by tolerance to imposed drought stress and altered transcriptional responses of markers of mitochondrial retrograde signaling. Putative orthologs of Arabidopsis DGS1 are conserved in eukaryotes, including the Nuclear Control of ATP Synthase2 (NCA2) protein in yeast (Saccharomyces cerevisiae), but lost in Metazoa. The genes encoding DGS1 and NCA2 are part of a similar coexpression network including genes encoding proteins involved in mitochondrial fission, morphology, and lipid homeostasis. Thus, DGS1 links mitochondrial protein and lipid import with cellular lipid homeostasis and whole plant stress responses.
Highlights
Mitochondrial biogenesis requires the import of proteins, RNAs, and lipids (Schneider, 2011; Mesmin, 2016; Wiedemann and Pfanner, 2017)
Using immunoblotting following blue-native PAGE (BN-PAGE), immunoprecipitation, and crosslinking with the membranepermeable chemical crosslinker disuccinimidyl glutarate (DSG), DGD1 SUPPRESSOR1 (DGS1) was found to be present in a multi-subunit protein complex that contains MIC60, the outer mitochondrial membrane (TOM) 40-kD subunit (TOM40), TOM 20-kD subunits (TOM20s), and the Rieske FeS protein (RISP) of the cytochrome (Cyt) bc1 complex (Figure 1)
The interaction between proteins is indicated by asterisks, and the corresponding molecular weight (MW) for each protein is indicated in kDa (C) Mitochondrial proteins incubated with or without crosslinker were resolved by SDS-PAGE, followed by immunodetection
Summary
Mitochondrial biogenesis requires the import of proteins, RNAs, and lipids (Schneider, 2011; Mesmin, 2016; Wiedemann and Pfanner, 2017). The signals and machinery for the import and assembly of proteins are well studied, and one emerging theme is that many proteins are dually targeted to both mitochondria and chloroplasts, highlighting the coordination of function of these organelles (Murcha et al, 2014). Both mitochondria and plastids contain their own genome, but they rely on the import of nuclearencoded proteins for the replication and expression of their genomes, with many of the involved proteins dually targeted (Elo et al, 2003; Carrie et al, 2009). A study in Arabidopsis (Arabidopsis thaliana) revealed that MIC60, interacting with the translocase of the outer mitochondrial membrane (TOM) via the TOM 40-kD subunit (TOM40), forms part of a mitochondrial transmembrane lipoprotein (MTL) complex and affects mitochondrial lipid trafficking (Michaud et al, 2016)
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