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Coordination and assembly of protein complexes encoded across mitochondrial and nuclear genomes is assisted by mtCLPXP in Arabidopsis thaliana

ABSTRACT: Protein homeostasis in eukaryotic organelles and their progenitor prokaryotes is regulated by a series of ATP-dependent proteases including the caseinolytic protease complex (ClpXP). In chloroplasts, ClpXP has essential roles in organelle biogenesis and maintenance , but the significance of the plant mitochondrial ClpXP remains unknown and factors that aid coordination of nuclear and mitochondrial encoded subunits for complex assembly in mitochondria await discovery. In this study, we generated knock-out lines of the single copy mitochondrial Clp protease subunit, CLPP2, in Arabidopsis thaliana. They have higher abundance of transcripts from mitochondrial genes encoding OXPHOS protein complexes, while transcripts for nuclear genes encoding other subunits of the same complexes showed no change in transcript abundance. In contrast, the protein abundance of specific nuclear-encoded subunits in OXPHOS complexes I and V increased in knockouts, without accumulation of mitochondrial-encoded counterparts in the same complex. Protein complexes mainly or wholly encoded in the nucleus were unaffected. Analysis of protein import, assembly and function of Complex I revealed that while function was retained, protein homeostasis was disrupted through slower assembly, leading to accumulation of soluble subcomplexes of nuclear-encoded subunits after import. It is proposed that CLPP contributes to the mitochondrial protein degradation network through supporting coordination and assembly of protein complexes encoded across mitochondrial and nuclear genomes.

ORGANISM(S): Arabidopsis thaliana

PROVIDER: GSE141942 | GEO | 2019/12/13

REPOSITORIES: GEO

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Coordination and assembly of protein complexes encoded across mitochondrial and nuclear genomes is assisted by mtCLPP in Arabidopsis thaliana.

Project description:Protein homeostasis in eukaryotic organelles and their progenitor prokaryotes is regulated by a series of proteases including the caseinolytic protease (CLPP). CLPP has essential roles in chloroplast biogenesis and maintenance, but the significance of the plant mitochondrial CLPP remains unknown and factors that aid coordination of nuclear and mitochondrial encoded subunits for complex assembly in mitochondria await discovery. We generated knock-out lines of the single copy mitochondrial CLP protease subunit, CLPP2, in Arabidopsis thaliana. Mutants have higher abundance of transcripts from mitochondrial genes encoding OXPHOS protein complexes, while transcripts for nuclear genes encoding other subunits of the same complexes showed no change in transcript abundance. In contrast, the protein abundance of specific nuclear-encoded subunits in OXPHOS complexes I and V increased in knockouts, without accumulation of mitochondrial-encoded counterparts in the same complex. Protein complexes mainly or entirely encoded in the nucleus were unaffected. Analysis of protein import, assembly and function of Complex I revealed that while function was retained, protein homeostasis was disrupted through slower assembly, leading to accumulation of soluble subcomplexes of nuclear-encoded subunits. Therefore, CLPP2 contributes to the mitochondrial protein degradation network through supporting coordination and assembly of protein complexes encoded across mitochondrial and nuclear genomes.

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