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Dysregulated 3'-end processing of 18S pre-rRNA decreases mtPNPase efficiency in plant mitochondria

Malgorzata Kwasniak-Owczarek1, Blazej Przystajko1, Artur Tomal1

  • 1Department of Cellular Molecular Biology, Faculty of Biotechnology, University of Wroclaw, F. Joliot-Curie 14A, 50-383 Wroclaw, Poland.

Nucleic Acids Research
|June 17, 2026
PubMed

Insights

Plant mitochondrial polynucleotide phosphorylase (mtPNPase) activity depends on mitoribosome biogenesis. Impaired ribosome assembly traps mtPNPase, disrupting mitochondrial RNA metabolism and transcriptome homeostasis.

Area of Science:

  • Mitochondrial Biology
  • Molecular Genetics
  • Plant Science

Background:

  • Mitochondrial polynucleotide phosphorylase (mtPNPase) is a crucial 3'→5' exoribonuclease in plant mitochondria.
  • mtPNPase plays a vital role in RNA processing and turnover within the mitochondrial environment.

Purpose of the Study:

  • To investigate the role of mitoribosome biogenesis in regulating mtPNPase function.
  • To understand how defects in mitoribosome assembly affect mtPNPase substrate levels and mitochondrial RNA metabolism.

Main Methods:

  • Analysis of Arabidopsis mutants with defects in mitoribosomal proteins (rps10, mtran1-2/2-2) and RNA polymerase (rpoTmp).
  • Quantification of mtPNPase substrates and assessment of mtPNPase expression levels.
  • Fractionation studies to determine the localization of mtPNPase and mitoribosomes.

Main Results:

  • Mutants with impaired mitoribosome biogenesis accumulate mtPNPase substrates.
  • This accumulation is linked to inefficient processing of 18S pre-ribosomal RNA, not reduced mtPNPase expression.
  • A spatial sequestration model is proposed where mtPNPase is trapped by immature ribosomal precursors.
  • The rps10 mutant shows altered localization of mtPNPase and mitoribosomes.

Conclusions:

  • Proper mitochondrial small-subunit (mtSSU) biogenesis is essential for mtPNPase function and balanced mitochondrial RNA metabolism.
  • Mitoribosomes act as regulators of mitochondrial RNA homeostasis, linking ribosome biogenesis to transcriptome composition and turnover.
  • This study highlights a novel role for mitoribosomes in controlling RNA processing and stability.

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