A mitochondrial prolyl aminopeptidase PAP2 releases N-terminal proline and regulates proline homeostasis during stress response

Plant J. 2020 Dec;104(5):1182-1194. doi: 10.1111/tpj.14987. Epub 2020 Oct 10.


Most mitochondrial proteins are synthesised in the cytosol and targeted into the organelle via N-terminal targeting peptides that are cleaved upon import. The free targeting peptide is subsequently processed in a stepwise manner, with single amino acids released as final products. Here, we have characterised a proline-cleaving aminopeptidase in Arabidopsis thaliana, prolyl aminopeptidase-2 (PAP2, At3g61540). Activity assays show that PAP2 has a preferred activity to hydrolyse N-terminal proline. Protein localisation studies revealed that PAP2 is exclusively targeted to mitochondria. Characterisation of pap2 mutants show defective pollen, enhanced dark-induced senescence and increased susceptibility to abiotic stresses, which are likely attributed to a reduced level of accumulated free proline. Taken together, these results demonstrate the role of PAP2 in proline cleavage from mitochondrial peptides and proline homeostasis, which is required for the development of male gametophyte, tolerance to abiotic stresses, and leaf senescence.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Motifs
  • Aminopeptidases / genetics
  • Aminopeptidases / metabolism*
  • Arabidopsis / cytology
  • Arabidopsis / genetics
  • Arabidopsis / metabolism*
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism*
  • Cellular Senescence / physiology
  • Darkness
  • Green Fluorescent Proteins / genetics
  • Loss of Function Mutation
  • Mitochondria / metabolism
  • Phylogeny
  • Plants, Genetically Modified
  • Pollen / physiology
  • Proline / metabolism*
  • Stress, Physiological / physiology*
  • Transcription Factors / genetics
  • Transcription Factors / metabolism*


  • Arabidopsis Proteins
  • PAP2 protein, Arabidopsis
  • Transcription Factors
  • Green Fluorescent Proteins
  • Proline
  • Aminopeptidases
  • At3g61540 protein, Arabidopsis