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Plant Cell Physiol. 2015 Sep;56(9):1697-710. doi: 10.1093/pcp/pcv098. Epub 2015 Jun 26.

Dual Targeting of the Protein Methyltransferase PrmA Contributes to Both Chloroplastic and Mitochondrial Ribosomal Protein L11 Methylation in Arabidopsis.

Author information

1
Université Grenoble Alpes, Laboratoire de Physiologie Cellulaire & Végétale, F-38041 Grenoble, France CNRS, UMR5168, F-38054 Grenoble, France CEA, iRTSV, Laboratoire de Physiologie Cellulaire & Végétale, F-38054 Grenoble, France INRA, USC1359, F-38054 Grenoble, France.
2
Université Grenoble Alpes, F-38041 Grenoble, France CEA, iRTSV, Biologie à Grande Echelle, F-38054 Grenoble, France INSERM, U1038, F-38054 Grenoble, France.
3
Université Grenoble Alpes, Laboratoire de Physiologie Cellulaire & Végétale, F-38041 Grenoble, France CNRS, UMR5168, F-38054 Grenoble, France CEA, iRTSV, Laboratoire de Physiologie Cellulaire & Végétale, F-38054 Grenoble, France INRA, USC1359, F-38054 Grenoble, France stephane.ravanel@cea.fr.

Abstract

Methylation of ribosomal proteins has long been described in prokaryotes and eukaryotes, but our knowledge about the enzymes responsible for these modifications in plants is scarce. The bacterial protein methyltransferase PrmA catalyzes the trimethylation of ribosomal protein L11 (RPL11) at three distinct sites. The role of these modifications is still unknown. Here, we show that PrmA from Arabidopsis thaliana (AtPrmA) is dually targeted to chloroplasts and mitochondria. Mass spectrometry and enzymatic assays indicated that the enzyme methylates RPL11 in plasto- and mitoribosomes in vivo. We determined that the Arabidopsis and Escherichia coli PrmA enzymes share similar product specificity, making trimethylated residues, but, despite an evolutionary relationship, display a difference in substrate site specificity. In contrast to the bacterial enzyme that trimethylates the ε-amino group of two lysine residues and the N-terminal α-amino group, AtPrmA methylates only one lysine in the MAFCK(D/E)(F/Y)NA motif of plastidial and mitochondrial RPL11. The plant enzyme possibly methylates the N-terminus of plastidial RPL11, whereas mitochondrial RPL11 is N-α-acetylated by an unknown acetyltransferase. Lastly, we found that an Arabidopsis prma-null mutant is viable in standard environmental conditions and no molecular defect could be associated with a lack of RPL11 methylation in leaf chloroplasts or mitochondria. However, the conservation of PrmA during the evolution of photosynthetic eukaryotes together with the location of methylated residues at the binding site of translation factors to ribosomes suggests that RPL11 methylation in plant organelles could be involved, in combination with other post-translational modifications, in optimizing ribosome function.

KEYWORDS:

Chloroplast; Dual targeting; Methylation; Mitochondrion; Post-translational modification; Ribosomes

PMID:
26116422
DOI:
10.1093/pcp/pcv098
[Indexed for MEDLINE]

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