Mitochondria are responsible for energy production through aerobic respiration and represent the powerhouse of eukaryotic cells. Their metabolism and gene expression processes combine bacterial-like features and traits that evolved in eukaryotes. Among mitochondrial gene expression processes, translation remains the most elusive. In plants, while numerous pentatricopeptide repeat (PPR) proteins are involved in all steps of gene expression, their fu nction in translation remained unclear. I will present the biochemical characterization of Arabidopsis mitochondrial ribosomes and describe their protein subunit composition. Complementary biochemical approaches identify 20 plant specific mitoribosome proteins, among which 10 are PPR proteins. The knock out mutations of ribosomal PPR genes result in lethality or in severe growth delays. The molecular analysis of rPPR1 mutant using ribosome profiling as well as the analysis of mitochondrial proteins reveal that this PPR protein is a generic translation factor. Finally, single particle cryo-electron microscopy reveals the unique structural architecture of Arabidopsis mitoribosomes, characterized by a very large small ribosomal subunit, larger than the large ribosomal subunit. Overall, results show that Arabidopsis mitoribosomes are completely distinct from bacterial and other eukaryote mitoriboso mes, both in terms of structure and of protein content.