Société Française de Biochimie et Biologie Moléculaire

Florent WALTZ - JUNE 2020

Université de Bordeaux, Inserm, Institut Européen de Chimie et Biologie, Bordeaux, France

" Cryo-EM structure of the RNA-rich plant mitochondrial ribosome " Nature Plants 6, 377-383 (2020) Florent Waltz, Heddy Soufari, Anthony Bochler, Philippe Giegé & Yaser Hashem


Florent WALTZ, 27, is a post-doctoral fellow in Yaser HASHEM's team « mRNA translation in eukaryotes and parasitic protozoa » at the European Institute of Chemistry and Biology (IECB), 33600 Pessac, France. During his PhD, carried out at the University of Strasbourg in Philippe GIEGE's team, he was mainly interested in mitochondrial gene expression. He studied mitochondrial ribosomes, the latter being particularly different from prokaryotic and eukaryotic cytosolic ribosomes. Following the biochemical study of the plant mitoribosome carried out during his PhD thesis, revealing the presence of numerous protein components until then unknown, he continued his work in post-doctorate by focusing on obtaining a high-resolution structure, using cryo-EM, of these same complexes in the team of Yaser HASHEM. This study led to the publication of the article entitled "Cryo-EM structure of the RNA-rich plant mitochondrial ribosome" in the journal Nature Plants on April 6, 2019, which notably highlighted the precise functions and mode of action of the numerous PPR proteins associated with this mitoribosome. The latter mainly acting on stabilization of long extensions of ribosomal RNAs, but also a probable role in the initiation of translation.


Université de Bordeaux, Inserm,Institut Européen de Chimie et Biologie
2 Rue Robert Escarpit, 33600 Pessac 

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The vast majority of eukaryotic cells contain mitochondria, essential powerhouses and metabolic hubs. These organelles have a bacterial origin and were acquired during an early endosymbiosis event. Mitochondria possess specialized gene expression systems composed of various molecular machines including the mitochondrial ribosomes (mitoribosomes). Mitoribosomes are in charge of translating the few essential mRNAs still encoded by mitochondrial genomes. While chloroplast ribosomes strongly resemble those of bacteria, mitoribosomes have diverged significantly during evolution and present strikingly different structures across eukaryotic species. In contrast to animals and trypanosomatids, plants mitoribosomes have unusually expanded ribosomal RNAs and conserved the short 5S rRNA, which is usually missing in mitoribosomes. We have previously characterized the composition of the plant mitoribosome revealing a dozen plant-specific proteins, in addition to the common conserved mitoribosomal proteins. In spite of the tremendous recent advances in the field, plant mitoribosomes remained elusive to high-resolution structural investigations, and the plant-specific ribosomal features of unknown structures. Here, we present a cryo-electron microscopy study of the plant 78S mitoribosome from cauliflower at near-atomic resolution. We show that most of the plant-specific ribosomal proteins are pentatricopeptide repeat proteins (PPR) that deeply interact with the plant-specific rRNA expansion segments. These additional rRNA segments and proteins reshape the overall structure of the plant mitochondrial ribosome, and we discuss their involvement in the membrane association and mRNA recruitment prior to translation initiation. Finally, our structure unveils an rRNA-constructive phase of mitoribosome evolution across eukaryotes.