An Update on Mitochondrial Ribosome Biology: The Plant Mitoribosome in the Spotlight

Abstract

Contrary to the widely held belief that mitochondrial ribosomes (mitoribosomes) are highly similar to bacterial ones, recent experimental evidence reveals that mitoribosomes do differ significantly from their bacterial counterparts. This review is focused on plant mitoribosomes, but we also highlight the most striking similarities and differences between the plant and non-plant mitoribosomes. An analysis of the composition and structure of mitoribosomes in trypanosomes, yeast, mammals and plants uncovers numerous organism-specific features. For the plant mitoribosome, the most striking feature is the enormous size of the small subunit compared to the large one. Apart from the new structural information, possible functional peculiarities of different types of mitoribosomes are also discussed. Studies suggest that the protein composition of mitoribosomes is dynamic, especially during development, giving rise to a heterogeneous populations of ribosomes fulfilling specific functions. Moreover, convincing data shows that mitoribosomes interact with components involved in diverse mitochondrial gene expression steps, forming large expressosome-like structures.

Structural Heterogeneities of the Ribosome: New Frontiers and Opportunities for Cryo-EM

“…In addition, mitochondrial ribosomes present important morphological differences with cytoplasmic ribosomes [ 27 ]. As cryo-EM technology allows to computationally sort ribosomes of different classes from the image data, the past few years have seen various new structures of mitochondrial ribosomes from yeast, plants, mammals and other eukaryotic cells [ 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ]. In contrast with bacteria, from which mitochondria originate according to the endosymbiotic hypothesis [ 36 ], new or modified ribosomal proteins in mitoribosomes form an extended network around the ribosomal RNA.…”

“…In contrast with bacteria, from which mitochondria originate according to the endosymbiotic hypothesis [ 36 ], new or modified ribosomal proteins in mitoribosomes form an extended network around the ribosomal RNA. This network can either be expanded or highly reduced [ 35 ], explaining how mitoribosomes dramatically diverge in composition and size (for more details, see the recent review by Tomal et al [ 29 ]).…”

Separation and Paired Proteome Profiling of Plant Chloroplast and Cytoplasmic Ribosomes

“…Several studies indicate that plant mitochondrial ribosomes considerably differ from bacterial ribosomes and from other eukaryotic mitochondrial ribosomes. They appear to have a higher molecular weight, an additional rRNA domain and appear to contain non-canonical proteins like peptidases, proteases and Pentatricopeptide Repeat (PPR) proteins [44,45,49,50]. Table 2.…”

The Chlamydomonas mitochondrial ribosome: how to build a ribosome from RNA fragments

“…Our study describes the structure and composition of the Chlamydomonas mitochondrial ribosome. The cryo-EM reconstructions show that this green alga mitoribosome differs significantly from prokaryotic ribosomes as well as its flowering plant counterpart (Tomal et al, 2019;Waltz et al, 2020b). In both the small and the large subunits, the mitoribosome has acquired several additional r-proteins that significantly reshape this ribosome's architecture.…”