Mitochondria are essential organelles found in most eukaryotic organisms. They produce ATP, the main source of cellular energy, and are involved in vital processes such as apoptosis and the synthesis of important metabolites. In plants, mitochondria operate in complementarity with chloroplasts, which generate energy but do not fulfill all metabolic requirements. Due to their symbiotic origin, mitochondria possess their own DNA as well as their own gene expression machinery, including the mitochondrial ribosome (mitoribosome), which is responsible for producing several proteins essential for cellular respiration.
Mitoribosomes have diverged considerably over the course of evolution and display great diversity among species. In plants, they are particularly large and complex, containing numerous specific proteins and expanded ribosomal RNAs. Despite recent advances, many aspects of their function and assembly have remained poorly understood.
In an article published in the journal Nature Communications, Philippe Giegé’s team at IBMP, in collaboration with researchers from Bordeaux and Basel, used cryo-electron microscopy to obtain very high-resolution images of the mitoribosome in action during messenger RNA translation, as well as at different stages of its maturation. They observed the ribosome associated with a transfer RNA and a fragment of messenger RNA, with a protein in the process of elongation. By combining these structural data with nanopore sequencing and mass spectrometry, they identified 19 specific modifications of ribosomal RNA.
The study also reveals a late assembly stage of the small subunit involving the protein RsgA. In plants, a specific extension of RsgA temporarily blocks the messenger RNA channel, thereby preventing premature translation. These findings provide essential insights into the unique functional and biogenetic features of plant mitochondrial ribosomes.
