title: Co-evolution of mitochondrial tRNA import and codon usage determines translational efficiency in the green alga Chlamydomonas.
abstract: Mitochondria from diverse phyla, including protozoa, fungi, higher plants, and humans, import tRNAs from the cytosol in order to ensure proper mitochondrial translation. Despite the broad occurrence of this process, our understanding of tRNA import mechanisms is fragmentary, and crucial questions about their regulation remain unanswered. In the unicellular green alga Chlamydomonas, a precise correlation was found between the mitochondrial codon usage and the nature and amount of imported tRNAs. This led to the hypothesis that tRNA import might be a dynamic process able to adapt to the mitochondrial genome content. By manipulating the Chlamydomonas mitochondrial genome, we introduced point mutations in order to modify its codon usage. We find that the codon usage modification results in reduced levels of mitochondrial translation as well as in subsequent decreased levels and activities of respiratory complexes. These effects are linked to the consequential limitations of the pool of tRNAs in mitochondria. This indicates that tRNA mitochondrial import cannot be rapidly regulated in response to a novel genetic context and thus does not appear to be a dynamic process. It rather suggests that the steady-state levels of imported tRNAs in mitochondria result from a co-evolutive adaptation between the tRNA import mechanism and the requirements of the mitochondrial translation machinery.
authors.affiliation: Génétique des Microorganismes, Department of Life Sciences, Institute of Botany, University of Liège, Liège, Belgium
authors.forename: Thalia
authors.initials: T
authors.lastname: Salinas
authors.forename: Francéline
authors.initials: F
authors.lastname: Duby
authors.forename: Véronique
authors.initials: V
authors.lastname: Larosa
authors.forename: Nadine
authors.initials: N
authors.lastname: Coosemans
authors.forename: Nathalie
authors.initials: N
authors.lastname: Bonnefoy
authors.forename: Patrick
authors.initials: P
authors.lastname: Motte
authors.forename: Laurence
authors.initials: L
authors.lastname: Maréchal-Drouard
authors.forename: Claire
authors.initials: C
authors.lastname: Remacle
mesh_terms: D001692:Biological Transport; D019069:Cell Respiration / Q000235:genetics; D002696:Chlamydomonas / Q000235:genetics*; D003062:Codon / Q000235:genetics; D019143:Evolution, Molecular; D054629:Genome, Mitochondrial; D053078:Membrane Potential, Mitochondrial; D008928:Mitochondria / Q000235:genetics* / Q000378:metabolism; D017354:Point Mutation; D014176:Protein Biosynthesis; D012343:RNA, Transfer / Q000235:genetics* / Q000378:metabolism
chemical_list: D003062:Codon; D012343:RNA, Transfer