Maintenance and segregation of the mitochondrial genome

Group leader : José Manuel GUALBERTO

Research area

Our team is interested in the mechanisms controlling the maintenance, segregation and repair of the mitochondrial genome (mtDNA) of plants, as well as in the processes of anterograde (nucleus to organelles) and retrograde (organelles to nucleus) regulation of mitochondrial gene expression.

Mitochondria of higher plants have large size genomes with a dynamic structure resulting from recombination events. These recombination mechanisms are necessary for the replication and stoichiometric segregation of the mitochondrial genetic information, but their activities are also responsible for the rapid structural evolution of the plant mtDNA. In addition, the oxidative environment generated by the respiratory chain constantly challenges the maintenance of the mtDNA, requiring efficient DNA repair pathways. We are especially interested in recombination-dependent repair, but also in base excision repair (BER) or nucleotide excision repair (NER). We investigate these processes, and the factors involved, using genetic, genomic, biochemical and cell biology tools available for the model plant Arabidopsis.

To study the processes of mitochondrial genetic regulation and coordination with the nucleus, we have developed an original strategy allowing inducible knock down of individual mitochondrial RNAs. This approach enables us to analyze the dynamics of the response to a sudden change in the regular balance of the mitochondrial transcriptome, whereas a classical mutant would on the contrary be representative of a new established balance.

Pour l’étude des processus de régulation génétique mitochondriale et de coordination avec le noyau, nous avons développé une stratégie originale permettant d’invalider de façon inductible des ARN mitochondriaux individuels. Cette approche nous permet d’analyser la dynamique de la réponse à un changement brutal dans l’équilibre normal du transcriptome mitochondrial, tandis qu’un mutant classique serait au contraire représentatif d’une nouvelle situation d’equilibre.


Dynamics of mtDNA replication and segregation

Project manager: José Manuel GUALBERTO

The homologous recombination activities required for mtDNA maintenance can mobilize short repeated sequences that are abundant in plant mitochondrial genomes. The ectopic recombination involving such repeats creates alternative mtDNA configurations that can become predominant by stoichiometric shift. This process is underlying the rapid structural evolution of the mtDNA. We analyze Arabidopsis mutants of genes involved in recombination surveillance functions to understand the replication and segregation of sub-genomes generated by recombination. From this knowledge we aim to develop genetic tools to create mitochondrial genetic diversity and new phenotypes of potential agronomical value.

Repair of the mitochondrial genome

Project manager: José Manuel GUALBERTO

We have characterized two repair pathways of the plant mtDNA, homologous recombination (HR) and base excision repair (BER). We investigate the factors and mechanisms that link repair and dynamics of the mtDNA. On the other hand, we identified in plants a mitochondrial homolog of the bacterial TRCF (Transcription-Repair Coupling Factor). We seek to establish whether this factor recruits actors of the nucleotide excision repair (NER) or BER pathways and serves as a basis of a transcription-coupled repair pathway of the mtDNA. Finally, we want to determine whether relocalization of the repair factors contributes to the regulation of these processes in response to a genotoxic stress.

Mitochondrial regulation, coordination and reverse genetics

In the absence of an established methodology to transform the mtDNA, we knock down individual mitochondrial RNAs through organellar targeting of trans-cleaving ribozymes driven by a shuttle RNA. By manipulating directly the level of specific transcripts in the organelles and analyzing the transcriptome response in the different cellular compartments, we seek to highlight coordination mechanisms of the mitochondrial gene expression and retrograde signaling processes. Substituting for reverse genetics, the approch is also used to knock down RNAs deriving from putative genes conserved in plant mitochondrial genomes, so as to determine the function of the corresponding proteins.