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Mitochondrial DNA recombination and transmission in Arabidopsis thaliana – MITARD

Submission summary

Mitochondrion contains its own genetic information, the mitochondrial genome (mtDNA), which codes for proteins essential for the assembly of the respiratory complexes and which is transmitted maternally in most higher eukaryote. Defects in mtDNA or in the machinery of its maintenance and expression are associated with a vast range of disorders. In humans, they can cause a wide spectrum of diseases associated to the tissues that are most dependent on mitochondrial oxidative phosphorilation. In plants, the mitochondrial genetic information influences several traits of agronomic importance including fertility, plant vigor, chloroplast function and cross-compatibility. Mutations that affect plant mtDNA are also the cause of many studied examples of cytoplasmic male sterility (CMS), that is an important agronomic trait used by breeders to produce high-yield hybrids. Several features of mtDNA replication and transmission seem to be common to most higher eukaryotes: recombination processes seem to have central roles in mtDNA repair and replication. Recombination is also responsible for the occurrence of alternative mtDNA configurations that co-exist at substoichiometric level with the main mtDNA. From parents with heteroplasmic mtDNA, individuals can segregate where these substoichiometric alternative genomes become predominant, a process that is called substoichiometric shifting (SSS). In the model plant Arabidopsis thaliana the msh1 mutation was identified as responsible for the accumulation of characteristic rearrangements of the mtDNA by SSS. In our laboratory, we have also recently identified another component of the SSS system: the Arabidopsis OSB1 gene, that codes for a ssDNA-binding protein specific of plant organelles. Deficiency in OSB1 results in phenotypes that are the consequence of the accumulation and segregation of alternative mtDNA structures resulting from the recombination between short repeats. OSB1 is preferentially expressed in the gametes, pollen and unfertilized ovules, clearly indicating that these are the tissues where the copy number of sub-genome is regulated. Our aim is to understand the genetic processes that regulate plant mitochondrial DNA replication and stoichiometric transmission, with a special interest in the roles that mtDNA recombination has in these processes. The msh1 and osb1 mutants are good models where these important questions can be addressed, exploiting the powerful genetic, cell biology and molecular tools that can be used in the Arabidopsis model plant. For that we intend to perform a comprehensive study of mtDNA replication and partitioning during plant gametogenesis, and the effects of the msh1 and osb1 mutations in these processes. The relative ratios between the main mtDNA genome, the alternative sub-genomes and the nuclear DNA will be determined in specific cell tissues sampled by laser microdissection. This research will provide a picture on the developmental stages that are critical in the transmission of a functional mitochondrial genome, and of the mechanism of SSS that result in the preferential transmission of recombined genomes to the progeny of certain mutants. We will also intend to characterize other components of the mtDNA maintenance machinery that we have already identified. We will study the spatial and developmental expression of these genes, in order to identify those that have important roles in mtDNA transmission during gametogenesis. This research will open the way for a more detailed analysis of their corresponding mutant phenotypes, of their interactions and of their functions during plant development.

Project coordination

jose GUALBERTO (Organisme de recherche)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

Help of the ANR 265,000 euros
Beginning and duration of the scientific project: - 36 Months

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