How does an obligate asexual plant parasitic species adapts to its host?

• Titre et résumé de la première partie:

Population genomics of Ostreococcus tauri (chlorophyta) : diversity and evolution of the smallest photosynthetic eukaryote.
 
 The smallest free-living photosynthetic eukaryote Otsreococcus tauri is identified based on its rDNA 18S encoding sequence. To estimate the genetic diversity associated with this molecular identification, whole DNA of 13 strains sampled in North-West Mediterranean Sea has been sequenced with Illumina. From whole genome polymorphisms analysis we estimated the genetic diversity at 0.004, which is similar to other unicellular eukaryotes such as yeasts. From single nucleotide polymorphisms we built the population scaled recombination map of O. tauri. Mutational pattern analysis inferred from polymorphisms frequencies allows us to test different evolutionary model at the origin of genome base composition. Our data is consistent with GC-biased gene conversion. Polymorphisms analysis along cytoplasmic genomes gives insight into the mode of transmission of the chloroplast and mitochondria along the green lineage. Last but not least we estimated the power of Illumina to assemble de novo the genome of O. tauri for its use to other eukaryotic phytoplankton. Overall this work gives insight into the diversity level and evolution of O. tauri. It fosters our understanding of the green lineage evolutionary history and mechanisms shaping this lineage.
 

• Titre et résumé de la deuxième partie:

How does an obligate asexual plant parasitic species adapts to its host? Looking for evidences in the multiple diverged copies genome of the root-knot nematode Meloidogyne incognita.

Obligate asexual root-knot nematodes do not undergo meiosis. As a consequence, their alleles are not shuffled and the expected benefits of recombination: the purge of deleterious mutations and spread of beneficial ones is not achieved. For this reason obligate asexual species are seen as evolutionary dead end. Challenging this view, the obligate asexual species M. incognitahas a wider hosts range and geographical distribution than its sexual counterpart M. hapla. Parallel to this observation the genome sequence of M. incognitais made of multiple diverged and rearranged copies. Such a feature is not observed in M. hapla's genome. We'll test the hypothesis that the multiple genes copies in the genome of M. incognita provide the raw material for genomic plasticity, fostering adaptation to their many hosts. We'll make use of genomics (dN/dS ratio between gene pairs) and transcriptomic data (differential gene expression level measured on different infested host plants ) to test this hypothesis.