1 Mer-Molécules- Santé (MMS), Le Mans Université, France
2 UMR_S 1232 Centre de Recherche en Cancérologie et Immunologie Nantes-Angers, Université de Nantes, France
Epigenetics refers to modifications of gene expression without modifying DNA sequence, which are highly influenced by environmental factors and pollutants. In the last years, epigenetics in microalgae has been studied in a few models like the marine pennate diatom Phaeodactylum tricornutum, for which a genome has already been sequenced, but not transgenerational epigenetic inheritance, as sexual reproduction has never been observed in this species. Haslea ostrearia is another marine pennate diatom known to product a blue pigment, name marennine, responsible for the greening oyster gills in oyster ponds in Western France. In the laboratory, we can control sexual reproduction in H. ostrearia, which makes this diatom a valuable model to study epigenetics and transgenerational epigenetic inheritance. A series of preliminary experiments demonstrated that a UV stress induced an hypomethylation of DNA in H. ostrearia. To go further, analyses on the impacts of a pesticide have been carried out. It has long been known that pollutants’ fate, in particular of plant protection chemicals, is to accumulate in the oceans. For instance, diuron used in agriculture as weed killer but also as an antifouling compound against algae in ship hull, can be observed at a high concentration in coastal waters. In the French Atlantic coast, diuron concentration can reach up to 4 µg/L. Diuron inhibits photosynthesis by blocking electron transfer around photosystem II. It has therefore become important to know the impact that this pollutant can have on photosynthetic organisms, and more particularly on diatoms, which are the basis of most food chains in aquatic ecosystems. A decrease in growth was observed for Haslea ostrearia in presence of diuron. Moreover, molecular tests (5mC ELISA and 5hmC ELISA) evidenced a global hypomethylation of some genes in these two species when concentration of diuron increased from 0 to 10 µg/L
Keywords : Diatom ; diuron ; epigenetics ; sexual reproduction
