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Thesis in phytoplankton, giant viruses, resistance, algal blooms, arms-race, co-existence (H/F)

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Français - Anglais

Date Limite Candidature : vendredi 8 juillet 2022

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General information

Reference : UMR7232-DIDPEU-016
Date of publication : Friday, June 17, 2022
Scientific Responsible name : YAU Sheree
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 October 2022
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly

Description of the thesis topic

Half of Earth's photosynthesis takes place in the ocean and is mediated by phytoplankton, which host a massive diversity of viruses. Among them, “giant” DNA viruses are a major cause of mortality of microbial algae, thus viruses modulate host populations and biogeochemical cycles. Algae from diverse lineages (green algae, haptophytes, dinoflagellates and diatoms) develop resistance to viruses, whereby after virus-induced lysis and population decline, virus-resistant cells regrow1,2. These cells no longer lyse when re-challenged with the initial virus. Despite their ecological importance, almost nothing is known about the molecular mechanisms mediating the emergence of anti-viral resistance. Ostreococcus are bacteria-sized (1 μm) green algae that predominate in coastal waters. The ability to easily culture and perform functional genomics on Ostreococcus and their “giant” prasinoviruses makes them a formidable system for discovering the molecular bases of microalgae-virus interactions. Foundational studies indicate that virus-resistance in Ostreococcus is linked to structural changes concentrated on one, so-called, “outlier” chromosome3–5, which moreover has a bipartite structure with the left portion encoding the genes over-transcribed in virus-resistance and the right the genes that are under-transcribed4.
The objectives of this PhD project are, therefore:
1) to elucidate the genome dynamics of the hypervariable “outlier” chromosome encoding the candidate resistance genes.
2) to identify factors regulating the unusual bipartite gene expression pattern by tracking expression changes in susceptible and resistant cell lines, as well as during infection.
3) to validate the function of regulators elements by genetic manipulation and screening for deregulation of antiviral resistance.

Work Context

This PhD fellowship and up to 5000 € per year in mobility costs is funded by the Weizmann-CNRS Israel-France Collaboration Program 2022 between the Genophy (CNRS: Evolutionary and Environmental Genomics of Phytoplankton) and Vardi (Weizmann) teams.

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