​Phytoplankton-virus interaction in the ocean: A new mechanism of viral immunity in marine phytoplankton

About the speaker:

Hervé Moreau is “Directeur de Recherche” at CNRS (Centre Nacional de la Recherche Scientifique) at the Oceanological Observatory of Banyuls (France) and currently Adjunct Scientific Director of the Biological Science Institute (ISB) of CNRS.  In the last 15 years he has been working on marine eukaryotes pico- phytoplankton and its interaction with viruses.  He has coordinated several European and French research projects including the international consortium for the sequencing and annotation of the microalga Ostreococcus tauri, known as the tiniest free living eukariotic cell. Recently, he is leading the PHYTADAPT project which focus on the adaptation of phytoplankton and acclimation of phytoplankton to the long Arctic winter night. He has published several papers in high impact journal on both genomics and physiology of green algae.

About the event:

Mamiellophyceae is an ecologically important class of green microalgae in ocean and Prasinoviruses infecting them are probably the most numerous kind of large DNA viruses of eukaryotes in the sea. Surviving a viral attack is essential for any species to avoid its irreversible removal from the ecosystem, and microbes must involve the resistance or susceptibility of individual cells. The co-existence between viruses and their hosts has led to the evolution of complex viral attack and host defence strategies. We showed that Mamiellophyceae, as all phytoplankton populations, is largely controlled by these hugely diverse populations of viruses. We sequenced many of them and showed that mechanisms of resistance operate in these species. Virus resistant cell lines arise in many independent cell lines during lytic infections. In these resistant lines, over-expression of all genes in more than half of an unusual chromosome in resistant lines, and karyotypic analyses showed physical rearrangements of this chromosome. It has an unusual genetic structure whose equivalent is found in all of the sequenced genomes in this ecologically important group of green algae. We propose that structural instability of this chromosome is under the control of viral infection and provide a viral immunity.