Doctoral School
Life and Health Sciences
Speciality
Biology-Health – Bioinformatics and Genomics Specialty
establishment
Aix-Marseille University
Keywords
Giant virus,Virophage,Transpoviron,Interactions,Hyperparasite,Transcriptomics
Keywords
Giant virus,Virophage,Transpoviron,Interactions,Hyperparasite,Transcriptomic
Thesis title
Interactions of a hyperparasitic system: Protist, Giant Virus, Virophage, Transpoviron
Hyperparasitic system interactions: Protista, Giant Virus, Virophage, Transpoviron
Date
Friday November 8, 2024 at 2:00 p.m.
Address
Campus Joseph Aiguier (CNRS)
31 Chem. Joseph Aiguier, 13009 Marseille
Pierre Desnuelle Amphitheater
Jury
Thesis summary
Giant viruses are double-stranded DNA viruses that infect a broad spectrum of eukaryotes, mainly single-celled. These viruses have the particularity of being themselves parasitized by other viruses, called virophages. But the story does not end there, virophages and giant viruses can also carry fragments of DNA, known as transpovirons, into their particles. A complex system with four partners is then established, including a cell, a giant virus, a virophage and a transpoviron. The objective of this thesis is to understand the interactions between the different partners of this type of quadripartite system. Transcriptomic analyzes were carried out by RNA-seq during infection kinetics involving the host amoebic cell Acanthamoeba castellanii and the giant virus Megavirus chilensis. Similar experiments were conducted by adding the virophage Zamilon vitis, Megavirus vitis transpoviron, or both. These data reveal the transcriptome of each partner, in particular of the virophage and the transpoviron, which are still unknown to date. Importantly, comparative analyzes of RNA-seq experiments reveal the impact of different partners of the quadripartite system on the gene expression of others. The giant virus drastically reconfigures the transcriptome of its amoebic host, illustrating their host-parasite interaction. The transpoviron does not affect the gene expression of any of the other partners, highlighting a commensal relationship with the giant virus and virophage. On the other hand, the virophage profoundly, but transiently, modifies the transcriptome of the giant virus, without altering the protein composition of mature viral particles. This study demonstrates that Zamilon vitis is a transient hyperparasite of the giant virus. Finally, the virophage induces overexpression of transpoviron genes, probably indirectly through the upregulation of transcription factors of the giant virus. This work highlights the complexity of the transcriptional regulatory networks established between giant viruses, virophages and transpovirons in the infected cell. Furthermore, the opportunistic pathogenic character of Acanthamoeba, the cellular host, highlights the integration of this system into a larger ecosystem, thus opening new perspectives for the exploration of similar nested parasitic systems.
Thesis resume
Giant viruses are double-stranded DNA viruses that infect a wide range of eukaryotes, primarily unicellular organisms. These viruses can themselves be parasitized by other viruses, known as virophages. Additionally, both virophages and giant viruses can carry episomal DNA molecules, called transpovirons, within their particles. This establishes a complex four-partner system involving a host cell, a giant virus, a virophage, and a transpoviron. The aim of this thesis is to understand the interactions between these different partners through the analysis of their respective transcriptome. RNA-seq was performed during an infection time course of the amoebal host cell Acanthamoeba castellanii by the giant virus Megavirus chilensis. Similar experiments were conducted with the addition of the virophage Zamilon vitis and/or Megavirus vitis transpoviron. These data reveal the gene expression of each partner, this study being the first to reveal the transcriptome of the virophage and transpoviron. Comparative RNA-seq analyses reveal the impact of the different partners of the quadripartite system on the gene expression of others. The giant virus dramatically reconfigures the transcriptome of its amoebal host, reflecting their host-parasite interaction. The transpoviron does not affect the gene expression of any of the other partners, underlining a commensal relationship with the giant virus and the virophage. In contrast, the virophage transiently but profoundly alters the transcriptome of the giant virus. However, this alteration dont impact the protein composition of the mature viral particles. This demonstrates that Zamilon vitis acts as a transient hyperparasite of the giant virus. Finally, the virophage induces the overexpression of transpoviron genes, likely by upregulating giant virus transcription factors. This work sheds light on the complexity of the transcriptional regulatory networks between the giant virus, virophage, and transpoviron within the infected cell. Furthermore, Acanthamoeba, the host cell itself can be an opportunistic pathogen of other organisms, demonstrating that this system is integrated into a larger ecosystem, and opens to exploring other similar nested parasitic systems.
