Project description
Evolutionary trajectory of giant viruses in the cellular world
Mimivirus (Mimiviridae family) is a giant icosahedral virus visible by light microscopy, which uses amoeba as the natural host. The discovery of this and other giant viruses has raised questions about their origin and evolution. The EU-funded VIREVOL project will investigate the co-evolution of these viruses and their amoebal hosts, focusing on specific features of the virions. The study hypothesis is that a transition from the rigid icosahedral virions to the more plastic amphora-shaped particles occurred via the hijacking of the host cellulose synthesis pathway by the ancestor of these viruses. The research will also focus on rod-shaped structure and the organisation of their genome to uncover evolutionary links with the genome packaging systems in the cellular world.
Objective
The discovery of Mimivirus, the first icosahedral virus visible by light microscopy, was followed by the characterization of many other relatives. Its aquatic relative Megavirus chilensis, has a 1.2 Mb genome and encodes more than 1000 proteins, 2/3 unique to the Mimiviridae. Their infectious cycle is cytoplasmic. During the last 10 years, my laboratory discovered three other giant virus families: -the pandoraviridae, with their unique amphora-shaped 1µm long virion morphologies, genome sizes reaching 3Mb and encoding thousands of proteins, most of which without homologues in the cellular or the viral world – the mollivirus, which was isolated from a 30,000 years old Siberian permafrost sample, presents common features with the pandoraviruses. They share 60 unique genes and the roughly spherical (0.6µm) mollivirions present an external tegument resembling the pandoravirions. Both viruses have an early nuclear phase – the pithovirus, despite its amphora-shaped virions, has a fully cytoplasmic cycle. Our work raised questions on the origin of these intriguing viral families and their position in the tree of life. My project is unique as it will address the coevolution of these viruses and their amoebal hosts by focusing on specific features of the virions in two overall aims. 1) Promising preliminary results led us to hypothesize that a progressive transition from the rigid icosahedral virions to the more plastic amphora-shaped particles was made possible through hijacking of the host cellulose synthesis pathway by the ancestor of pandoraviruses. 2) The icosahedral mimivirus package its genome in a complex rod-shaped structure. My team will investigate this structure to unveil possible evolutionary links with the genome packaging systems in the cellular world. We will characterize the machinery responsible for such organization. These two high-risk/high-gain aims will continue to revisit the concept of virus and their evolutionary trajectory in the living world.
Fields of science
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Funding Scheme
ERC-ADG - Advanced GrantHost institution
75794 Paris
France