Genome Evolution of Mutualistic Viruses

  • Webb, Bruce (PI)

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Description

Microbes are successful, in part, because they exist in varied associations with multicellular organisms. Bacteria and fungi are found in sophisticated and diverse beneficiaJ, commensal and parasitic associations with every eukaryotic organism. However, the diversity ofvirus-eukaryotic host associations either is more limited or not fully appreciated. Genome sequencing projects clearly demonstrate that eukaryotic genomes are extensively modified through the action of transposable elements and retroviruses. Persistent and latent virus infections ar..so ubiquitous but virus-host associations that are clearly beneficial to the host are rarely described. Our respective laboratories have investigated mutualistic associations that exist between two large groups of replication-defective viruses, the polydnaviruses. Polydnaviruses exist in obligate mutualistic associations with some parasitic wasps. The two polydnavirus genera, the ichnoviruses and the bracoviruses have in common their obligatory association with parasitic wasps and their unique genome organization. However, they have no sequence homology and do not have a common origin suggesting that they are derived from different ancestral viruses. Thus, the common features of polydnaviruses may result from their similarrities in their life cycles. We have completed the sequence analyses of one ichnovirus genome and will complete sequencingof a bracovirus genome this year. Polydnavirus genomes are very unusual. They are largely non-coding. Viral genes having pathogenic effects exist in large gene families while genes involved in virus replication are not packaged within the virion. Presumably, genes required for virus replication now reside in the nuclear genome. Moreover, there are clear distinctions within the two virus groups. Because polydnaviruses are inherited viruses that exist in phylogenetically ancient and diverse lineages it is possible to approach the evolution of these beneficial viruses through comparative genome sequencing. We propose to sequence a total of 10 polydnavirus genomes that are selected to represent the major PDV-containing groups. This will describe shared and unique features of the polydnavirus-containing lineages over their estimated 60 million year period of co-evolution. We then propose to assess the expression and evolution of polydnavirus genes in 8 additional species that focus on genera of particular interest. This work will be the first truly comparative anaylsis of polydnavirus genomes, genes, gene families and segments.
StatusFinished
Effective start/end date9/15/019/30/04

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