Polydnavirus

Figure 1: Polydnaviridae under a microscope

Image From: https://ars.els-cdn.com/content/image/3-s2.0-B9780123848581000035-f03-01-9780123848581.jpg

Introduction

There are two genuses of Polydnaviridae. These are the Ichnovirus and Brachovirus (Strand & Burke, 2014)
It is a virus, not a cellular organism, so its taxonomy doesn't start until family (Strand & Burke, 2014)
Primary literature article: Scientists wanted to find the evolutionary intersection of three large DNA viruses: Iridovirus, Ascovirus, and Ichnovirus using genome sequencing and phylogenetic analysis (Bigot et al., 2009).

Figure 2: A parasitoid wasp, the host of PDV

Image from: https://agsci.colostate.edu/agbio/wp-content/uploads/sites/127/2022/03/giant-ichneumon-wasp-scaled-1.jpeg

Background

Polydnavirus reproduces via viral replication in the nucleus, and uses DNA-templated transcription (Strand & Burke, 2014)
They are cylindrical and their genome is segmented
the parasitoid wasp is a host for poydnavirus and they are in a mutualistic symbiotic relationship (Strand & Burke, 2014)
- expression of the PDV gene prevent the immune system of the wasp's host from killing the wasp's eggs, and in return PDV has a host for itself
There are two theories for the evolution of PDV (Strand & Burke, 2014)
- The virus itself is derived from the wasp's genes
- Ancestral wasps developed a positive association with an existing virus that led to the eventual integration of PDV into the wasp's genome
Family: Polydnaviridae
Genus: Brachovirus and Ichnovirus

Figure 3: A table from the study showing the number of genes shared between viruses

Image from: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0006397#s2

DNA Analysis

Scientists wanted to discover what, if any, DNA viruses are related to each other and how they came to exist in the first place
They decided to track the evolution of three large DNA viruses: Ascoviridae, Iridoviridae, and Ichnoviridae (Bigot et al., 2009).
The method used to compare their evolution was phylogenetic analysis and genome sequencing (Bigot et al., 2009).
They discovered that the Ichnoviridae genus of PDV is not derived from the wasp DNA itself, but is related to two other viruses tested: Ascoviridae and Iridoviridae (Bigot et al., 2009).
They used these results to create a figure that shows how they are all related to one another, and their data led to the conclusion that all of these viruses are related to one another and evolved from one another (Bigot et al., 2009).

Figure 4: Diagram showing the evolution of the viruses

Image from: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0006397#s2

Conclusion

All three viruses do share an evolutionary intersection (Bigot et al., 2009).
- PDV is related to DpAV4a, which is descended from Iridoviruses
- PDV is related to Ascoviridae, which are decided from Iridoviridae
- There may be to Ichnoviridae subfamilies that are unrelated
This leads to a greater understadning of how these DNA viruses came about, and can help us form hypotheses about other simialr DNA viruses and their evolution.This will also help with conducting future studies in this area

Citations

•Bigot, Y., Renault, S., Nicolas, J., Moundras, C., Demattei, M.-V., Samain, S., Bideshi, D. K., & Federici, B. A. (2009). Symbiotic virus at the evolutionary intersection of three types of large DNA viruses; iridoviruses, ascoviruses, and ichnoviruses. PLoS ONE, 4(7). https://doi.org/10.1371/journal.pone.0006397

•Herniou, E. A., Huguet, E., Thézé, J., Bézier, A., Periquet, G., & Drezen, J.-M. (2013). When parasitic wasps hijacked viruses: Genomic and functional evolution of polydnaviruses. Philosophical Transactions of the Royal Society B: Biological Sciences, 368(1626), 20130051. https://doi.org/10.1098/rstb.2013.0051

•Strand, M. R., & Burke, G. R. (2014). Polydnaviruses: Nature's genetic engineers. Annual Review of Virology, 1(1), 333–354. https://doi.org/10.1146/annurev-virology-031413-085451

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