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Microplitis demolitor bracovirus genome segments vary in abundance and are individually packaged in virions

Markus H Beck1, Ross B Inman, Michael R Strand

  • 1Department of Entomology and Center for Tropical and Emerging Global Diseases, University of Georgia, Athens, GA 30602, USA.

Virology
|October 13, 2006
PubMed

Insights

Polydnaviruses (PDVs) have segmented genomes with varying segment abundance. This study used electron microscopy and real-time PCR to analyze Microplitis demolitor bracovirus (MdBV) genome packaging and segment distribution in wasps and hosts.

Area of Science:

  • Virology
  • Insect Pathology
  • Molecular Biology

Background:

  • Polydnaviruses (PDVs) are unique viruses associated with parasitoid wasps.
  • Their segmented double-stranded DNA genomes have non-equimolar segment abundance, with limited knowledge on genome packaging and segment distribution.
  • Microplitis demolitor bracovirus (MdBV) replicates in female wasp ovaries, forming virions in calyx fluid.

Purpose of the Study:

  • To characterize the genome packaging and segment abundance of Microplitis demolitor bracovirus (MdBV).
  • To investigate the distribution and relative abundance of MdBV genome segments within the wasp and its host.
  • To correlate viral segment abundance with transcript levels.

Main Methods:

  • Electron microscopy (EM) was used to analyze virion structure and DNA packaging.
  • A semi-quantitative real-time PCR assay with SYBR Green I was developed to quantify viral DNA segment abundance.
  • MdBV segment abundance was analyzed in wasp calyx fluid, parasitized host larvae (Pseudoplusia includens), and different wasp tissues.

Main Results:

  • EM revealed MdBV virions contain a single nucleocapsid encapsidating one circular DNA of variable size.
  • Five MdBV segments (J, O, H, N, B) constituted over 60% of viral DNA in calyx fluid, correlating with DNA size distributions.
  • Segment copy numbers varied between hosts, but relative abundance within a host mirrored calyx fluid; segments were most abundant in hemocytes and least in salivary glands, with similar relative abundance across tissues.
  • No clear relationship was found between MdBV segment and transcript abundance in hemocytes and fat body.

Conclusions:

  • MdBV genome packaging involves single nucleocapsids with variable DNA, and segment abundance is non-equimolar, with specific segments dominating.
  • The relative abundance of MdBV segments is consistent within the wasp and its host, suggesting regulated packaging or replication.
  • Tissue-specific distribution of viral segments occurs, but their relative proportions remain consistent, indicating tissue-specific regulation of segment expression or stability rather than packaging.

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