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1.
J Gen Virol ; 91(Pt 10): 2610-9, 2010 Oct.
Article in English | MEDLINE | ID: mdl-20554796

ABSTRACT

Polydnaviruses (PDVs) are unique symbiotic viruses associated with parasitic wasps; they replicate only in the calyx cells of a wasp's ovaries and are transferred at oviposition along with the parasitoid egg into the lepidopteran host. The DNA packaged in the viral particles encodes factors that manipulate the host's immune defences and development to benefit the parasitoid. PDVs are found in two subfamilies of ichneumonids (ichnoviruses) and in braconids of the microgastroid complex (bracoviruses). We recently showed that the latter derive from an ancestral nudivirus, as 24 nudivirus-related genes were identified in ovaries of two distantly related braconids at the stage of virion formation. Here, we present a comprehensive analysis of the viral particle proteins of the Chelonus inanitus bracovirus (CiBV). Proteins of purified CiBV particles were analysed by mass spectrometry and amino acid sequences matched to the existing ovarian-cDNA database. In addition, transcript quantities of identified genes were measured by quantitative real-time PCR in female pupae at the onset and peak of virion formation and at corresponding stages in male pupae. This combined approach allowed the identification of 44 CiBV particle proteins: 16 were nudivirus-related, three had similarity to ovarian proteins of another braconid, 11 had similarity to cellular proteins and 14 had no similarity to known proteins. The transcripts of all of them increased in female, but not male, pupae. These data confirm the important contribution of nudivirus genes but also indicate the presence of many lineage- or species-specific proteins possibly involved in the parasitoid-host interaction.


Subject(s)
Hymenoptera/virology , Polydnaviridae/chemistry , Viral Proteins/analysis , Virion/chemistry , Animals , Gene Expression Profiling , Gene Library , Genes, Viral , Mass Spectrometry , Polydnaviridae/isolation & purification , Pupa/virology , Viral Proteins/genetics , Virion/isolation & purification
2.
Science ; 323(5916): 926-30, 2009 Feb 13.
Article in English | MEDLINE | ID: mdl-19213916

ABSTRACT

Many species of parasitoid wasps inject polydnavirus particles in order to manipulate host defenses and development. Because the DNA packaged in these particles encodes almost no viral structural proteins, their relation to viruses has been debated. Characterization of complementary DNAs derived from braconid wasp ovaries identified genes encoding subunits of a viral RNA polymerase and structural components of polydnavirus particles related most closely to those of nudiviruses--a sister group of baculoviruses. The conservation of this viral machinery in different braconid wasp lineages sharing polydnaviruses suggests that parasitoid wasps incorporated a nudivirus-related genome into their own genetic material. We found that the nudiviral genes themselves are no longer packaged but are actively transcribed and produce particles used to deliver genes essential for successful parasitism in lepidopteran hosts.


Subject(s)
DNA, Viral , Polydnaviridae/genetics , Wasps/virology , Amino Acid Sequence , Animals , Baculoviridae/genetics , Biological Evolution , DNA, Viral/analysis , Expressed Sequence Tags , Female , Genome, Insect , Molecular Sequence Data , Ovary/virology , Polydnaviridae/physiology , Viral Structural Proteins/genetics , Virion/genetics , Virus Integration
3.
Arch Insect Biochem Physiol ; 66(1): 9-22, 2007 Sep.
Article in English | MEDLINE | ID: mdl-17694561

ABSTRACT

Polydnaviruses are symbiotic viruses of endoparasitic wasps, which are formed in their ovary and injected along with the eggs into the host. They manipulate the host in a way to allow successful parasitoid development. A hallmark of polydnaviruses is their segmented genome consisting of several circles of double-stranded DNA. We are studying the solitary egg-larval parasitoid Chelonus inanitus (Braconidae) parasitizing Spodoptera littoralis (Noctuidae). The polydnavirus of Chelonus inanitus (CiV) protects the parasitoid larva from encapsulation by the host's immune system, slightly modifies host nutritional physiology, and induces a developmental arrest of the host in the prepupal stage. Here we present data on newly identified CiV genes and their expression patterns in the course of parasitization. None of these genes has similarity to other genes and so far no gene families could be found. A rough estimation of transcript quantities revealed that even the most highly expressed CiV genes reach maximal values, which are 250 times lower than actin. This indicates that the CiV-induced alterations of the host are brought about by a concerted action of low levels of transcripts. In an overview, we show the expression patterns of all CiV genes analysed up to now; they indicate that several genes with similar expression patterns (early, persistent, intermediate, or late) are grouped together on the same segment. This is the first observation of this type. It suggests that one function of the segmentation of the polydnavirus genome may be the grouping together of genes, which are regulated in a similar manner.


Subject(s)
Gene Expression Regulation, Viral , Hymenoptera/metabolism , Hymenoptera/virology , Polydnaviridae/genetics , Transcription, Genetic , Viral Proteins/genetics , Animals , Antioxidants/metabolism , Fat Body , Gene Expression Profiling , Hemolymph , Larva/virology , Longevity , Malondialdehyde/metabolism , Organ Specificity , Ovum/virology
4.
J Gen Virol ; 88(Pt 2): 450-457, 2007 Feb.
Article in English | MEDLINE | ID: mdl-17251562

ABSTRACT

Polydnaviruses are only found in symbiotic association with parasitic wasps within the families Ichneumonidae and Braconidae (ichnoviruses and bracoviruses). They have a segmented genome consisting of circular double-stranded DNA. In the proviral linear form they are integrated in the wasp's genome; in two bracoviruses, segments were found to be clustered. Proviral segments have direct terminal repeats. Segment excision has been proposed to occur through juxtaposition of these repeats by formation of a loop and recombination; one copy of the repeat then ends up in the circular segment and one in the rejoined DNA. Here we analysed the excision/circularization site of four segments of the Chelonus inanitus bracovirus (CiV) and found that they are similar to the two already known sites; on the basis of the combined data an extended excision site motif was found. Analyses of segment flanking sequences led to the first identification of one complete and several partial spacers between proviral segments in a polydnavirus. The spacer between the proviral segments CiV14 and CiV22.5 has a length of 2065 bp; the terminal repeats of CiV14 and CiV22.5 were seen to have an opposite orientation and from this a model on the spacial organization of the loops of the proviral cluster is proposed. Through various approaches it was shown that spacers are not excised or injected into the host. Measurement of relative abundances of various segments in proviral and excised form indicates for the first time that abundant segments are present in multiple copies in the proviral form.


Subject(s)
Genome, Viral , Polydnaviridae/genetics , Proviruses/genetics , Wasps/virology , Animals , Base Sequence , DNA, Viral/genetics , Female , Molecular Sequence Data , Polydnaviridae/chemistry , Proviruses/chemistry
5.
J Gen Virol ; 86(Pt 4): 973-983, 2005 Apr.
Article in English | MEDLINE | ID: mdl-15784890

ABSTRACT

Successful parasitism of some endoparasitic wasps depends on an obligately symbiotic association with polydnaviruses. These unique viruses have a segmented genome consisting of circles of double-stranded (ds) DNA and do not replicate in the parasitized host. They are produced in the wasp's ovary and injected into the host along with the egg. Chelonus inanitus is an egg-larval parasitoid; its polydnavirus (CiV) has been shown to protect the parasitoid larva from the host's immune system and to induce developmental arrest in the prepupal stage. The genome of CiV consists of at least 10-12 segments and five have been sequenced up to now. Here, the complete (CiV12g2) or partial (CiV12g1, CiV16.8g1) cloning of three new CiV genes is reported. All three occur only on one viral segment and have no similarity to other known polydnavirus genes, with the exception of a high similarity of CiV12g1 to CiV14g1 and CiV12g2 to CiV14g2. Furthermore, the first attempt of in vivo application of RNA interference to study the function of polydnavirus genes is shown. Injection of dsRNA of two late- and one early- and late-expressed CiV genes into CiV/venom-containing host eggs partially rescued last-instar larvae from developmental arrest. Injection of the same dsRNAs into parasitized eggs partially reduced parasitoid survival, mainly by preventing the successful emergence of the parasitoid from the host. These viral genes thus seem to be involved in inducing developmental arrest and in keeping the cuticle soft, which appears to be necessary for parasitoid emergence and host feeding.


Subject(s)
Cloning, Molecular , Gene Expression Regulation, Viral , Polydnaviridae/genetics , RNA Interference , Viral Proteins/metabolism , Wasps/virology , Amino Acid Sequence , Animals , Base Sequence , Genes, Viral , Host-Parasite Interactions , Larva/virology , Molecular Sequence Data , Ovum/virology , Polydnaviridae/metabolism , Pupa/virology , Spodoptera/growth & development , Spodoptera/virology , Viral Proteins/genetics , Wasps/growth & development
6.
J Insect Physiol ; 50(11): 1015-26, 2004 Nov.
Article in English | MEDLINE | ID: mdl-15607504

ABSTRACT

Chelonus inanitus (Braconidae) is a solitary egg-larval parasitoid of Spodoptera littoralis (Noctuidae). Along with the egg it also injects polydnaviruses (CiV) and venom, which are prerequisites for successful parasitoid development. CiV protects the parasitoid from encapsulation by the host's immune system and induces a developmental arrest in the prepupal stage. The polydnavirus genome consists of several double-stranded circular DNA segments. Proviral DNA is integrated in the wasp's genome and virus replication is restricted to the wasp's ovary. Here, the analysis of eight CiV genes located on five different segments revealed four patterns of expression in the course of parasitization: early, late, persistent but variable, and early and late. The comparison between parasitized and CiV/venom only containing hosts indicated that the presence of the parasitoid larva modulates transcript levels. Haemocytes, fat body and nervous tissue contained viral transcripts, values being highest in haemocytes. Small amounts of CiV transcripts were also observed in parasitoid larvae and pupae, suggesting transcription from the proviral integrated form of viral DNA. This is the first comparative analysis of the expression patterns of several viral genes in both parasitized and CiV/venom only containing hosts over the entire period of parasitization, and it reveals intricate interactions between the parasitoid, the polydnavirus and the host.


Subject(s)
Hymenoptera/physiology , Polydnaviridae/genetics , Spodoptera/parasitology , Animals , DNA, Viral/genetics , DNA, Viral/isolation & purification , Gene Expression Regulation, Viral , Host-Parasite Interactions , Hymenoptera/growth & development , Hymenoptera/virology , Larva , Ovum , Polymerase Chain Reaction , Pupa , RNA, Viral/isolation & purification , Transcription, Genetic
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