Institut de Recherche sur la Biologie de l'Insecte, CNRS UMR 7261, Université de Tours, Tours, France.
Commissariat à l'Energie Atomique et aux Energies Alternatives, Genoscope (Centre National de Séquençage), Evry, France.
J Virol. 2018 Jul 17;92(15). doi: 10.1128/JVI.00438-18. Print 2018 Aug 1.
Polydnaviruses (PDVs) are essential for the parasitism success of tens of thousands of species of parasitoid wasps. PDVs are present in wasp genomes as proviruses, which serve as the template for the production of double-stranded circular viral DNA carrying virulence genes that are injected into lepidopteran hosts. PDV circles do not contain genes coding for particle production, thereby impeding viral replication in caterpillar hosts during parasitism. Here, we investigated the fate of PDV circles of Cotesia congregata bracovirus during parasitism of the tobacco hornworm, , by the wasp Sequences sharing similarities with host integration motifs (HIMs) of Microplitis demolitor bracovirus (MdBV) circles involved in integration into DNA could be identified in 12 CcBV circles, which encode and gene families involved in host immune disruption. A PCR approach performed on a subset of these circles indicated that they persisted in parasitized hemocytes as linear forms, possibly integrated in host DNA. Furthermore, by using a primer extension capture method based on these HIMs and high-throughput sequencing, we could show that 8 out of 9 circles tested were integrated in hemocyte genomic DNA and that integration had occurred specifically using the HIM, indicating that an HIM-mediated specific mechanism was involved in their integration. Investigation of BV circle insertion sites at the genome scale revealed that certain genomic regions appeared to be enriched in BV insertions, but no specific target site could be identified. The identification of a specific and efficient integration mechanism shared by several bracovirus species opens the question of its role in braconid parasitoid wasp parasitism success. Indeed, results obtained here show massive integration of bracovirus DNA in somatic immune cells at each parasitism event of a caterpillar host. Given that bracoviruses do not replicate in infected cells, integration of viral sequences in host DNA might allow the production of PTP and VANK virulence proteins within newly dividing cells of caterpillar hosts that continue to develop during parasitism. Furthermore, this integration process could serve as a basis to understand how PDVs mediate the recently identified gene flux between parasitoid wasps and Lepidoptera and the frequency of these horizontal transfer events in nature.
多粒包病毒（PDV）是成千上万种寄生蜂成功寄生的关键。PDV 以前病毒的形式存在于黄蜂基因组中，作为双链环状病毒 DNA 的模板，该 DNA 携带毒力基因，并注入鳞翅目宿主。PDV 环不含编码颗粒产生的基因，从而阻碍了寄生期间毛毛虫宿主中的病毒复制。在这里，我们研究了 Cotesia congregata 多粒包病毒（CcBV）在寄生烟草角蝉时的命运， 由黄蜂 可以在 12 个 CcBV 环中鉴定出与 Microplitis demolitor 多粒包病毒（MdBV）环中涉及整合到 DNA 的宿主整合基序（HIM）具有相似性的序列，这些序列编码参与宿主免疫破坏的 和 基因家族。对这些环中的一部分进行的 PCR 方法表明，它们以线性形式存在于被寄生的 血细胞中，可能整合到宿主 DNA 中。此外，通过使用基于这些 HIM 和高通量测序的引物延伸捕获方法，我们可以证明在测试的 9 个环中的 8 个整合到 血细胞基因组 DNA 中，并且整合是特异性地使用 HIM 发生的，这表明涉及特定 HIM 介导的特异性机制。对 BV 环插入位点的基因组规模调查表明，某些基因组区域似乎富含 BV 插入，但无法确定特定的 靶位点。几种多粒包病毒物种共享的特定和有效的整合机制的鉴定提出了其在 Braconid 寄生蜂寄生成功中的作用的问题。事实上，这里获得的结果表明，在鳞翅目宿主的每次寄生事件中，大量的多粒包病毒 DNA 整合到体细胞免疫细胞中。鉴于感染细胞中不复制多粒包病毒，病毒序列在宿主 DNA 中的整合可能允许在继续发育的鳞翅目宿主的新分裂细胞中产生 PTP 和 VANK 毒力蛋白。此外，这个整合过程可以作为理解 PDV 如何介导最近在寄生蜂和鳞翅目之间发现的基因流以及这些水平转移事件在自然界中的频率的基础。
