Department of Entomology, University of Georgiagrid.213876.9, Athens, Georgia.
J Virol. 2022 Mar 9;96(5):e0157321. doi: 10.1128/JVI.01573-21. Epub 2022 Jan 5.
Bracoviruses (BVs) are endogenized nudiviruses in parasitoid wasps of the microgastroid complex (family Braconidae). Microgastroid wasps have coopted nudivirus genes to produce replication-defective virions that females use to transfer virulence genes to parasitized hosts. The microgastroid complex further consists of six subfamilies and ∼50,000 species but current understanding of BV gene inventories and organization primarily derives from analysis of two wasp species in the subfamily Microgastrinae ( and ) that produce M. demolitor BV (MdBV) and C. congregata BV (CcBV). Notably, several genomic features of MdBV and CcBV remain conserved since divergence of and ∼53 million years ago (MYA). However, it is unknown whether these conserved traits more broadly reflect BV evolution, because no complete genomes exist for any microgastroid wasps outside the Microgastrinae. In this regard, the subfamily Cheloninae is of greatest interest because it diverged earliest from the Microgastrinae (∼85 MYA) after endogenization of the nudivirus ancestor. Here, we present the complete genome of , which is an egg-larval parasitoid in the Cheloninae that produces C. insularis BV (CinsBV). We report that the inventory of nudivirus genes in is conserved but are dissimilarly organized compared to and . Reciprocally, CinsBV proviral segments share organizational features with MdBV and CcBV but virulence gene inventories exhibit almost no overlap. Altogether, our results point to the functional importance of a conserved inventory of nudivirus genes and a dynamic set of virulence genes for the successful parasitism of hosts. Our results also suggest organizational features previously identified in MdBV and CcBV are likely not essential for BV virion formation. Bracoviruses are a remarkable example of virus endogenization, because large sets of genes from a nudivirus ancestor continue to produce virions that thousands of wasp species rely upon to parasitize hosts. Understanding how these genes interact and have been coopted by wasps for novel functions is of broad interest in the study of virus evolution. This work characterizes bracovirus genome components in the parasitoid wasp , which together with existing wasp genomes captures a large portion of the diversity among wasp species that produce bracoviruses. Results provide new information about how bracovirus genome components are organized in different wasps while also providing additional insights on key features required for function.
β 病毒（BVs）是微腔腹寄生蜂中的内共生核型多角体病毒（Braconidae 科）。微腔腹寄生蜂已采用核型多角体病毒基因来产生具有复制缺陷的病毒粒子，而这些雌性寄生蜂则使用这些病毒粒子将毒性基因转移到被寄生的宿主身上。微腔腹寄生蜂进一步分为 6 个亚科和大约 50,000 个物种，但目前对 BVs 基因库和组织的了解主要来自于对两个亚科的黄蜂物种（ 和 ）的分析，这两个黄蜂物种分别产生了 M. demolitor BV（MdBV）和 C. congregata BV（CcBV）。值得注意的是，自从 5300 万年前（Mya）以来，MdBV 和 CcBV 的几个基因组特征仍然保持保守。然而，由于没有任何关于微腔腹寄生蜂以外的黄蜂的完整基因组，因此尚不清楚这些保守特征是否更广泛地反映了 BVs 的进化。在这方面，Cheloninae 亚科最具研究意义，因为它是在 nudivirus 祖先内共生之后最早从 Microgastrinae 分化出来的（∼85Mya）。在这里，我们介绍了Cheloninae 的卵幼虫寄生蜂 的完整基因组，它产生了 C. insularis BV（CinsBV）。我们报告说， 在 nudivirus 基因的库存是保守的，但与 和 的组织方式不同。相反，CinsBV 前病毒片段具有与 MdBV 和 CcBV 相同的组织特征，但毒性基因库几乎没有重叠。总的来说，我们的研究结果表明，nudivirus 基因的保守库存和一组动态的毒性基因对于成功寄生宿主具有重要功能。我们的研究结果还表明，以前在 MdBV 和 CcBV 中发现的组织特征可能不是 BV 病毒粒子形成所必需的。BVs 是病毒内共生的一个显著例子，因为 nudivirus 祖先的大量基因继续产生病毒粒子，数千种黄蜂物种依赖这些病毒粒子来寄生宿主。了解这些基因如何相互作用以及被黄蜂用于新功能是病毒进化研究的一个重要课题。这项工作描述了寄生蜂 的 BVs 基因组成分，与现有的黄蜂基因组一起，捕获了大量产生 BVs 的黄蜂物种的多样性。结果提供了有关 BVs 基因组成分在不同黄蜂中组织方式的新信息，同时也提供了有关功能所需关键特征的更多见解。
