Polydnaviruses are obligate mutualists of parasitoid wasps and are divided into two genera, Bracovirus and Ichnovirus. Bracoviruses are thought to originate from a single integration of an ancestral nudivirus into the ancestor of microgastroid complex ~100 million years ago. However, all the known nudiviruses are only distantly related to bracoviruses, and much remains obscure about the origin of bracoviruses. Here we employ a paleovirological method to screen endogenous nudivirus-like elements across arthropods. Interestingly, we identify many endogenous nudivirus-like elements within the genome of Eurytoma brunniventris, a species of the Chalcidoidea superfamily. Among them, we find 14 core gene sequences are likely to be derived from a betanudivirus (designated EbrENV-β), suggesting that betanudivirus has been circulating in parasitoid wasps. Phylogenomic analysis suggests that EbrENV-β is the known closest relative of bracoviruses. Synteny analyses show the order of core genes is not well conserved between EbrENV-β and nudiviruses, revealing the dynamic nature of the evolution of nudivirus genome structures. Our findings narrow down the evolutionary gap between bracoviruses and nudiviruses and provide novel insights into the origin and evolution of polydnaviruses.

中文翻译：

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拟南芥黄蜂古病毒弥合了Braco病毒和Nudivirus的进化差距。

Polydnaviruses是专一的寄生类黄蜂的共生者，分为两类：Bracovirus和Ichnovirus。人们认为Bracoviruses起源于大约1亿年前的祖传纳迪病毒与微消化道复合体的祖先的单次整合。但是，所有已知的裸病毒都与Bracoviruses远缘相关，并且对于Bracoviruss的起源还不清楚。在这里，我们采用了一种古病毒学方法来筛选节肢动物中的内源性纽迪病毒样元件。有趣的是，我们在欧洲蓝藻（Eurytoma brunniventris）的基因组中鉴定了许多内源性纽地病毒样元件，该物种属于金合欢属超家族。在它们当中，我们发现14种核心基因序列很可能来自贝努氏病毒（命名为EbrENV-β），这表明贝努氏病毒已经在类寄生蜂中传播。系统生物学分析表明，EbrENV-β是已知的杆状病毒的近亲。同源性分析表明，EbrENV-β与nudiviruses之间核心基因的顺序并不十分保守，这揭示了nudivirus基因组结构进化的动态性质。我们的发现缩小了Bracoviruses和Nudiviruses之间的进化差距，并为polydnaviruses的起源和进化提供了新颖的见解。