Webb Bruce A, Strand Michael R, Dickey Stephanie E, Beck Markus H, Hilgarth Roland S, Barney Walter E, Kadash Kristy, Kroemer Jeremy A, Lindstrom Karl G, Rattanadechakul Walaikorn, Shelby Kent S, Thoetkiattikul Honglada, Turnbull Matthew W, Witherell R Andrews
Department of Entomology, University of Kentucky, Lexington, KY 40506, USA.
Virology. 2006 Mar 30;347(1):160-74. doi: 10.1016/j.virol.2005.11.010. Epub 2005 Dec 27.
Symbionts often exhibit significant reductions in genome complexity while pathogens often exhibit increased complexity through acquisition and diversification of virulence determinants. A few organisms have evolved complex life cycles in which they interact as symbionts with one host and pathogens with another. How the predicted and opposing influences of symbiosis and pathogenesis affect genome evolution in such instances, however, is unclear. The Polydnaviridae is a family of double-stranded (ds) DNA viruses associated with parasitoid wasps that parasitize other insects. Polydnaviruses (PDVs) only replicate in wasps but infect and cause severe disease in parasitized hosts. This disease is essential for survival of the parasitoid's offspring. Thus, a true mutualism exists between PDVs and wasps as viral transmission depends on parasitoid survival and parasitoid survival depends on viral infection of the wasp's host. To investigate how life cycle and ancestry affect PDVs, we compared the genomes of Campoletis sonorensis ichnovirus (CsIV) and Microplitis demolitor bracovirus (MdBV). CsIV and MdBV have no direct common ancestor, yet their encapsidated genomes share several features including segmentation, diversification of virulence genes into families, and the absence of genes required for replication. In contrast, CsIV and MdBV share few genes expressed in parasitized hosts. We conclude that the similar organizational features of PDV genomes reflect their shared life cycle but that PDVs associated with ichneumonid and braconid wasps have likely evolved different strategies to cause disease in the wasp's host and promote parasitoid survival.
共生体通常表现出基因组复杂性的显著降低，而病原体则常常通过获取毒力决定因素并使其多样化来表现出基因组复杂性的增加。一些生物体已经进化出复杂的生命周期，在其中它们作为共生体与一个宿主相互作用，而作为病原体与另一个宿主相互作用。然而，在这种情况下，共生和致病的预测性且相反的影响如何影响基因组进化尚不清楚。多DNA病毒科是一类双链（ds）DNA病毒，与寄生其他昆虫的寄生蜂相关。多DNA病毒（PDV）仅在黄蜂中复制，但会感染被寄生的宿主并导致严重疾病。这种疾病对于寄生蜂后代的生存至关重要。因此，PDV与黄蜂之间存在真正的互利共生关系，因为病毒传播依赖于寄生蜂的生存，而寄生蜂的生存则依赖于黄蜂宿主的病毒感染。为了研究生命周期和祖先如何影响PDV，我们比较了索诺拉 Campoletis sonorensis 卵病毒（CsIV）和毁侧沟茧蜂 Microplitis demolitor 杆状病毒（MdBV）的基因组。CsIV和MdBV没有直接的共同祖先，但它们的衣壳化基因组具有几个共同特征，包括分段、毒力基因分化成家族以及缺乏复制所需的基因。相比之下，CsIV和MdBV在被寄生宿主中表达的基因很少。我们得出结论，PDV基因组的相似组织特征反映了它们共有的生命周期，但与姬蜂科和茧蜂科黄蜂相关的PDV可能已经进化出不同的策略来在黄蜂宿主中引发疾病并促进寄生蜂的生存。
