Real and Apparent Complexity in Polydnavirus Genomes

本研究将阐明多聚核糖核酸病毒(PDV)基因组结构在病毒基因变异中的作用。PDV基因组结构似乎促进了病毒基因家族内的可变性，促进了基因表达水平的改变，并允许获得新的基因。支持这一假说的证据有：1)PDV基因组中功能显著的变异的鉴定；2)PDV基因组和节段结构的保守性；3)节段类型之间的功能专化。初步数据表明，通过改变拷贝数来调节基因表达只是更大的PDV组织范例的一部分。这些数据支持更普遍的假设，即PDV基因组分段不仅影响基因表达水平，而且有助于产生基因变体和从宿主基因组中获取新基因。这一假说是在三个研究目标下被验证的，目的是：1)确定松突弯孢菌细小病毒(Campoletis sonorensis ichnoVirus，CsIV)的遗传变异是否影响病毒功能和寄生虫寄主范围；2)确定CsIV的结构组织是否代表其他细小病毒；3)确定整合能力片段是否支持基因进入病毒基因组。多聚核糖核酸病毒必须抑制宿主免疫，并改变其他宿主生理系统，以支持寄生虫的发展，使病毒垂直传播。一个寄主抗击进化中的寄主抗性机制的能力可能需要不断产生功能变异，以使寄主能够继续利用或入侵新的寄主物种。在黄蜂寄生虫中，宿主和寄生虫的生命周期是同步的，PDV可能提供寄生虫所选择的高度可变的基因组，以允许持续产生免疫抑制基因变体，从而赋予可持续的进化优势。在更广泛的背景下，这项工作将阐明圈养基因组对真核生物高度可变特征进化的一些关键贡献。在人类和其他生物中，转座元件、逆转录病毒和非编码序列占DNA的90%以上，但这种类型的DNA经常被描述为垃圾DNA，因为它的功能还不清楚。这项研究还可能阐明病毒和非编码序列在多核糖核酸病毒生物学相关特征进化中的作用，从而有助于更好地理解这些在其他生物中显然不必要的序列。

This research will elucidate the role of polydnavirus (PDV) genome structure in generating viral gene variants. PDV genome structure appears to promote variability within viral gene families, facilitate alteration of the level to which genes are expressed and allow for acquisition of novel genes. Evidence in support of this hypothesis the: 1) identification of functionally significant variants in PDV genomes, 2) conservation of PDV genome and segment structure and 3) functional specialization among segment types. The preliminary data suggest that regulation of gene expression by changing copy number in ichnoviruses is but one part of a larger PDV organizational paradigm. These data support the more general hypothesize that PDV genome segmentation not only influences gene expression levels but also facilitates production of gene variants and acquisition of novel genes from the host genome. This hypothesis is tested under three research objectives intended to: 1) determine if Campoletis sonorensis ichnovirus (CsIV) genetic variation impacts virus function and parasite host range, 2) To determine if the structural organization of CsIV is representative of other ichnoviruses, 3) To determine if integration-competent segments support gene entry into viral genomes. Polydnaviruses must suppress host immunity and alter other host physiological systems in support of parasite development for the virus to be vertically transmitted. A parisite's ability to counter evolving host resistance mechanisms may require continual production of functional variants that enable continued host exploitation or invasion of new host species. In wasp parasites, where host and parasite life cycles are synchronized, PDVs may provide a highly mutable genome co-opted by the parasite to allow continual production of immunosuppressive gene variants that confer a sustainable evolutionary advantage. In a broader context, this work will elucidate some of the critical contributions of captive genomes to the evolution of highly variable traits in eukaryotic organisms. Transposable elements, retroviral and non-coding sequence comprise over 90% of the DNA in humans and other organisms but this type of DNA is often described as junk DNA because its functional role is not clearly understood. This research may also elucidate the role of viral and non-coding sequences in the evolution of biologically relevant traits in polydnaviruses and thereby contribute to a better understanding of these apparently non-essential sequences in other organisms.