Desjardins Christopher A, Gundersen-Rindal Dawn E, Hostetler Jessica B, Tallon Luke J, Fadrosh Douglas W, Fuester Roger W, Pedroni Monica J, Haas Brian J, Schatz Michael C, Jones Kristine M, Crabtree Jonathan, Forberger Heather, Nene Vishvanath
J Craig Venter Institute, Rockville, MD 20850, USA.
Genome Biol. 2008;9(12):R183. doi: 10.1186/gb-2008-9-12-r183. Epub 2008 Dec 30.
Polydnaviruses, double-stranded DNA viruses with segmented genomes, have evolved as obligate endosymbionts of parasitoid wasps. Virus particles are replication deficient and produced by female wasps from proviral sequences integrated into the wasp genome. These particles are co-injected with eggs into caterpillar hosts, where viral gene expression facilitates parasitoid survival and, thereby, survival of proviral DNA. Here we characterize and compare the encapsidated viral genome sequences of bracoviruses in the family Polydnaviridae associated with Glyptapanteles gypsy moth parasitoids, along with near complete proviral sequences from which both viral genomes are derived.
The encapsidated Glyptapanteles indiensis and Glyptapanteles flavicoxis bracoviral genomes, each composed of 29 different size segments, total approximately 517 and 594 kbp, respectively. They are generated from a minimum of seven distinct loci in the wasp genome. Annotation of these sequences revealed numerous novel features for polydnaviruses, including insect-like sugar transporter genes and transposable elements. Evolutionary analyses suggest that positive selection is widespread among bracoviral genes.
The structure and organization of G. indiensis and G. flavicoxis bracovirus proviral segments as multiple loci containing one to many viral segments, flanked and separated by wasp gene-encoding DNA, is confirmed. Rapid evolution of bracovirus genes supports the hypothesis of bracovirus genes in an 'arms race' between bracovirus and caterpillar. Phylogenetic analyses of the bracoviral genes encoding sugar transporters provides the first robust evidence of a wasp origin for some polydnavirus genes. We hypothesize transposable elements, such as those described here, could facilitate transfer of genes between proviral segments and host DNA.
多分DNA病毒是一种基因组呈片段化的双链DNA病毒，已进化成为寄生蜂的专性内共生体。病毒粒子缺乏复制能力，由雌蜂从整合到黄蜂基因组中的前病毒序列产生。这些粒子与卵一起被注射到毛虫宿主中，在那里病毒基因表达促进寄生蜂的存活，从而使前病毒DNA得以存活。在此，我们对与舞毒蛾寄生蜂相关的多DNA病毒科中的杆状病毒的衣壳化病毒基因组序列进行了表征和比较，并对产生这两种病毒基因组的近乎完整的前病毒序列进行了比较。
衣壳化的印度扁股小蜂和黄股扁股小蜂杆状病毒基因组，各自由29个不同大小的片段组成，分别总计约517和594千碱基对。它们由黄蜂基因组中至少七个不同的位点产生。对这些序列的注释揭示了多DNA病毒的许多新特征，包括类似昆虫的糖转运蛋白基因和转座元件。进化分析表明，正选择在杆状病毒基因中广泛存在。
证实了印度扁股小蜂和黄股扁股小蜂杆状病毒前病毒片段的结构和组织为多个位点，每个位点包含一到多个病毒片段，两侧和中间由黄蜂编码基因的DNA隔开。杆状病毒基因的快速进化支持了杆状病毒基因在杆状病毒与毛虫之间的“军备竞赛”中的假说。对编码糖转运蛋白的杆状病毒基因的系统发育分析首次有力证明了一些多DNA病毒基因起源于黄蜂。我们推测，此处描述的转座元件可能促进基因在前病毒片段和宿主DNA之间的转移。
