Genomic Sequence Analysis of Granulovirus Isolated from the Tobacco Cutworm, Spodoptera litura

BackgroundSpodoptera litura is a noctuid moth that is considered an agricultural pest. The larvae feed on a wide range of plants and have been recorded on plants from 40 plant families (mostly dicotyledons). It is a major pest of many crops. To better understand Spodoptera litura granulovirus (SpliGV), the nucleotide sequence of the SpliGV DNA genome was determined and analyzed. Methodology/Principal FindingsThe genome of the SpliGV was completely sequenced. The nucleotide sequence of the SpliGV genome was 124,121 bp long with 61.2% A+T content and contained 133 putative open reading frames (ORFs) of 150 or more nucleotides. The 133 putative ORFs covered 86.3% of the genome. Among these, 31 ORFs were conserved in most completely sequenced baculovirus genomes, 38 were granulovirus (GV)-specific, and 64 were present in some nucleopolyhedroviruses (NPVs) and/or GVs. We proved that 9 of the ORFs were SpliGV specific. Conclusions/SignificanceThe genome of SpliGV is 124,121 bp in size. One hundred thirty-three ORFs that putatively encode proteins of 50 or more amino acid residues with minimal overlap were determined. No chitinase or cathepsin genes, which are involved in the liquefaction of the infected host, were found in the SpliGV genome, explaining why SpliGV-infected insects do not degrade in a typical manner. The DNA photolyase gene was first found in the genus Granulovirus. When phylogenic relationships were analyzed, the SpliGV was most closely related to Trichoplusia ni granulovirus (TnGV) and Xestia c-nigrum granulovirus (XecnGV), which belong to the Type I-granuloviruses (Type I-GV).

背景 斜纹夜蛾（Spodoptera litura）为夜蛾科蛾类，是公认的农业害虫。其幼虫寄主范围广泛，目前已记录其取食40余个植物科的植物（多为双子叶植物），是多种农作物的重大害虫。为深入解析斜纹夜蛾颗粒体病毒（Spodoptera litura granulovirus, SpliGV）的生物学特性，研究人员对该病毒的DNA基因组核苷酸序列进行了测定与分析。

方法与主要结果 本研究完成了SpliGV基因组的全序列测定。SpliGV基因组全长124121 bp，A+T碱基含量为61.2%，共包含133个长度不小于150 nt的推定开放阅读框（open reading frame, ORF），这些推定ORFs覆盖了基因组86.3%的区域。其中，31个ORF在已完成全序列测定的多数杆状病毒（baculovirus）基因组中保守存在，38个为颗粒体病毒（GV）特异性ORF，剩余64个ORF则存在于部分核型多角体病毒（nucleopolyhedrovirus, NPV）和/或GV中。本研究证实其中9个ORF为SpliGV所特有。

结论与意义 SpliGV基因组大小为124121 bp。本研究共鉴定出133个推定开放阅读框，均可编码至少50个氨基酸残基的蛋白质，且相互间重叠程度极低。SpliGV基因组中未发现参与感染宿主组织液化过程的几丁质酶（chitinase）和组织蛋白酶（cathepsin）基因，这解释了受SpliGV感染的昆虫不会以典型方式发生组织降解的原因。DNA光解酶（DNA photolyase）基因首次在颗粒体病毒属（Granulovirus）中被发现。系统发育分析结果显示，SpliGV与属于I型颗粒体病毒（Type I-GV）的粉纹夜蛾颗粒体病毒（Trichoplusia ni granulovirus, TnGV）及八字地老虎颗粒体病毒（Xestia c-nigrum granulovirus, XecnGV）亲缘关系最为密切。