Abstract
Thysanoplusia orichalcea multiple nucleopolyhedrovirus (ThorMNPV) has high virulence to Trichoplusia ni and Pseudoplusia includens larvae, with a potential for biological control of insect pests. The genome of ThorMNPV was sequenced and found to be 132,978 bp, with a G+C content of 37.9%. There are 145 predicted open reading frames (ORFs), encoding proteins of 50 or more amino acid residues with minimal overlap. Of the 145 ORFs, 141 appeared to be homologous to those of Autographa californica MNPV (AcMNPV). In comparison to AcMNPV, 9 ORFs of AcMNPV were absent in ThorMNPV, including the superoxide dismutase (sod) gene.
GENOME ANNOUNCEMENT
Nucleopolyhedroviruses (NPVs) in the family of Baculoviridae are insect-specific, double-stranded, circular DNA viruses with a genome size of 80 to 180 kbp. Thysanoplusia orichalcea multiple nucleopolyhedrovirus (ThorMNPV) was isolated from T. orichalcea L. (Lepidoptera: Noctuidae) larvae from Indonesia (2). ThorMNPV replicates well in Hi5 cells derived from Trichoplisia ni but poorly in Sf21 cells derived from Spodoptera frugiperda (5, 7).
ThorMNPV was plaque purified in Hi5 cells (4), and one plaque (Top2) was chosen for genome sequencing. Top2 genomic DNA was extracted from budded viruses generated from Hi5 cell infections (4), and sequencing was performed with the Solexa Genome Analyzer at BGI (Beijing Genome Institution, Shenzhen, China). A total of 5,622,224 clean pair-end (PE) reads were obtained, with an average insert fragment size of 500 bp, roughly 500 million nucleotides, representing 3,800× coverage of the 130-kbp ThorMNPV genome (2). A total of 300,000 PE reads were randomly selected and assembled into a single contig with Edena (3). The assembled genome sequence was confirmed by comparing three predicted restriction endonuclease (REN) profiles with the actual REN digestions (2).
The genome of ThorMNPV has 132,978 nucleotides with a G+C content of 37.9%. We predicted 145 open reading frames (ORFs) with at least 50 amino acids and 6 hr regions in the genome of ThorMNPV. In comparison to Autographa californica MNPV (AcMNPV), 141 ORFs have corresponding orthologs in AcMNPV and the other two ORFs were unique to ThorMNPV. Baculovirus repeated ORFs (bro) are widely distributed in lepidopteran NPVs and granuloviruses (GVs). The number of bro genes varies in different baculoviruses from none in Rachiplusia ou MNPV and 1 in AcMNPV to 16 copies in Lymantria dispar MNPV. In the ThorMNPV genome, 2 bro genes were identified. There were 9 ORFs in AcMNPV (Ac7, Ac31, Ac45, Ac48, Ac97, Ac116, Ac121, Ac134, and Ac140) that were not detected in ThorMNPV, including the superoxide dismutase (sod) gene (Ac31). The sod gene is believed to play an important role in interacting with host cells (1). Homologs of sod were found in the genomes of almost all of the lepidopteran baculovirus genomes, with exceptions only in Epiphyas postvittana NPV, Spodoptera litura MNPV, and Spodoptera littoralis granulovirus. Insect hemocytes can destroy invading pathogens by the production of superoxide (1). The superoxide can be inactivated by SOD through conversion of superoxide to hydrogen peroxide. Hydrogen peroxide can then, in turn, be spontaneously broken down to yield water and oxide. The expression of viral SOD might mitigate the effects of superoxide production by hemocytes. However, the enzymatic activity of SOD could not be confirmed with AcMNPV, and the viruses with sod deleted showed no reduction in viral DNA replication in cultured cells and insect larvae (6). In a different scenario, Bombyx mori NPV viruses with a deletion of the sod gene showed a significant reduction in replication during BmN cell infection (8). Therefore, ThorMNPV, with different replication kinetics in Sf21 and Hi5 cells, is a useful system to investigate how SOD influences viral DNA replication in different insect cells.
Nucleotide sequence accession number.
The GenBank accession number of ThorMNPV is JX467702.
ACKNOWLEDGMENTS
This work was supported by the National Natural Science Foundation of China (grant no. 31228020) and the National Major Science and Technology Project of the 12th Five-year Plan (grant no. 2012BAD27B00).
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