GENOME ANNOUNCEMENT
Genome Sequence of a Bombyx mori Nucleopolyhedrovirus Strain with Cubic Occlusion Bodies Ruo-Lin Cheng, Yi-Peng Xu, and Chuan-Xi Zhang Ministry of Agriculture Key Laboratory of Agricultural Entomology, Institute of Insect Science, Zhejiang University, Hangzhou, China
Bombyx mori nucleopolyhedrovirus (BmNPV) is a typical species of Baculoviridae. The complete genome sequence of a BmNPV strain with cubic occlusion bodies is reported here. The genome of this strain consists of 127,465 nucleotides with a GⴙC content of 40.36% and is 97.3% and 97.5% identical to those of BmNPV strain T3 and Bombyx mandarina NPV S1, respectively. Despite the abnormal polyhedra it forms, the polyhedrin gene of the BmNPV cubic strain is 100% identical to those of the other two strains. Baculovirus repeated ORFs and homologous repeat regions cause the major differences in genome size of these BmNPV isolates.
T
he Bombyx mori nucleopolyhedrovirus (BmNPV) is a typical species of Baculoviridae, a diverse group of invertebrate viruses with double-stranded, circular, supercoiled DNA genomes. Two distinct types of virions are formed during virus infection: the occlusion-derived virion (ODV) and the budded virion (BV). The ODVs are embedded in a crystalline protein matrix called the occlusion body. Occlusion bodies of nucleopolyhedroviruses are commonly polyhedral. However, mutations in polyhedrin and some other genes may affect polyhedron morphogenesis. Here we report the complete genome sequence of a BmNPV strain with cubic occlusion bodies (referred to here as the cubic strain) (3). The BmNPV cubic strain was isolated from a diseased silkworm in Jiangsu Province, China. Virus DNA was extracted with phenol-chloroform from occlusion bodies purified from infected silkworm larvae. The genomic DNA was sheared into fragments of 200 to 300 bp by ultrasonication. Sequencing was accomplished with a Solexa genome analyzer. Ambiguous regions were amplified by PCR and sequenced. The genome of the BmNPV cubic strain consists of 127,465 nucleotides with a G⫹C content of 40.36%, similar to that of the other two reported BmNPV isolates. The whole-genome sequence of BmNPV cubic strain is 97.3% and 97.5% identical to those of BmNPV T3 (2) and Bombyx mandarina NPV (BomaNPV) S1 (5), respectively. These three viruses share 133 common potential open reading frames (ORFs) encoding predicted proteins of over 60 amino acids in the same orientation and organization. Most ORFs are highly conserved, and in particular, 27 of them (including the core genes vp1054, odv-nc42, p33, lef-5, odv-e18, and odvec27) show 100% identity. A total of 107 mutations relative to T3 strains were identified in the 133 ORFs at the amino acid level. Baculovirus repeated ORFs (bro) and homologous repeat (HR) regions cause the major differences in genome size of these BmNPV isolates. According to the classification by Kang et al., bro genes can be divided into three subgroups (4). Like BmNPV T3, the cubic strain possesses all three subgroups of bro genes, while BomaNPV S1 only has two subgroups (subgroups A and B). But the bro-b gene of subgroup C seems to be absent from the genome of the BmNPV cubic strain. HR regions are believed to serve as replication origins and transcriptional enhancers in several bacu-
September 2012 Volume 86 Number 18
loviruses. There are eight HR regions (hr2L, hr2R, hr3, hr4a, hr4b, hr4c, hr5, and hr1) in the genome of the cubic strain, the same as in BmNPV T3 and BomaNPV S1. However, the total numbers and distribution of their inner palindromes are somewhat different. A previous study revealed that a single point mutation in polyhedrin of Autographa californica multiple nucleocapsid nucleopolyhedrovirus (AcMNPV) results in a cubic phenotype of occlusion bodies (1). However, despite the abnormal polyhedra it forms, the polyhedrin gene of BmNPV cubic strain is 100% identical to those of the other two strains with normal polyhedra, indicating that differences or mutations in genes other than polyhedrin seem to contribute to the formation of the cubic occlusion bodies. Nucleotide sequence accession number. The GenBank accession number of the BmNPV cubic strain is JQ991009. ACKNOWLEDGMENTS We thank Cheng-Liang Gong and Wen-Bing Wang (Suzhou University) for providing the BmNPV strains. This work was supported by the National Natural Science Foundation of China (31070136).
REFERENCES 1. Carstens EB, Krebs A, Gallerneault CE. 1986. Identification of an amino acid essential to the normal assembly of Autographa californica nuclear polyhedrosis virus polyhedra. J. Virol. 58:684 – 688. 2. Gomi S, Majima K, Maeda S. 1999. Sequence analysis of the genome of Bombyx mori nucleopolyhedrovirus. J. Gen. Virol. 80:1323–1337. 3. Gong CL, Lu KM. 1993. Study on the nuclear polyhedrosis virus with tetragonal polyhedron. Canye Kexue 19:25–31. 4. Kang W, Suzuki M, Zemskov E, Okano K, Maeda S. 1999. Characterization of baculovirus repeated open reading frames (bro) in Bombyx mori nucleopolyhedrovirus. J. Virol. 73:10339 –10345. 5. Xu YP, et al. 2010. Comparative analysis of the genomes of Bombyx mandarina and B. mori nucleopolyhedroviruses. J. Microbiol. 48:102–110.
Received 27 June 2012 Accepted 28 June 2012 Address correspondence to Chuan-Xi Zhang,
[email protected]. Copyright © 2012, American Society for Microbiology. All Rights Reserved. doi:10.1128/JVI.01639-12
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