Analysis of the genomic sequence of Philosamia cynthia nucleopolyhedrin virus and comparison with Antheraea pernyi nucleopolyhedrin virus

BACKGROUND: Two species of wild silkworms, the Chinese oak silkworm (Antheraea pernyi) and the castor silkworm Philosamia cynthia ricini, can acquire a serious disease caused by Nucleopolyhedrin Viruses (NPVs) (known as AnpeNPV and PhcyNPV, respectively). The two viruses have similar polyhedral morphologies and their viral fragments share high sequence similarity. However, the physical maps of the viral genomes and cross-infectivity of the viruses are different. The genome sequences of two AnpeNPV isolates have been published. RESULTS: We sequenced and analyzed the full-length genome of PhcyNPV to compare the gene contents of the two viruses. The genome of PhcyNPV is 125, 376 bp, with a G + C content of 53.65%, and encodes 138 open reading frames (ORFs) of at least 50 amino acids (aa) (GenBank accession number: JX404026). Between PhcyNPV and AnpeMNPV-L and -Z isolates, 126 ORFs are identical, including 30 baculovirus core genes. Nine ORFs were only found in PhcyNPV. Four genes, cath, v-chi, lef 10 and lef 11, were not found in PhcyNPV. However, most of the six genes required for infectivity via the oral route were found in PhcyNPV and in the two AnpeNPV isolates, with high sequence similarities. The pif-3 gene of PhcyNPV contained 59 aa extra amino acids at the N-terminus compared with AnpeNPV. CONCLUSIONS: Most of the genes in PhcyNPV are similar to the two AnpeNPV isolates, including the direction of expression of the ORFs. Only a few genes were missing from PhcyNPV. These data suggest that PhcyNPV and AnpeNPV might be variants of each other, and that the differences in cross-infection might be caused by gene mutations.