| Baculoviridae is a family of large, enveloped viruses characterized by rod-shaped virions and covalently closed double-stranded circular DNA genomes ranging in size from 80 to 180 kb. Baculoviruses are infectious mostly to insects within the order Lepidoptera. They have been isolated only from arthropods and have relatively narrow host ranges.The Indian eri silkworm (Philosamia cynthia ricini ) and the Chinese oak silkworm (Antheraea pernyi ) are both economically important insects primarily for the silk production, but the jaundice disease of the silkmoth caused by the infection of nucleopolyhedrovirus is a major threat to the silk industry. The full length genomic DNA of AnpeNPV has been revealed, however, molecular information of PcrNPV is still unknown. In previous study, PcrNPV and AnpeNPV had contact on infection. In order to find out their relationship and compare the characteristics between PcrNPV and AnpeNPV, in this thesis, we purified the PcrNPV and AnpeNPV, studied the infective characteristics of PcrNPV and AnpeNPV, and analyzed the helicase genes of the two nucleopolyhedroviruses. It will be helpful to learn the infective interaction between the two viruses and the host range determination mechanisms. The main conclusions are followed:1. Philosamia cynthia ricini nucleopolyhedrovirus and Antheraea pernyi nucleopolyhedrovirus were isolated and purified. The electron micrograph study revealed that both the polyhedra of PcrNPV and AnpeNPV were triangular in shape, varing in size from 1 to 3μm.2. The larvae of Philosamia cynthia ricini and Antheraea pernyi were infected by the two NPVs, respectively, and the infected larvae showed the typical symptoms of NPV disease. The results turned out that AnpeNPV can infect both Antheraea pernyi and Philosamia cynthia rici larvae, with the infectivities of 78% and 57%, and PcrNPV only produced a fatal infection in the larvae of Philosamia cynthia ricini, with the infectivity of 79%, and had almost no infection in Antheraea pernyi. The DNA extracted from the larvae of Philosamia cynthia rici and Antheraea pernyi infecting with AnpeNPV was digested by Hind III, Sal I, Xho I, and Pst I and it turned out to be AnpeNPV.3. The PcrNPV and AnpeNPV DNA were transfected into BmN and Tn5 cells by Lipofectin-mediated transfection, respectively. These viruses had no obvious infecting ability to BmN and Tn5 cells.4. A PcrNPV genomic library was generated by Pst I digestion and the positive clones were sequenced and analysed. The sequences had high identity with those of AnpeNPV, at least 95%.5. Phylogenetic tree of amino acid sequences of baculoviridae helicase genes showed: PcrNPV had the closest relationship to the AnpeNPV and had the further relationship to the AcMNPV and BmNPV.6. The two viral helicase (p143) genes related to the host range of baculovirus, were cloned and sequenced. Subsequent analysis of their nucleotide and amino acid sequences showed that none of the domains determining the host range region was different except for the amino acid position 974 where the Ia motif and helix-turn-helix motif was found nearby. Accordingly, we inferred helicae might be not the main cause determinating the host range difference between the two viruses.So PcrNPV and AnpeNPV have high DNA homology, but different host range characteristics.
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