Influences of chitinase gene deletion from BmNPV on the cell lysis and host liquefaction.

A Bombyx mori nucleopolyhedrovirus (BmNPV) mutant with chi- tinase gene (chiA) deletion (BmchiA-) was constructed. The effects of chiA deletion on virus infected BmN cells and silkworm larvae were examined. The egfp gene expression under the control of the chiA promoter, in BmchiA- -infected BmN cells could be detected as early as 8 h p.i. The fluorescence reached its peak at 48 h p.i., and was prevalent until the cell lysis. Cytopathological comparison of the cells infected with wild type and mutant viruses showed that deletion of chiA could evidently delay the cell lysis. SDS-PAGE analysis suggested that the content of polyhedrin in BmchiA- -infected cells at 7 days p.i. was about 28% of the total cellular proteins, about 7% lower than that in wild-type BmNPV virus-infected cells. The symptoms of B. mori larvae infected with BmchiA- were different from those of wild-type BmNPV-infected larvae, e.g., clear haemolymph and less degradation of the body after larval death.