Influence of polyhedrin and host cell on the polyhedra morphology of Autographa californica nucleopolyhedrovirus

A substitution of the polyhedrin of Autographa californica nucleopolyhedrovirus (AcNPV) with that of Spodoptera exigua NPV (SeNPV) and Bombyx mori NPV, respectively, resulted in morphological changes of the polyhedra. Morphological features and quantity of polyhedra of recombinant AcNPVs were examined and compared in three cell lines: Spodoptera frugiperda (Sf9), S. exigua (Se301) and Trichoplusia ni (M) cells. The shape of the polyhedra produced by each virus did not change significantly according to the cell line. The size of the polyhedra differed, however, with the largest in Se301 cells, followed by Hi5 and SO cells in decreasing order. The yield of polyhedra and the appearance of polyhedra-positive cells in each cell line also showed significant differences. Especially notable was the change of polyhedra shapes from irregular to regular in the recombinant AcNPV containing SeNPV polyhedrin in all cell lines. These results suggest that the shape and uniformity of polyhedra depend on some viral gene other than the polyhedrin gene. It is also suggested that there is a host cell factor that is responsible for the determination of polyhedra size.