Enhancement of baculovirus infection in Spodoptera exigua (Lepidoptera: Noctuidae) larvae with Autographa californica nucleopolyhedrovirus or Nicotiana tabacum engineered with a granulovirus enhancin gene

A baculovirus virulence-associated protein, enhancin, was engineered for production in a baculovirus-insect cell expression system and used for transformation of tobacco plants. A recombinant Autographa californica nucleopolyhedrovirus (AcNPV) with the enhancin gene from Trichoplusia ni granulovirus, AcEnh26, was propagated in Sf9 cells. The infected cultured cells combined with either AcNPV occlusion bodies (OBs) or Spodoptera exigua NPV (SeNPV) OBs were fed to 3rd stadium larvae of S. exigua. Feeding larvae with AcEnh26-infected cells resulted in a 21-fold and 10-fold enhancement of infection by AcNPV and SeNPV, respectively, compared to controls. When a similar feeding assay was performed with engineered tobacco plants, a 10-fold enhancement of AcNPV infection was observed, but a marked enhancement of SeNPV infection was not observed. Thus, the engineering and expression of the baculovirus enhancin gene in homologous and heterologous organisms allowed us to analyze its effects on NPV infection of larvae which demonstrated its viral enhancement function.