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Title: Assessment of a Basement Membrane-Degrading Protease on Dissemination and Secondary Infection of Autographa californica Multiple Nucleopolyhedrovirus in Heliothis virescens L.

Author
item LI, HUARONG - IOWA STATE UNIV.
item TANG, HAILIN - IOWA STATE UNIV.
item Harrison, Robert - Bob
item BONNING, BRYONY - IOWA STATE UNIV.

Submitted to: Journal of General Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/21/2006
Publication Date: 3/1/2007
Citation: Li, H., Tang, H., Harrison, R.L., Bonning, B.C. 2007. Assessment of a Basement Membrane-Degrading Protease on Dissemination and Secondary Infection of Autographa californica Multiple Nucleopolyhedrovirus in Heliothis virescens L. Journal of General Virology. 88:1109-1119.

Interpretive Summary: Insect pests cause billions of dollars of damage to crops each year. The use of chemical insecticides to control insect pests can have negative ecological, environmental, and health consequences. Baculoviruses are insect viruses that can kill harmful insects on plants without the need to use chemical insecticides. However, the success of baculoviruses for insect control is limited by their slow speed of action against insect pests. In this study, a gene was inserted into a baculovirus that caused the baculovirus to kill insect pests faster. The gene caused the baculovirus to make a new protein that quickly killed the insect. The information in this study will help researchers develop baculovirus strains with better insecticidal activity. Baculoviruses have a wide range of applications in addition to their use in controlling insects, and this study will be of interest to scientists in academia, government, and industry who work with this group of viruses.

Technical Abstract: ScathL is a cathepsin L-like cysteine protease from the flesh fly, Sarcophaga peregrina, that digests components of the basement membrane during insect metamorphosis. A recombinant baculovirus that expresses ScathL (AcMLF9.ScathL) kills larvae of the tobacco budworm, Heliothis virescens, significantly faster than the wild-type virus and triggers melanization and tissue fragmentation in infected larvae shortly before death. Since basement membranes are a potential barrier to the spread of baculovirus secondary infection to other tissues in the host, we tested the hypothesis that the rapid death of insects infected with AcMLF9. ScathL was caused by accelerated secondary infection resulting from the degradation of host basement membranes by ScathL. Viruses expressing catalytically active or inactive ScathL were used to examine the effects of ScathL activity on the appearance and timing of budded virus in the hemocoel during infection, the production of polyhedra in infected larvae, and the rate of infection of the gut, trachea, hemocyte, fat body, and malpighian tubules. We conclude that the enhanced insecticidal efficacy of the recombinant baculovirus that expresses ScathL does not result from altered tissue tropism or accelerated systemic infection. Implications for the role of the basement membrane as a barrier to baculovirus dissemination within the host insect are discussed.