Article

Insecticidal activity of a basement membrane-degrading protease against Heliothis virescens (Fabricius) and Acyrthosiphon pisum (Harris)

Department of Entomology, Iowa State University, 418 Science II, Ames, IA 50011-3222, USA.
Journal of Insect Physiology (Impact Factor: 2.47). 06/2008; 54(5):777-89. DOI: 10.1016/j.jinsphys.2008.02.008
Source: PubMed

ABSTRACT

ScathL is a cathepsin L-like cysteine protease derived from the flesh fly Sarcophaga peregrina that functions in basement membrane (BM) remodeling during insect development. A recombinant baculovirus expressing ScathL (AcMLF9.ScathL) kills larvae of the tobacco budworm, Heliothis virescens, significantly faster than the wild-type virus. Here, we show that the occurrence of larval melanization prior to death was closely associated with the onset of high cysteine protease activity of ScathL in the hemolymph of fifth instars infected with AcMLF9.ScathL, but not with AcMLF9.ScathL.C146A, a recombinant baculovirus expressing a catalytic site mutant of ScathL. Fragmented fat body, ruptured gut and malpighian tubules, and melanized tracheae were observed in AcMLF9.ScathL-infected larvae. Phenoloxidase activity in hemolymph was unchanged, but the pool of prophenoloxidase was significantly reduced in virus-infected larvae and further reduced in AcMLF9.ScathL-infected larvae. The median lethal dose (LD(50)) for purified ScathL injected into fifth-instar H. virescens was 11.0 microg/larva. ScathL was also lethal to adult pea aphids, Acyrthosiphon pisum with a similar loss of integrity of the gut and fat body. Injection with purified ScathL.C146A or bovine trypsin at 20 microg/larva did not produce any effect in either insect. These results illustrate the potent insecticidal effects of ScathL cysteine protease activity and the potential for use of ScathL in development of insect resistant transgenic plants when combined with an appropriate delivery system.

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    • "In response to bacteria, for example, our previous study shows that PO-catalyzed oxidation of dopamine generates reactive compounds that immobilize, aggregate, and kill Escherichia coli and Bacillus subtilis (Zhao et al., 2007). Against viruses, Trudeau et al. (2001) reported that Helicoverpa zea, a semipermissive host of Autographa californica multi-capsid nucleopolyherdrovirus (AcMNPV), melanizes infection foci, whereas this response was not observed in the fully permissive host Heliothis virescens due to AcMNPV reducing proPO levels in the hemolymph (Li et al., 2008). Shelby and Popham (2006) elaborated on these results by showing that PO inhibitors abolish the virucidal activity of H. virescens plasma against a baculovirus, while Clarke and Clem (2002) report that hemocytes also affect spreading of AcMNPV in Trichoplusia ni and Spodoptera frugiperda. "
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