Submitted to: Archives of Insect Biochemistry and Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/7/2008
Publication Date: 10/6/2008
Citation: Shelby, K., Popham, H.J. 2008. Cloning and Characterization of the Secreted Hemocytic Prophenoloxidases of Heliothis virescens. Archives of Insect Biochemistry and Physiology. 69(3):127-142. Interpretive Summary: How an insect survives a bacterial, fungal or viral infection is a question that needs to be answered to develop insect control measures that ultimately outwit an insect's defense mechanism. One of the main defense mechanisms insects have developed is the production of an enzyme called phenoloxidase which works to fight off infection in many different species of insects. In this study, two phenoloxidase genes were identified and sequenced from the budworm, Heliothis virescens. Initial information was gathered about how these genes react when larvae were challenged with bacteria or virus. This finding will impact scientists working on how an insect resists infection because it identifies new genes that can be used to study why some infections are fatal while others are not and how the larval defense machinery can be overcome in the field.
Technical Abstract: The plasma enzyme phenoloxidase plays an important role in host resistance against microbial, filarial and parasitoid challenge. Two Heliothis virescens prophenoloxidase transcripts, HvPPO-1 and HvPPO-2, were assembled from ESTs derived from a hemocyte cDNA library and completed by 5’-RACE. The 2363 bp HvPPO-1 clone hybridizes to a transcript of approximately 1.64 kb and encodes a 696 amino acid protein. The 3255 bp HvPPO-2 clone hybridized to a transcript of approximately 1.28 kb and encodes a 684 amino acid protein. Both proteins exhibited high homology to other insect prophenoloxidases and encoded N-terminal serine proteinase activation motifs, and conserved copper binding histidine residue positions. Hemocyte transcript levels of HvPPO-1 and HvPPO-2 were not upregulated by bacterial infection nor were transcript levels altered by per os infection with Helicoverpa zea SNPV at up to 72 hrs post infection. These results indicate that the prophenoloxidases are constitutively expressed in larval H. virescens hemocytes, and that their transcription is not affected by an ongoing bacterial or viral infection.