Location: Biological Control of Insects ResearchTitle: Pteromalus puparum venom impairs host cellular immune responses by decreasing expression of its scavenger receptor gene) Author
Submitted to: Insect Biochemistry and Molecular Biology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/13/2011
Publication Date: 7/22/2011
Citation: Fang, Q., Wang, L., Zhu, Y., Stanley, D.W., Chen, X., Hu, C., Ye, G. 2011. Pteromalus puparum venom impairs host cellular immune responses by decreasing expression of its scavenger receptor gene. Insect Biochemistry and Molecular Biology. 41:852-862. Interpretive Summary: Long-term agricultural sustainability is severely threatened by widespread use of classical insecticides. Threats include increasing resistance to insecticides and sharply decreasing environmental quality. The concept of biological control of insects is a potentially powerful alternative to classical insecticides. Biological control is based on the idea that direct application of certain insect-specific predators, pathogens and parasites can reduce pest insect populations to a point that the pests exert only negligible economic damage. A major problem, however, is that many insect parasites have a very narrow range of hosts. This limits the usefulness of any given parasite species in biological control programs. In this paper, we examined the relationship of a parasitic insect and its host, a pest insect. We learned that venom from the parasite is essential to the success of the parasite. Scientists who study host/parasite relationships will use this information in future research designed understand how parasite venom can be manipulated to broaden the host range of a parasite. Ultimately, this research will benefit growers who produce vegetable crops and the people who consume vegetables.
Technical Abstract: Insect host/parasitoid interactions are co-evolved systems in which host defenses are balanced by parasitoid mechanisms to disable or hide from host immune effectors. Although there is a rich literature on these systems, parasitoid immune-disabling mechanisms have not been fully elucidated. Here we report on a newly discovered immune-disabling mechanism in the Pieris rapae/Pteromalus puparum host/parasitoid system. Because venom injections and parasitization suppresses host phagocytosis, we turned attention to the P. rapae scavenger receptor (Pr-SR), posing the hypothesis that P. puparum venom suppresses expression of the host Pr-SR gene. To test our hypothesis, we cloned a full-length cDNA of the Pr-SR. Multiple sequences alignment showed the deduced amino acid sequence of Pr-SR is similar to scavenger receptors of other lepidopterans. Bacterial and bead injections induced Pr-SR mRNA and protein expression, which peaked at 4 h post-bead injection. Venom injection inhibited Pr-SR expression. Pr-SR was specifically expressed in granulocytes compared to plasmatocytes. We localized the Pr-SR protein in cytoplasm and cellular membrane, with no evidence of secretion into host plasma. Double-strand RNA designed to Pr-SR mRNA silenced expression of Pr-SR and significantly impaired host phagocytosis and encapsulation reactions. Venom injections similarly silenced Pr-SR expression during the first 8 h post-treatment, after which the silencing effects gradually abated. We infer from these findings that one mechanism of impairing P. rapae hemocytic immune reactions is by silencing expression of Pr-SR.