Cotesia vestalis parasitization suppresses expression of a Plutella xylostella thioredoxin

Authors: MIN, SHI - Zheijiang University; ZHAO, SHUANG - Zheijiang University; WANG, ZE-HUA - Zheijiang University; Stanley, David; CHEN, XUE-XIN - Zheijiang University

Submitted to: Insect Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2016
Publication Date: 7/4/2016
Citation: Min, S., Zhao, S., Wang, Z., Stanley, D.W., Chen, X. 2016. Cotesia vestalis parasitization suppresses expression of a Plutella xylostella thioredoxin. Insect Molecular Biology. doi:10.1111/imb.12252.

Interpretive Summary: Application of classical insecticides has introduced severe problems in agricultural sustainability. Pest insect biological control programs are based on using beneficial agents to reduce pest insect populations. Such programs reduce use in insecticides globally. Among biological control agents, endoparasitoids are small insects that develop inside another insect. They are highly efficacious. The success of these agents depends on suppressing host immunity and development by maternal factors injected into hosts during oviposition, including venom and viruses. The problem, however, is the lack of detailed understanding of the mechanism involved in the relationship between parasites and their pest insect hosts. Although substantial information documents the point that parasitization results in suppressing host immunity, the complete range of suppressed immune functions remains unknown. We posed the hypothesis that parasitization suppresses expression of a particular gene; this gene encodes an enzyme responsible for protecting cells from internal damage. The gene is expressed in all tissues and life stages we analyzed and it stimulates cell proliferation. The significance of our finding is the identification of a specific gene that is suppressed by parasitoids. These new research results will be directly useful to scientists who are working to improve the efficacy of biological control methods. The ensuing improved biological control methods will benefit a wide range of agricultural producers by reducing use of classical insecticides and supporting the long-term sustainability of agriculture.

Technical Abstract: Thioredoxins (Trxs) are a family of small, highly conserved and ubiquitous proteins involved in protecting organisms against toxic reactive oxygen species (ROS). In this study, a typical thioredoxin gene, PxTrx, was isolated from Plutella xylostella. The full-length cDNA sequence is composed of 959 bp containing a 321 bp open reading frame that encodes a predicted protein of 106 amino acids, 11.7 kDa and an isoelectric point of 5.03. PxTrx was mainly expressed in larval Malpighian tubules and fat body. An enriched recombinant PxTrx had insulin disulfide reductase activity and stimulated HEK293 cell proliferation. It also protected super-coiled DNA and living HEK293 cells from H2O2-induced damage. Parasitization by Cotesia vestalis and injections of 0.05 and 0.01 equivalents of Cotesia vestalis Bracovirus (CvBv), the symbiotic virus carried by the parasitoid, led to down-regulation of PxTrx expression in host fat body. Taken together, our results indicate that PxTrx contributes to the maintenance of P. xylostella cellular hemostasis. Fat body expression of PxTrx is strongly attenuated by parasitization and by injections of CvBv.