Preface: Papers selected from the symposium “Parasitoid Polydnaviruses: Genomes and Physiological Functions,” presented at the 11th International Congress on Parasitology in August 2006

Abstract

AbstractAmong the many exciting areas of insect science, it would be extremely difficult to exaggerate the interest and importance of our growing knowledge on polydnaviruses (PDVs). In recent years, the available molecular and genomic‐level information has grown exponentially as a result of genome and expressed sequence tag sequencing projects. These projects already have an important impact on PDV research and provide novel insights in the evolution of genes coding for important components of PDV–insect interactions. This Special Issue of Archives of Insect Biochemistry and Physiology presents four papers on the leading PDV research.Lee and Kim report on an approximately 15‐kDa protein found in the hemolymph of the diamondback moth, Plutella xylostella, exclusively after the larvae were parasitized by the wasp, Cotesia plutellae. The protein is the product of two homologous genes, named CpBV15α and CpBV15β. The ORFs of both genes are similar, although there are internal differences. Southern blots indicate the genes are located on the C. plutellae bracovirus (BV) genome. These are late genes, appearing 7–8 days after parasitization. Antibodies prepared using protein purified from an expression system demonstrated that the appearance of the protein in the hemolymph of parasitized larvae corresponded in time with the expression of the late genes. Based on bioinformatic studies, this protein is probably a host translation inhibitory factor.Bezier et al. contribute an important insight into bracovirus genomics. In their analyses of Cotesia congregata bracovirus (CcBV) genes, they found that CcBV virulence gene products are not more closely related to insect proteins than they are related to human proteins. This finding prompted the questions on the apparent distances between CcBV and insect proteins. Specifically, the distance between the two groups could be related to something about BV proteins or it could be related to a broadly high divergence. Bezier et al. conclude that the high divergence of BV proteins is a character of the viral products. Their discussion adds new insights into the origins of wasp–BV associations.Doucet et al. contribute new information on prophenoloxidase (PPO), one of the major defense mechanisms insects evolved to protect themselves from parasitoids. The spruce budworm, Choristoneura fumiferana, is parasitized by the wasp Tranosema rostrale. Parasitism by the wasp effectively inhibit melanization in 6th‐instar budworms. To learn more about the mechanism of inhibiting melanization, Doucet et al. cloned two PPO homologs (CfPPO1 and CfPPO2) from budworms. In their analysis, they discovered three mRNA variants of CfPPO1, from which they suggest there may be more than one copy of CfPPO1. Following injection of large doses of polydnavirus‐rich calyx fluid prepared from the wasp, the authors found that the fluid exerted only a minor influence on CfPPO1 and CfPPO2 transcript accumulation. Doucet et al. propose that down‐regulation at the transcriptional level is not the major mechanism of inhibiting melanization in hemolymph of parasitized budworms.One of the important barriers to progress in PDV genomics is the enormous amount of time and labor invested in culturing and dissecting several thousands of ovaries from parasitic wasps. The ovaries are needed to prepare viral DNA for genomic sequencing because the viruses do not replicate in cell culture systems. One of the few tools available to improve this lengthy process would be to optimize the preparation of viral DNA.Rodriguez‐Perez and Beckage take on this challenge with a direct study of three methods to prepare PDV genomic DNA. They used the BV of Cotesia flavipes, a parasite of the sugarcane borer, for their comparisons. Two protocols were based on phenol‐chloroform DNA extractions steps. Both of these methods were inferior to a modified Qiagen DNA kit procedure for extraction of viral DNA. The kit procedure was the most efficient of the three protocols because the kit requires far less time to complete and it is more cost effective. This work contributes a reliable, standard protocol that may be applied on a very wide scale to speed international work on PDV genomic sequencing. This should unleash new possibilities in gene discovery and enhance the deployment of PDVs in serious insect management problems in agricultural and medical settings.We bring these reports together to illuminate progress in the broad field of insect PDVs. The future holds real promise for great advances in a research area that easily embraces a broad spectrum of insect science, ranging from fundamental areas of biology to real‐world applications of advancing science.