Venom of Parasitoid, Pteromalus puparum, Suppresses Host, Pieris rapae, Immune Promotion by Decreasing Host C-Type Lectin Gene Expression

Abstract

BackgroundInsect hosts have evolved immunity against invasion by parasitoids, and in co-evolutionary response parasitoids have also developed strategies to overcome host immune systems. The mechanisms through which parasitoid venoms disrupt the promotion of host immunity are still unclear. We report here a new mechanism evolved by parasitoid Pteromalus puparum, whose venom inhibited the promotion of immunity in its host Pieris rapae (cabbage white butterfly).Methodology/Principal FindingsA full-length cDNA encoding a C-type lectin (Pr-CTL) was isolated from P. rapae. Quantitative PCR and immunoblotting showed that injection of bacterial and inert beads induced expression of Pr-CTL, with peaks of mRNA and Pr-CTL protein levels at 4 and 8 h post beads challenge, respectively. In contrast, parasitoid venom suppressed Pr-CTL expression when co-injected with beads, in a time and dose-dependent manner. Immunolocalization and immunoblotting results showed that Pr-CTL was first detectable in vesicles present in cytoplasm of granulocytes in host hemolymph, and was then secreted from cells into circulatory fluid. Finally, the secreted Pr-CTL bound to cellular membranes of both granulocytes and plasmatocytes. Injection of double-stranded RNA specific for target gene decreased expression of Pr-CTL, and a few other host immune-related genes. Suppression of Pr-CTL expression also down-regulated antimicrobial and phenoloxidase activities, and reducing phagocytotic and encapsulation rates in host. The inhibitory effect of parasitoid venom on host encapsulation is consistent with its effect in suppressing Pr-CTL expression. Binding assay results showed that recombinant Pr-CTL directly attached to the surface of P. puparum egges. We infer that Pr-CTL may serve as an immune signalling co-effector, first binding to parasitoid eggs, regulating expression of a set of immune-related genes and promoting host immunity.Conclusions/Significance P. puparum venom inhibits promotion of host immune responses by silencing expression of host C-type lectin gene Pr-CTL, whose expression affected transcription of other host immune-related genes.

Transcriptomic Immune Response of Tenebrio molitor Pupae to Parasitization by Scleroderma guani

“…Especially, it was reported that the gene lectin - 24A was massively up-regulated in parasitized Drosophila larvae after parasitization at the time when the capsule was formed [51]. A similar investigation indicated that the inhibitory effect of P. puparum venom on host encapsulation is consistent with its effect in suppressing CTL expression [52]. Thus, CLT is an important immune candidate involved in the suppression of host cellular immune defense induced by the parasitoid.…”

“…For example, transcript levels of cecropin and gloverin in eggs of M. sexta were suppressed after parasitization by Trichogramma evanescens [57]. After Pieris rapae pupae injected with P. puparum venom, ten potential antimicrobial molecules including cecropin, lysozyme, attacin, lebocin, proline-rich AMP, cysteine-rich peptide, gallerimycin and immune inducible peptide had lower transcript levels in hemocytes or fat body of the venom injected hosts[52], demonstrating that the transcriptional down regulation of these antimicrobial genes is due to the venom. Nevertheless, parasitization of Drosophila resistant strain by the corresponding parasitoids did not induce transcripts of diptericin and cecropin whilst the susceptible strain did [55], [56].…”

Parasitization by Cotesia chilonis Influences Gene Expression in Fatbody and Hemocytes of Chilo suppressalis

“…This gene (GAJS01016295) was down-regulated (log 2 Ratio  =  –4.9) in fatbody and up-regulated (log 2 Ratio  =  12.9) in hemocytes (Table 3). Although PRRs are up-regulated by infections [38], these genes can be suppressed by parasitoid venom [20], [21] or PDVs [39]. In our results, certain PRRs included peptidoglycan recognition protein B (GAJS01023399, PF/CF: –1.2), hemicentin 1 (GAJS01000005, PH/CH: –4.5), leureptin (GAJS01018114, PF/CF: –4.5) and Scavenger receptor class B (GAJS01011562, PH/CH: –2.2) were down-regulated.…”

A Venom Serpin Splicing Isoform of the Endoparasitoid Wasp Pteromalus puparum Suppresses Host Prophenoloxidase Cascade by Forming Complexes with Host Hemolymph Proteinases

“…Other virulence factors found in some parasitoids, such as PDVs, virus-like particles, or teratocytes, have not been recorded in P. puparum (29). As the major maternal virulence factor in P. puparum, P. puparum venom regulates host development and metabolism (30) and suppresses cellular (27,28,31) and humoral immunity of the host (32)(33)(34). Here we report a serpin gene with 16 predicted splicing isoforms in P. puparum and show that one of these isoforms is a venom protein, which inhibits host PPO activation by forming complexes with host hemolymph proteinases.…”