Expression and hemocyte-targeting of aCampoletis sonorensis polydnavirus cysteine-rich gene inHeliothis virescens larvae

Abstract

The polydnavirus associated with the parasitic wasp Campoletis sonorensis is injected into the lepidopteran insect, Heliothis virescens, during parasitization, after which viral gene products suppress the cellular immune system of the hosts. Four related cysteine‐rich polydnavirus genes have been identified in parasitized H. virescens larvae and grouped into a family. In this study, we investigated the expression and hemocyte targeting of the cysteine‐rich Vhv1.4 protein. Full‐ length and truncated Vhv1.4 proteins were produced in a bacterial expression system, and the purified proteins were used to raise polyclonal antisera. In immunoblots the Vhv1.4 protein was detected in parasitized insects as early as 6 h and throughout the entire course of parasitism. The Vhv1.4 protein appeared predominantly in the plasma fraction of hemolymph from parasitized larvae, suggesting that this protein is secreted. The Vhv1.4 protein expressed from a recombinant baculovirus was secreted in two lepidopteran cell lines and in larvae injected with the recombinant virus. Digestion with endoglycosidases suggests that the Vhv1.4 protein is glycosylated at multiple N‐glycosylation sites. Immunofluorescence assays showed that the Vhv1.4 protein binds to the hemocytes, most notably the granulocytes, in H. virescens larvae. After binding, the Vhv1.4 protein was internalized, probably by endocytosis. Specific binding of the Vhv1.4 to granulocytes implies an important function in the suppression of host cellular encapsulation response. Arch. Insect Biochem. Physiol. 36:251–271, 1997. © 1997 Wiley‐Liss, Inc.

Tissue specificity of a baculovirus-expressed, basement membrane-degrading protease in larvae of Heliothis virescens

“…These multigene families were characterized based on similarities in sequence, protein structure, expression pattern and function (Cui, Soldevila, and Webb, 1997;Cui, Soldevila, and Webb, 2000;Cui and Webb, 1996;Kroemer and Webb, 2005). Here we focus on the viral ankyrin or vankyrin gene family, in C. sonorensis IV.…”

Iκβ-Related vankyrin Genes in the Campoletis sonorensis Ichnovirus: Temporal and Tissue-Specific Patterns of Expression in Parasitized Heliothis virescens Lepidopteran Hosts

“…Earlier publications have described the existence of three gene families within this genome: the cys-motif, rep, and vinnexin gene families. These multigene families have been characterized based on similarities in sequence, protein structure, expression patterns, and function (9,10,13,14,16,19,29,38,41,68,78,79,81). Here we describe the existence of a fourth gene family, the viral ankyrin or vankyrin gene family, in C. sonorensis IV.…”

“…Virions are then transferred to the parasitoid's lepidopteran hosts with eggs, ovarian proteins, and venom during parasitization, where they infect local tissues, express encoded genes, and induce pathologies essential to the survival of the developing endoparasite (38,64,70,75,81,84). These pathological alterations include disruption of host development, immunosuppression, and mobilization of host protein stores for parasitoid utilization (2,3,13,17,30,41,50,62,64,66,74,85).…”

Presence of polydnavirus transcripts in an egg-larval parasitoid and its lepidopterous host.

“…In the parasitized host, polydnavirus DNA appears to persist without replication (Theilmann & Summers, 1986 ;Strand et al, 1992), and transcriptional activity has been documented in several hosts (reviewed in Stoltz, 1993 ;Strand et al, 1992 ;Harwood et al, 1994 ;Hayakawa et al, 1994 ;Yamanaka et al, 1996 ;Cui et al, 1997). In the case of the parasitoid\host system Campoletis sonorensis\Heliothis virescens, viral transcripts were also reported in the female parasitic wasp ; viral gene expression was different in the two insect hosts, some transcripts being seen only in the parasitized host, others only in the female wasp and a third category in both hosts (Fleming et al, 1983 ;Theilmann & Summers, 1988).…”

“…These observations were all made with hosts of larval parasitoids, i.e. where the wasp oviposits into a larva, and it appears that the majority of transcripts analysed up to now are related to the strong immunosuppressive activity of the polydnaviruses in these systems (Dib-Hajj et al, 1993 ;Li & Webb, 1994 ;reviewed in Lavine & Beckage, 1995 ;Asgari et al, 1996 ;Cui et al, 1997).…”