Expression of polydnavirus genes under polydnavirus promoter regulation in insect larvae infected with baculovirus recombinants

Abstract

We have evaluated the use of baculoviruses to deliver Campoletis sonorensis polydnavirus (CsPDV) genomic DNA into lepidopteran larvae to facilitate the identification of functional CsPDV genes. Genomic fragments consisting of regulatory (promoter) and coding sequences for two CsPDV genes (VHv 1.1 and WHvl.6) were used to generate CsPDVbaculovirus recombinants and evaluate the expression of genes under the regulation of the CsPDV promoters. Northern blot and primer extension studies established that CsPDV genes were expressed under the control of their own promoters in these CsPDV-baculovirus recombinants. Transcripts were detected as early as 4 h post-infection indicating that temporal activity of CsPDV promoters was retained. The VHvl.1 gene product as expressed from CsPDV-baculovirus recombinants was identical in size and in functional properties to that produced in CsPDV-infected insects. CsPDVbaculovirus recombinants may be useful for the screening and characterization of polydnavirus genes with functional activities that can only be evaluated in insect larvae.

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

“…All infected cell lines contained smaller immunoreactive proteins suggesting partial degradation of the VHv1.4 protein. This result is consistent with observations about the lower efficiencies of processing by Sf9 cells of proteins destined for secretion (O'Reilly et al, 1992;Wickman et al, 1992;Wickman and Nemerow, 1993;Soldevila and Webb, 1996). The VHv1.4 protein in recombinant baculovirus infected H. virescens larvae was secreted, appearing indistinguishable form the protein produced in naturally parasitized hosts.…”

A single parasitoid segregating factor controls immune suppression in Drosophila

“…The singlefactor inheritance in L. boulardi should therefore be interpreted cautiously; the trait may be controlled by a cluster of genes that cannot be dissected by Mendelian genetic methods. We do not know to date whether the viral genes in C. sonorensis that are expressed in the host are associated in a cluster or dispersed among the parasitoid chromosomes (Soldevila and Webb 1996). The other interpretation of the result is that only one or a few of the factors that are injected into the host by Leptopilina or Campoletis are detected in the crosses because only some can suppress the immune system of a particular host strain.…”

Expression of a Tranosema rostrale polydnavirus gene in the spruce budworm, Choristoneura fumiferana

“…Several studies have examined the transcription of polydnaviral genes in lepidopteran hosts and, in some cases, the expressed genes and their protein products have been isolated and characterized (Webb, 1998 ). So far, most of these investigations have pointed to an involvement of the identified genes, transcripts or protein products in immune suppression (as opposed to developmental regulation), either on the basis that polydnavirus genes were expressed predominantly in host haemocytes (Asgari et al , 1996 ; Hayakawa et al , 1994 ; Strand, 1994 ; Strand et al , 1992 , 1997 ; Yamanaka et al , 1996 ) or that the recombinant protein products had the ability to alter haemocyte behaviour and to inhibit encapsulation (Asgari et al , 1997 ; Cui et al , 1997 ; Li & Webb, 1994 ; Soldevila & Webb, 1996 ; Soldevila et al , 1997 ). However, a recent study examining the temporal pattern of PDV transcription in Spodoptera littoralis larvae parasitized by the braconid wasp Chelonus inanitus has shown that the levels of viral transcripts increase in the final instar, coincident with the induction of developmental arrest, an observation that suggests a role for some polydnaviral genes in the disruption of S. littoralis metamorphosis (Johner et al , 1999 ).…”