POLYDNAVIRUS-FACILITATED ENDOPARASITE PROTECTION AGAINST HOST IMMUNE DEFENSES

The polydnavirus of Campoletis sonorensis has evolved with an unusual life cycle in which the virus exists as an obligate symbiont with the parasite insect and causes significant physiological and developmental alterations in the parasite's host. The segmented polydnavirus genome consists of double-stranded superhelical molecules; each segment is a pparently integrated into the chromosomal DNA of each male and female wasp. The virus replicates in the nucleus of calyx cells and is secret ed into the oviduct, When the virus is transferred to the host insect during oviposition, gene expression induces host immunosuppression and developmental arrest, which ensures successful development of the imm ature endoparasite. In the host, polydnavirus expression is detected b y 2 hr and during endoparasite development. Most of the abundantly exp ressed viral genes expressed very early after parasitization belong to multigene families, Among these families, the ''cysteine-rich'' gene family is the most studied, and it may be important in inducing host m anifestations resulting in parasite survival. This gene family is char acterized by a similar gene structure with introns at comparable posit ions within the 5' untranslated sequence and just 5' to a specific cys teine codon (C-) within a cysteine motif, C-C-*-CC-C-C, Another unusu al feature is that the nucleotide sequences of introns 2 in the subfam ily WHVv1.0/WHv1.6 are more conserved than those of the flanking exons . The structures of these viral genes and possible functions for their encoded protein are considered within the context of the endoparasite and virus strategy for genetic adaptation and successful parasitizati on.