Cardiochiles nigriceps polydnavirus: molecular characterization and gene expression in parasitized Heliothis virescens larvae

Cardiochiles nigriceps Viereck is an endophagous parasitoid of larval stage s of the tobacco budworm, Heliothis virescens (F.). This hymenopteran paras itoid, belonging to the family Braconidae, is associated with a polydnaviru s (CnPDV), injected at oviposition along with the egg. The infection of var ious tissues by CnPDV determines the suppression of the host immune system and the developmental arrest of mature host larvae. In this study, CnPDV ha s been characterized at the structural and molecular level. The negatively stained nucleocapsids show evident 'end stnrctures' and a tail-like appenda ge. The CnPDV genome is typically segmented, with circular dsDNA molecules, ranging in size from 2.5 kb to more than 23 kb. The early expression patte rn of CnPDV in parasitized hosts has been analysed and viral clones, genomi c and cDNAs, identifying genes expressed within 48 h after parasitization h ave been isolated. The molecular organization of one of these genes, named CnPDV1, and its putative protein product have been determined. Significant sequence homologies with other known proteins were not detected. In situ hy bridization experiments indicated that this gene is expressed in the protho racic glands of parasitized host mature larvae. A functional analysis of Cn PDV1 gene product is required to assess its possible role in the regulation of parasitoid-induced alterations of host larvae. (C) 1999 Elsevier Scienc e Ltd. All rights reserved.