Cloning three host translation inhibitory factors (HTIFs) encoded in Cotesia glomerata bracovirus

An endoparasitoid, Cotesia glomerata (Braconoid: Hymenoptera), parasitizes the diamondback moth, Plutella xylostella (Yponomeutidae: Lepidoptera). Parasitized P. xylostella exhibits immunosuppression and developmental alteration. Host translation inhibitory factor (HTIF) has been identified in C. plutellae bracovirus (CpBV), a closely related specie of C. glomerata. Parasitization by C. glomerata inhibited hemocyte-spreading behavior and synthesis of larval storage protein of P. xylostella. Here we report putative HTIFs derived from C. glomerata bracovirus (CgBV), which is a polydnavirus symbiotic to the wasp. Gene specific primers of Cg-HTIF produced three homologous genes (Cg-HTIF(I), Cg-HTIF(II), Cg-HTIF(III)) when they were applied to cDNAs constructed from P. xylostella parasitized by C. glomerata. Cg-HTIF(I) shares high homology with CpBV15α. Cg-HTIF(II) and Cg-HTIF(III) are highly similar with CpBV15β. These genes were mostly expressed at late parasitization period. This was confirmed by a quantitative and reverse transcriptase-polymerase chain reaction and immunoblotting assay using an antibody specific for HTIF. Its effect on the host's physiological processes was also investigated by transient expression and RNA interference techniques. Transfection of a recombinant Cg-HTIF in P. xylostella by microinjection expressed the gene as early as 12 h until 72 h. Levels of plasma proteins from larvae injected with recombinant Cg-HTIF was significantly reduced and this was confirmed by immunoblotting assay using antibody specific for storage proteins of the host. RNA interference further reavealed the role of Cg-HTIF in immunosuppression and alteration of host physiology. The double stranded RNA of Cg-HTIF co-injected with the recombinant vector notably recovered the hemocyte spreading behavior and synthesis of plasma proteins.