Selectivity of a translation-inhibitory factor, CpBV15β, in host mRNAs and subsequent alterations in host development and immunity

An endoparasitoid wasp, Cotesia plutellae, parasitizes young larvae of the diamondback moth, Plutella xylostella. Its symbiotic virus, C. plutellae bracovirus (CpBV), has been shown to play a crucial role in inducing physiological changes in the parasitized host. A viral gene, CpBV15p, exhibits a specific translational control against host mRNAs by sequestering a eukaryotic translation initiation factor, elF4A. Inhibitory target mRNAs have high thermal stability (>1,-2,9 kcal/mol) of their secondary structures in 5'UTR. To determine the specificity of translational control in terms of 5'UTR complexity, this study screened target/nontarget mRNAs of CpBV158 using a proteomics approach through an in vivo transient expression technique. A proteomics analysis of host plasma proteins showed that 12.9% (23/178) spots disappeared along with the expression of CpBV158. A total of ten spots were chosen, in which five spots ('target') were disappeared by expression of CpBV158 and the other five ('nontarget') were insensitive to expression of CpBV158, and further analyzed by a tandem mass spectroscopy. The predicted genes of target spots had much greater complexity (-12.3 to 25.2 kcal/mol) of their 5'UTR in terms of thermal stability compared to those (-3.70 to 9.00 kcal/mol) of nontarget spots. 5'UTRs of one target gene (arginine kinase:Px-AK) and one nontarget gene (imaginal disc growth factor:Px-IDGF) were cloned and used for in vitro translation (IVT) assay using rabbit reticulocyte lysate. IVT assay clearly showed that mRNA of Px-IDGF was translated in the presence of CpBV150, but mRNA of Px-AK was not. Physiological significance of these two genes was compared in immune and development processes of P. xylostella by specific RNA interference (RNAi). Under these RNAi conditions, suppression of Px-AK exhibited much more significant adverse effects on larval immunity and larva-to-pupa metamorphosis compared to the effect of suppression of Px-IDGF. These results support the hypothesis that 5'UTR complexity is a molecular motif to discriminate host mRNAs by CpBV158 for its host translational control and suggest that this discrimination would be required for altering host physiology to accomplish a successful parasitism of the wasp host, C plutellae. (C) 2013 Elsevier Ltd. All rights reserved.