Identification of Core Genes of Toll-like Receptor Pathway from Lymantria dispar and Induced Expression upon Immune Stimulant

SIMPLE SUMMARY: The gypsy moth, Lymantria dispar is one of the main forest defoliators worldwide. The baculovirus, Lymantria dispar multiple nucleopolyhedrovirus (LdMNPV), can naturally control this pest and is safe to non-target organisms. However, Toll-like receptor (TLR) signaling pathway, which plays a critical role in innate immunity both in vertebrates and invertebrates, and its underlying immune mechanism against LdMNPV invasion in L. dispar have not been investigated. In this study, eleven TLRs and five downstream TLR pathway components of L. dispar were identified. All of these proteins comprised typical domain architecture. Primary and tertiary structure analysis revealed that Toll/interleukin-1 receptor (TIR) domains of TLRs from L. dispar were conserved during evolution. Expression analysis showed that several TLRs and all identified downstream genes of TLR pathway in L. dispar were significantly up-regulated in response to LdMNPV infection, implying that the TLR pathway of L. dispar was activated and may be involved in L. dispar innate immunity against LdMNPV infection. Taken together, this research contributed to the clarification of innate immunity in L. dispar. ABSTRACT: The gypsy moth, Lymantria dispar, is a polyphagous forest pest worldwide. The baculovirus, Lymantria dispar multiple nucleopolyhedrovirus (LdMNPV) is a natural pathogen of L. dispar. The Toll-like receptors (TLR) pathway plays a crucial role in both innate and adaptive immunity in animals. However, The TLR pathway and its underlying immune mechanism against baculovirus in L. dispar have not been explored. In this study, eleven TLRs and five downstream TLR pathway components were identified and characterized from L. dispar. Structural analysis indicated that intracellular Toll/interleukin-1 receptor (TIR) domains of LdTLRs and LdMyD88 contained three conserved motifs, and the 3D structures of TIR domains of LdTLRs possessed similar patterns in components arrangement and spatial conformation. The TLR proteins of L. dispar were placed into five monophyletic groups based on the phylogenetic analysis. LdTLR1, 2, 5, 6, 7, 8 and all identified downstream TLR pathway factors were highly induced upon LdMNPV infection, indicating that the TLR pathway of L. dispar was activated and might play a role in the immune response to LdMNPV infection. Collectively, these results help elucidate the crucial role of the TLR pathway in the immune response of L. dispar against LdMNPV, and offer a foundation for further understanding of innate immunity of the pest.