Tenebrio molitor Gram-negative-binding protein 3 (TmGNBP3)is essential for inducing downstream antifungal Tenecin 1 gene expression against infection with Beauveria bassiana JEF-007

The Toll signaling pathway is responsible for defense against both Grampositive bacteria and fungi.Gram-negative binding protein 3(GNBP3)has a strong affinity for the fungal cell wall component,β-1,3-glucan,which can activate the prophenoloxidase (proPO)cascade and induce the Toll signaling pathway.Myeloid differentiation factor 88 (MyD88)is an intracellular adaptor protein involved in the Toll signaling pathway.In this study,we monitored the response of 5 key genes (TmGNBP3,TmMyD88,and Tenecin 1,2, and 3)in the Toll pathway of the mealworm Tenebrio molitor immune system against the fungus Beauveria bassiana JEF-007 using RT-PCR.TmGNBP3,Tenecin 1,and Tenecin 2 were significantly upregulated after fungal infection.To better understand the roles of the Toll signaling pathway in the mealworm immune system,TmGNBP3and TmMyD88 were knocked down by RNAi silencing.Target gene expression levels decreased at 2 d postknockdown and were dramatically reduced at 6 d post-dsRNA injection.Therefore, mealworms were compromised by B.bassiana JEF-007at 6d post-dsRNA injection. Silencing of TmMyD88 and TmGNBP3 resulted in reduced resistance of tilde host to fun- gal infection.Particularly,reducing TmGNBP3 levels obviously downregulated Tenecin 1 and Tenecin 2expression levels,whereas silencing TmMyD88 expression resulted in de- creased Tenecin 2 expression.These results indicate that TmGNBP3 is essential to induce downstream antifungal peptide Tenecin i expression against B.bassiana JEF-007.