A tetraspanin from domestic silkworm could inhibit the proliferation of Bombyx mori nucleopolyhedrovirus (BmNPV) by participating in the autophagy pathway

The domestic silkworm (Bombyx mori:Linnaeus) is one of the most important economic insects, occupying a significant position in the silk industry and trade. Autophagy is a process of cell self-degradation and recycling. It plays important functions in maintaining cell homeostasis, adapting to starvation and nutritional deficiencies, resisting infections and pathogens, participating in cell development, and regulating cell death. Tetraspanins play key roles in regulating autophagy, viral recognition and entry, and promoting membrane fusion. In this study, we performed bioinformatics analysis on the B. mori gene BmTsp.D and determined it encodes a novel tetraspanin. The expression profiles ascertained that BmTsp.D was highly expressed in the midgut and its transcription was dramatically increased after infection with B. mori nucleopolyhedrovirus (BmNPV). Through immunofluorescence localization, we found that BmTsp.D was mainly distributed in the cell membrane. Overexpression and siRNA-mediated knockdown showed that BmTsp.D was able to inhibit viral proliferation. Overexpression assay indicated BmTsp.D could upregulate the transcription of autophagy pathway-related genes and this was also confirmed by observations of autophagosomes and detection of ATG8/ATG8-PE. Moreover, rescue experiment with 3-methyladenine (3-MA) suggests that BmTsp.D may inhibit the proliferation of BmNPV by regulating the autophagy pathway. Furthermore, bimolecular fluorescence complementation (BiFC) results indicated that there may be a potential interaction between BmTsp.D and BmTsp.B. In total, our results provide a preliminary exploration of the effect of the BmTsp.D gene on viral invasion and reveal its regulatory role in the autophagy signaling pathway. The above results may lay the foundation for subsequent investigation of interaction mechanism between BmNPV and host silkworm, and provide a potential target for breeding antiviral silkworm strains and developing viral control strategies.