Bombyx mori β-1,3-Glucan Recognition Protein 4 (BmβGRP4) Could Inhibit the Proliferation of B. mori Nucleopolyhedrovirus through Promoting Apoptosis

Abstract

β-1,3-glucan recognition proteins (βGRPs) as pattern recognition receptors (PRRs) play an important role in recognizing various pathogens and trigger complicated signaling pathways in insects. In this study, we identified a <i>Bombyx mori</i> β-1,3-glucan recognition protein gene named <i>BmβGRP4</i>, which showed differential expression, from a previous transcriptome database. The full-length cDNA sequence was 1244 bp, containing an open reading frame (ORF) of 1128 bp encoding 375 amino acids. <i>BmβGRP4</i> was strongly expressed in the larval stages and highly expressed in the midgut of <i>B. mori</i> larvae in particular. After BmNPV infection, the expression of <i>BmβGRP4</i> was reduced significantly in the midgut. Furthermore, a significant increase in the copy number of BmNPV was observed after the knockdown of <i>BmβGRP4</i> in 5th instar larvae, while the overexpression of <i>BmβGRP4</i> suppressed the proliferation of BmNPV in BmN cells. Subsequently, the expression analysis of several apoptosis-related genes and observation of the apoptosis morphology demonstrated that overexpression of <i>BmβGRP4</i> facilitated apoptosis induced by BmNPV in BmN cells. Moreover, <i>BmβGRP4</i> positively regulated the phosphatase and tensin homolog gene (<i>BmPTEN</i>), while expression of the inhibitor of apoptosis gene (<i>BmIAP</i>) was negatively regulated by BmβGRP4. Hence, we hypothesize that BmNPV infection might suppress <i>BmPTEN</i> and facilitate <i>BmIAP</i> to inhibit cell apoptosis by downregulating the expression of <i>BmβGRP4</i> to escape host antiviral defense. Taken together, these results show that <i>BmβGRP4</i> may play a role in <i>B. mori</i> response to BmNPV infection and lay a foundation for studying its functions.