Bombyx mori ER Chaperones Calnexin and Calreticulin Promote BmNPV Infection Through Facilitating GP64 Expression

Calnexin (CNX) and calreticulin (CRT) are two essential endoplasmic reticulum chaperones involved in the folding pathway dedicated to N-glycosylated proteins. The N-glycosylated protein GP64, located in the budded virus envelope of Bombyx mori nucleopolyhedrovirus (BmNPV), plays a key role in viral entry. However, the roles of CNX and CRT in GP64 processing and maturation, as well as in BmNPV infection, remain incompletely understood. In this study, we identified the two genes BmCNX and BmCRT from a B. mori transcriptome database. Spatiotemporal expression profiles showed that BmCNX and BmCRT displayed similar patterns, with expression detected in all tissues and elevated levels in the gonad, trachea, and malpighian tubule, as well as during the egg and larval stages. Following BmNPV infection, the expression of BmCNX and BmCRT was significantly upregulated in both the midgut and BmN cells. Overexpression of BmCNX and BmCRT enhanced BmNPV proliferation and GP64 expression, while knockdown of either gene suppressed both viral proliferation and GP64 expression. Furthermore, GP64 was shown to interact with BmCNX and BmCRT, respectively. These results suggest that BmNPV infection requires both BmCNX and BmCRT to facilitate GP64 expression and promote viral proliferation. This study lays the foundation for further investigation into the roles of endoplasmic reticulum chaperones in response to BmNPV infection.