Chinese sacbrood virus destroys AcPPAN-copper homeostasis to evade phenoloxidase-based antiviral immunity in Apis cerana

The Chinese sacbrood virus (CSBV) poses a serious threat to the Apis cerana, a major plant and crop pollinator. CSBV primarily infects larvae early in their development causing liquefaction of the larval epidermis preventing normal pupation. Bee larvae can resist viral infection through immune responses, with phenoloxidase (PO) being a key link between host cellular and humoral immunity. It is unknown whether host genes can modulate the PO cascade to affect viral replication. Herein, we performed RNA-Seq on CSBV-infected Apis cerana larvae and identify expression of the gene Peter Pan (AcPPAN), the gene had no significant effect on the development of larvae. After silencing AcPPAN, we found that the immune response of the larvae is suppressed and promoted CSBV replication. Subsequently, we fluorescently labeled copper ions in the larval hemolymph and found that AcPPAN responds to CSBV infection and is involved in limiting virus-induced copper accumulation within the hemolymph. Our findings indicate that CSBV promotes viral replication in larvae by suppressing AcPPAN expression, elevating hemolymph copper ion concentration, and inhibiting phenoloxidase-mediated antiviral immune responses. A gene AcPPAN of Apis cerana was identified by transcriptomics and knocking down AcPPAN inhibits the innate immune response of larvae and facilitates viral replication. Knockdown of AcPPAN increased copper concentration in hemolymph. CSBV disrupts the balance of copper ion concentration in hemolymph by inhibiting the expression of AcPPAN, thereby inhibiting the antiviral immune response mediated by phenoloxidase.