Functional dissection of dorsal gene isoforms in Eastern honeybee in response to Ascosphaera apis infection

The Toll pathway primarily responds to fungal and Gram-positive bacterial infections in insects. Dorsal, a nuclear factor of kappa B family member, is activated via the Toll pathway to regulates the expression of antimicrobial peptides (AMPs). We previously found Apis cerana (A. cerana) have two dorsal genes (dorsal1 and dorsal2) and seven splicing isoforms of dorsal1 (RNA9886, RNA9888, RNA9889, RNA9890, RNA9891, ONT.3970.1, and ONT.3970.2). To evaluate the functions of Dorsal isoforms of A. cerana in the immune response to Ascosphaera apis (A. apis) infection, we used RNA interference (RNAi) to silencing dorsal genes and dorsal1 isoforms (RNA9886, RNA9888, RNA9890), and analyzed the expression levels of AMPs in A. apis-infected A. cerana larvae. Down-regulation of abaecin, apidaecin, and defensin1 was specifically induced by dorsal1 knockdown, whereas only defensin1 was down-regulated when RNA9890 was silenced; apidaecin was down y silencing RNA9886, RNA9888, and RNA9890; defensin1 was reduced following the knockdown of RNA9888 and RNA9890. The results indicated that Dorsal and its isoforms collectively regulate the expression of AMPs, maximizing the activation of defense mechanisms against A. apis infection. Our findings provide new insights into the antifungal immune response of honeybees.