Spz4 Plays an Important Role in Regulating the Production of Antimicrobial Peptides in Response to and Infections.

Spätzle family proteins activate the Toll pathway and induce antimicrobial peptide (AMP) production against microbial infections. However, the functional importance of spätzle4 () in the immune response of has not been reported. Therefore, here, we have identified and functionally characterized the role of against bacterial and fungal infections. We showed that expression was significantly induced in hemocytes at 6 h post-injection with , , and . knock-down significantly reduced larval survival against and To understand the reason for the survivability difference, the role of in AMP production was examined in -silenced larvae following microbe injection. The AMPs that are active against Gram-negative bacteria, including , , , , and , were significantly downregulated in response to in -silenced larvae. Similarly, the expression of , , and , , , and were downregulated in response to in -silenced larvae. In addition, the transcription factor NF-κB ( and expression was significantly suppression in -silenced larvae. In conclusion, these results suggest that plays a key role in regulating immune responses of against to and .