Broad-Complex Mediates 20-Hydroxyecdysone-Induced Antimicrobial Peptide Expression in the Silkworm Bombyx mori

Abstract

Simple Summary Silkworms are vulnerable to bacterial infections, but how hormones help them fight these infections remains poorly understood. In this study, we investigated whether 20-hydroxyecdysone, a hormone that controls insect growth and development, also strengthens the natural immune defenses of silkworms. We found that treating silkworm larvae with this hormone before bacterial infection improved their survival and helped them eliminate bacteria more rapidly. The hormone also increased the activity of several genes responsible for producing antimicrobial peptides, small proteins that help defend against harmful microbes. Further experiments revealed that a protein called Broad-Complex plays an important role in activating these immune defense genes. Different forms of this protein regulated different genes, and a newly identified form, although unable to activate genes on its own, significantly enhanced the activity of other forms in promoting the expression of a specific antimicrobial peptide gene. These findings reveal a previously unknown mechanism linking insect development hormones to immune defense and provide new insights into how silkworms protect themselves against bacterial infections. This knowledge may contribute to future strategies for improving silkworm health and disease resistance.