Activation of BmToll9-1 in Silkworm (Bombyx mori) Larval Midgut by Escherichia coli and Regulation of Growth

Insects rely on their innate immune system to defend against pathogens, and the Toll signaling pathway plays an important role in immune regulation. Our previous studies have shown that <i>BmToll9-1</i> functions as a positive regulator in the Toll pathway. This study seeks to elucidate the role of <i>BmToll9-1</i>, as a sensor to bacterial challenge, in modulating larval development and downstream Toll signaling pathways. Silkworm larvae were subjected to infection with either Gram-negative <i>Escherichia coli</i> or Gram-positive <i>Staphylococcus aureus</i> bacteria following silencing of <i>BmToll9-1</i> by RNA interference (RNAi). This bacterial challenge triggered a compensatory re-induction of <i>BmToll9-1</i> expression, which resulted in the recovery of larval weight and size to levels observed in untreated controls. Furthermore, upon bacterial infection of <i>BmToll9-1</i>-silenced larvae, there was an up-regulation in the expression of both signaling genes in the Toll pathway and downstream effector genes, with a marked preference for Gram-negative bacteria. These results highlight the involvement of <i>BmToll9-1</i> in the Toll signaling pathway as a positive regulator, influencing silkworm development. Additionally, <i>BmToll9-1</i> and <i>BmToll9-2</i> were cross-validated to be genetically distinct genes, even though they were confirmed to be functionally analogous in the silkworm.