A Toll-Spätzle Pathway in the Immune Response of Bombyx mori

Abstract

The Toll-Spätzle pathway is a crucial defense mechanism in insect innate immunity, it plays an important role in fighting against pathogens through the regulation of antimicrobial peptide gene expression. Although <i>Toll</i> and <i>Spätzle</i> (<i>Spz</i>) genes have been identified in <i>Bombyx mori</i>, little is known regarding the specific <i>Spz</i> and <i>Toll</i> genes members involved in innate immunity. There is also limited direct evidence of the interaction between Spz and Toll. In this study, the dual-luciferase reporter assay results showed that BmToll11 and BmToll9-1 could activate both <i>drosomycin</i> and <i>diptericin</i> promoters in S2 cells. Furthermore, <i>BmToll11</i>, <i>BmToll9-1</i>, and five <i>BmSpzs</i> genes were found to be significantly upregulated in <i>B. mori</i> infected by <i>Escherichia coli</i> and <i>Staphylococcus aureus</i>. Additionally, the yeast two-hybrid assay results confirmed that BmSpz2, but not other BmSpzs, could interact with both BmToll11 and BmToll9-1. These findings suggest that the activated BmSpz2 can bind with BmToll11 and BmToll9-1 to induce the expression of AMPs after the silkworm is infected by pathogens.