The IMD pathway regulates lysozyme-like proteins (LLPs) in the silkmoth Antheraea mylitta

Lysozyme-like proteins (LLPs) are members of the glycoside hydrolase family 22 (CAZY GH22). Unlike conventional c-type lysozymes (EC 3.2.1.17), LLPs lack specific catalytic amino acid residues essential for muramidase activity. Previous reports indicated upregulation of LLPs upon bacterial infection in the wild silkworm, Antheraea mylitta as well as in the domesticated silkworm, Bombyx mori. In the present work, we studied the signaling pathways mediating the production of LLPs using RNA interference-mediated knockdown of Spätzle, Relish and STAT, the key regulators of Toll, IMD (Immune deficiency) and JAK/STAT pathways, respectively. We observed that knockdown of the Relish variant RD1 resulted in reduced expression levels of the ALLP1. We also showed that recombinant LLP has antiviral activity. We infer that LLPs showing both antibacterial and antiviral activity are regulated by the conventional IMD pathway in the silkmoths.