Silencing of the immune gene BmPGRP‐L4 in the midgut affects the growth of silkworm (Bombyx mori) larvae

• Published in: Insect molecular biology 2023-08, Vol.32 (4), p.340-351
• Main Authors: Liang, Yebin, Wang, Tao, Yang, Weiyi, Chen, Zemin, Li, Qingrong, Swevers, Luc, Liu, Jisheng
• Format: Article
• Language: English
• Subjects: Amidase; Amino Acid Sequence; Animals; bacterial challenge; BmPGRP‐L4; Bombyx - metabolism; Bombyx mori; E coli; Epidermis; Fat body; Immune response; Immune system; Insect Proteins - metabolism; Insects; Larva; Larvae; Midgut; Oral infection; Peptidoglycan recognition proteins; RNA-mediated interference; RNAi; Silk; Silk gland; Silkworms; Weight reduction
• ISSN: 0962-1075; 1365-2583
• DOI: 10.1111/imb.12834

Peptidoglycan recognition proteins (PGRPs) are one of the receptors in insects' immune pathways, essential for insects to recognize the exogenous pathogens in order to activate the Toll and immune deficiency (IMD) pathway. In the silkworm Bombyx mori, previous studies focused on the short PGRPs and less is known about the long PGRPs. In this study, a long PGRP in silkworm BmPGRP‐L4 was cloned and its expression and function were analysed. The results showed that BmPGRP‐L4 contains a transmembrane region, a conserved PGRP domain, and an amidase‐2 domain. The expression profile demonstrated that BmPGRP‐L4 existed in diverse tissues including epidermis, fat body, midgut, and silk glands, with remarkably high expression in the midgut in the 5th instar. Oral infection with Escherichia coli and Staphylococcus aureus significantly induced BmPGRP‐L4 in the midgut and epidermis, as well as in the fat body and silk glands. Peptidoglycan also induced the expression of BmPGRP‐L4 in midgut tissue ex vivo and BmN4 cells in vitro. RNAi of BmPGRP‐L4 was effective in the midgut and epidermis, while the efficiency in the fat body was transient. RNAi‐mediated knock‐down of BmPGRP‐L4 reduced the weight and growth of the silkworm, possibly due to its participation in the immune response and the regulation of the microbiota in the midgut lumen of the silkworm larvae. Predominant expression of BmPGRP‐L4 in the midgut of the 5th instar silkworm larvae. Up‐regulation of BmPGRP‐L4 to bacterial infection in vivo or PGN ex vivo and in vitro. RNAi‐mediated knock‐down of BmPGRP‐L4 reduced the weight and growth of the silkworm larvae.