Abstract: As the frontline encountering various microbes, intestine plays critical roles in insect immune responses. In order to investigate the immune responses in the silkworm midgut, we identified 18 differentially expressed genes after oral infection by Pseudomonas aeruginosa and Staphylococcus aureus using annealing control primer (ACP) based reverse transcriptional PCR technique. The expression profile of four genes during the first 24 hours post infection was monitored by quantitative real-time PCR. The results showed that the peptidoglycan recognition protein L1 (PGRP-L1) gene and a serine protease precursor gene were up-regulated by P. aeruginosa infection exclusively, while the 30kP protease A precursor gene was up-regulated significantly by both P. aeruginosa and S. aureus infection. Our study identified genes involved in recognition of invading bacteria and immune signaling pathways in the larval midgut of the silkworm after oral infection and may give some clues for further functional investigation of these genes.

Key words: Bombyx mori, midgut, bacterial infection, immune response, differentially expressed gene