Early responses of silkworm midgut to microsporidium infection--A Digital Gene Expression analysis.

Host-pathogen interactions are complex processes, which have been studied extensively in recent years. In insects, the midgut is a vital organ of digestion and nutrient absorption, and also serves as the first physiological and immune barrier against invading pathogenic microorganisms. Our focus is on Nosema bombycis, which is a pathogen of silkworm pebrine and causes great economic losses to the silk industry. A complete understanding of the host response to infection by N. bombycis and the interaction between them is necessary to prevent this disease. Silkworm midgut infected with N. bombycis is a good model to investigate the early host responses to microsporidia infection and the interaction between the silkworm and the microsporidium. Using Digital Gene Expression analysis, we investigated the midgut transcriptome profile of P50 silkworm larvae orally inoculated with N. bombycis. At 6, 12, 18, 24, 48, 72, and 96 h post-infection (hpi), 247, 95, 168, 450, 89, 80, and 773 DEGs were identified, respectively. KEGG pathway analysis showed the influence of N. bombycis infection on many biological processes including folate biosynthesis, spliceosome, nicotinate and nicotinamide metabolism, protein export, protein processing in endoplasmic reticulum, lysosome, biosynthesis of amino acids, ribosome, and RNA degradation. In addition, a number of differentially expressed genes involved in the immune response were identified. Overall, the results of this study provide an understanding of the strategy used by silkworm as a defense against the invasion by N. bombycis. Similar interactions between hosts and pathogens infection may exist in other species.