Transcriptome analysis of the response of silkworm to drastic changes in ambient temperature

Bombyx mori is a poikilothermic insect and is economically important for silk production. Drastic changes in the ambient temperature have a negative impact on sericulture. However, the reason as to why high temperature is associated with the occurrence of diseases in silkworm and the response of silkworm to low temperature remain unclear and were the focus of the present study. Dazao silkworm exposed to 13 degrees C (DZ-13), 25 degrees C (DZ-25), and 37 degrees C (DZ-37) were used for RNA-seq analysis. There were 478 and 194 upregulated differentially expressed genes (DEGs) in DZ-13 and DZ-37 while 49 and 273 downregulated DEGs in DZ-13 and DZ-37, respectively. Eight DEGs were co-upregulated, in which seven genes were for heat shock proteins (Hsps), implying that Hsps play important roles in the tolerance of silkworm to high and low temperature. Gene ontology analysis revealed that the developmental process was downregulated in DZ-13. All the DEGs in the oxidative phosphorylation and insulin signaling pathways were upregulated in DZ-13. Several cuticular proteins and ATP synthesis-related genes were upregulated in DZ-13, suggesting that thickening of the cuticle and increase in the ATPase expression would help silkworms to protect themselves from low temperature-induced stress. Several immune-related genes, such as BmRel and BmSerpin-2, were downregulated in DZ-37, revealing that the resistance of silkworm is decreased under high temperature shock resulting in susceptibility to pathogens. Thus, the increase in the thermo-tolerance of silkworm should be related to the enhancement in the pathogen resistance.