Comparative analysis of iTRAQ-based proteomes for cocoons between the domestic silkworm (Bombyx mori) and wild silkworm (Bombyx mandarina)

The domestic silkworm Bombyx mori was domesticated from wild silkworm B. mandarina about 5000 years ago. Long-term domestication and breeding selection have led to the weight of domestic silkworm cocoon being ten times greater than that of wild silkworm cocoon. However, we found that wild silkworm cocoon has significantly much more abundance of sericin proteins than domestic silkworm cocoon. Strikingly, we found that many protease inhibitors have been significantly down-regulated in domestic silkworm cocoon compared with its wild progenitor by using isobaric tag for relative and absolute quantitation (iTraq) approach. Both real-time qPCR experiment and transcriptome data in silk gland also verified these results. In addition, our data indicated that protease inhibitor activity of wild silkworm cocoon was stronger than that of domestic silkworm cocoon, implying that relatively up-regulated protease inhibitors in wild silkworm cocoon may play protection roles against microorganisms. Thus, these protease inhibitors up-regulated in wild silkworm cocoon may have potential values in sericulture and medical practice.This study revealed that there is a big difference in abundance of sericin proteins in cocoon between domestic and wild silkworms. Strikingly, many protease inhibitors have been significantly down-regulated in domestic silkworm cocoon compared with its wild progenitor. This may be due to different environments where the two silkworms live. In addition, the results also implied that relatively up-regulated protease inhibitors in wild silkworm cocoon may play protection roles against microorganisms. Thus, these protease inhibitors may have potential values in sericulture and medical practice.