Comparative Proteomic Analysis of Posterior Silk Glands of Wild and Domesticated Silkworms Reveals Functional Evolution during Domestication

The wild silkworm Bombyx mandarina was domesticated to produce silk in China approximately 5000 years ago. Silk production is greatly improved in the domesticated silkworm B. mori, but the molecular basis of the functional evolution of silk gland remains elusive. We performed shotgun proteomics with label-free quantification analysis and identified 1012 and 822 proteins from the posterior silk glands (PSGs) of wild silkworms on the third and fifth days of the fifth instar, respectively, with 128 of these differentially expressed. Bioinformatics analysis revealed that, with the development of the PSG, the up-regulated proteins were mainly involved in the ribosome pathway, similar to what we previously reported for B. mori. Additionally, we screened 50 proteins with differential expression between wild and domesticated silkworms that might be involved in domestication at the two stages. Interestingly, the up-regulated proteins in domesticated compared to wild silkworms were enriched in the ribosome pathway, which is closely related to cell size and translation capacity. Together, these results suggest that functional evolution of the PSG during domestication was driven by reinforcing the advantageous pathways to increase the synthesis efficiency of silk proteins in each cell and thereby improve silk yield.