A comparison of co-expression networks in silk gland reveals the causes of silk yield increase during silkworm domestication

Abstract

Background Long-term domestication and breeding selection have led to that silk yield of the domestic silkworm (Bombyx mori) have increased several times higher than that of its wild ancestor (B. mandarina). However, little is known about the molecular mechanisms of silk yield increase during silkworm domestication. Results Based on dynamic patterns of functional divergence in silk gland between the domestic and wild silkworms, we found that at early and intermediate stages of silk gland development, the up-regulated genes of the domestic silkworm mainly include DNA integration, nucleic acid binding and transporter activity, which is related to division and growth of cell. This has led to that posterior silk gland (PSG) of the domestic silkworm has significantly more cells (“factories” of fibroin protein synthesis) than that of wild silkworm. At the late stage of silk gland development, the up-regulated genes in the domestic silkworm are enriched in protein processing and ribosome pathways, suggesting that protein synthesis efficiency is greatly improved during silkworm domestication. The synthetic capacity of fibroin proteins of the domestic silkworm has increased, however, the synthetic capacity of sericin proteins has decreased relative to wild silkworm. This reflects that the domestic and wild silkworms have been under different selection pressures. Importantly, we found that the network co-expressed with silk-coding genes for the domestic silkworm is much larger than that for wild silkworm. Furthermore, much more genes co-expressed with silk-coding genes in the domestic silkworm have been subject to artificial selection than those in wild silkworm. Conclusion Our results revealed that increase in silk yield during silkworm domestication is involved in improvement of a biological system which includes not only expansion of “factories” (cells of PSG) of protein synthesis but also high expression of silk-coding genes as well as silk production related genes such as biological energy, transport, and ribosome pathway genes. In addition, a combination of comparative multi-omics and dynamic network biological method used in this study provides a methodology reference for investigation of molecular mechanisms of formation of a complex trait for other domestic animals.

Gene coexpression networks provide deeper insights into sucrose accumulation in sugarcane cultivars

“…Chamaemelum mobile (Tai et al, 2020), Cicer arietinum (Yadav et al, 2019), Oryza sativa (Childs et al, 2011), Bombyx mandarina (Zhou et al, 2020), and also humans (Liao et al, 2020a). The most common strategy applied for studying these biological systems is the construction of a coexpression network, usually employing a WGCNA methodology (Horvath, 2011), followed by an identification of functional modules in the network.…”