Mutation in Bombyx mori sericin5 gene alters silk gland growth and protein components and results in decreased secretion and performance of silk fiber

Abstract Insects spin non‐cocoon silk for protection, adhesion, and transfer with the environment. Sericin is a major component of non‐cocoon silk fibers, yet our understanding of the sericin proteins is quite limited. In this study, we used CRISPR/Cas9‐mediated gene editing to prepare a homozygous mutant strain that resulted in premature termination of the translation of non‐cocoon sericin protein Ser5. We found that the silk glands of the Ser5 mutant ( Ser5 −/− ) were smaller than those of the wild‐type (WT), and both silk yield and major silk proteins significantly decreased in the larval stage. Seven kinds of non‐cocoon silk were collected, and we found that the morphology of silk did not vary, but the diameter of the silk was significantly reduced in Ser5 −/− . Further research revealed that the adhesive strength of native silk dope in Ser5 −/− was significantly lower than that of the WT silkworm. Proteomic data indicated that the autophagy and apoptosis proteins increased significantly in Ser5 −/− ; differentially expressed proteins were enriched in pathways related to cellular stress responses and transcription and translation. Detection of the autophagy‐related gene ATG8 also indicated that knockout of the Ser5 gene may lead to a level of cell stress, thus affecting the synthesis and secretion of silk proteins. Our study highlights the importance of the silk sericin gene in silk formation, silk protein adhesion, and the cellular developmental processes of the silkworm. These findings enhance our understanding of the functional roles of sericin genes in insects and provide a foundation for the development of sericin‐based biomaterials.