Transcriptome analysis of molting variation in dominant trimolter silkworms, Bombyx mori

The silkworm (Bombyx mori) is a holometabolous insect economically vital for silk production. The trimolter silkworms have garnered significant interest among sericulturists owing to their superior filament fineness, shorter larval duration, and reduced labor inputs. These traits render the trimolters suitable for diversified raw silk manufacturing. However, some individuals from the same trimolter strains may undergo an additional molt and thus become tetramolter silkworms. The cause of this change is unclear and thus was the focus of this study. Specifically, we investigated 'Guangri 3', a stable bivoltine trimolter strain with some individuals occasionally exhibiting increased molting. In this study, 'Guangri 3' trimolter silkworms were reared under natural conditions in spring (25°C, Group A) and autumn (30°C, Group B) seasonal conditions. Group A consisted of normal trimolters (TA) and tetramolter variants (FA), while Group B included normal trimolters (TB) and tetramolter variants (FB). Statistical analysis revealed that the variation incidence of FA was 1.10% and 16.10% of FB. Subsequently, RNA-seq analysis was performed on these groups. Results showed that 1044 genes were upregulated and 846 were downregulated in differentially expressed genes (DEGs) from FA vs. TA comparison, while 808 were found upregulated and 707 were downregulated in those from FB vs. TB comparison. GO and KEGG enrichment analyses of DEGs revealed shared pathways related to insect moltinism, such as chitin catabolism. By analyzing the intersection of these DEGs, we identified 17 consistently upregulated and 22 consistently downregulated genes as high-priority candidates. Within these pathways, multiple key gene families were identified, including CYP, CPR, and Rp. Additionally, from the protein-protein interaction (PPI) network analysis of the DEGs from FB vs. TB comparison, potential hub genes like Hsp83, were identified. Their potential role in altered moltinism under the autumn rearing conditions warrants further investigation.