Artificial selection on cis-element of Abl contributes cocoon yield increase in domestic silkworm

<p><span>The silkworm (</span><em><span>Bombyx mori</span></em><span>) is an important silk-producing domestic insect.</span><span> The quality and yield of the silk produced by <em>B. mori </em>exceeds that of its ancestor, the wild silkworm <em>B. mandarina</em>. However, to date little is known about the molecular mechanisms underlying domestication-related increases in silk yield. Here, we identified a gene associated with both domestication and silk-related quantitative trait locus (QTL): Abelson tyrosine protein kinase (<em>Abl</em>). </span><span>Population genomic data for <em>B. mori</em> and <em>B. mandarina</em> identified obvious signatures of artificial selection in the genomic region bearing the <em>Abl</em></span><span><em> </em>gene. T</span><span>here were two fixed nucleotide substitutions (−244 and −1311) in the </span><span>tran</span><span>scription factor binding motif of the upstream regulatory region of <em>B. mori Abl</em>.</span> <span>Compared to <em>Abl </em>in the wild silkworm <em>B. mandarina</em>, <em>B. mori Abl</em> exhibited significantly greater promoter activity and was upregulated in the silk gland from the last day of the 5^th larval instar to pupal stage (P0). Compared to the wild type, CRISPR/Cas9-generated <em>Abl </em>loss-of-function mutants </span><span>exhibited a higher sensitivity to diseases, shorter developmental duration, and reductions in economically important silk traits, including cocoon weight, pupal weight, and cocoon layer thickness. Comparison of silk-gland transcriptomes between the wild type and the mutant indicated that genes enriched in ribosome biosynthesis, splicing, RNA transport, and the carbon metabolism were significantly downregulated in the mutants. Weighted gene co-expression network analysis (WGCNA) confirmed that genes related to ribosome biosynthesis were pivotal, driving the significant differentiation in silk yield between <em>B. mori</em> and <em>B. mandarina</em>. Here, we demonstrated that artificial selection acts on the cis-elements of silk-trait QTL gene <em>Abl </em>in a novel case (the domestic silkworm), and that this selection pressure increased <em>Abl </em>promoter activity and expression level. By promoting protein translation and synthesis, artificial selection further enhanced the robustness of silkworm larvae and improved cocoon silk synthesis.</span></p>