Transcriptome and Coexpression Network Analyses Provide In-Sights into the Molecular Mechanisms of Hydrogen Cyanide Synthesis during Seed Development in Common Vetch ( Vicia sativa L.).

The common vetch ( Vicia sativa L.) seed is an ideal plant-based protein food for humans, but its edible value is mainly limited by the presence of cyanogenic glycosides that hydrolyze to produce toxic hydrogen cyanide (HCN), and the genes that regulate HCN synthesis in common vetch are unknown. In this study, seeds from common vetch at 5, 10, 15, 20, 25, 30, and 35 days after anthesis were sampled, and the seven stages were further divided into five developmental stages, S1, S2, S3, S4, and S5, based on morphological and transcriptome analyses. A total of 16,403 differentially expressed genes were identified in the five developmental stages. The HCN contents of seeds in these five stages were determined by alkaline titration, and weighted gene coexpression network analysis was used to explain the molecular regulatory mechanism of HCN synthesis in common vetch seeds. Eighteen key regulatory genes for HCN synthesis were identified, including the VsGT2 , VsGT17 and CYP71A genes, as well as the VsGT1 gene family. VsGT1 , VsGT2 , VsGT17 and CYP71A jointly promoted HCN synthesis, from 5 to 25 days after anthesis, with VsGT1-1 , VsGT1-4 , VsGT1-11 and VsGT1-14 playing major roles. The HCN synthesis was mainly regulated by VsGT1, from 25 to 35 days after anthesis. As the expression level of VsGT1 decreased, the HCN content no longer increased. In-depth elucidation of seed HCN synthesis lays the foundations for breeding common vetch with low HCN content.