Improving sulforaphane content in broccoli sprouts by applying Se: transcriptome profiling and coexpression network analysis provide insights into the mechanistic response

Sulforaphane (SF) is a sulfur (S)-containing isothiocyanate found in cruciferous vegetables and is known for its potent anticancer properties. Broccoli sprouts, in particular, are considered safe and healthy dietary choices due to their high SF content and other beneficial biological activities, such as enhanced metabolite ingestion. The application of selenium (Se) is an excellent approach to enhance the abundance of SF. Previous studies have often focused on gene expression and changes in the synthetic substrates of glucoraphanin (RAA) to explain SF variation in response to Se application. However, the regulatory network and other physiological and biochemical reactions involved in the regulation of SF biosynthesis are poorly understood. In this study, Se-treated broccoli sprouts had higher SF and RAA contents; they increased with increasing Se application. Using RNA-seq in combination with KEGG, GO, phenotypic, and WGCNA analyses, it was observed that not only gene expression was induced but also that glutathione serves as an S donor for SF biosynthesis and acts as an oxidative stress reliever as a result of Se treatment. Additionally, a module related to glucosinolate biosynthesis was identified. Yeast one-hybrid system and dual luciferase reporter assay were utilized. These assays demonstrated the hub transcription factors GATA22, ERF12-like, and MYB108 would directly bind to SUR1 promoter and positively regulate its expression. Our study presents the first global overview of the role of GSH metabolism in response to Se for SF biosynthesis, and provides a novel and valuable gene resource for the molecular breeding of high-SF broccoli.