BoMyrosinase plays an essential role in sulforaphane accumulation in response to selenite treatment in broccoli

Sulforaphane, a naturally specialized metabolite, plays significant roles in human disease prevention and plant defense. Myrosinase (MY) is a key gene responsible for the catalysis of sulforaphane formation, but the molecular mechanisms through which MY regulates sulforaphane biosynthesis in plants remains largely unknown. Here, we discovered that the change of sulforaphane content in broccoli sprouts caused by exogenous selenite treatments is positively related to BoMY expression. BoMY overexpression in the Arabidopsis thaliana tgg1 mutants could dramatically increase myrosinase activity and sulforaphane content in the rosette leaves of 35S::BoMY/tgg1 and rescue its phenotypes. Moreover, an obvious increase of myrosinase activity and sulforaphane content was displayed in transgenic BoMY-overexpressed broccoli lines. In addition, a 2 033 bp promoter fragment of BoMY was isolated. Yeast one-hybrid (Y1H) library screening experiment uncovered that one bHLH transcription factor, BoFAMA, could directly bind to BoMY promoter to activate its expression, which was further evidenced by Y1H assay and dual-luciferase reporter assay. BoFAMA is a selenite-responsive transcription factor that is highly expressed in broccoli leaves; its protein is solely localized to nucleus. Additionally, genetic evidence suggested that the knockdown of FAMA gene in Arabidopsis thaliana could significantly decrease sulforaphane yield by inhibiting the expression of myrosinase genes. Interestingly, exogenous selenite supply could partially restore the low level of sulforaphane content in transgenic Arabidopsis FAMA-silencing plants. Our findings uncover a novel function of FAMA-MY module in the regulation of selenite-mediated sulforaphane synthesis and provide a new insights into the molecular mechanism by which selenite regulates the accumulation of sulforaphane in plants.