Selenomethionine regulates flavonoid biosynthesis through the BroMYB34–BroCHSs module in kale (Brassica oleracea var. acephala)

Kale is a super vegetable that is rich in a variety of nutrients and has antioxidant and anti-cancer properties. Selenomethionine (SeMet) is a type of organic selenium compound that enhances fruit quality; however, there is a lack of research on its application in kale. The study identified 10 mg·L−1 as the optimal SeMet concentration for kale, and selenium gradually accumulated after SeMet treatment, which significantly improved the antioxidant capacity of kale. Metabolome and transcriptome analysis of exogenous SeMet in kale revealed flavonoids as the main differential metabolites, and differential genes were most significantly enriched in flavonoid-related pathways. In addition, SeMet significantly induced the expression of MYB-type transcription factor BroMYB34. BroMYB34 binds to the BroCHSs promoter, a key gene for flavonoid synthesis, to activate its transcription. Transient overexpression of BroMYB34 could significantly increase the expression of BroT26.C02gCHS, BroT26.C03gCHS3, and BroT26. C09gCHS3 stimulates flavonoid synthesis to enhance the antioxidant capacity of kale. Overall, the findings of this study preliminarily reveal the molecular mechanism of SeMet promoting flavonoid biosynthesis of kale seedlings.