Transcriptome Analysis Reveals How Melatonin Regulates Glucoraphanin and Sulforaphane by Mediating Hormone Signaling in Hairy Roots of Broccoli

Sulforaphane (SF), the degradation product of glucoraphanin (GRA), can exhibit anticancer properties. In this study, the detection via high-performance liquid chromatography (HPLC) showed that the content of GRA and SF were increased in hairy roots of broccoli following their exogenous melatonin (MT) treatment. To explore the molecular mechanisms by which MT regulates the GRA and SF contents, gene expression profiles were investigated by transcriptome sequencing applied to the MT-treated hairy roots of broccoli. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed that the 'plant hormone signaling transduction' pathway strongly responded the MT treatment and the expression patterning of these differentially expressed genes (DEGs) was related to the biosynthesis of four phytohormones: jasmonic acid (JA), salicylic acid (SA), ethylene (ETH), and abscisic acid (ABA), which entailed pronounced up- or downregulation. Furthermore, the respective content of JA, SA, ETH, and ABA was detected by enzyme-linked immunosorbent assay (ELISA); these results confirmed the four phytohormones were promoted by the MT treatment at 6 and 12 h in comparison with 0 h. Taken together, this study could provide a theoretical basis for the complex molecular mechanism through which MT regulates secondary metabolites by mediating plant hormone signal transduction in plants.

Automated summary

Exogenous melatonin treatment increased the content of glucoraphanin and sulforaphane in broccoli roots, with transcriptome sequencing revealing a strong response in the plant hormone signaling transduction pathway. Enzyme-linked immunosorbent assay confirmed the promotion of four phytohormones by the melatonin treatment. This study provides a theoretical basis for understanding the complex molecular mechanism by which melatonin regulates secondary metabolites through mediating plant hormone signal transduction.