An HDG11-mediated transcriptional network regulates 1-deoxynojirimycin biosynthesis in mulberry

1-Deoxynojirimycin (DNJ) is an iminosugar with notable pharmacological properties, and mulberry (Morus spp.) represents the richest natural source of this compound, particularly in young leaves and roots. Despite its tissue-specific distribution, the transcriptional regulatory mechanisms underlying its biosynthesis remain poorly understood. In this study, we integrated transcriptomic profiling, molecular assays, and phytohormone analyses to uncover a multilayered transcriptional network controlling DNJ biosynthesis in mulberry. Weighted gene co-expression network analysis identified a DNJ-associated module (MEblue) that includes 4 potential transcription factors: zinc-finger homeodomain-6 (ZFHD6), HOMEODOMAIN GLABROUS11 (HDG11), TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTOR-14 (TCP14), and ARABIDOPSIS THALIANA HOMEBOX-40 (ATHB40). ZFHD6, TCP14, and ATHB40 directly interacted with and activated the MnGutB1 promoter, a key biosynthetic gene. Although HDG11 did not target MnGutB1 directly, it transcriptionally activated ZFHD6, TCP14, and ATHB40, and formed protein complexes with TCP14 or ATHB40, thereby indirectly promoting DNJ biosynthesis. Furthermore, exogenous application of trans-zeatin riboside or abscisic acid induced HDG11 and MnGutB1 expression, concomitant with elevated DNJ levels. Our findings identify an HDG11-centered regulatory hierarchy that integrates phytohormonal and developmental signals to regulate DNJ biosynthesis, offering insights for metabolic engineering of DNJ production in plants.