A Grapevine MYC2-MYB24 Regulatory Module Activates Terpenoid Biosynthesis Upon Methyl Jasmonate Elicitation

Abstract

Terpenes contribute to the characteristic flavor and aroma of grapes and their derived products while serving protective roles in plants against radiation, oxidative stress, and biotic challenges. The phytohormone methyl jasmonate (MeJA) mediates many of these processes and enhances terpene content in grape berries, but its underlying regulatory mechanism remains unclear. To address this, we treated Vitis vinifera cv. Gamay Freaux berry cell suspensions with MeJA (100 M) and cyclodextrins (50 mM), generating transcriptomic data. Upregulated genes (URGs) were enriched in jasmonic acid biosynthesis and signaling pathways, and transcription factors (TF) that represent novel candidates modulating MeJA responses. Inspection of these TFs in terms of their co-expressed genes allowed us to focus on MYC2, the sole bHLH IIIe subgroup member in grapevine. Using DAP-seq, we identified MYC2-bound genes and integrated them with MeJA-URGs and MYC2 co-expressed genes (CEGs) to produce a high-confidence target list. These targets were bound via a conserved G-box motif and included jasmonate-related genes (e.g., LOX and JAZ) and TFs such as MYB24, previously found to interact with MYC2 to activate terpenoid biosynthesis genes. Consistently, MeJA treatment induced 15 terpene synthase genes (TPS), eleven of which were bound by MYB24, MYC2, or both. Terpenoid compounds associated with these induced TPSs accumulated both intra- and extracellularly following treatment with MeJA and cyclodextrins, but not with abscisic acid (ABA). Our findings suggest that MYC2 regulates the jasmonate pathway and cooperates with MYB24 to mediate MeJA-induced terpene biosynthesis, shedding light on mechanisms that may extend to flower and fruit development, where this MYB-bHLH complex is also expressed.