Abstract MEDIATOR 25 (MED25) is a key component of the universally conserved multi-subunit mediator complex. In plants, MED25 regulates diverse biological processes, including flowering, seed germination, cell proliferation, defense responses, and phytohormone signaling, largely through interactions with transcription factors. However, its role in specialized metabolism remains poorly understood. MED25 is a crucial component of the jasmonate (JA) signaling pathway, and JA is a major elicitor of specialized metabolites such as terpenoid indole alkaloids (TIAs) in Madagascar periwinkle (Catharanthus roseus) and flavonoids in Arabidopsis (Arabidopsis thaliana). Using C. roseus and Arabidopsis as models, we investigated the regulatory role of MED25 in these two distinct metabolic pathways. RNAi-mediated silencing of CrMED25 in C. roseus hairy roots significantly altered the expression of TIA biosynthetic genes and reduced TIA accumulation. We demonstrated that CrMED25 interacts with CrMYC2 and C. roseus jasmonate ZIM domain 1 (CrJAZ1), key regulators of the TIA pathway. Additionally, CrMED25 silencing suppressed the expression of flavonoid pathway genes in C. roseus hairy roots and flowers. Parallel analysis in Arabidopsis showed that the med25 mutant exhibited strong repression of flavonoid pathway genes and regulators. Protein–protein interaction assays revealed that AtMED25 interacts with GLABRA3 (GL3), MYB12, and MYB111, well-established regulators of flavonoid biosynthesis. These findings establish MED25 as a conserved co-activator of specialized metabolism, integrating JA signaling with transcriptional programs governing alkaloid and flavonoid biosynthesis. This work uncovers a previously unrecognized regulatory role of MED25 and highlights molecular entry points for engineering pharmaceutically important plant metabolites.
Singleton et al. (Tue,) studied this question.