The transcription factor CiMYC2 positively regulates terpenoid biosynthesis by activating the expression of CiHMGR and CiTPS4 in Chrysanthemum indicum var. aromaticum.

Abstract

Chrysanthemum indicum var. aromaticum is a rare aromatic variant, and deciphering its molecular basis could facilitate the breeding of scented chrysanthemums. Here, we introduced its transcription factor CiMYC2 into Chrysanthemum indicum (C. indicum) to investigate the role and mechanism of CiMYC2 in regulating terpenoid biosynthesis. Results demonstrated that overexpression of CiMYC2 significantly increased the density of glandular trichomes on leaves (up to 3.94-fold) and elevated the total relative terpenoid content in leaf exudates by up to 21.88%. Transcriptomic analysis revealed strong upregulation of key terpenoid pathway genes, including CiHMGR and CiTPS4, and their induction was confirmed by quantitative real-time PCR, with CiTPS4 expression increasing up to 22.58-fold. Yeast one-hybrid (Y1H) and dual-luciferase (dual-LUC) assays confirmed that CiMYC2 directly bound to enhancer box (E-box) elements in the promoters of CiHMGR and CiTPS4 to activate their transcription. Furthermore, yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BIFC) assays showed that CiMYC2 physically interacted with specific jasmonic acid (JA) signaling repressors CiJAZ4/5/7/8. Our findings reveal that the transcription factor CiMYC2 integrates JA signaling by interacting with CiJAZ proteins and directly activates terpenoid biosynthetic genes (CiHMGR and CiTPS4), thereby promoting glandular trichome development and terpenoid accumulation in C. indicum. This work provides a theoretical basis for the molecular breeding of fragrant chrysanthemum varieties.