Activating the MYB51 and MYB122 to upregulate the transcription of glucosinolates biosynthesis genes by copper ions in Arabidopsis.

Copper ions (Cu) are key constituents of copper-based antimicrobial compounds (CBACs), which are extensively used in agriculture. Previously, we demonstrated that a low concentration of Cu induced plant defenses associated with callose deposition in Arabidopsis as well as flg22, a microbe-associated molecular pattern (MAMP) peptide. However, the details and differences of the mechanisms between Cu- and flg22-mediated callose deposition remain unclear. Here, we reported that Cu- and flg22-induced defense responses and callose deposition are dependent on AtACS8 and AtACS2/AtACS6, respectively. After the RNA sequencing data were mined, the expression of MYB51, MYB122, CYP79B2/B3 and CYP83B1 implied that a conserved downstream indole glucosinolate (IGS) metabolic pathway is regulated by Cu. In the Cu-induced response, the ethylene biosynthesis rate-limiting gene AtACS8 and the signal transduction pathway were found to be required for Cu-activated MYB51 and MYB122 transcription. Functional redundancy of MYB51 and MYB122, the key regulators of the IGS metabolic pathway, was identified in the Cu-mediated regulation of IGS gene transcription, promotion of callose deposition, and increase in Arabidopsis resistance to bacterial pathogens. Furthermore, IGS genes such as CYP79B2, CYP81F2 and PAD2 were required for Cu-induced callose deposition and defense responses. Our results demonstrate that Cu activates MYB51 and MYB122 through distinct ethylene signal transduction to regulate the IGS metabolic pathway, resulting in an enhanced defense response in Arabidopsis.