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Plant JASMONATE ZIM‐DOMAIN (JAZ) genes play crucial roles in regulating the biosynthesis of specialized metabolites and stressful responses. However, understanding of JAZs controlling these biological processes lags due to numerous JAZ copies. Here, we found that two leaf‐specific CwJAZ4/9 genes from Curcuma wenyujin are strongly induced by methyl‐jasmonate (MeJA) and negatively correlated with terpenoid biosynthesis. Yeast two‐hybrid, luciferase complementation imaging and in vitro pull‐down assays confirmed that CwJAZ4/9 proteins interact with CwMYC2 to form the CwJAZ4/9‐CwMYC2 regulatory cascade. Furthermore, transgenic hairy roots showed that CwJAZ4/9 acts as repressors of MeJA‐induced terpenoid biosynthesis by inhibiting the terpenoid pathway and jasmonate response, thus reducing terpenoid accumulation. In addition, we revealed that CwJAZ4/9 decreases salt sensitivity and sustains the growth of hairy roots under salt stress by suppressing the salt‐mediated jasmonate responses. Transcriptome analysis for MeJA‐mediated transgenic hairy root lines further confirmed that CwJAZ4/9 negatively regulates the terpenoid pathway genes and massively alters the expression of genes related to salt stress signaling and responses, and crosstalks of multiple phytohormones. Altogether, our results establish a genetic framework to understand how CwJAZ4/9 inhibits terpenoid biosynthesis and confers salt tolerance, which provides a potential strategy for producing high‐value pharmaceutical terpenoids and improving resistant C. wenyujin varieties by a genetic approach. Summary statement: CwJAZ4/9 interacts with CwMYC2 and negatively regulates MeJA‐induced terpenoid biosynthesis by inhibiting jasmonate response in Curcuma wenyujin. Meanwhile, CwJAZ4/9 can confer salt tolerance and sustain hairy root growth by weakening the salt‐mediated JA response and upregulating the expression of stress‐responsive genes. [ABSTRACT FROM AUTHOR]