| Summary: | Although smoke-isolated karrikins (KAR<sub>1</sub>) could regulate secondary metabolism in medicinal plants, the signal transduction mechanism has not been reported. This study highlights the influence of KAR<sub>1</sub> on tanshinone I (T-I) production in <i>Salvia miltiorrhiza</i> and the involved signal molecules. Results showed KAR<sub>1</sub>-induced generation of nitric oxide (NO), jasmonic acid (JA) and T-I in <i>S. miltiorrhiza</i> hairy root. KAR<sub>1</sub>-induced increase of T-I was suppressed by NO-specific scavenger (cPTIO) and NOS inhibitors (PBITU); JA synthesis inhibitor (SHAM) and JA synthesis inhibitor (PrGall), which indicated that NO and JA play essential roles in KAR<sub>1</sub>-induced T-I. NO inhibitors inhibited KAR<sub>1</sub>-induced generation of NO and JA, suggesting NO was located upstream of JA signal pathway. NO-induced T-I production was inhibited by SHAM and PrGall, implying JA participated in transmitting signal NO to T-I accumulation. In other words, NO mediated the KAR<sub>1</sub>-induced T-I production through a JA-dependent signaling pathway. The results helped us understand the signal transduction mechanism involved in KAR<sub>1</sub>-induced T-I production and provided helpful information for the production of <i>S. miltiorrhiza</i> hairy root.
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