SmbZIP5 Integrates Abscisic and Jasmonic Acid Signalling to Positively Regulate Tanshinone Biosynthesis in Salvia miltiorrhiza

Salvia miltiorrhiza produces pharmacologically bioactive diterpenoid tanshinones which are regulated by jasmonate (JA) and abscisic acid (ABA) signalling, while their crosstalk in this process remains unclear. Here, we demonstrated that MeJA and ABA acted synergistically to enhance tanshinone biosynthesis. We reported that a novel bZIP transcription factor, SmbZIP5, was involved in ABA- and JA-induced tanshinone biosynthesis. ABA-activated SmSnRK2.6 kinase phosphorylated SmbZIP5 at four residues (S33, S127, S129, T171), enhancing its stability and transactivation activity. Conversely, the JA signalling repressor SmJAZ9 physically interacted with SmbZIP5, suppressing its transactivation activity. Overexpression of SmbZIP5 enhanced the tanshinone production and biosynthetic genes expression, while knockout of SmbZIP5 abolished ABA- and MeJA-induced tanshinone accumulation. Moreover, SmbZIP5 directly bound to the ABA-responsive element (ABRE) in the promoter of SmGGPPS1 and CYP76AK1. These findings suggest that a SnRK2-bZIP-JAZ regulatory module integrates ABA and JA signalling to coordinately activate tanshinone biosynthesis, providing novel insights into phytohormone crosstalk and a potential strategy for metabolic engineering in S. miltiorrhiza.