Lipopolysaccharide Enhances Tanshinone Biosynthesis via a Ca2+-Dependent Manner in Salvia miltiorrhiza Hairy Roots

Tanshinones, the major bioactive components inSalvia miltiorrhizaBunge (Danshen), are synthesized via the mevalonic acid (MVA) pathway or the 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway and the downstream biosynthesis pathway. In this study, the bacterial component lipopolysaccharide (LPS) was utilized as a novel elicitor to induce the wild type hairy roots ofS. miltiorrhiza.HPLC analysis revealed that LPS treatment resulted in a significant accumulation of cryptotanshinone (CT) and dihydrotanshinone I (DTI). qRT-PCR analysis confirmed that biosynthesis genes such asSmAACTandSmHMGSfrom the MVA pathway,SmDXSandSmHDRfrom the MEP pathway, andSmCPS,SmKSLandSmCYP76AH1from the downstream pathway were markedly upregulated by LPS in a time-dependent manner. Furthermore, transcription factorsSmWRKY1 andSmWRKY2, which can activate the expression ofSmDXR,SmDXSandSmCPS, were also increased by LPS. Since Ca2+signaling is essential for the LPS-triggered immune response, Ca2+channel blocker LaCl3and CaM antagonist W-7 were used to investigate the role of Ca2+signaling in tanshinone biosynthesis. HPLC analysis demonstrated that both LaCl3and W-7 diminished LPS-induced tanshinone accumulation. The downstream biosynthesis genes includingSmCPSandSmCYP76AH1were especially regulated by Ca2+signaling. To summarize, LPS enhances tanshinone biosynthesis throughSmWRKY1- andSmWRKY2-regulated pathways relying on Ca2+signaling. Ca2+signal transduction plays a key role in regulating tanshinone biosynthesis inS. miltiorrhiza.Keywords:lipopolysaccharide;tanshinones;Ca2+signaling;SmWRKY