Sarocladium kiliense DF2 enhances tanshinone biosynthesis in Salvia miltiorrhiza roots via salicylic acid signaling

Salvia miltiorrhiza is a commercially important medicinal plant, prized for its roots which accumulate abundant tanshinones—lipophilic diterpenoids with broad pharmaceutical applications. While endophytic fungi are known to influence plant secondary metabolism, the underlying hormonal mechanisms remain poorly understood. This study investigated the role of the endophytic fungus Sarocladium killense DF2 in modulating tanshinone biosynthesis via hormonal signaling pathways in S. miltiorrhiza . We analyzed tanshinone content, salicylic acid (SA) levels, and gene expression in DF2-treated seedling, and employed SA pathway modulators to validate the mechanism. Results showed that DF2 inoculation increased primary root thickness by 2.42-fold, and strongly promoted tanshinones accumulation, with dihydrotanshinone and tanshinone IIA levels rising by 3.08-fold and 7.3-fold, respectively. SA content in roots also significantly increased, peaking at 237 pmol/L at week4—1.76 times that of controls. qRT-PCR analysis indicated that DF2 upregulated of both SA biosynthesis genes and key tanshinone biosynthetic genes, including GGPPS, CPS, KSL, CYP76AH1, CYP76AK1, and CYP76AH3 . Critically, pharmacological inhibition of SA synthesis with paclobutrazol (PAC) abolished DF2-induced tanshinone production, confirming SA signaling as the essential mediator of this plant-fungal interaction. Our findings not only reveal a novel SA-dependent mechanism in plant-fungal symbiosis, but also position DF2 as a promising microbial inoculant for sustainable enhancing tanshinone yield in S. miltiorrhiza cultivation. • Sarocladium kiliense DF2 enhances tanshinones in S . miltiorrhiza by activating SA signaling. • DF2 colonization upregulates key tanshinone genes GPPS , CPS , KSL , and CYPs. • Novel SA-mediated crosstalk with an endophyte boosts tanshinone production.