Salvia miltiorrhiza Bunge (Danshen) is a medicinal plant of the Lamiaceae family, and its dried roots have long been used in traditional Chinese medicine with hydrophilic phenolic acids and tanshinones as pharmaceutically active components (Xu et al., 2016; Zhang et al., 2014). The first step of tanshinone biosynthesis is the bicyclization of the general diterpene precursor (E, E, E)-geranylgeranyl diphosphate (GGPP) to copalyl diphosphate (CPP) by CPP synthases (CPSs), which is followed by cyclization or rearrangement reaction catalyzed by kaurene synthase-like enzymes (KSL). The resulting intermediate is usually an olefin, which requires the insertion of oxygen by cytochrome P450 mono-oxygenases (CYPs) for the final production of diterpenoids (Zi et al., 2014). While the CPS, KSL and several early acting CYPs (CYP76AH1, CYP76AH3 and CYP76AK1) for tanshinone biosynthesis have been identified in S. miltiorrhiza (Gao et al., 2009; Guo et al., in press; Guo et al., 2013; Zi and Peters, 2013), the majority of the overall biosynthetic pathway, as well as the relevant regulatory factors associated with tanshinone production, remains elusive (Figure 1B).