Dear Editor,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 (Zhang et al.,2014;Xu et al.,2016).The first step of tanshinone biosynthesis is bicyclization of the general diterpene precursor (E,E,E)-geranylgeranyl diphosphate (GGPP) to copalyl diphosphate (CPP) by CPP synthases (CPSs),which is followed by a 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.,2013,2016;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).