Diterpene gene cluster involved in abietane-type diterpenoids in S. rosmarinus
Comparisons of microsynteny blocks detected in S. rosmarinus ,S. miltiorrhiza and S. splendens , revealed the presence of two diterpene gene clusters (DGC) in S. rosmarinus distributed in Chr1 and Chr2, spanning 220 Kb and 200 Kb, respectively (Figure S27). Previous studies have reported the loss of shoot KSL and three CYP76AH  genes (CYP76AH59CYP76AH58 , andCYP76AH56 ) in S. militiorrhiza DGC, and silencing or inactivity of SmCPS2 in tanshinone biosynthesis, leading to the abrogation of abietane-type diterpenoid biosynthesis in shoots (C.-Y. Li et al., 2022). Despite the loss of CYP76AH59 on rosemary chromosomes, SrCYP76AH58 , SrCYP76AH56 , SrCPS , andSrKSL were identified in the rosemary DGC, providing precursors for abietane-type diterpenoid biosynthesis. CPS2 had been silenced in DGCS of S. miltiorrhiza and rosemary, however,SrCPS1 on Chr1 and Chr2 highly expressed in rosemary leaves (4.03-fold and 6.42-fold), and remained active in diterpene biosynthesis. HPLC-MS results also revealed that the accumulation of carnosic acid and carnosolin rosemary leaves. These findings demonstrate that the, two DGCs in rosemary retain the ability of produce abietane-type diterpenoids in its leaves.