Increasing the synthesis of bioactive abietane diterpenes in Salvia sclarea hairy roots by elicited transcriptional reprogramming

Key message: Transcriptional activation of genes belonging to the plastidial MEP-derived isoprenoid pathway by elicitation with methyl jasmonate and coronatine enhanced the content of bioactive abietane diterpenes inSalvia sclareahairy roots.Abstract: We have shown that aethiopinone, an abietane diterpene synthesized in Salvia sclarea roots is cytotoxic and induces apoptosis in human melanoma cells. To develop a production platform for this compound and other abietane diterpenes, hairy root technology was combined with the elicitation of methyl jasmonate (MeJA) or the phytotoxin coronatine (Cor). Both MeJA and Cor induced a significant accumulation of aethiopinone, but prolonged exposure to MeJA irremediably caused inhibition of hairy root growth, which was unaffected by Cor treatment. Considering together the fold increase in aethiopinone content and the final hairy root biomass, the best combination was a Cor treatment for 28 days, which allowed to obtain up to 105.34 ± 2.30 mg L−1 of this compound to be obtained, corresponding to a 24-fold increase above the basal content in untreated hairy roots. MeJA or Cor elicitation also enhanced the synthesis of other bioactive abietane–quinone diterpenes. The elicitor-dependent steering effect was due to a coordinated transcriptional activation of several biosynthetic genes belonging to the plastidial MEP-derived isoprenoid pathway. High correlations between aethiopinone content and MeJA or Cor-elicited level of gene transcripts were found for DXS2 (r2 = 0.99), DXR (r2 = 0.99), and GGPPS (r2 = 0.98), encoding enzymes acting upstream of GGPP, the common precursor of diterpenes and other plastidial-derived terpenes, as well as CPPS (r2 = 0.99), encoding the enzyme involved in the first cyclization steps leading to copalyl-diphosphate, the precursor of abietane-like diterpenes. These results point to these genes as possible targets of metabolic engineering approaches to establish a more efficient production platform for such promising anti-proliferative plant-derived compounds.