Investigating phenolic diterpenes in rosemary (Rosmarinus officinalis) and sage (Salvia fruticosa)

Abstract

Plant secondary metabolites contribute substantially to the human pharmacopeae. To better exploit the medicinal plants that produce these compounds, it is necessary to understand how these compounds are synthesized within the plant. Identification of the biosynthetic pathway genes will allow both the breeding of plant varieties with improved productivity and/or metabolic profile, and the development of alternative production methods using biotechnology. The phenolic diterpenes (PDs) carnosic acid (CA) and carnosol have high antioxidant activities and display potential for the treatment of neurodegenerative disorders. CA and carnosol are found in Rosmarinus and Salvia sp. which are known for their health promoting properties since ages. As part of the EU-financed TERPMED project, PD biosynthesis is being investigated. To elucidate the pathway, the localization of the biosynthesis of PDs was determined. Glandular trichomes appear to contribute significantly to the biosynthesis of PDs and the transcriptome of glandular trichomes was thus determined by next generation sequencing of cDNA. A set of gene candidates was selected according to alignment searches and analysis of trichome-specific gene expression profile. The search for terpene synthases yielded two types of candidates for the first steps of the pathway: a copalyl diphosphate synthase (CPS) and kaurene synthase-like (KSL) encoding genes. Genes encoding oxidases of cytochrome P450 clade were the most promising candidates for the downstream steps of the PDs pathway. Finally, the first steps of the biosynthesis of PDs are reconstituted and further investigations on the role of P450 candidates in downstream steps are being carried out using N. benthamiana transient expression and heterologous expression in yeast.