Metabolic engineering and elicitation of pharmaceutically active metabolites in Rhazya stricta (Apocynaceau)

Rhazya stricta Decne., a small evergreen shrub native to the Middle East and Indian sub-continent, is a rich source of pharmacologically active terpenoid indole alkaloids (TIAs). The plant has been in the focus of phytochemical, pharmacological and ethnobotanical studies due to its long use in folk medicine to treat a variety of ailments. More recently especially the antimicrobial and anticancer properties of certain constituents (Fig. 1) have been established. TIAs are formed by the condensation of the indole and iridoid moieties catalysed by strictosidine synthase (STR) to form the precursor strictosidine. High STR activity associated with the induction of rate-limiting enzyme activities of the iridoid pathway (GES, G10 H) favours TIA production. Biosynthetic steps in the TIA pathway are co-ordinately regulated at the level of transcription of the structural genes by transcription factors (e.g. orca3). Wild type hairy root cultures were established in order to study TIA production and enable metabolic engineering. A validated GC-MS method was developed and 20 compounds were identified. Rhazinilam, rhazine and vallesiachotamine were present in several lines (Fig. 1). Gene(s) from the early part of the TIA pathway, single gene geraniol synthase (ges), geraniol 10-hydroxylase (g10h) and strictosidine synthase (str) and double-gene (str+orca3), were introduced to R. stricta to investigate their over-expression effects on the TIA biosynthesis in transgenic hairy root lines. Integration and expression of the gene(s) were confirmed by molecular techniques. Suitable elicitations by methyl jasmonate to stimulate TIA accumulation were evaluated. Chemical analysis of transformed hairy roots and elicited samples showed an increased level of selected TIAs compared to the wild type hairy root lines and non-elicited samples. Further analysis revealed higher accumulation of total alkaloids in transformed and elicited hairy roots.