Catharanthus roseus, also known as the Madagascar periwinkle, produces low levels of unique dimeric monoterpenoid indole alkaloids (MIAs) that are harvested and used as anticancer drugs to treat Hodgkin’s disease and other cancers. The trace levels of dimers occurring in C. roseus have made them very expensive to isolate. It is well known that C. roseus leaves are the main sites of biosynthesis of the precursors, catharanthine and vindoline, and that each MIA is localized in different leaf cell types, making it difficult to understand how dimer formation takes place. Research efforts in the past 6 years on the assembly of these monoterpenoid indole alkaloids (MIAs) in C. roseus has led to the molecular and biochemical characterization of the remaining genes involved in the 29-step pathway required for their biosynthesis from geraniol diphosphate. The formation of strictosidine from geraniol and tryptophan involves 9-steps, most of which have recently been solved and have led to prototype strictosidine expressing pathways in yeast. Enzyme-mediated hydrolysis of strictosidine leads to formation of precursors used in the biosynthesis of several thousand MIAs, including these well-known anticancer drugs. We recently reported the discovery and functional characterization of 10 remaining genes to complete the description of enzymes for tabersonine and catharanthine assembly [PNAS (2018) 115: 3180- 3185; Planta (2018) 247:625-634; Plant J., (2108) 97: 257-266]. These discoveries with our recent successful assembly of vindoline from tabersonine [PNAS (2015) 112: 6224-6229) completed the description of the vindoline and catharanthine pathways from geraniol and tryptophan and has set the stage for developing biological systems for synthesis of many different biologically active MIAs. The basic tools and developments leading to these discoveries will be discussed and analyzed. The impacts of elucidation of the vinblastine/vincristine pathways will also be discussed in relation to future discoveries of MIA pathways of biological and biomedical importance.
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