Discovering biosynthetic pathways for medicinal diterpenoids from Euphorbiaceae family

Context

The Euphorbiaceae family of flowering plants produce a diverse range of casbene-derived diterpenoids exhibiting diverse biological activities, including anti-cancer (lathyranes, jatrophanes and ingenanes),  antiviral  (phorbol-esters),  anti-nociception (daphnanes) and antimicrobial (lathyranes, jatrophanes), including compounds which are already in medicinal use such as ingenol mebutate licenced for actinic keratosis treatment and tigilanol tiglate approved for veterinary use in mast cell tumour treatment.  Low abundance of many of these compounds in their natural hosts together with challenging chemical synthesis due to high structural complexity means that alternative production platforms are needed if the full potential of these compounds for industrial applications is to be realised. Although early biosynthetic steps for the casbene and lathyrane (jolkinol C) pathways have been discovered in Euphorbiaceae species, the nature of the intramolecular cyclization and rearrangement reactions leading from casbene to other polycyclic diterpenoids remain hypothetical.

The research

We use multi-omics approaches to discover diterpenoid biosynthetic pathways in Euphorbia peplus, Jatropha curcas and other Euphorbiaceae species. Metabolomics-led trancriptomic analysis combined with genomic approaches have been used to identify candidate genes involved in casbene derived diterpenoid production. Candidate genes have been functionally characterised using the Nicotiana benthamiana transient expression system. Novel activities are further confirmed by VIGS (Virus Induced Gene Silencing) in E. peplus. We consider E. peplus to be an excellent model species for the dissection of casbene derived diterpenoid production due to the complexity of diterpenoid classes present, the relatively small diploid genome, small stature and short life cycle.  Whole genome sequencing and screening of mutagenized populations of E. peplus are now facilitating discovery and functional characterisation of diterpenoid related genes. Our work contributes both knowledge and tools necessary for engineering production of bioactive diterpenoids in heterologous host systems, thus enabling their further evaluation and development.