With 230 described species, Eremophila R. Br. is the largest genus in the tribe Myoporeae (Scrophulariaceae) and exhibits incredible morphological diversity throughout the Eremean biome, which covers approximately 70 % of the Australian continent. It is an ecologically and culturally important genus for Indigenous Australians, who have traditionally used several Eremophila species as sources of medicines. Despite the importance of this genus, it is poorly characterized taxonomically as well as phytochemically.The scarce studies that have been carried out point to ses qui- and diterpenoids as the bioactive ingredients of Eremophila extracts. In particular, serrulatane and viscidane type diterpenoids, which feature prominently in the chemical profile of many species from this genus, have shown anti-diabetic and anti-microbial activities. The aims of the present PhD thesis are twofold: the study of the Myoporeae associated metabolite diversity to uncover chemo-evolutionary relationships within this tribe and the discovery of biosynthetic pathways that lead to Eremophila specific diterpenoids. I have investigated the metabolite diversity of the tribe Myoporeae in a chemo-evolutionary framework by applying a combination of state-of-the-art phylogenetics and computational metabolomics tools to a dataset involving leaf extracts from a total of 291 taxa representing Eremophila and allied genera. Molecular network based tanglegram and heatmap analyses unveiled chemo-evolutionary relationships, with serrulatane and viscidane diterpenoid chemistry being responsible for a major split of the specialized metabolome. Additional integration of information about leaf morphology (resin and hairiness), environmental factors (pollination and biogeographical distribution) and medicinal properties (Aboriginal uses and antibacterial studies) was used to bring the chemical information into a systematic context. From this, I found that these diterpenoids coincide with leaf resin and antibacterial properties, suggesting to be the result of an adaptation to harsh conditions during the relatively recent formation of the Eremean zone in central Australia. The scope and methodology of this study are ground-breaking and reveal the power of interdisciplinary big-data processing in bioscience. This study shows that interlinking multiple layers of information to the chemical space and in an evolutionary context, augments our understanding of the complex interactions found in biological systems andfurther facilitates targeted drug discovery. I was interested in the biosynthetic pathways that lead towards the diverse array of serrulatane, viscidane and cembrane type diterpenoids. Therefore, I have investigated thebiosynthesis of diterpenoids in three species: Eremophila lucida, Eremophila denticulata subsp. trisulcata and Eremophila drummondii. I localised these diterpenoids to the leaf surface - associated with the occurrence of glandular trichomes. Transcriptome databases generated from leaf glandular trichomes of the investigated species revealed the presence of several highly expressed prenyltransferase, terpene synthase and cytochrome P450 monooxygenase homologous genes. I was able to describe the first steps in the biosynthetic pathways towards serrulatane, viscidane and cembrane type diterpenoids, via heterologous expression of selected candidate genes in N. benthamiana and E. coli. I have determined four terpene synthases (TPS) with diterpene biosynthesis activity: ElTPS31 and ElTPS3 from E. lucida were found to produce (3Z,7Z,11Z)-cembratrien-15-ol and 5- hydroxyviscidane, respectively, and EdTPS22 and EdtTPS4, from E. drummondii and E. denticulata subsp. trisulcata, respectively, were found to produce 8,9-dihydroserrulat-14- ene which readily aromatized to serrulat-14-ene. In all cases, the identified TPSs used the cisoid nerylneryl diphosphate (NNPP) as substrate. Subsequently, cis-prenyl transferases capable of making NNPP were identified in each species.After I elucidated the two biosynthetic steps towards three of the major diterpene backbones found in Eremophila, I was encouraged to study their downstream functionalization. For extending the pathway discovery toolbox I used a mutualistic E. coli - Saccharomyces cerevisiae co-culture expression system. This approach helped me to identify six active cytochrome P450 monooxygenases (CYP) and one alcohol dehydrogenase with varying degrees of promiscuity towards the three tested diterpenoid backbones. Notably, all six CYPs act on the serrulatane scaffold despite low sequence similarity, suggesting the prevalence of serrulatane metabolism in Eremophila. With these results, the poorly investigated and recognized cisoid terpene branch comes to the forefront of plant biochemistry research, with Eremophila as a unique plant genus where this type of terpenoids prevail. Serrulatane and viscidane type diterpenoids are promising candidates for new drug leads. The identification of an enzymatic route to their synthesis opens up the possibility of biotechnological exploitation.