Detailed Profiling of 17-Hydroxygeranyllinalool Diterpene Glycosides from Species Reveals Complex Reaction Networks of Conjugation Isomers.

Background: Specialised anti-herbivory metabolites are abundant in the solanaceous genus . These metabolites include the large family of 17-hydroxygeranyllinalool diterpene glycosides (HGL-DTGs). Many HGL-DTGs occur exclusively within the genus, but information from the molecular model species , , and the tree tobacco is limited.

Objectives: We studied HGL-DTG occurrence and complexity in these species with the aim of providing in-depth reference annotations and comprehensive HGL-DTG inventories.

Methods: We analysed polar metabolite extracts in comparison to the previously investigated wild reference species using positive ESI(+) and negative ESI(-) mode electrospray ionisation LC-MS and MS/MS.

Results: We provide annotations of 66 HGL-DTGs with in-source and MS/MS fragmentation spectra for selected HGL-DTGs with exemplary fragment interpretations of ESI(+) as well as less studied ESI(-) spectra. We assemble a potential biosynthesis pathway comparing the presence of HGL-DTGs in , , and to . Approximately one-third of HGL-DTGs are chromatographically resolved isomers of hexose, deoxyhexose, or malonate conjugates. The number of isomers is especially high for conjugates with low numbers of deoxyhexose moieties.

Conclusions: We extend the number of known HGL-DTGs with a focus on model species and demonstrate that the HGL-DTG family of plants can be surprisingly complex. Our study provides an improved basis with detailed references to previous studies of wild species and enables inference of HGL-DTG pathways with required enzymes for the biosynthesis of this important family of specialised defence metabolites.