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.