(25-04-22) Successful master thesis defense by Felicia Wolters at WUR

Abstract

Diversity of plant secondary metabolites evolved dynamically by a continuous arms-race of plant defense and herbivore counteradaptation. Hydroxygeranyllinalool diterpene glycosides (HGL-DTGs) have been found to confer plant resistance against herbivorous insects in the Solanaceae family. Specific decorations of the HGL aglycone result in a diverse palette of HGL-DTGs. In Nicotiana attenuata, key enzymes involved in HGL-DTG biosynthesis have been characterized recently. In other species however, the genetic background underlying HGL- DTG biosynthesis is still understudied. In this thesis project, orthologues in ten Solanaceae species were phylogenetically analysed. A family-wide gene cluster search revealed clustering of glycosyltransferase candidates in Capsicum annuum. The diversity of constitutive HGL-DTG decorations was studied in C. annuum accessions by LC-MS/MS analysis. Specific HGL glycosylation occurred in a resistant accession. Herbivore induced HGL- DTG related gene expression was investigated in resistant and susceptible genotypes of C. annuum upon induction by Jasmonic acid (JA) or cell-content feeding spider-mites. While candidate genes were strongly induced by JA, herbivory by spider mites resulted in downregulation. Malonyltransferase inducibility by JA was specific for a susceptible C. annuum accession. This project elucidated phylogeny and specificity of inducible defense compound decorations in Solanaceae, by combining phylogenetics, transcriptomics and metabolomics analysis.