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Current Research (PhD Thesis):

Molecular and genetic characterization of diterpene glycosides in Nicotiana attenuata

17-hydroxygeranyllinalool diterpene glycosides (HGL-DTGs) constitute a highly abundant compound class that occurs in concentration equivalent to starch (mg/g fresh mass) in aboveground tissues of Nicotiana attenuata. HGL-DTGs consist of an acyclic C20 17-hydroxygeranyllinalool skeleton conjugated to sugar groups (glucose and rhamnose) via bonds at C-3 and C-17 hydroxylated carbons; additional sugars are conjugated to the C’-2, C’-4, or C’-6 hydroxyl groups. Malonyl groups are typically connected to the C’-6 hydroxyl group of the glucose(s).
Herbivory and jasmonate-mediated signaling induces the conjugation of malonyl groups to diterpene glycoside sugars and have been shown to reduce growth of the tobacco hornworm (Manduca sexta) in N. attenuata.

My objective is to elucidate the ecological function of HGL-DTGs and more precisely the herbivore induced malonylation of HGL-DTGs in N. attenuata. To this end, I am first developing a mass spectrometric-based method for the identification, classification and quantification of all HGL-DTG molecular species in metabolic profiles of diverse Solanaceae species (f. e.: Nicotiana sp., Capsicum sp., Lycium sp.) in order to unravel conserved and divergent tissue-specific variations in the accumulation of these defense molecules and to test the hypothesis that malonylation is a widespread phenomenon among the Solanaceous taxa. I intend to perform field and glasshouse bioassays to identify the bioactive portion of the HGL-DTGs. In parallel, I am identifying and functionally characterizing novel glycosyl-, rhamnosyl- and malonyl transferases that participate in the biosynthesis of HGL-DTGs in N. attenuata plants. This will allow engineering N. attenuata plants with reduced or increased levels of each HGL-DTG form to test the impact of each individual compound class for insect resistance and to understand the connectivity of HGL-DTG metabolism with other branches of the plant’s herbivory-regulated metabolism.
last updated on 2011-08-10