Regulatory elements in the terpenoid biosynthesis of defensive secretions in leaf beetle larvae
Chrysomelina larvae possess a sophisticated strategy in terms of chemical defense eminently adapted to their natural habitat. In case of predatory attack, the deterrent secretions are released from dorsal thoracic and abdominal glands. The source of the deterrent compound for this ingenious mechanism depends on different biosynthetic strategies and subdivides the Chrysomelina in three different groups. The ancestral strategy represents the de-novo production of iridoids. Species belonging to this group e.g. Phaedon cochleariae and Gastrophysa viridula produce the deterrent compound independently of host plant derived precursors. More evolved species of the Chrysomela as well as Phratora vitellinae use the approach of sequestering phenol glucosides to produce salicylaldehyde. Based on the precursor salicin, this defense strategy is highly adapted to the secondary metabolites of the salicaceous plant which restricts the larvae in their forage. The third group is represented by several species of the interrupta-group belonging to the genus Chrysomela. They exhibit a combined biosynthetic strategy by using de-novo produced and phytogenic derived precursors to generate butyrate-esters as defensive compounds. Irrespective of different deterrent substances, the defensive systems of all groups exhibit per se a uniform architecture and morphology. Together with the self-contained biosynthesis of these compounds, the Chrysomelina larvae represent an excellent system to analyze regulatory processes as well as uncover evolutionary relationships regarding the defensive system. In the present thesis, I identified and characterized enzymes essentially involved in the de-novo biosynthesis of the defensive compound Chrysomelidial of P. cochleariae.