PhD defence: The Role and Plasticity of Plant Metabolism – University of Copenhagen

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PhD defence: The Role and Plasticity of Plant Metabolism

PhD defence of Mette Sørensen

Plants are extraordinary biochemists producing a great arsenal of metabolites offering a remarkable metabolic plasticity. Plant metabolites group into general metabolites, which are common to all plants and essential for growth and reproduction, and specialized metabolites, which typically occur in specific plant lineages and are essential for how plants respond to the environment.

This thesis highlights the complex mechanisms behind plant plasticity and illustrates the intricate network regulating plant metabolism from gene to final metabolite product. In particular, the role and plasticity of plant metabolism is studied in ferns (Phebodium aureum and Pteridium aquilium), a grass (Sorghum bicolor) and flowering trees (Eucalyptus and Corymbia sp.) using cyanogenic glucosides as a model compound class. A key enzyme class playing a role in mediating the metabolic complexity seen in plants is the cytochrome P450 monooxygenases (CYPs), including the biosynthesis of cyanogenic glucosides. In particular, this work focuses on CYPs from the CYP79 family with their unique ability produce oximes, compounds placed at metabolic bifurcation points between general and specialized metabolism.

The work includes a review on the role of CYP79-catalyzed oximes in plant metabolism. In sorghum it is demonstrated that the CYP79A1 specifically catalyzes the formation of (E)-p-hydroxyphenylacetaldoxime and further how the oxime-metabolizing step and specific oxime geometric isoform (E- or Z-oxime) determines the downstream product. In the cyanogenic fern, Pteridium aquilium, CYP79s are not present, and it is demonstrated that a flavin monooxygenase (FMO) called FOS1 catalyzes the conversion of the oxime. Moreover, the full biosynthetic pathway of the cyanogenic glucoside prunasin is characterized in Eucalyptus cladocalyx with an oxime as first intermediate. Eucalyptus contains a great diversity of volatile and non-volatile specialized metabolites in addition to cyanogenic glucosides. Thus, an exhaustive study of the leaf and flower branch volatiles emitted by eucalypt trees in the field was conducted using nine different Eucalyptus and Corymbia species.

Supervisors

Professor Birger Lindberg Møller
Assistant professor Elizabeth H. J. Neilson

Assessment committee

Professor Robert A. Raguso, Cornell University, USA
Divisional visitor Carsten Kulheim, The Australian National University, Canberra
Professor Barbara Halkier (chair)

Reception afterwards in the 117 meeting rooms.