PhD defence - Joachim Møller Christensen
Title
An FMOdyssey - An epic journey into flavin-containing monooxygenase evolution and function.
Assessment Committee
- Professor David B. Collinge, PLEN, University of Copenhagen, Denmark
- Professor Pietro D. Spanu, Imperial College, London, UK
- Professor Bai Yuling, Wageningen University, The Netherlands
Supervisors
- Associate Professor Elizabeth Heather Jakobsen Neilson
- Professor Meike Burow
Place
Festauditoriet (A1-01-01), Bülowsvej 17, 1870 Frederiksberg
The defence is followed by a reception in Konsistoriesalen next to Festauditoriet.
Everybody is welcome.
Ask for a copy of the thesis here: Associate Professor Elizabeth Heather Jakobsen Neilson (en@plen.ku.dk)
Summary
Class B Flavin-containing monooxygenases (FMOs) constitute a diverse enzyme family found throughout all kingdoms of life. By incorporating molecular oxygen into small organic substrates, FMOs modify chemical properties and thus play essential roles in numerous physiological processes. Their broad catalytic capabilities also make them attractive candidates as biocatalysts in industrial chemical synthesis. Plants serve as a rich repository of FMO diversity, yet plant class B FMOs remain relatively unexplored, with only a few enzymes functionally characterized to date. Consequently, these FMOs represent an untapped source of enzymatic activities, holding great potential for both fundamental plant biology and applied synthetic biochemistry. Existing phylogenetic analyses of plant FMOs have often included limited species diversity, heavily favoring model angiosperms, or have primarily examined individual class B FMO families. Addressing these gaps provided the motivation for the comprehensive evolutionary and functional studies presented in this thesis.
This thesis explores the evolutionary, structural, and functional diversity of plant FMOs. It presents a curated database encompassing major plant class B FMO families—including YUCCAs, FMO N-OX, and FMO S-OX—constructed through extensive sequence retrieval and manual curation to ensure high-confidence class B FMO gene datasets. Additionally, a comprehensive phylogenetic analysis of plant class B FMOs is provided, expanding and clarifying previously known class B FMO families and revealing three novel, lineage-specific FMO families. Structural diversity within these families is examined, and previously established class B FMO motifs are reassessed in light of these findings.
Furthermore, this thesis investigates the family-specific phylogeny of the critically important YUCCA family, which catalyzes the rate-limiting step in auxin biosynthesis, a key plant hormone. It conducts a phylogenetic analysis to trace the evolutionary relationships within this class B FMO family. The analysis presented includes a comprehensive classification system, accompanied by detailed motif and expression analyses of each identified subfamily.
This thesis presents the characterization of two novel class B FMOs. The first enzyme, named 2-oxo-tryptamine synthase (2OTS), is associated with barley defense responses. A comprehensive metabolomics analysis of barley infected with the pathogen Pyrenophora teres reveals numerous defense-related metabolites, including serotonin, tryptamine, and a previously unknown plant metabolite, 2-oxo-tryptamine (2OT). Co-expression and transcriptomic analyses identify 2OTS, an uncharacterized FMO from the N-OX family, which is biochemically characterized to catalyze the conversion of tryptamine into 2OT. Additionally, this thesis characterizes Orchid Oxime Synthase 1 (OOS1), an FMO involved in the production of volatile oximes derived from phenylalanine and leucine. These volatile compounds play a critical role in mediating plant-pollinator interactions in Darwin’s orchid (Angraecum sesquipedale). A family-specific phylogenetic analysis of the FMO N-OX family identifies this catalytic activity as an instance of convergent evolution.
The findings presented in this thesis establish a foundation for understanding plant class B FMOs and provide essential resources for future research. The developed phylogenetic database and framework enable functional characterization of novel FMOs across diverse plant species. Characterization of two new FMOs expands the catalytic scope of class B FMOs, facilitating future discoveries in plant metabolism, defense responses, biotechnology applications, and ecological interactions.