Congratulations Niels Christian!

In front of colleagues, friends and family Niels Christian succesfully defended his PhD thesis as a partly online and partly physical defence.

The thesis is entitled: Systemic infrastructure in plants. From sieve elements to seed filling

A snapshot from the discussion with the assessment committee consisting of Chairperson Professor Anja Fuglsang, Professor Yrjö Helariutta, Finland and Professor Mark Belmonte from Canada, who took the trip to Denmark for the defence.

Summary

We encounter plants every day and almost any small piece of land on the globe will have its own distinct flora. Flowering plants conquered terrestrial ecological niches with tremendous success and today account for the vast majority of plant biomass and species richness. Several evolutionary inventions make flowering plants special - in my thesis, I investigated topics related to two important features: The vascular tissue and the seed.

The vasculature allow plants to transport water and solutes between organs. Dead cell remains in the xylem bring water from the roots to the leaves, whereas a living tissue, the phloem, translocates sugars from sources leaves to sink tissues such as roots and fruits. In the phloem, a special cell type - the sieve element - loses most of its cellular contents upon maturation and becomes a "hollow" tube that facilitates sap flow. Mature sieve elements lack the means to make their own proteins, which makes the protein machinery inside them an interesting population.

In Niels Christians thesis, he reviewed the literature of known sieve element proteins and generated a list of new putative sieve element genes. He selected seven of these genes and showed that indeed, their protein products localize in mature sieve elements.

Although sugars are the main transported solutes in the phloem, several other classes of molecules enter the translocation stream to move from source leaves to sink tissues. Niels Christian investigated a special case of this: The transport of glucosinolates in Arabidopsis from source tissues to the seed. Glucosinolates are specialized metabolites found in the Brassicales order, which act as defense compounds. Seeds are full of glucosinolates (responsible for e.g. the sharp taste of mustard seeds) but cannot synthesize them on their own and instead depend on maternal supply, which requires transporter proteins.

Niels Christian contributed to the characterization of a newly discovered glucosinolate exporter and investigated at the cell-type level, where this exporter and well-characterized importers must be present to achieve seed loading of glucosinolates.

Niels Christian holds a BSc and MSc in Biology- Biotechnology from University of Copenhagen in 2016.

His PhD supervisors were DynaMo partner Professor Alexander Schulz and Head of DynaMo Barbara Ann Halkier. Niels Christian will continue as Postdoc at the DynaMo Center

Congratulations NC!