The Centre for Organelle Research (CORE) was founded in 2007 at the University of Stavanger. The staff of approximately 5 professors and 25 postdocs and PhD students now reside in 1.400 m2 of custom designed laboratories in a new research building at the Stavanger Innovation Park. CORE is temporary headed by professor Peter Ruoff, who has taken over after Simon Geir Møller who recently left for a position at St. John’s University in New York.
As its name implies, the centre is dedicated to research in organelles, but although the main focus is on plants some of the group leaders prefer other model organisms like archaeons, C. elegans and Atlantic cod. The four group leaders studying plant organelles are:
- Cathrine Lillo: Signalling between organelles
- Lutz Eichacker: Organelle protein complexes
- Sigrun Reumann: Peroxisomes of plants and microalgae
- Jodi Maple-Grødem: Chloroplasts and plastid division
- Peter Ruoff: reaction kinetics and nitrate homeostasis
In this overview, we will only address the plant related research and thus we will not mention the work of Svein Bjelland (microbial systems) and Maria Doitsidou (C. elegans).
The research by Cathrine Lillo is centered around nitrogen metabolism and how this is being regulated by protein phosphatase 2A (PP2A). In an early study from 2009, she showed that the regulatory B subunit of PP2A existed in several versions that targeted different organelles in plants. More recently in 2013, she showed in a paper in PLOS ONE that PP2A is also involved in regulation of flowering time. Mutations in different versions of the B subunit could lead to either late or early flowering phenotypes with advancements and delays as long as 7 and 8 days, respectively. The exact way that PP2A is involved in regulation of flowering time is not know, but the results suggested that at least late flowering involved repression of the flowering gene FLC.
The work of Lutz Eichacker focuses on plant photosystem biogenesis. He develops and makes use of proteome technology to study how assembly of protein complexes and how long-term morphogenetic and short-term adaptation processes of plants to the environment are regulated. His publications about the regulation of cofactor synthesis and assembly of protein subunits to enzymatically active complexes in the membrane of plastids define further key area of his molecular interest. His present research at CORE focuses on the question how the cytochrome b6f complex assembles during skotomorphogenesis and how delivery of a single chlorophyll molecule to the complex is regulated when plants switch the developmental program in the light.
Proteomics is also of interest for Sigrun Reumann in her study of plant and microalgae peroxisomes. Peroxisomes are tiny organelles involved in several metabolic functions, including beta-oxidation of fatty acids, photorespiration and generation of hydrogen peroxide (H2O2), superoxide (O2*-) and other radicals used in the defense against pathogens. In order to identify novel peroxisome functions it is necessary to isolate the organelles first, but this is challenging since they are very fragile. Consequently she developed and published in Plant Cell a new protocol for isolation of Arabidopsis leaf peroxisomes suitable for proteome analyses.
Sigrun Reumann has also taken a very different approach for identification of peroxisome proteins. In another paper in Plant Cell from 2011 she used the known peroxisome targeting signals type 1 (PTS1) of 60 Arabidopsis proteins to perform a homology search for other proteins with putative peroxisome targeting sequences. From this dataset a discriminative machine learning approach was used to predict peroxisome targeted proteins, and their putative PTS1-sequences were then fused to a reporter protein and used for subcellular localization analysis. This revealed that the tripeptide motif of PTS1 allows for more diversity than previously thought and thirty novel PTS1 tripeptides were identified. In another long-term project dubbed Microalgae 2021, Sigrun Reumann aims at using microalgae for large scale production of omega-3 fatty acids. To this end she will develop tools for genetic engineering of microalgae and also a non-GM approach using forward genetic screens to optimize omega-3 fatty acid productivity.
Unlike the other group leaders, Jodi Maple-Grødem is not yet a professor, but rather a senior postdoc. She has taken over Simon Geir Møller’s group and carries on the work on chloroplasts and plastid division. In a study from 21013 published in Plant Molecular Biology, she studied the interaction between the dynamin related protein 5B (DRP5B) – that forms a ring around the chloroplast and presumably exerts constrictional force during division – and plastid division protein 1 and 2 (PDV1 and PDV2). By fusing the latter two proteins to YFP she was able to show that they interact with DRP5B and inhibit its GTPase activity, suggesting that PDV proteins exert control over chloroplast division.
Last but not least, Peter Ruoff – who is a physical chemist specialising in reaction kinetics – has studied how plant roots are able to keep cytosolic nitrate at a homeostatic controlled level. Nitrate is taken up by the roots to very different extents depending on its concentration in the soil and homeostasis is achieved by a complex combination of nitrate reductase mediated assimilation in plastids, storage/remobilization in vacuoles, transport to the xylem and efflux. Using a kinetic approach, Peter Ruoff showed in 2012 that a set of eight inflow and outflow controllers can form a regulatory network that maintains cytosolic nitrate homeostasis even when assimilation levels and external nitrate levels fluctuate.
By Gorm Palmgren, science writer, PhD, www.palmgren.dk