Research group of Prof. Dr. Sigrun Reumann
Our research concentrates on peroxisomes. Almost all organisms consist of cells, and almost all cells possess and need peroxisomes. Peroxisomes are small organelles (or compartments, "rooms" surrounded by membranes) that can be found in almost all eukaryotic cells – from simple yeast cells to crop plants and humans. Peroxisomes are critical for the survival of cells. Patients with inherited peroxisome defects often have a very low life expectancy. Also the seeds of crop plants with damaged peroxisomes can no longer germinate and adult plants are compromised in photosynthetic efficiency.
For the identification and molecular characterization of new proteins and functions of plant peroxisomes we have established fundamental large-scale methods, namely experimental proteome technology and Applied Bioinformatics for Arabidopsis. Our research interest focuses on the function of peroxisomes in the plant immune system and for plant resistance against pathogenic bacteria. In a relatively recent project dealing with microalgae we want to optimize the production of omega-3 fatty acids and recombinant proteins in microalgae. Besides, we investigate aspects of the biogenesis (proliferation) and the dismantling of plant peroxisomes.
Identification of novel plant peroxisomal proteins
Even though being essential organelles, peroxisomes of animals, fungi and particularly of plants have been insufficiently investigated up to now. Only in the past few years unexpected functions and tasks of plant peroxisomes have been uncovered, for instance in pathogen defence and in the biosynthesis of biotin and phyllochinon.
To identify novel peroxisomal proteins and functions, our group developed two complementary approaches. On the one hand we developed experimental proteome research for leaf peroxisomes in the model plant Arabidopsis which led to the identification and molecular characterization of more than 50 novel proteins of peroxisomes (Reumann et al., 2007, 2009; Babujee et al., 2010). At present we optimize differential proteome analyses to identify additional peroxisomal proteins that might be involved in pathogen defence or the adaptation to abiotic stress.
On the other hand, we developed, in collaboration with Dr. Thomas Lingner (University of Göttingen, Germany), new prediction algorithms by machine learning techniques to reliably predict which proteins possess peroxisome targeting signals type 1 (PTS1) for peroxisomes (Lingner et al., 2011). The corresonding prediction tool „PredPlantPTS1“ has been made publicly available to the scientific community (http://ppp.gobics.de, Reumann et al., 2012). At present we are trying to improve the predicton models in iterative approaches combining experimental wet-lab research and bioinformatics (Skoulding et al., 2014). Work in progress deals with the development and experimental validation of PTS2 prediction models.
The research projects are funded by the project „Perox-MPI“ (2011-2015) by the Norwegian Research Council and the EU Marie Curie Initial Training Network (ITN) „PERFUME“ (PERoxisome, FUnction, MEtabolism, 2013-2016). The projects are carried out by the PhD students Piotr Lisik, Delphine Crappe and Manish Budathoki and the postdoctoral fellow Dr. Gopal Chowdhary.
The function of peroxisomes in plant innate immunity
Like humans and animals plants also possess an immune system that allows them to combat pathogens successfully. Peroxisomes play an important role in the resistance to pests; For example, the plant hormone jasmonic acid is synthesized in peroxisomes. We try to identify still unknown peroxisomal proteins that are relevant for the defense of pathogens. We examine under which conditions and in which manner novel resistance proteins are directed to peroxisomes. For other defence proteins we investigate their interaction partners and in which signal transduction pathways they are involved.
These research projects were funded by the project "Perox-MPI" (in 2011-2015) of the Norwegian Research Council and the EU Marie Curie Initial Training Network (ITN) "PERFUME" (PERoxisome, FUnction, MEtabolism, in 2013-2016) and are presently pursued by the postdoctoral researcher Dr. Christian Falter and the doctoral candidates Thu Nguyen, Saugat Pokhrel and Ebenezer Ntiriakwa. Delphine Crappe successfully defended her PhD thesis and graduated at the University of Stavanger (Norway) on 30 November 2016.
Improvement of the production of omega-3 fatty acids and recombinant proteins in microalgae
Microalgae (single-cell eukaryotic algae) are also called the „agricultural plants of the 21st century“, because they are characterized by high growth rates, efficient photosynthesis, a low need of nutrients, robustnes towards changing environmental conditions and high biosynthesis rates of biotechnologically interesting products. For instance, microalgae are able to accumulate fat up to 20-30% of their dry weight. However, most technologies for low-cost production of microalgae in photobioreactors are still in the early phase.
Peroxisomes of microalgae play an important role in the accumulation of fat and omega-3 fatty acids, because they control the degradation of fatty acids. However, very little is known about the function and biogenesis of peroxisomes in microalgae to date. We want to understand which reactions of lipid metabolism take place in peroxisomes and develop strategies how even higher production rates of interesting organic products can be achieved in a robust and cost-efficient manner.
The research project is funded by the project "Microalgae 2021" (in 2013-2018) by the Norwegian Research Council and is presently pursued by Dr. Imke de Grahl and Sweta Rout. Dmitry Kechasov carried out his doctoral research on the omega-3 fatty acid project and graduated at the University of Stavanger, Norway) in September 2017.
Biogenesis and degradation of peroxisomes
Biogenesis and dismantling of peroxisomes are finely adjusted. On the one hand, a constant number of peroxisomes per cell must be guaranteed under normal growth conditions. On the other hand, the cellular number of peroxisomes is adapted under extreme and stress conditions to the current requirements and is increased when fatty acid β-oxidation, metabolism of reactive oxygen species or photorespiration must be intensified.
First in 2013 it was demonstrated worldwide and independently by several working groups that plant peroxisomes are degraded by the mechanism of macroautophagy (pexophagy). We have established heterotrophic tobacco BY2 cell suspension cultures as an experimental system for the study of the plant pexophagy and proved that peroxisomes are recycled by pexophagy. Interestingly, peroxisome degradation and recycling does not only happen under adverse environmental conditions, such as abiotic stress, but also under optimal growth conditions, most probably to replace oxidatively damaged peroxisomes (Voitsekovskaja et al., 2014; Tyutereva et al., 2017).
The research project was funded by a DFG project of the German Research Council and by the DAAD and has been carried out by Dr. Olga Voitsekovskaja (Komarov Botanical Institute, Russian Academy of Sciences, Saint Petersburg, Russia).
