Our research focuses on the role of catabolic pathways such as RNA degradation and proteolysis, particularly about cell development and stress responses. We pursue multilevel and multidisciplinary approaches, ranging from the organismal level down to single molecules.
Our main projects
Role of proteolysis in plant development
Cell polarity refers to a set of mechanisms that establish and maintain specialised domains within a cell or the plasma membrane. It is suggested to have evolved from an archetype machinery responsible for restricting senescence to one daughter during division by enabling the differential segregation of damaged material. One of the most important functions of cell polarity is the control of asymmetric cell division that has a fundamental role in the control of cell fate by producing two cells of unequal size and function. The establishment of cell polarity is achieved through protein and vesicle trafficking along cytoskeleton.
Above image: Co-localization of Norway spruce separase homologue PaESP with microtubules (green) during anaphase. DNA staining was done with DAPI (blue). Densitometry scans were performed in the framed areas. Scale bars, 5 µm.
We discovered that at the cellular level protein asymmetry can also be achieved by the selective degradation of proteins at the apical or the basal side of the cells by specific proteases. We identified the protease separase in Arabidopsis thaliana as an important component in this process (Plant Cell 2013 25(6):2171-86). We showed that separase forms a complex with molecular motors known as kinesins (Dev Cell 2016, 37(4):350-361). Kinesin and separase collaborate to control cytoskeleton dynamics, cell polarity and division, thereby affecting cell fate and division fidelity. In these works, we developed tools, such as inducible lines with depleted separase, which will enable us the study of interconnections between proteolysis, cell polarity and fate decisions. We recently obtained a high-resolution map of cleavage events that are required for polarity establishment. We now focus on the elucidation of the function of proteolytic targets to provide a functional proteolytic map of cell polarity.
Also, we have also brought to bear the unique advantages offered by the model plant Picea abies (Norway spruce) as an experimental system in relation to cell polarity research. Norway spruce is the most important tree for the Swedish economy. It is an excellent platform for cell biology studies owing to the large size of its cells, a tractable developmental pattern and ease of transformation. More recently, we identified potential applications of our work by showing that cell polarity regulation in Norway spruce is important for somatic embryogenesis (New Phytologist 2016, 212(1):232-43).
Ribonucleoprotein complexes in development and stress
During development or stress, new proteins are produced to accommodate new cellular needs. A repertoire of molecular pathways remodels the proteome by promoting selective transcription or translation. Transcription or translation of other proteins, on the contrary, is transiently suppressed through mRNA decay or storage.
Our recent work revealed that transcriptome remodelling during heat stress is intimately connected with the formation of microtubule-based cytoplasmic ribonucleoprotein (RNP) complexes called stress granules (SGs) and processing bodies (PBs) (Plant Cell 2015; 27: 926-43). Although both types of RNP complexes are present under stress conditions, they serve distinct functions. While SGs are thought to play a role in sequestering, stabilising and storing mRNAs and translation factors, the main function of PBs is attributed to translational repression and mRNA decay. While much progress has been made in understanding how SGs and PBs control stress tolerance, substantial gaps remain in our knowledge. We discovered that PBs are intimately linked to the kinesin-separase complex by direct interaction. As RNPs are important throughout plant development and during stress, manipulation of RNPs could conceivably find diverse applications. For example, manipulation of PBs activity may allow greater control over diverse processes such as developmental transitions; alternatively, it might be used to improve stress tolerance in a variety of crop species.
Image: Localization of the PBs marker GFP-DCP1, and SGs eIF4E. 5-day-old Col Arabidopsis seedlings expressing GFP-DCP1 (green) were heat stressed at 39°C for 40 min and then immunostained with anti-elF4E (red) as described previously. Root cells were examined by confocal laser microscopy. Control seedlings were grown at 23°C. Note the proximity between eIF4E and DCP1 denoted by arrowheads. Scale bars, 2 μm. (Plant Signal Behav. 2015; 10: e1071005).
Furthermore, factors regulating dynamics of chromatin structure in the nucleus have a direct impact on the expression of genetic information. Cohesin is a multi-subunit protein complex and represents a proteolytic target of KISC. Cohesin is crucial for pairing sister chromatids during cell division, DNA repair and regulation of gene transcription and silencing. We discovered that cohesin is loaded on chromatin by the Scc2-Scc4 complex (also known as the NIBPL-MAU2 complex) in plants (J. Cell Sci. 2017 130: 1051-1063). The NIBPL-MAU2 complex is indispensable for cell fate establishment during early stages of embryo development. NIBPL-MAU2 mutants show fate reversion of the terminally differentiated suspensor cells of the embryonic tissue. Our findings have established the NIBPL-MAU2 complex as an evolutionary conserved machinery controlling cohesin loading and chromatin structure maintenance, and provide new insight into the plant-specific role of this complex in controlling cell fate during embryogenesis. Our research seeks to achieve a comprehensive understanding of cellular and nuclear ribonucleoprotein complexes, using a full spectrum of molecular, cellular, genetic, and biochemical approaches.
Biotechnology of rapeseed (Brassica napus)
Brassicaceae [mustard] family includes >3,300 species, with many economically important vegetable crops, e.g. cabbage, broccoli, cauliflower, turnip, rapeseed, mustard, radish, horseradish, cress, wasabi, watercress, Arabidopsis and rapeseed. Rapeseed is an important allotetraploid oilseed crop, with important economic relevance providing biodiesel, vegetable oil, and meal for animal feed with a close relationship to Arabidopsis. This relationship is wonderfully fortuitous; fundamental knowledge produced using Arabidopsis can be easily translated in breeding B. napus and by extension many other essential crops. Thus, rapeseed is now regarded as an important model for crops. Because B. napus is a tetraploid species, it represents an excellent model for studying means to overcome complex genetic traits or for producing allelic variation using the recent advancements in genome editing methods. Our group exploits the power of the editing method of CRISPR/Cas9 to produce allelic variants and mutants to complement natural allelic variation, in an attempt to improve rapeseed (Dev Biol 2018 pii: S0012-1606(17)30760-1). We are focusing on the control of pathways affecting protein catabolism, emphasising on proteolysis.
Our team in 2017 harvesting rapeseed.