Format: ORAL

Natalia Borowska-Zuchowska1*, Ewa Robaszkiewicz1, Artur Pinski1, Bozena Kolano1, Serhii Mykhailyk1, Natalia Matysiak2, Lukasz Mielanczyk2,3, Maria Drapikowska4, Ewa Kazimierczak-Grygiel5, Justyna Wiland-Szymanska5,6, Romuald Wojnicz2,3, Robert Hasterok1

1 Plant Cytogenetics and Molecular Biology Group, Institute of Biology, Biotechnology and Environmental Protection, Faculty of Natural Sciences, University of Silesia in Katowice, Poland 2 Department of Histology And Cell Pathology, Faculty of Medical Sciences in Zabrze, The Medical University of Silesia in Katowice, Poland 3 Silesian Nanomicroscopy Centre in Zabrze, Silesia LabMed – Research and Implementation Centre, Medical University of Silesia in Katowice, Poland 4 Department of Ecology and Environmental Protection, Faculty of Environmental and Mechanical Engineering, Poznan University of Life Sciences, Poland 5 Botanical Garden, Adam Mickiewicz University in Poznan, Poland 6 Department of Systematic and Environmental Botany, Faculty of Biology, Adam Mickiewicz University in Poznan, Poland

The nucleolus is one of the most prominent structures in the eukaryotic cell due to its indispensable role in 35-45S rRNA gene transcription and subsequent ribosomal subunit assembly. In addition to proteins and rRNA, the nucleolus also contains the 35S/45S ribosomal DNA (35S/45S rDNA). These tandemly repeated genes encoding for 18S, 5.8S and 25/28S rRNA are transcribed as a single 45/35S pre-rRNA by DNA-dependent RNA polymerase I (PolI). Despite the presence of nucleolus in almost every eucaryotic cell, many questions about its structure and function remain unanswered. Also, the question of how diverse the nucleoli are among the different seed plant representatives is still pending attention. Hence, in this study, we aimed to shed new light on the seed plant nucleolus structure by integrating insights from the ultrastructure of nucleoli components and through the lens of modern superresolution microscopy. Both the model (such asBrachypodium distachyonandArabidopsis thaliana, monocot and eudicot, respectively) and non-model species were analysed. The localisation of the selected nucleolar proteins,i.e.,fibrillarin, nucleolin, and subunits of RNA Pol I, were visualisedin vivousing the GreenGate cloning system. The patterns of selected nucleolar proteins were then compared with the 3-dimensional localisation of the decondensed fraction of 35S rDNA by fluorescentin situhybridisation (FISH). As a result of our study, the functional characterisation of particular nucleolar components has been proposed, shedding new light on the role of the specific nucleolar subcompartments, e.g., the nucleolar vacuoles. The authors gratefully acknowledge financial support from the National Science Centre, Poland (grant no. 2018/31/B/NZ3/01761 and 2018/02/X/NZ3/03197).