Format: ORAL

Daniel Vitales1, Joan Pere Pascual-Daz1, Teresa Garnatje1, Andrew Leitch2, Ales Kovarik3, Snia Garcia1

1 Institut Botànic de Barcelona (CSIC-CMCNB), Barcelona, Spain 2 School of Biological and Chemical Sciences, Queen Mary University of London, London, United Kingdom 3 Institute of Biophysics, Academy of Sciences of the Czech Republic, Brno, Czech Republic

Here we explore the evolutionary dynamism of ribosomal RNA genes (rDNA), a dynamism that is surprisingly high given their crucial role in the synthesis of ribosomes and thus for life-on-Earth. rDNA units are present in high numbers, from 50 to 13,000 copies per cell that are typically tandemly arranged at one or a few loci. However, despite their importance and abundance, several aspects of the biology remain enigmatic, particularly their mode of molecular evolution and genomic arrangements. We aim to deconstruct ribosomal DNA structure to define the model of evolution that best explains its high evolutionary dynamism and the differences in behaviour of 35S and 5S rRNA genes. We have used 74 species in the sunflower family (Asteraceae) as models for this analysis, which together represent a diversity of rDNA arrangements, genome sizes, ploidy levels, and rDNA copy numbers. Indeed, family Asteraceae shows a particularly large diversity of rDNA arrangements amongst its 24,000 species, including in subfamily Asteroideae (tribe Anthemideae and some tribes of the Heliantheae alliance), where there is an exceptional arrangement of 35S and 5S rRNA genes being linked together. Using next-generation sequencing (NGS) and analytical approaches we address central questions allowing us novel, fundamental insights into genomic mechanisms related to concerted evolution, pseudogenisation, the relationship with genome size and rDNAs or their interplay with transposable elements. Our results impact our global understanding of molecular evolution and repetitive DNA organisation in plant genomes.