Format: ORAL

Pol Fernndez 1,2, Ilia J. Leitch 3, Andrew R. Leitch 4, Lisa Pokorny 5,3, Oriane Hidalgo 1,3, Maarten J. M. Christenhusz 3, Rmy Amice 6, David Bruy 7,8 , Jaume Pellicer 1,3

1 Institut Botànic de Barcelona (IBB), CSIC-CMCNB, Passeig del Migdia s.n., Parc de Montjuïc, 08038 Barcelona, Spain 2 Facultat de Farmàcia i Ciències de l’alimentació, Campus Diagonal, Universitat de Barcelona, Av. de Joan XXIII, 27-31, 08028 Barcelona, Spain 3 Royal Botanic Gardens, Kew, Richmond TW9 3AE, United Kingdom 4 School of Biological and Behavioural Sciences, Queen Mary University of London, London E1 4NS, United Kingdom 5 Real Jardín Botánico (RJB-CSIC), Plaza de Murillo 2, 28014 Madrid, Spain 6 Independent researcher, Nouméa, Nouvelle-Calédonie 7 AMAP, IRD, Herbier de Nouvelle-Calédonie, Nouméa, Nouvelle-Calédonie 8 UMR AMAP, Université Montpellier, IRD, CIRAD, CNRS, INRAE, F-34000, Montpellier, France

Genomic architecture in ferns stands out significantly from that of other plant lineages. Ferns exhibit a unique response to whole genome multiplication (WGM), deviating from the typical diploidization pattern observed in angiosperms. Instead, ferns tend to accumulate chromosomes and trigger the silencing of newly acquired gene copies following WGM. Consequently, ferns display higher mean chromosome numbers (n=61) compared to angiosperms (n=17). Nevertheless, while average fern genome sizes (1C=12.11 Gbp) are larger when compared to angiosperms (1C=5.13 Gbp), the underlying mechanisms responsible for such differences remain unclear. Certainly, the contribution of repetitive DNA in driving shifts in genome size is well studied in angiosperms, but needs to be further explored in ferns. This study seeks to address this knowledge gap by conducting a comprehensive comparative analysis to identify and quantify the main types of repetitive DNA sequences in 50 fern species. The sampling covers a genome size range varying over 222-fold (0.72160.4 Gbp), including the largest eukaryote genome recently discovered in the fern Tmesipteris oblanceolata (1C=160.4 Gbp). The central focus of this research is to enhance our understanding of the genomic processes contributing to the unique characteristics observed in fern genomes, shedding light on the broader evolutionary implications for plant genome size. The composition of the repetitive DNA fraction of the genome for each species has been identified and quantified through low-coverage genome skimming sequence data analysed with the RepeatExplorer2 pipeline. Overall, our results show that fern genomes have a more heterogenous genome landscape than angiosperms and, unlike them, they show a positive correlation of repetitive elements with genome size. Future studies will focus on identifying the particular role of specific families of repeats that are enriched or depleted in fern genomes, while diving deeper into the relationship between the accumulation of chromosomes and its implication on genome composition.