Giant Fern Genomes Show Complex Evolution Patterns: A Comparative Analysis in Two Species of Tmesipteris (Psilotaceae)

Giant genomes are rare across the plant kingdom and their study has focused almost exclusively on angiosperms and gymnosperms. The scarce genetic data that are available for ferns, however, indicate differences in their genome organization and a lower dynamism compared to other plant groups. Tmesipteris is a small genus of mainly epiphytic ferns that occur in Oceania and several Pacific Islands. So far, only two species with giant genomes have been reported in the genus, T. tannensis (1C = 73.19 Gbp) and T. obliqua (1C = 147.29 Gbp). Low-coverage genome skimming sequence data were generated in these two species and analyzed using the RepeatExplorer2 pipeline to identify and quantify the repetitive DNA fraction of these genomes. We found that both species share a similar genomic composition, with high repeat diversity compared to taxa with small (1C < 10 Gbp) genomes. We also found that, in general, characterized repetitive elements have relatively high heterogeneity scores, indicating ancient diverging evolutionary trajectories. Our results suggest that a whole genome multiplication event, accumulation of repetitive elements, and recent activation of those repeats have all played a role in shaping these genomes. It will be informative to compare these data in the future with data from the giant genome of the angiosperm Paris japonica, to determine if the structures observed here are an emergent property of massive genomic inflation or derived from lineage specific processes.This research was funded by the Spanish Research Council (Ref: PID2019-108173GA-I00) funded by MCIN/AEI/ 10.13039/501100011033. J.P. benefited from a Ramón y Cajal grant (Ref: RYC-2017-2274) funded by MCIN/AEI/10.13039/501100011033 and by “ESF Investing in your future”. P.F. benefited from a FPU Fellowship (Ref: FPU21/03564) funded by Spanish Ministry of Universities.Abstract Introduction Results Discussion Materials and Methods Conclusions Supplementary Materials Author Contributions Funding Institutional Review Board Statement Informed Consent Statement Data Availability Statement Acknowledgments Conflicts of Interest Reference