Format: ORAL

Jakub Sawicki, Mateusz Mazdziarz, Mateusz Kurzynski,Lukasz Paukszto, Katarzyna Krawczyk, Pawel Sulima, Monika Szczecinska

Department of Botany and Nature Protection, University of Warmia and Mazury in Olsztyn, Poland

Amphibious plants, adept at thriving in the transition zone between terrestrial and aquatic environments, exhibit remarkable adaptability by adjusting their morphology and physiology to fluctuating environments. Riccia fluitans, an aquatic liverwort, serves as an excellent example. This species can grow as floating mats in water or on moist land, demonstrating its versatile adaptability. In our study, we employed genomics and transcriptomics approaches to shed light on the molecular mechanisms that underpin this adaptation. To assemble and annotate the Riccia genome, we utilized nanopore-based native DNA and RNA sequencing, nanopore full-length cDNA transcript sequencing, Illumina-based RNA-seq and DNA-seq of paired-reads, and Hi-C libraries. The genome of Riccia fluitans was 448 Mbp, scattered over 8 chromosome-scale contigs. Interestingly, the genome size was double that of Marchantia polymorpha, mainly due to the expansion of transposons. By comparing the water and land forms of Riccia fluitans, we identified over a thousand differentially expressed genes involved in a variety of biological processes. Our analysis of alternative splicing (AS) revealed over 800 splicing events with significant inclusion levels that differentiated the water and land forms. The majority of these events were classified as intron retention (RI), followed by alternative 3 splice site (A3SS) and alternative 5 splice site (A5SS). The least frequent AS events were exon skipping (SE) and mutually exclusive exons (MXE). We also applied native, direct RNA sequencing to identify m6A sites along the transcriptomes of both water and land forms. This revealed 152 methylated sites across 110 genes in the water form and 25 modified sites across 18 genes in the land form. Interestingly, even among the shared genes (16), different adenosines were methylated in the compared ecotypes. This study thus provides a comprehensive insight into the molecular mechanisms underlying the aquatic adaptation in Riccia fluitans.