Format: ORAL

Ale Kovark1, Terezie Mandkov2, Alice Krumpolcov1,3, Roman Matyek1, Roman Volkov4, Martin Lysk2

1 Department of Molecular Epigenetics, Institute of Biophysics, Academy of Sciences of the Czech Republic, Královopolská 135, 61200 Brno, Czech Republic 2 Central European Institute of Technology (CEITEC), Masaryk University, 625 00 Brno, Czech Republic 3 Department of Experimental Biology, Faculty of Science, Masaryk University, 611 37 Brno, Czech Republic 4- Yuriy Fedkovych Chernivtsi National University, Kotsiubynsky str. 2, 58012 Chernivtsi, Ukraine

Introduction: While uniparental silencing of 35S rDNA in interspecific hybrids and allopolyploids is a well-known phenomenon there is no information on whether silencing also affects the 5S RNA component of ribosomes. To address this question we analyzed the expression of 5S rDNA and 26S rDNA in Cardamine (Brassicaceae) allopolyploids including C. insueta (genome composition ARR, 2n=3x=24), C. flexuosa (AAHH) and C. scutata (AAPP) (both 2n=4x=32). These combine diploid genomes derived from C. amara (A-genome) shared by all three allopolyploids and divergent genomes derived from C. rivularis (R-genome), C. hirsuta (H-genome) and C. parviflora (P-genome) (all 2n=2x=16). Bioinformatic pipelines included high-throughput sequencing of transcriptomes and genomes followed by variant calls and phylogenetic analyses of ribotypes. Genomic organization of rDNA was analyzed by SNPs, clustering and rDNA FISH. Results: In C. insueta allotriploid hybrid we observed uniparental dominant expression of 35S and 5S rDNA loci from the C. rivularis genome. In C. flexuosa and C. scutata allotetraploids 35S rDNA was expressed from the A-genome while 5S rDNA was expressed from the partner H- and P- genomes, respectively. FISH showed relatively intact 5S and 35S loci in C. insueta (twenty populations) while both C. flexuosa and C. scutata allotetraploids showed copy and locus number changes. Intergenomic translocation of the H-genome 5S rDNA was identified in all populations of C. flexuosa which however did not influence its dominant expression. Conclusion: Both 5S and 35S rDNA loci undergo uniparental silencing in Cardamine allopolyploids. In stabilized allopolyploids both rDNA loci are transcribed from different subgenomes. This apparently leads to formation of chimeric ribosomes composed of rRNA molecules originating from different parents. We speculate that epigenetic silencing and rDNA rearrangements generate another layer of variation in multi-molecule ribosomal complexes which may contribute to the evolutionary success of allopolyploids.