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    Determination of nuclear dna content and ploidy of some bromus l. Germplasm by flow cytometery
    (Pakistan Botanical Society, 2020) Nizam, İlker; Gülcü, R.; Tuna, G.S.; Tuna, M.
    The objective of this study was to determine nuclear DNA content and ploidy of 48 Bromus L. gene bank accessions obtained from USDA by flow cytometry. Based on the results of the flow cytometric analysis, the mean 2C nuclear DNA content of Bromus accessions used in the study varied between 11.43 pg with 26.62 pg. The nuclear DNA content differences among Bromus L. accessions were statistically significant at P<0.01 level. The accessions were easily separated into three distinct groups according to their DNA contents. The mean 2C nuclear DNA content of the groups were 11.82, 22.43 and 26.17 pg (min. and max. values of group were between 11.43–12.65 pg, 21.45–22.77 pg, 25.48–26.62 pg, respectively). Nuclear DNA content of the accessions were correlated with their ploidy levels by counting chromosomes of the one plant from each group with classical staining methods. In conclusion, majority of the Bromus accessions (33 out of 48) analysed in the study were tetraploid with 2n=4x=28 chromosomes. Ten and five of the remaining accessions were octaploid (2n=8x=56) and (2n=10x=70) decaploids, respectively. No decaploid B. inermis plant reported until today. However, decaploids were reported for B. riparius and B. biebersteini species. Therefore, decaploid plants determined in this study should be considered as either B. riparius or B. biebersteini. © 2020, Pakistan Botanical Society. All rights reserved.
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    The fate of 35S rRNA genes in the allotetraploid grass Brachypodium hybridum
    (Blackwell Publishing Ltd, 2020) Borowska-Zuchowska, N.; Kovarik, A.; Robaszkiewicz, E.; Tuna, Metin; Tuna, G.S.; Gordon, S.; Hasterok, R.
    Nucleolar dominance (ND) consists of the reversible silencing of 35S/45S rDNA loci inherited from one of the ancestors of an allopolyploid. The molecular mechanisms by which one ancestral rDNA set is selected for silencing remain unclear. We applied a combination of molecular (Southern blot hybridization and reverse-transcription cleaved amplified polymorphic sequence analysis), genomic (analysis of variants) and cytogenetic (fluorescence in situ hybridization) approaches to study the structure, expression and epigenetic landscape of 35S rDNA in an allotetraploid grass that exhibits ND, Brachypodium hybridum (genome composition DDSS), and its putative progenitors, Brachypodium distachyon (DD) and Brachypodium stacei (SS). In progenitor genomes, B. stacei showed a higher intragenomic heterogeneity of rDNA compared with B. distachyon. In all studied accessions of B. hybridum, there was a reduction in the copy number of S homoeologues, which was accompanied by their inactive transcriptional status. The involvement of DNA methylation in CG and CHG contexts in the silencing of the S-genome rDNA loci was revealed. In the B. hybridum allotetraploid, ND is stabilized towards the D-genome units, irrespective of the polyphyletic origin of the species, and does not seem to be influenced by homoeologous 35S rDNA ratios and developmental stage. © 2020 The Authors. The Plant Journal published by Society for Experimental Biology and John Wiley & Sons Ltd.