The intergenic spacer region of the rDNA in Haplopappus gracilis (Nutt.) Gray

Abstract

In this paper, we provide further information on the genome organisation of Haplopappus gracilis, one of the six angiosperms showing the lowest chromosome number, i.e. 2n = 4, by determining the nucleotide sequence of the intergenic spacer region of the ribosomal RNA genes and its cytological localization on metaphase chromosomes. DNA sequence analysis reveals the occurring of a product of 4,382 bp in length, characterised by the presence of four blocks of different repeated sequences. Our analysis also evidenced putative promoter regions with three transcription initiation sites for polymerase I, as previously reported in Artemisia absinthium, belonging to the same Asteraceae family. A fluorescent in situ hybridization with the intergenic spacer probe indicates the presence of rDNA genes only in the satellited chromosomes of H. gracilis; besides, differences in the signal intensity between homologous chromosomes were frequently observed, thus suggesting for these chromosome sites the presence of a variable number of rDNA gene copies, even if a divergent chromatin organisation in corresponding regions cannot be ruled out.

Phylogenetic implications of nuclear rRNA IGS variation in Stipa L. (Poaceae)

“…The species included in the study also differed significantly regarding the presence of regions rich in AT sites. These regions are of special concern because they putatively contain protein binding sites involved in regulation of transcription and are associated with a proximity of gene promoter 8 , 39 , 40 . The presence of AT-rich sequence adjacent to TIS sites was reported, for example for Arabidopsis thaliana 41 , Olea europea 42 Haplopappus gracilis 39 , Fagus sylvatica , Quercus suber 43 and Brassica oleracea 32 .…”

Cytomolecular Analysis of Ribosomal DNA Evolution in a Natural Allotetraploid Brachypodium hybridum and Its Putative Ancestors—Dissecting Complex Repetitive Structure of Intergenic Spacers

“…Similar to rice (Cordesse et al, 1993 ), all of the putative TISs were placed within repetitive sequences in Brachypodium species. Spacer promoters that have blocks of tandemly repeated sequences represent putative transcription enhancers (Schlögelhofer et al, 2002 ; Castiglione et al, 2013 ). Their role in establishing ND was revealed in Xenopus hybrids, in which the 35S rDNA loci that had longer IGS and contained more subrepeats upstream to the TIS, dominate over the loci with a lower number of subrepeats.…”

High Penetrance of a Pan-<b><i>Canina</i></b> Type rDNA Family in Intersection <b><i>Rosa</i></b> Hybrids Suggests Strong Selection of Bivalent Chromosomes in the Section <b><i>Caninae</i></b>

“…However, 1 site was extremely weak, while 3 sites were strong. Asymmetrical signal intensity on homologous chromosomes has been noted by cytogeneticists in other systems [Denduangboripant et al, 2007;Castiglione et al, 2008Castiglione et al, , 2013 and has been attributed to a variation in gene copies, epigenetic modification, differential condensation of rDNA chromatin, and overall heterozygosity. The latter is supported by microsatellite genotyping indicating that the diploid pollen of 'André Brichet' is heterogeneous in contrast to the homogenous pollen of R. rubiginosa [Werlemark, unpubl.…”