Chromosome characterization in Thinopyrum ponticum (Triticeae, Poaceae) using in situ hybridization with different DNA sequences

Abstract

Thinopyrum ponticum (2n = 10x = 70, JJJJ s J s ) belongs to the Triticeae tribe, and is currently used as a source of pathogen resistance genes in wheat breeding. In order to characterize its chromosomes, the number and position of 45S and 5S rDNA sites, as well as the distribution of the repetitive DNA sequences pAs1 and pSc119.2, were identified by fluorescent in situ hybridization. The number of nucleoli and NORs was also recorded after silver nitrate staining. Seventeen 45S and twenty 5S rDNA sites were observed on the short arms of 17 chromosomes, the 45S rDNA was always located terminally. On three other chromosomes, only the 5S rDNA site was observed. Silver staining revealed a high number of Ag-NORs (14 to 17) on metaphase chromosomes, whereas on interphase nuclei there was a large variation in number of nucleoli (one to 15), most of them (82.8%) ranging between four and nine. The pAs1 probe hybridized to the terminal region of both arms of all 70 chromosomes. In addition, a disperse labeling was observed throughout the chromosomes, except in centromeric and most pericentromeric regions. When the pSc119.2 sequence was used as a probe, terminal labeling was observed on the short arms of 17 chromosomes and on the long arms of five others. The relative position of 45S and 5S rDNA sites, together with the hybridization pattern of pAs1 and pSc119.2 probes, should allow whole chromosomes or chromosome segments of Th. ponticum to be identified in inbred lines of wheat x Th. ponticum.

Classical and Molecular Cytogenetic Tools to Resolve the Bixa Karyotypes

“…Considering that, during mitosis, active NORs possess transcription factors of rDNA genes, that impregnate with silver (Morais-Cecílio et al 2000, Besendorfer et al 2002, Brasileiro-Vidal et al 2003, Neves et al 2005, the presence of a single active NOR was confirmed at the portion of chromosome 1 adjacent to the centromere, in B. arborea (Fig. 1c), indicating that this region contains the chromosomal domain around which nucleoli are organized at the end of mitosis, when rDNA transcription is initiated.…”

Heterochromatin diversity and its co-localization with 5S and 45S rDNA sites in chromosomes of four Maxillaria species (Orchidaceae)

“…Secondary constrictions can be observed by conventional chromosome staining techniques, but are more easily identified by silver nitrate (Ag) staining or in situ hybridization with 45S rDNA probes (see e.g. Brasileiro-Vidal et al, 2003). These constrictions are largely known as 45S rDNA location sites, although smaller or less active 45S rDNA sites may exist in chromosomes which apparently do not form secondary constrictions (Guerra et al, 1996).…”

Cytogenetic and identification of the nucleolus organizer region in Heliconia bihai (L.) L.

“…During mitosis, the active NORs are those where rDNAs are associated with proteins that associate themselves with silver (Roussel , 1996;Morais-Cecílio et al, 2000;Besendorfer et al, 2002;Brasileiro-Vidal et al, 2003;Almeida & Carvalho, 2004;Neves et al, 2005;Clarindo & Carvalho, 2006). The presence of the active NOR on pairs (1 and 2) indicates, according to Mergonar et al (2010), that these chromosomal regions have chromosome domains around which nucleoli at the end of mitosis are arranged, when the rDNA transcription is initiated.…”