Comparative Analysis of rDNA Distribution in Chromosomes of Various Species of Brassicaceae

Abstract

The number of rDNA sites can differ up to 5-fold in species with the same chromosome number. In addition to the eight previously reported chromosomal types with ribosomal genes, three new variant types are described. The extent of polymorphism is genome dependent. Comparing the A, B and C genomes revealed the highest rDNA polymorphism in the A genome. The loci carrying presumably inactive ribosomal RNA genes are particularly prone to polymorphism. It can also be concluded that there is no obvious polyploidization-related tendency to reduce the number of ribosomal DNA loci in the allotetraploid species, when compared with their putative diploid progenitors. The observed differences are rather caused by the prevailing polymorphism within the diploids and allotetraploids. This would make it difficult to predict expected numbers of rDNA loci in natural polyploids.

FISH Karyotype and GISH Meiotic Pairing Analyses of a Stable Intergeneric Hybrid xBrassicoraphanus Line BB#5

“…The FISH technique has been shown to be especially useful for more accurate karyotype analysis because it provides good diagnostic markers for identification of each chromosome. Tandem repeat sequences such as 5S and 45S rDNAs have primarily been used as probes for FISH (Fujii and Ohmido, 2011;Fukui et al, 1998;Hasterok et al, 2006;Kim et al, 1998;Lim et al, 2007;Snowdon et al, 1997). Several researchers applied FISH in Brassica rapa using 5S and 45S rDNA probes and reported three and five 5S and 45S rDNA pairs, respectively (Hwang et al, 2009;Koo et al, 2011;Lim et al, 2005;Xiong and Pires, 2011).…”

“…In Brassica, Maluszynska and Heslop-Harrison (1993) first reported the number of 45S rDNA loci in diploids (B. rapa, n = 10, AA genome; B. nigra; n = 8, BB genome; B. oleracea, n = 9, CC genome,) and allo-tetraploids (B. carinata, n = 17, BBCC genome; B. juncea, n = 18, AABB genome; B. napus, n = 19, AACC genome). Genomic distributions of rDNA sites on prometaphase and metaphase chromosomes were described more precisely upon further investigations (Fukui et al, 1998;Muluszynska, 2000a, 2000b;Hasterok et al, 2006;Hwang et al, 2009;Kim et al, 1998;Snowdon et al, 1997). Some chromosomes of the complements were identified exactly, enabling a detailed karyotype analysis for the genus Brassica.…”

Chinese cabbage (Brassica rapa ssp. pekinensis) – a valuable source of resistance to clubroot (Plasmodiophora brassicae)

“…Whole seedlings were then treated with 2 mM 8-hydroxyquinoline for 1-4 h at room temperature, fixed in a 3:1 (v/v) mixture of ethanol and glacial acetic acid, and stored at −20°C until required. Further treatment was performed according to Hasterok et al (2006). Chromosome analysis was carried out using an Olympus BX 60 epifluorescence microscope on 3-5 well-spread metaphase phase cells.…”

“…For ribosomal genes, we followed the nomenclature allowing attribution of each chromosome to a linkage group in B. rapa (Kim et al 2009) and B. oleracea (Howell et al 2002). In case of sites which are located on the cytogenetically undistinguishable A5, A6, and A9 chromosomes (collectively grouped as Brassica chromosomal type VIII), we followed the nomenclature proposed by Hasterok et al (2006). The base chromosomal types, numbered I-VIII, have been introduced and described in detail by Hasterok et al (2001), with the exception that the 5S rDNA site in chromosome type V is now assigned to the short arm (Hasterok et al 2006).…”

“…In case of sites which are located on the cytogenetically undistinguishable A5, A6, and A9 chromosomes (collectively grouped as Brassica chromosomal type VIII), we followed the nomenclature proposed by Hasterok et al (2006). The base chromosomal types, numbered I-VIII, have been introduced and described in detail by Hasterok et al (2001), with the exception that the 5S rDNA site in chromosome type V is now assigned to the short arm (Hasterok et al 2006). The ribosomal probes used in this study were 26S rDNA (Unfried and Gruendler 1990), used for detection of 35S rDNA loci, and pTa794 (Gerlach and Dyer 1980), which contained the 5S rDNA.…”