The molecular cytogenetics of Vigna unguiculata (L.) Walp: the physical organization and characterization of 18s-5.8s-25s rRNA genes, 5s rRNA genes, telomere-like sequences, and a family of centromeric repetitive DNA sequences

Abstract

A knowledge of genome organization is important for understanding how genomes function and evolve, and provide information likely to be useful in plant breeding programmes involving hybridization and genetic manipulation. Molecular techniques, including in situ hybridization, molecular cloning and DNA sequencing, are proving valuable tools to investigate the structure, organization, and diversity of chromosomes in agricultural crops. Heterologous labelled 18 s-5.8 s-25 s (pTa71) and 5 s rDNAs (pTa794) were used for in situ hybridization on Vigna unguiculata (L.) Walp. chromosomes. Hybridization with 18 s-5.8 s-25 s rRNA gene probes occurred at the same chromosomal sites which were positive to the CMA fluorochrome. Silver staining of nucleolar-organizing regions indicated that all the rDNA sites detected using the 18 s-5.8 s-25 s rRNA gene probe possessed active genes. Degenerate telomeric repeats gave hybridization signals at the telomeres of most chromosomes and no intercalary sites were detected at metaphase; the sequences appear to have no preferential distribution in interphase nuclei. A repetitive DraI family from V. unguiculata was cloned (pVuKB1) and characterized. The DraI repeat is 488 nucleotides long, AT rich (74%), and hybridized on all chromosomes in the centromeric areas. The presence of this sequence family was investigated by Southern hybridization in different Vigna species and other Leguminoseae. It was only detected in V. unguiculata, and hence represents a species-specific DNA sequence.

Plant polytene chromosomes

“…According to , the variation in the number of rDNA sites observed between species of related taxa could be due to the differ-ential amplification and fixation of rDNA sequences at different chromosomal sites. On the other hand, four 5S ribosomal sites were observed in V. radiata and V. unguiculata , confirming the previous reports for V. unguiculata (Galasso et al, 1995), although these reports were first published for V. radiata.…”

Cytotaxonomic studies inVigna.IV. Variation of the number of active and silent rDNA sites inVigna unguiculatapopulations

“…la) and in other six accessions (Table 1) showed the presence of three telomeric CMA + blocks per haploid genome on chromosomes named 2, 4, and 5 plus a block located at the secondary constriction of chromosome 3 following the numenclature of GALASSO et al (1993); chromosome 1, the most prominent chromosome of the complement, is also indicate in all pictures. All the accessions showing this pattern belonged to v. unguiculata subsp.…”

Karyotype studies on populations of two Hypochaeris species (H. catharinensis and H. lutea), Asteraceae, endemics to southern Brazil

“…These signals were confirmed as bright spots in the interphase nuclei of H. catharinensis ( Figure 1C). Whereas the co-location of CMA 3 -positive bands with rDNA loci is common in Hypochaeris (Cerbah et al, 1998;Ruas et al, 2005) as well as in other plant groups (Galasso et al, 1995;Fukui and Nakayama, 1996;Vanzela et al, 2002), the unusual distribution of GC-rich heterochromatin identified in H. catharinensis differs from any pattern already described for other Hypochaeris species. Although we could not detect any AT-rich block in H. catharinensis, Reck et al (2011) described a DAPI fluorescent signal located at the intersticial position on short arms of chromosome pair 4 of this species.…”