Nicotiana tabacum (tobacco) is an allotetraploid derived from ancestors of the modern diploids, N. sylvestris and N. tomentosiformis. We identified and characterized two distinct families of 5S ribosomal DNA (rDNA) in N. tabacum; one family had an average 431 bp unit length and the other a 646 bp unit length. In the diploid species, N. sylvestris and N. tomentosiformis, the 5S rDNA unit lengths are 431 bp and 644 bp respectively. The non-coding spacer sequence of the short unit in tobacco had high sequence homology to the spacer of N. sylvestris5S rDNA, while the longer spacer of tobacco had high homology with the 5S spacer of N. tomentosiformis. This suggests that the two 5S families in tobacco have their origin in the diploid ancestors. The longer spacer sequence had a GC rich sub-region (called the T-genome sub-region) that was absent in the short spacer. Pulsed field gel analysis and fluorescent in situ hybridization to tobacco metaphase chromosomes showed that the two families of 5S rDNA units are spatially separate at two chromosomal loci, on chromosomes S8 (short family) and T8 (long family). The repeat copy number at each chromosomal locus showed heterogeneity between different tobacco cultivars, with a tendency for a decrease in the copy number of one family to be compensated by an increase in the copy number of the second family. Sequence analysis reveals there is as much diversity in 5S family units within the diploid species as there is within the T and S-genome 5S family units respectively, suggesting 5S diversification within each family had occurred before tobacco speciation. There is no evidence of interlocus homogenization of the two 5S families in tobacco. This is therefore substantially different to 18-26S rDNA where interlocus gene conversion has substantially influenced most sequences of S and T genome origin; possible reasons are discussed.

Institute of Biophysics Academy of Sciences of the Czech Republic CZ 61265 Brno Czech Republic

Citace poskytuje Crossref.org

Analysis of 5S rDNA Genomic Organization Through the RepeatExplorer2 Pipeline: A Simplified Protocol

Personal Perspectives on Plant Ribosomal RNA Genes Research: From Precursor-rRNA to Molecular Evolution

Ancient Origin of Two 5S rDNA Families Dominating in the Genus Rosa and Their Behavior in the Canina-Type Meiosis

The Utility of Graph Clustering of 5S Ribosomal DNA Homoeologs in Plant Allopolyploids, Homoploid Hybrids, and Cryptic Introgressants

The origin of exon 3 skipping of paternal GLOBOSA pre-mRNA in some Nicotiana tabacum lines correlates with a point mutation of the very last nucleotide of the exon

Inhibition of SAH-hydrolase activity during seed germination leads to deregulation of flowering genes and altered flower morphology in tobacco

Faithful inheritance of cytosine methylation patterns in repeated sequences of the allotetraploid tobacco correlates with the expression of DNA methyltransferase gene families from both parental genomes

Low abundant spacer 5S rRNA transcripts are frequently polyadenylated in Nicotiana