RFLP and physical mapping with an rDNA-specific endonuclease reveals that nucleolus organizer regions of Arabidopsis thaliana adjoin the telomeres on chromosomes 2 and 4

The physical mapping of genes can reveal the organization of a genome and identify relationships of plant species, especially where they are involved in interspecific hybridization and polyploidy. Here we determine the chromosomal locations of the major ribosomal gene family (18S-5.8S-26S rDNA) by fluorescent in situ hybridization in two Icelandic birch species, Betulapubescens Ehrh. and Betulanana L. In the tetraploid birch (B. pubescens), the rDNA was localized on four major and two minor sites, while the diploid dwarf birch (B. nana) had four major sites. The major loci in both species were in nucleolus organizer regions, close to the centromeres of a pair of metacentric and a pair of sub-metacentric chromosomes. The dispersed interphase in situ hybridization pattern showed gene expression at all major sites. The two additional loci in B. pubescens, when detected, appeared to be sub-telomeric and inactive at interphase. Southern analysis of rDNA showed considerable restriction fragment length polymorphism in B. pubescens. Some polymorphism may reflect gene flow among populations and between the two co-existing birch species. The understanding of genome relationships, gene introgression, and evolution of birch species will be important to the breeding programmes steered towards environmental conservation and forestry.

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Comparative physical mapping reveals features of microsynteny between Glycine max, Medicago truncatula, and Arabidopsis thaliana

Genome ◽

10.1139/g03-106 ◽

2004 ◽

Vol 47 (1) ◽

pp. 141-155 ◽

Cited By ~ 38

Author(s):

H H Yan ◽

J Mudge ◽

D-J Kim ◽

R C Shoemaker ◽

D R Cook ◽

...

Keyword(s):

Arabidopsis Thaliana ◽

Glycine Max ◽

Medicago Truncatula ◽

Physical Mapping ◽

Large Scale ◽

Sequence Similarity ◽

Artificial Chromosome ◽

Bac Contig ◽

Cross Hybridization ◽

Bac Contigs

To gain insight into genomic relationships between soybean (Glycine max) and Medicago truncatula, eight groups of bacterial artificial chromosome (BAC) contigs, together spanning 2.60 million base pairs (Mb) in G. max and 1.56 Mb in M. truncatula, were compared through high-resolution physical mapping combined with sequence and hybridization analysis of low-copy BAC ends. Cross-hybridization among G. max and M. truncatula contigs uncovered microsynteny in six of the contig groups and extensive microsynteny in three. Between G. max homoeologous (within genome duplicate) contigs, 85% of coding and 75% of noncoding sequences were conserved at the level of cross-hybridization. By contrast, only 29% of sequences were conserved between G. max and M. truncatula, and some kilobase-scale rearrangements were also observed. Detailed restriction maps were constructed for 11 contigs from the three highly microsyntenic groups, and these maps suggested that sequence order was highly conserved between G. max duplicates and generally conserved between G. max and M. truncatula. One instance of homoeologous BAC contigs in M. truncatula was also observed and examined in detail. A sequence similarity search against the Arabidopsis thaliana genome sequence identified up to three microsyntenic regions in A. thaliana for each of two of the legume BAC contig groups. Together, these results confirm previous predictions of one recent genome-wide duplication in G. max and suggest that M. truncatula also experienced ancient large-scale genome duplications.Key words: Glycine max, Medicago truncatula, Arabidopsis thaliana, conserved microsynteny, genome duplication.

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