Localization of ribosomal DNA and CMA3/DAPI heterochromatin in cultivated and wild Amaranthus species

• The distribution patterns of 35S and 5S rDNA sites as well as GC-rich regions in the chromosomes of fourteen Amaranthus species were established.
• The genus Amaranthus showed considerable inter- and intraspecific variability in rDNA site number.
• FISH with 5S and 35S rDNA probes allowed to identify from one to eight chromosome pairs depending on the accessions.
• CG-rich regions were associated with the 35S rDNA sites and in some accessions also with 5S rDNA sites.

The distributional pattern of GC-rich regions and the physical mapping of ribosomal DNA (location of 35S and 5S rDNA) in the chromosomes of fourteen Amaranthus species were established using fluorochrome banding and fluorescence in situ hybridization (FISH). The karyotypes are composed of 2n = 32 or 2n = 34 chromosomes. Some species were also shown to exhibit infraspecific polymorphism in the chromosome number and consisted of accessions with both of these chromosome numbers. Two families of ribosomal genes, 35S and 5S rDNA, were separated onto different pairs in chromosome complements of most of the species examined. Both 35S and 5S rDNA sites were always located in the terminal part of the chromosomes and usually 35S rDNA sites were present in a lower number than the 5S rDNA sites in most of the species that were analyzed. Polymorphism of the rDNA site number was observed in three species. Fluorochrome banding revealed that CMA+/DAPI− bands were associated with the 35S rDNA sites in all of the species that were analyzed. In some amaranth accessions, 5S rDNA regions were also GC-rich. The possible mechanisms of the evolution of rDNA loci are discussed.