The structure, abundance and location of repetitive DNA sequences on chromosomes can characterize the nature of higher plant genomes. Here we report on three new repeat DNA families isolated from Anemone hortensis L.; (i) AhTR1, a family of satellite DNA (stDNA) composed of a 554-561 bp long EcoRV monomer; (ii) AhTR2, a stDNA family composed of a 743 bp long HindIII monomer and; (iii) AhDR, a repeat family composed of a 945 bp long HindIII fragment that exhibits some sequence similarity to Ty3/gypsy-like retroelements. Fluorescence in-situ hybridization (FISH) to metaphase chromosomes of A. hortensis (2n = 16) revealed that both AhTR1 and AhTR2 sequences co-localized with DAPI-positive AT-rich heterochromatic regions. AhTR1 sequences occur at intercalary DAPI bands while AhTR2 sequences occur at 8-10 terminally located heterochromatic blocks. In contrast AhDR sequences are dispersed over all chromosomes as expected of a Ty3/gypsy-like element. AhTR2 and AhTR1 repeat families include polyA- and polyT-tracks, AT/TA-motifs and a pentanucleotide sequence (CAAAA) that may have consequences for chromatin packing and sequence homogeneity. AhTR2 repeats also contain TTTAGGG motifs and degenerate variants. We suggest that they arose by interspersion of telomeric repeats with subtelomeric repeats, before hybrid unit(s) amplified through the heterochromatic domain. The three repetitive DNA families together occupy approximately 10% of the A. hortensis genome. Comparative analyses of eight Anemone species revealed that the divergence of the A. hortensis genome was accompanied by considerable modification and/or amplification of repeats.

The 35S ribosomal DNA (rDNA) intergenic spacer (IGS) of Allium cernuum is examined. Initial sequencing of IGS clones revealed that some rDNA units contain a truncated retrotransposon sequence most similar to members of the Copia superfamily. Fluorescence in situ hybridisation (FISH) to metaphase chromosomes indicates that this element is dispersed along both pairs of major rDNA arrays. Southern hybridisation confirmed the presence of this ‘relic’ Copia-like element in more than 10% of 35S rDNA units, in the same position within the IGS. To measure the intragenomic divergence of the relic retroelement and its flanking sequences amongst different rDNA units, a 1.1-kb region was amplified and cloned. These data collectively point to a single origin for units containing the putative retrotransposon fragment. It is likely that units containing the putative retroelement increased in copy number and dispersed via rDNA homogenisation mechanisms, rather than by multiple retrotransposition events.