Repetitive sequences in the genome of Anemone blanda: identification of tandem arrays and of dispersed repeats.

Abstract

A tandemly repetitive sequence family (AbS1) and a repetitive sequence (Hd) forming part of a larger dispersed element (dorf-1) of Anemone blanda were characterised. The AbS1 satellite sequence family is located in all 4',6-diamidino-2-phenylindole (DAPI) positive intercalary heterochromatic bands and in the DAPI positive heterochromatic terminal region of chromosome 3, while the dispersed Hd homologous sequences are preferentially associated with euchromatic chromosome regions. The major component of the AbS1 satellite is AbS1-H1 with a basic repeat unit of 1640 bp; a minor fraction (AbS1-H5) consists of 320 bp units. A subsection of the AbS1-H1 repeat unit exhibits homologies to the 25S rRNA gene of flowering plants suggesting that the 1.64 kb satellite was generated by amplification of a precursor satellite and/or single copy sequence together with an rDNA fragment. The rDNA homologous region is considered to evolve at a rate similar to pseudogenes and thus the age of this satellite DNA fraction can be roughly estimated as about 27 million years. The dispersed repeated sequence Hd (about 1300 bp) is associated with the 8 kb element dorf-1. A. blanda dorf-1 constitutes about 0.2% of the genome (3 x 10(4) copies), is bounded by identical long terminal repeats, and exhibits partial homology to the Lilium gypsy-type element del1, but has yet to be confirmed as a retrotransposon. In contrast to the AbS1 satellite sequence family, Hd homologous sequences were found not only in A. apennina, the closest relative of A. blanda, but also in A. nemorosa and A. ranunculoides indicating that a progenitor sequence of dorf-1 was present in a common ancestor before speciation occurred.