Repetitive DNA sequences in Crocus vernus Hill (Iridaceae): The genomic organization and distribution of dispersed elements in the genus Crocus and its allies

Eight clones of repetitive DNA were isolated from Crocus vernus Hill. The g enomic organization of the clones was analyzed by in situ hybridization to C. vernus and Southern hybridization to a range of Crocus and other species . Seven clones were used for in situ hybridization. Sequence analysis showe d that all eight clones were nonhomologous, and thus represented eight diff erent sequence-families. In situ hybridization showed that six were dispers ed in high copy numbers on all chromosomes of the C. vernus genome, whereas one was localized proximal to the secondary constriction, at the NOR (nucl eolar organizer region) and was not further analyzed, as it was considered part of the 18S-25S rDNA repeat. Except for short palindromes, none of the sequences showed notable internal structures. Clone pCvKB4 showed homology to the reverse transcriptase gene of Ty1-copia-like retrotransposons; the o thers showed no homology to known sequences. When used as probes for Southe rn hybridization, four showed a ladder of 3-4 bands superimposed by irregul ar patterns, indicating organization in short tandem arrays. Each clone had a unique distribution among Crocus species (12-16 species analyzed with ea ch clone) and six species of Iridaceae, Liliaceae, and Amaryllidaceae; all seven investigated sequences were Iridaceae specific and four were Crocus s pecific. The species distribution of these seven clones showed notable disc repancies with the taxonomic subdivision of the genus at the subgenus, sect ion, and series levels. The results suggest that the phylogeny and taxonomi c structure of the genus Crocus might need reconsideration. The analysis of repetitive DNA as a major and rapidly evolving part of the genome could co ntribute to the study of species relationships and evolution.