Closely related Allium species (Alliaceae) share a very similar satellite sequence

A satellite sequence repeat of Allium cepa was tested by fluorescent in situ hybridization (FISH) for cross-hybridization to chromosomes of 27 species (in 37 accessions) belonging to 14 sections of four subgenera of Allium. All investigated species of sect. Cepa, With the two subsects. Cepa and Phyllodolon, revealed clear satellite-specific hybridization signals mainly at their chromosome termini. The tested species belonging to other sections/subgenera revealed no hybridization signals. An exception was A. roylei, assigned to sect. Oreiprason. Its chromosomes also showed strong terminal hybridization signals. This and other features suggest a close relationship of A. roylei to the species of sect. Cepa in spite of deviating morphological characters. The divergence between the satellite repeats to species to which the A. cepa repeat cross-hybridized was determined and revealed high degrees of similarity. Therefore, we conclude that this satellite sequence had evolved already in progenitor forms of sect. Cepa and remained unusually well conserved during speciation. This might indicate selection pressure exerted on a secondarily acquired telomere function of the satellite sequence.