Interstitial telomeric repeats are enriched in the centromeres of chromosomes in Solanum species

Interstitial telomeric repeats (ITRs) were reported in a number of animal and plant species. Most ITRs are organized as short tandem arrays and are likely evolutionary relics derived from chromosomal rearrangements and DNA repairs. However, megabase-sized ITR arrays were reported in Solanum species. Here, we report a fluorescence in situ hybridization (FISH) survey of ITRs in all representative diploid Solanum species, including potato, tomato, and eggplant. FISH revealed massive amplification of ITRs in the centromeric regions of chromosomes from the Solanum species containing the B and P genomes. A significant proportion of the ITR FISH signals was mapped within the primary constrictions of the pachytene chromosomes of Solanum pinnatisectum (B genome). In addition, some ITR sites overlapped with St49, a satellite repeat enriched in centromeric DNA sequences associated with CENH3 nucleosomes, in both A and B genome Solanum species. These results show that some ITR subfamilies have been amplified and invaded in the functional centromeres of chromosomes in Solanum species.