Centromeric Sequences Change in Wheat and its Distant Hybrids

Centromeres typically contain repeat sequences, but centromere function does not necessarily depend on these sequences. In aneuploid wheat (Triticum aestivum) and the offspring of wide hybrid, we found functional centromeres with severe quantitative changes regarding the content of centromeric retrotransposon of wheat (CRW) sequences. CRWs were strongly reduced in the ditelosomic lines 1BS, 5DS, 5DL, which did not affect centromere function. A wheat-Thinopyrum elongatum addition line and they were completely lost in the ditelosomic line 4DS. A 994-kb ectopic genomic DNA sequence near the former centromeres was involved in de novo centromere formation on 4DS chromosome. The 994-kb region revealed no differential enrichment of histone modification comparing to normal centromere. In addition, two ectopic sequences were incorporated in a de novo centromere of a wheat-Th. intermedium addition line. Stable alien chromosomes with two and three regions containing CRW sequences were found in wheat-Th. elongatum hybrid derivatives, but only one represented a functional centromere. In wheat-rye (Secale cereale) hybrids, rye centromere specific sequences spread along one the chromosome arm and may cause centromere expansion. Thus, Chromosome rearrangement during the formation of wheat aneuploidy and its distant hybrid caused centromere sequence elimination, expansion and multi-centromere formation, which may be associated with chromosome stability and novel chromosome formation.