Abstract
Speciation and allopolyploidization in cereals may be accompanied by dramatic changes in abundance of centromeric repeated transposable elements. Here we demonstrate that the reverse transcriptase part of Ty3/gypsy centromeric retrotransposon (RT-CR) is highly conservative in the segmental hexaploid Thinopyrum intermedium (JrJvsSt) and its possible diploid progenitors Th. bessarabicum (Jb), Pseudoroegneria spicata (St) and Dasypyrum villosum (V) but the abundance of the repeats varied to a large extent. Fluorescence in situ hybridization (FISH) showed hybridization signals in centromeric region of all chromosomes in the studied species, although the intensity of the signals drastically differed. In Th. intermedium, the strongest signal of RT-CR probe was detected on the chromosomes of Jv, intermediate on Jr and faint on Js and St subgenome suggesting different abundance of RT-CR on the individual chromosomes rather than the sequence specificity of RT-CRs of the subgenomes. RT-CR quantification using real-time PCR revealed that its content per genome in Th. bessarabicum is ~ 2 times and P. spicata is ~ 1,5 times higher than in genome of D. villosum. The possible burst of Ty3/gypsy centromeric retrotransposon in Th. intermedium during allopolyploidization and its role in proper mitotic and meiotic chromosome behavior in a nascent allopolyploid is discussed.
Highlights
Centromeres are responsible for kinetochore assembly that links chromosome to microtubes and play a key role in equal chromosome segregation and transmission during cell division
PCR with the TAIDF/R primers using genomic DNA of Th. intermedium, Th. bessarabicum, P. spicata and D. villosum resulted in the amplification of a pool of closely related ~ 490 bp fragments of the reverse transcriptase gene of centromeric retrotransposons (RT-CR)
Bessarabicum, Jb) and St (P. spicata, St) subgenomes. These results differ from those that could be expected based on the Fluorescence in situ hybridization (FISH) results obtained for chromosomes of each subgenome of Th. intermedium, namely, that four Jv chromosomes are more abundant in CRs in centromeres than other chromosomes
Summary
Centromeres are responsible for kinetochore assembly that links chromosome to microtubes and play a key role in equal chromosome segregation and transmission during cell division. The centromere sequences are usually represented by DNA satellites interspersed with long terminal repeat (LTR) centromeric retrotransposons (CR), both are associated with CENH3, centromere specific variant of histone H3 [1,2,3,4,5,6,7]. CRs were found as highly conserved centromere-specific sequences in grasses [2, 3] and are represented by Cereba. The abundance of centromeric repeat may be associated with the ploidy level and their amplification and transposition may occur in response to polyploidization event [19]. In bread wheat (Triticum aestivum), a recently formed polyploid (BBAADD), two centromere-specific elements have been found: CRW ( called Cereba) and Quinta that are the youngest elements at the centromeres of common wheat and its diploid ancestors. It was shown that the D subgenome chromosomes contained fewer copies of CRW than either the A or B subgenome chromosomes [18]
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