Centromere Functional Sequences In Wheat And Wheatgrass

Centromere, as a basic composition of chromosomes in eukaryotes, guarantees the stabilization of the genetic information transmission during cell division. Centromere component is very complex, containing DNA sequences, such as tandem satellite repeats and retrotransposons interacting with centromere special histone and phosphorylation proteins. Furthermore, centromeric sequences which combine with centromere special histone H3 (CENH3) play a key role for exercising the centromeric function.Thinopyrum genus is the most successfully used perennial alien species in wheat breeding. There are three characteristics in hybridization between wheatgrass and wheat. One is that Thinopyrum species are easy to hybrid with wheat. Other one is that Thinopyrum chromosomes can stay relatively stable in wheat nuclear. Last one is that it shows higher recombination frequency with wheat chromosomes including spontaneous and inducible recombination compaired with alien chromosomes from other species. Therefore, the combining ability between centromeric sequences and TaCENH3 can provide a scientific and rational explanation for the above phenomenon. And it also can provide scientific basis for wheat breeding in the future.In our previous study, we found that the major DNA components of wheat centromeres are CRW (centromeric retrotransposons of wheat) and Quinta (retrotransposon). In order to dissect composition, function and evolution of wheatgrass centromeric sequences during the evolution and polyploidization of species, some materials including diploids containing A, B, D, E, St, H and R-genomes, polyploidy species such as Ps. strigosa (StSt), Th.elongatum (EeEe) Th. intermedium (StEbEe),Th. ponticum (StStEbEeEx) and some partial amphiploids derived from wheat and wheat-grass hybrids were employed to reveal the components and evolution of centromeres in the Thinopyrum genus. Major results and conclusions were summarized at here.1. CRWs were mainly distributed on E-genomes, but also existed on St-genome chromosomes in less quantity in Thinopyrum ponticum and Th. intermedium. Quinta were existed on both St- and E-genome chromosomes. Both CRWs and Quinta were showing the phenomenon of expanding during formation of Thinopyrum polyploidy species.2. The Unnamedfam6, one type of Tyl/copia-like retrotransposons was detected at centromere regions of all chromosomes uniformly regardless St- or E-genome chromosomes. Few chromosomes of E-genomes had tandem satellite repeat DNA (CentSt), because it came from St-genome (Pseudorogneria). Both Unnamedfam6 and CentSt were lost their territory gradually for being squeezed to pericentromeric regions by CR W and Quinta.3. FISH (Fluorecence in situ hybridization) and GISH (Genome in situ hybridization) analysis on the wheat-grass and some partial amphiploids derived from hybrids of wheat and wheat-grasses showed that besides CRW, Quinta, Unnamedfam6 and CentSt, there should be other retrotransposons or tandem satellite repeats in Thinopyrum centromeres. Some repeat DNAs were obtained by screening the plasmids library of Th. ponticum via dot hybridization. One clone contains specific sequence possibly existing partial E-genome chromosomes, and the other one distributed on all chromosome centromeres.4. Immunostaining and co-localization analysis of DNA sequences and TaCENH3 (Immuno-FISH) showed that CRW and Quinta were still playing function on centromeres, while Unnamedfam6 and CentSt played partial function.5. We estimated that homologous of centromeric sequences between species were very crucial for relatively stable of alien chromosomes in wheat nuclear, and it created the possibility for alien recombination. We also believed that formation of kinetochore domains and function of centromeres were deeply affected by centromeric sequences. High homology of centromere functional sequences between wheat and wheatgrasses provide the base for wheatgrass chromosomes to stay in the nuclear of wheat in higher frequency. This creates more chances for alien recombination. This may be one of the major reasons why more translocations were obtained in hybrids of wheat with Thinopyrum species than most of the other alien species.