Retrotransposons And DNA Repeats In Centromeric Regions Of Thinopyrum Genus And Wheat-Th. Ponticum Translocation Lines With Broad-spectrum Resistance To Stripe Rusts

The Thinopyrum specics are the most successful relative species in wheat distanthybridization breeding, providing numerous useful genes in bread wheat improvement. Centromeresmaintain the integrity of the chromosomes during cell division. The deletion and preservation of alienchromosomes in cells related to the centromere. For understanding the centromere sequencecomposition of Thinopyrum and providing theoretical basis of distant hybridization breeding, in thisdissertation, three aspects of studies were performed surrounding the Thinopyrum’s centromere andwheat-Th.ponticum translocation lines.1． A BAC library of Pseudoroegneiria stipifolia (2n=14, StSt) was constructed. The BAC librarywas screened via PCR by primers designed based on cereal centromeric sequence (CCS1). Afterfluorescent in situ hybridization (FISH) analysis, one centromere-specific BAC and two centromericassociated BACs were obtained. Shotgun libraries were constructed for the three BAC clones. Theywere sequenced, assembled and annotated.2． We found that centromeres of Ps.stipifolia contained the homologous sequences of CRW,Quinta and unnamedfam6, which were found in wheat, and their similarity was more than85%. Acetromeric tandem repeat was found in Ps. stipifolia, which was named as CentSt. Homologoussequence of CentSt was also found in wheat and its D genome donor, Aegilops tauschii.3． CRW, Quinta, unnamedfam6and CentSt were used to analysis the centromere of tetraploid Ps.stipifolia, tetraploid Th. elongatum (2n=28, EeEe), Th. intermedium (2n=42, StEbEe) and Th. ponticum(2n=70, StStEbEeEx). We found that except the tetraploid Th. elongatum which we didn’t detect thesignal of unnamedfam6in its chromosome, all of the other three species contained these centromericelements. But the distribution of the centromeric elements was different from each other. It wassuggested that in the progress of polyploidization inThinopyrum, the sequence compositon of thecentromeres changed a lot.4． CENH3genes were cloned from Ps. stipifolia, Th. elongatum (2n=14, EeEe), Th.bessarabicum (2n=14, EbEb), Th. intermedium and Th. ponticum. The similarity of CENH3cordingsequences between wheat and genome donors of Thinopyrum genus was more than95%. And wheatCENH3antibody can perfectly attach on the centromere of the Thinopyrum chromosomes. All of theseresults suggested that the wheat and Thinopyrum have high homology centromere sequences andCENH3genes. This provides the base for Thinopyrum chromosomes stably being transmitted in wheatgenetic background, which creats chance for recombination.4. To transfer stripe rust resistance from Th. ponticum to common wheat, hybrid progeniesbetween them were screened for stripe rust resistance.The progenies were characterized by their diseaseresistance, agronomic traits, genomic in situ hybridization and quality related protein analysis. Eightlines with good resistance or immune to the pathogens at adult stage were obtained. All of them have42chromosomes, in which seven lines convey a new translocation,4DS/4St. In addition, besides this translocation, the GDR3conveys another distal translocation, which may be derived from the E-genomechromosome of Th. ponticum. The GDR3performed very good resistance in whole life. It was immuneto yellow rusts. We estimated that both of the alien segments convey resistant genes to the stripe rusts.All of the eight lines convey the good subunits14+15at Glu-B1, which should be inherited fromXiaoyan6. Wild relatives of wheat usually convey genes with broad spectrum resistance to pathogens.This is the genetic base for their surviving in extreme environments, which also provide excellent generesource for disease resistant breeding in wheat.In summary, the Triticum aestivum and Thinopyrum have simliar centromere sequences and CENH3genes. This provides the possibility that Thinopyrum chromosomes can stay and transmission stably inwheat genetic background, which creates chance for recombination between wheat and alienchromosomes. The occurrence of spontaneous translocations between wheat and Th. ponticumillustrates the reliability of ourspeculation. This work sheds light for chose of donor species in cropwide hybridization breeding.