title: Wheat centromeric retrotransposons: the new ones take a major role in centromeric structure.
abstract: The physical map of the hexaploid wheat chromosome 3B was screened using centromeric DNA probes. A 1.1-Mb region showing the highest number of positive bacterial artificial chromosome (BAC) clones was fully sequenced and annotated, revealing that 96% of the DNA consisted of transposable elements, mainly long terminal repeat (LTR) retrotransposons (88%). Estimation of the insertion time of the transposable elements revealed that CRW (also called Cereba) and Quinta are the youngest elements at the centromeres of common wheat (Triticum spp.) and its diploid ancestors, with Quinta being younger than CRW in both diploid and hexaploid wheats. Chromatin immunoprecipitation experiments revealed that both CRW and Quinta families are targeted by the centromere-specific histone H3 variant CENH3. Immuno colocalization of retroelements and CENH3 antibody indicated that a higher proportion of Quinta than CRWs was associated with CENH3, although CRWs were more abundant. Long arrays of satellite repeats were also identified in the wheat centromere regions, but they lost the ability to bind with CENH3. In addition to transposons, two functional genes and one pseudogene were identified. The gene density in the centromere appeared to be between three and four times lower than the average gene density of chromosome 3B. Comparisons with related grasses also indicated a loss of microcollinearity in this region. Finally, comparison of centromeric sequences of Aegilops tauschii (DD), Triticum boeoticum (AA) and hexaploid wheat revealed that the centromeres in both the polyploids and diploids are still undergoing dynamic changes, and that the new CRWs and Quintas may have undertaken the core role in kinetochore formation.
authors.affiliation: Key Laboratory of Crop Gene Resource and Germplasm Enhancement, Ministry of Agriculture, Institute of Crop Science, Chinese Academy of Agricultural Sciences, Beijing, 100081, China.
authors.forename: Baochun
authors.initials: B
authors.lastname: Li
authors.forename: Frédéric
authors.initials: F
authors.lastname: Choulet
authors.forename: Yanfang
authors.initials: Y
authors.lastname: Heng
authors.forename: Weiwei
authors.initials: W
authors.lastname: Hao
authors.forename: Etienne
authors.initials: E
authors.lastname: Paux
authors.forename: Zhao
authors.initials: Z
authors.lastname: Liu
authors.forename: Wei
authors.initials: W
authors.lastname: Yue
authors.forename: Weiwei
authors.initials: W
authors.lastname: Jin
authors.forename: Catherine
authors.initials: C
authors.lastname: Feuillet
authors.forename: Xueyong
authors.initials: X
authors.lastname: Zhang
mesh_terms: D002503:Centromere / Q000235:genetics*; D022202:Chromosomes, Artificial, Bacterial; D032461:Chromosomes, Plant; D004251:DNA Transposable Elements; D002523:Edible Grain / Q000235:genetics; D006657:Histones / Q000235:genetics; D010802:Phylogeny; D020161:Physical Chromosome Mapping; D006109:Poaceae / Q000235:genetics; D011123:Polyploidy; D011544:Pseudogenes; D018626:Retroelements / Q000235:genetics*; D026801:Synteny; D014908:Triticum / Q000235:genetics*
chemical_list: D004251:DNA Transposable Elements; D006657:Histones; D018626:Retroelements