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Genomic and genetic characterization of rice Cen3 reveals evolutionary remnants of a complex centromere (small RNA data)

ABSTRACT: The centromere is the chromosomal site for assembly of the kinetochore where spindle fibers attach during cell division. In most muticellular eukaryotes, centromeres are composed of long tracks of satellite repeats that are recalcitrant to sequencing and fine scale genetic mapping. Here we report the genomic and genetic characterization of the complete centromere of rice chromosome 3. Using a DNA fiber-fluorescence in situ hybridization approach, we demonstrated that the centromere of chromosome 3 (Cen3) contains ~414 kb of the centromeric satellite repeat CentO. Cen3 includes a ~1,851-kb domain associated with CENH3, the centromere-specific histone H3 variant. This CENH3-associated chromatin domain is embedded within a 3,083-kb region that lacks genetic recombination. We detected several active genes within the CENH3-binding domain based on a comprehensive annotation and a survey for matches with mRNA signatures. However, the gene density in the CENH3-binding domain is significantly lower than in the pericentromeric domains. In contrast, the CENH3-binding domain contains a higher percentage of repetitive DNA sequences than the pericentromeric regions. These results suggest that Cen3 is in the process of evolving from a genic region toward an accumulation of satellite repeats and transposable elements that is more characteristic of centromeres in most complex eukaryotic species. Keywords: MPSS, small RNA, rice, centromere, Cen3, chromosome 3

ORGANISM(S): Oryza sativa

PROVIDER: GSE4912 | GEO | 2006/05/26

SECONDARY ACCESSION(S): PRJNA104463

REPOSITORIES: GEO

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Project description:The centromere is defined by the presence of a centromere-specific histone H3 variant, CENH3. Establishment and maintenance of the centromeric chromatin (CEN chromatin) is determined by poorly understood epigenetic mechanisms. Interestingly, CEN chromatin in several eukaryotes showed euchromatic characteristics although being embedded within pericentromeric heterochromatin. Specifically, H3K4me2 appeared to be a unique histone modification mark associated with animal centromeres. We developed a genomic tiling array for four fully sequenced rice centromeres. A ChIP-chip approach was used to study the patterns of several euchromatic histone modification marks, including H3K4me2, H3K4me3, H3K36me3, and H3K4K9a, associated with rice centromeres. We demonstrate that the CENH3 subdomains within the four centromeres are depleted with the four histone H3 marks. The vast majority of the four histone marks were associated with the genes located in the H3 subdomains within the centromeric cores. Genes in the centromeres showed similar histone modification patterns as those located outside of the centromeres. Thus, the euchromatic characteristics of rice CEN chromatin are trademarks of the transcribed sequences embedded in the H3 subdomains of the centromeres. We propose that the constitutively expressed genes located in rice centromeres may provide a barrier for loading of CENH3 into the H3 subdomains. The separation of CENH3 into the H3 subdomains is favorable for the three dimensional structure and its associated function of rice centromeres. We developed a genomic tiling array that covers four rice centromeres (Cen4, Cen5, Cen7, and Cen8) using the NimbleGen 3x720K array based on the NimbleGen HD2 platform. We used four antibodies (H3K4me3, H3K4me2, H3K36me3, H3K4K9ac) to perform ChIP-chip experiments. ChIP was conducted using leaf tissue from two-week old rice seedlings. We have 3 biological replicates for each antibody and 6 technological replicates of hybridization with position exchange on the array. Thus, each histone modification included 18 hybridization experiments.

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Genomic and genetic characterization of rice Cen3 reveals evolutionary remnants of a complex centromere (small RNA data)

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