title: Conservation and purifying selection of transcribed genes located in a rice centromere.
abstract: Recombination is strongly suppressed in centromeric regions. In chromosomal regions with suppressed recombination, deleterious mutations can easily accumulate and cause degeneration of genes and genomes. Surprisingly, the centromere of chromosome8 (Cen8) of rice (Oryza sativa) contains several transcribed genes. However, it remains unclear as to what selective forces drive the evolution and existence of transcribed genes in Cen8. Sequencing of orthologous Cen8 regions from two additional Oryza species, Oryza glaberrima and Oryza brachyantha, which diverged from O. sativa 1 and 10 million years ago, respectively, revealed a set of seven transcribed Cen8 genes conserved across all three species. Chromatin immunoprecipitation analysis with the centromere-specific histone CENH3 confirmed that the sequenced orthologous regions are part of the functional centromere. All seven Cen8 genes have undergone purifying selection, representing a striking phenomenon of active gene survival within a recombination-free zone over a long evolutionary time. The coding sequences of the Cen8 genes showed sequence divergence and mutation rates that were significantly reduced from those of genes located on the chromosome arms. This suggests that Oryza has a mechanism to maintain the fidelity and functionality of Cen8 genes, even when embedded in a sea of repetitive sequences and transposable elements.
authors.affiliation: Arizona Genomics Institute, School of Plant Sciences, Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona 85721, USA.
authors.forename: Chuanzhu
authors.initials: C
authors.lastname: Fan
authors.forename: Jason G
authors.initials: JG
authors.lastname: Walling
authors.forename: Jianwei
authors.initials: J
authors.lastname: Zhang
authors.forename: Cory D
authors.initials: CD
authors.lastname: Hirsch
authors.forename: Jiming
authors.initials: J
authors.lastname: Jiang
authors.forename: Rod A
authors.initials: RA
authors.lastname: Wing
mesh_terms: D001483:Base Sequence; D002503:Centromere / Q000235:genetics*; D047369:Chromatin Immunoprecipitation; D032461:Chromosomes, Plant / Q000235:genetics*; D004251:DNA Transposable Elements; D018744:DNA, Plant / Q000235:genetics; D019143:Evolution, Molecular; D017343:Genes, Plant / Q000235:genetics*; D014644:Genetic Variation / Q000235:genetics*; D018745:Genome, Plant / Q000235:genetics; D008969:Molecular Sequence Data; D059645:Mutation Rate; D012275:Oryza / Q000145:classification / Q000235:genetics*; D020641:Polymorphism, Single Nucleotide; D012091:Repetitive Sequences, Nucleic Acid; D012641:Selection, Genetic; D017422:Sequence Analysis, DNA; D014158:Transcription, Genetic
chemical_list: D004251:DNA Transposable Elements; D018744:DNA, Plant