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[This corrects the article DOI: 10.3389/fpls.2021.802222.].
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The precise assembly of the kinetochore complex at the centromere is epigenetically determined by substituting histone H3 with the centromere-specific histone H3 variant CENH3 in centromeric nucleosomes. The wheat-rye 1BL/1RS translocation chromosome in the background of wheat resulted from a centric misdivision followed by the fusion of the broken arms of chromosomes 1B and 1R from wheat and rye, respectively. The resulting hybrid (dicentric)centromere is composed of both wheat and rye centromeric repeats. As CENH3 is a marker for centromere activity, we applied Immuno-FISH followed by ultrastructural super-resolution microscopy to address whether both or only parts of the hybrid centromere are active. Our study demonstrates that only the rye-derived centromere part incorporates CENH3 of wheat in the 1BL/1RS hybrid centromere. This finding supports the notion that one centromere part of a translocated chromosome undergoes inactivation, creating functional monocentric chromosomes to maintain chromosome stability.
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Haploid production is of great importance in plant breeding programs. Doubled haploid technology accelerates the generation of inbred lines with homozygosity in all loci in a single year. Haploids can be induced in vitro via cultivating the haploid gametes or in vivo through inter- and intraspecific hybridization. Haploid induction through centromere engineering is a novel system that is theoretically applicable to many plant species. The present review chapter discusses the proposed molecular mechanisms of selective chromosome elimination in early embryogenesis and the effects of kinetochore component modifications on proper chromosome segregation. Finally, the advantages and limitations of the CENH3-mediated haploidization approach and its applications are highlighted.
Assuntos
Centrômero/genética , Plantas/genética , Animais , Produtos Agrícolas/genética , Genoma de Planta/genética , Haploidia , Humanos , Hibridização Genética/genética , Cinetocoros/fisiologia , Melhoramento Vegetal/métodosRESUMO
The ability to generate haploids and subsequently induce chromosome doubling significantly accelerates the crop breeding process. Haploids have been induced through the generation of plants from haploid tissues (in situ gynogenesis and androgenesis) and through the selective loss of a parental chromosome set via inter- or intraspecific hybridization. Here, we focus on the mechanisms responsible for this selective chromosome elimination. CENH3, a variant of the centromere-specific histone H3, has been exploited to create an efficient method of haploid induction, and we discuss this approach in some detail. Parallels have been drawn with chromosome-specific elimination, which occurs as a normal part of differentiation and sex determination in many plant and animal systems.
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Centrômero , Cromossomos de Plantas , Genoma de Planta , Haploidia , Melhoramento Vegetal , Plantas/genética , Engenharia Genética , Histonas/genéticaRESUMO
The chromosomal position of the centromere-specific histone H3 variant CENH3 (also called "CENP-A") is the assembly site for the kinetochore complex of active centromeres. Any error in transcription, translation, modification, or incorporation can affect the ability to assemble intact CENH3 chromatin and can cause centromere inactivation [Allshire RC, Karpen GH (2008) Nat Rev Genet 9 (12):923-937]. Here we show that a single-point amino acid exchange in the centromere-targeting domain of CENH3 leads to reduced centromere loading of CENH3 in barley, sugar beet, and Arabidopsis thaliana. Haploids were obtained after cenh3 L130F-complemented cenh3-null mutant plants were crossed with wild-type A. thaliana. In contrast, in a noncompeting situation (i.e., centromeres possessing only mutated or only wild-type CENH3), no uniparental chromosome elimination occurs during early embryogenesis. The high degree of evolutionary conservation of the identified mutation site offers promising opportunities for application in a wide range of crop species in which haploid technology is of interest.
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Autoantígenos/genética , Centrômero/genética , Proteínas Cromossômicas não Histona/genética , Haploidia , Plantas/genética , Mutação Puntual , Arabidopsis/genética , Arabidopsis/metabolismo , Autoantígenos/metabolismo , Western Blotting , Centrômero/metabolismo , Proteína Centromérica A , Proteínas Cromossômicas não Histona/metabolismo , Genótipo , Histonas/genética , Hordeum/genética , Hordeum/metabolismo , Cinetocoros/metabolismo , Microscopia Eletrônica de Varredura , Microscopia de Fluorescência , Modelos Genéticos , Fenótipo , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Plantas/metabolismo , Plantas Geneticamente Modificadas , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Sementes/genética , Sementes/metabolismo , Sementes/ultraestruturaRESUMO
The organization of centromeric chromatin of diploid barley (Hordeum vulgare) encoding two (α and ß) CENH3 variants was analysed by super-resolution microscopy. Antibody staining revealed that both CENH3 variants are organized in distinct but intermingled subdomains in interphase, mitotic and meiotic centromeres. Artificially extended chromatin fibres illustrate that these subdomains are formed by polynucleosome clusters. Thus, a CENH3 variant-specific loading followed by the arrangement into specific intermingling subdomains forming the centromere region appears. The CENH3 composition and transcription vary among different tissues. In young embryos, most interphase centromeres are composed of both CENH3 variants, while in meristematic root cells, a high number of nuclei contain ßCENH3 mainly dispersed within the nucleoplasm. A similar distribution and no preferential arrangement of the two CENH3 variants in relationship to the spindle poles suggest that both homologs meet the same function in metaphase cells.
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Centrômero/genética , Genes de Plantas , Variação Genética , Histonas/genética , Hordeum/genética , Regulação da Expressão Gênica de Plantas , Interfase/genética , Meiose , Mitose , Modelos Biológicos , Especificidade de Órgãos/genética , Transcrição GênicaRESUMO
B chromosomes (Bs) are dispensable components of the genomes of numerous species. In contrast with the prevalent view that Bs do not harbor genes, our recent sequence analysis revealed that Bs of rye (Secale cereale) are rich in gene-derived sequences. We compared these gene-like fragments of the rye B with their ancestral A-located counterparts and confirmed an A chromosomal origin and the pseudogenization of B-located gene-like fragments. About 15% of the pseudogene-like fragments on Bs are transcribed in a tissue-type and genotype-specific manner. In addition, B-located sequences can cause in trans down- or upregulation of A chromosome-encoded genic fragments. Phenotypes and effects associated with the presence of Bs might be explained by the activity of B-located pseudogenes. We propose a model for the evolution of B-located pseudogenes.
