RESUMO
Hybridization and polyploidization are pivotal to plant evolution. Genetic crosses between distantly related species are rare in nature due to reproductive barriers but how such hurdles can be overcome is largely unknown. Here we report the hybrid genome structure of xBrassicoraphanus, a synthetic allotetraploid of Brassica rapa and Raphanus sativus. We performed cytogenetic analysis and de novo genome assembly to examine chromosome behaviors and genome integrity in the hybrid. Transcriptome analysis was conducted to investigate expression of duplicated genes in conjunction with epigenome analysis to address whether genome admixture entails epigenetic reconfiguration. Allotetraploid xBrassicoraphanus retains both parental chromosomes without genome rearrangement. Meiotic synapsis formation and chromosome exchange are avoided between nonhomologous progenitor chromosomes. Reconfiguration of transcription network occurs, and less divergent cis-elements of duplicated genes are associated with convergent expression. Genome-wide DNA methylation asymmetry between progenitors is largely maintained but, notably, B. rapa-originated transposable elements are transcriptionally silenced in xBrassicoraphanus through gain of DNA methylation. Our results demonstrate that hybrid genome stabilization and transcription compatibility necessitate epigenome landscape adjustment and rewiring of cis-trans interactions. Overall, this study suggests that a certain extent of genome divergence facilitates hybridization across species, which may explain the great diversification and expansion of angiosperms during evolution.
Assuntos
Brassicaceae , Genoma de Planta , Brassicaceae/genética , Metilação de DNA/genética , Hibridização GenéticaRESUMO
BACKGROUND: Hybridization and polyploidization events are important driving forces in plant evolution. Allopolyploids formed between different species can be naturally or artificially created but often suffer from genetic instability and infertility in successive generations. xBrassicoraphanus is an intergeneric allopolyploid obtained from a cross between Brassica rapa and Raphanus sativus, providing a useful resource for genetic and genomic study in hybrid species. OBJECTIVE: The current study aims to understand the cause of hybrid sterility and pollen abnormality in different lines of synthetic xBrassicoraphanus from the cytogenetic perspective. METHODS: Alexander staining was used to assess the pollen viability. Cytogenetic analysis was employed to monitor meiotic chromosome behaviors in pollen mother cells (PMCs). Origins of parental chromosomes in xBrassicoraphanus meiocytes were determined by genome in situ hybridization analysis. RESULTS: The xBrassicoraphanus lines BB#4 and BB#6 showed high rates of seed abortion and pollen deformation. Abnormal chromosome behaviors were observed in their PMCs, frequently forming univalents and inter-chromosomal bridges during meiosis. A positive correlation also exists between meiotic defects and the formation of micronuclei, which is conceivably responsible for unbalanced gamete production and pollen sterility. CONCLUSION: These results suggest that unequal segregation of meiotic chromosomes, due in part to non-homologous interactions, is responsible for micronuclei and unbalanced gamete formation, eventually leading to pollen degeneration and inferior fertility in unstable xBrassicoraphanus lines.
Assuntos
Brassica rapa/genética , Gametogênese Vegetal/genética , Meiose/genética , Micronúcleos com Defeito Cromossômico , Infertilidade das Plantas/genética , Raphanus/genética , Brassica rapa/citologia , Brassica rapa/embriologia , Cromossomos de Plantas , Cruzamentos Genéticos , Pólen/citologia , Raphanus/citologia , Raphanus/embriologia , SementesRESUMO
A young male patient diagnosed with Klinefelter syndrome was admitted to our hospital via the emergency room with chief complaints of acute chest pain and dyspnea. Pulmonary thromboembolism was diagnosed from his chest CT images. His symptoms improved after he underwent thrombolysis and anticoagulation treatment. Klinefelter syndrome has a tendency towards hypercoagulability due to hormonal imbalance and one or more inherited thromophilic factors. Thus, Klinefelter syndrome patients with a past medical history of venous thromboembolism require continuous oral anticoagulation therapy for a period of at least six months.
