Hosub Shin1, Hye Rang Park1, Jeong Eun Park1, Seung Hwa Yu2, Gibum Yi3, Jung Hyo Kim2, Wonjun Koh1, Hyun Hee Kim4, Soo-Seong Lee5, Jin Hoe Huh6,7,8,9. 1. Department of Agriculture, Forestry and Bioresources, Seoul National University, Seoul, 08826, South Korea. 2. Interdisciplinary Program in Agricultural Genomics, Seoul National University, Seoul, 08826, South Korea. 3. Plant Genomics and Breeding Institute, Seoul National University, Seoul, 08826, South Korea. 4. Department of Life Science, Chromosome Research Institute, Sahmyook University, Seoul, 01795, South Korea. 5. BioBreeding Institute, Anseong, 17544, South Korea. 6. Department of Agriculture, Forestry and Bioresources, Seoul National University, Seoul, 08826, South Korea. huhjh@snu.ac.kr. 7. Interdisciplinary Program in Agricultural Genomics, Seoul National University, Seoul, 08826, South Korea. huhjh@snu.ac.kr. 8. Plant Genomics and Breeding Institute, Seoul National University, Seoul, 08826, South Korea. huhjh@snu.ac.kr. 9. Research Institute of Agriculture and Life Sciences, Seoul National University, Seoul, 08826, South Korea. huhjh@snu.ac.kr.
Abstract
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.
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.
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