Interspecific or intergeneric hybridization can give rise to genetic diversity, but the resulting hybrids often suffer from diverse genetic and developmental defects. Notable among them are chromosomal instability and infertility, mainly caused by genome incompatibility between distantly related genomes. xBrassicoraphanus is a synthetic allotetraploid (2n = 4x = 38) derived from an intergeneric cross between Chinese cabbage (Brassica rapa; 2n = 20) and radish (Raphanus sativus; 2n = 18). Four cultivars of xBrassicoraphanus BB1, BB4, BB6, and B50 were all descended from a genetically fixed individual, but display varying degrees of phenotypic diversity and pollen viability. For instance, the BB1 cultivar is the most stable in terms of phenotypic and genetic uniformity, whereas BB4 is relative unstable with a high frequency of inviable pollen formation. Microscopic analysis revealed that more than half of BB4 pollens aborted with irregular morphology, while producing significantly large numbers of polyads during microsporogenesis, approximately 6.98% of which contained micronuclei. We also observed mispairing and abnormal segregation of meiotic chromosomes during microsporogenesis in BB4. Our findings suggest that chromosome instability is persistent in the genome of hybrid offspring, accompanied with the formation of micronuclei and aborted pollen. Thus, the divergent genomes in the hybrid species still require a comprehensive stabilization process after hybridization, presumably involving gradual genome reconstruction and/or epigenetic changes to produce stable and fertile individuals over successive generations.
Interspecific or intergeneric hybridization can give rise to genetic diversity, but the resulting hybrids often suffer from diverse genetic and developmental defects. Notable among them are chromosomal instability and infertility, mainly caused by genome incompatibility between distantly related genomes. xBrassicoraphanus is a synthetic allotetraploid (2n = 4x = 38) derived from an intergeneric cross between Chinese cabbage (Brassica rapa; 2n = 20) and radish (Raphanus sativus; 2n = 18). Four cultivars of xBrassicoraphanus BB1, BB4, BB6, and B50 were all descended from a genetically fixed individual, but display varying degrees of phenotypic diversity and pollen viability. For instance, the BB1 cultivar is the most stable in terms of phenotypic and genetic uniformity, whereas BB4 is relative unstable with a high frequency of inviable pollen formation. Microscopic analysis revealed that more than half of BB4 pollens aborted with irregular morphology, while producing significantly large numbers of polyads during microsporogenesis, approximately 6.98% of which contained micronuclei. We also observed mispairing and abnormal segregation of meiotic chromosomes during microsporogenesis in BB4. Our findings suggest that chromosome instability is persistent in the genome of hybrid offspring, accompanied with the formation of micronuclei and aborted pollen. Thus, the divergent genomes in the hybrid species still require a comprehensive stabilization process after hybridization, presumably involving gradual genome reconstruction and/or epigenetic changes to produce stable and fertile individuals over successive generations.
2B7 - Building 2 GSA2018_APCC6 GSACC62018@canberra.edu.au
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