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Abstract:
Author summary Seed failure in response to interspecific hybridizations is a well-known reproductive barrier preventing interbreeding of closely related species and thus maintaining species boundaries. This reproductive barrier is established in the endosperm, a nourishing tissue supporting embryo growth. In this study, we discovered that the endosperm of interspecific hybrids between the recently diverged species Capsella rubella and C. grandiflora suffers from mitotic abnormalities and random chromosome loss. We found that the endosperm has reduced levels of DNA methylation and chromatin condensation, likely accounting for the chromosome loss. Importantly, we found that genes located in pericentromeric regions were preferentially deregulated, suggesting that reduced DNA methylation exposes transcription factor binding sites in pericentromeric regions, leading to hyperactivation of genes and seed arrest. In support of the relevance of pericentromeric regions for hybrid seed arrest, we identified three QTL connected with the phenotype that were all located in pericentromeric regions. These results link epigenetic changes in hybrid endosperm with distinct genetic loci underpinning hybrid seed failure.
