Decoding hybridization barriers: the molecular and genetic orchestration of the triploid block in Arabidopsis thaliana

Plant evolution has been greatly influenced by polyploidization phenomena. Polyploid plants yield more and are more resistant to unfavorable environments than their diploid relatives. The triploid block, a postzygotic barrier that causes failure of endosperm development and thus seed arrest, often prevents polyploid breeding. Alterations in the parental dose in interploidy crosses alter endosperm development by changing the correct maternal: paternal ratio (2m:1p) that this tissue requires to properly fulfill its proliferation and cellularization. After many years of research, the study of epigenetic regulation of gene expression during seed development has greatly increased our understanding of the triploid block. In plants, epigenetic regulation of genes has been shown to play a critical role in transcriptional control. This may be important for identifying novel and unexpected epigenetic mechanisms in the plant genome. Recent advances in understanding how epigenetic mechanisms control the expression of imprinted genes in seeds have contributed to understanding how different seed compartments interact at fertilization for successful seed formation. We here also review the potential role of maternally derived sporophytic tissues (seed coat) in the establishment of the triploid block. We also present a data analysis that includes spatiotemporal expression patterns of key genes involved in controlling hybridization barriers. This review provides an overview of the triploid block in plants, discussing how understanding its epigenetic regulation could offer new strategies to overcome hybridization barriers. We explore how these insights may enhance crop productivity and resilience.