Reshaping epigenomic landscapes in facilitating the speciation of bread wheat

Polyploidization is a driving force of wheat evolution and speciation, yet its impact on epigenetic regulation and gene expression remains unclear.

Here, we constructed a high-resolution epigenetic landscape across leaves, spikes, and roots of hexaploidy wheat and its tetraploid and diploid relatives. Inter-species stable-expression genes exhibited conserved amino acid sequences under strong purifying selection, while dynamic-expression genes were linked to species-specific adaptation. During hexaploidization, dominant D-subgenome homoeolog expression was suppressed via reduced activating epigenetic signals, converging expression with the A and B subgenomes. Proximal chromatin regions near genes were more stable, whereas distal regions, particularly enhancer-like elements mediated by H3K27ac and H3K4me3, exhibit higher dynamism. Sequence variations in these enhancers lead to differential gene regulation, influencing traits such as spike development. For instance, the two haplotypes of dCRE region of TaDEP-B1 resulted in significant differences in its expression and spikelet numbers. We also observed a coevolution of transcription factors and their binding sites, particularly within the expanded ERF family, which regulates spike morphology.

This study highlights the interplay between sequence variation and epigenetic modifications in shaping transcriptional regulation during wheat speciation, offering valuable insights for genetic improvement.