Haplotype-resolved 3D genome maps reveal RNAPII-mediated allelic regulation in hybrid rice

To understand how the two parental genomes coordinate transcription in hybrids, chromatin architecture must be resolved at the haplotype level. Here, using phased Bridge-Linker Hi-C, we reconstructed a haplotype-resolved three-dimensional (3D) genome of the elite hybrid rice (Oryza sativa) line Shanyou 63 (SY63). We identified extensive allele-specific chromatin conformations. Furthermore, we generated allele-resolved RNAPII ChIA-PET maps and phased transcriptomes to explore how chromatin interactions contribute to allelic regulation. Although maternal and paternal homologs share broadly similar chromatin features, we detected widespread haplotype-biased RNAPII binding and chromatin looping at high resolution. These allele-specific RNAPII-mediated contacts were significantly associated with biased expression. Stronger RNAPII binding on one haplotype promoted the formation of long-range regulatory loops with distal genes, thereby contributing to allele-biased transcription at a subset of loci, even when promoter-proximal RNAPII occupancy was comparable between alleles. These results demonstrate that subtle differences in RNAPII engagement and 3D regulatory wiring between parental haplotypes can reshape transcriptional output in hybrids, providing new insights into the mechanisms underlying the allelic regulation of gene expression.