Haplotype-resolved genome assembly of barberry reveals structural divergence and allele-specific expression during infection by wheat stripe rust pathogen

Barberry is an ecologically and medicinally important perennial shrub and an alternate host of Puccinia striiformis f. sp. tritici ( Pst ), the causal agent of wheat stripe rust. However, its genome architecture and molecular responses to Pst infection remain poorly understood. Here, we generated a haplotype-resolved, chromosome-level genome assembly of Berberis aggregata using PacBio HiFi and Hi-C sequencing. The two haplotypes, Ba5A and Ba5B, were assembled into 14 pseudochromosomes each, with genome sizes of approximately 1.13 and 1.16 Gb, respectively, and showed high continuity and completeness. Comparative analyses revealed extensive divergence between the haplotypes, including widespread structural variation, substantial hemizygosity, and TE-rich, gene-poor non-alignable regions. Haplotype-specific hemizygous genes also exhibited distinct functional biases, with Ba5A enriched in immune-related processes and Ba5B associated with transport and cell-envelope functions. Dual RNA-seq across infection stages revealed stage-dependent host transcriptional reprogramming, characterized by early pathogen perception followed by stronger defense activation and photosynthesis repression, whereas Pst displayed a coordinated colonization program consistent with its biotrophic lifestyle. Allele-specific expression analysis showed that ∼25–28% of genes exhibited significant haplotype-biased expression, and a subset transitioned from unbiased expression at 0 dpi to Ba5A- or Ba5B-biased expression during infection. Integration with differential expression analysis further identified infection-responsive induced-biased genes associated with defense-related processes, including responses to fungal pathogens. These findings show that haplotype divergence and dynamic allele-specific regulation jointly contribute to transcriptional responses during Pst infection, providing new insights into the genomic basis of barberry–rust pathogen interactions.