A genus-wide pangenome of Hordeum

The genus Hordeum, which includes cultivated barley and its wild relatives, represents a diverse group of grasses with agricultural, ecological, and evolutionary importance. Here, we present a genus-wide pangenome based on 25 chromosome-scale genome sequences encompassing all known diploid Hordeum species and selected tetraploids. Comparative analysis reveals extensive structural variations, including large-scale inversions and chromosomal rearrangements, which disrupt proximal chromosomal collinearity and reflect lineage-specific genome remodeling. Using single-copy gene phylogenies, we identify multiple deep interspecific hybridization events, segmental exchanges, and introgressions, particularly in regions enriched for conserved inversions. We also uncover widespread horizontal gene transfer from Panicoideae grasses into Hordeum, with functional integration of transferred genes. Transposable element dynamics, especially retrotransposon proliferation, account for much of the observed genome size variation and offer insights into polyploid genome evolution. Whole-genome alignments reveal contrasting evolutionary patterns: while coding genes remain highly conserved, regulatory elements show rapid turnover, providing a substrate for phenotypic diversification. Case studies of vernalization and glume development demonstrate how natural variation in regulatory and coding sequences contributes to flowering time and floral morphology. This comprehensive pangenomic framework establishes Hordeum as a model for studying genome evolution, structural variation, and the genetic basis of adaptive traits, offering new avenues for barley improvement.