Aristolochia fimbriata (A. fimbriata), a magnoliid species similar to Amborella trichopoda, has not undergone additional whole genome duplications since the origin of extant flowering plants. Due to its low genetic redundancy and suitability for large-scale cultivation, A. fimbriata emerges as an exceptional reference and potential model species for comparative and functional genomic studies of angiosperm evolution. Here, we present a complete telomere-to-telomere (T2T) genome assembly of A. fimbriata and characterize its centromeric architecture and epigenetic landscape. Our analysis reveals remarkably short (34-bp) and highly homogenized satellite monomers in its centromeric regions. Furthermore, we identify approximately 1,020 topologically associating domain-like structures and 23,852 non-redundant accessible chromatin regions. Notably, over 50% of accessible chromatin regions participate in long-range chromatin loops that bypass at least one intervening gene, suggesting widespread distal gene regulation in this species. We also demonstrate that an expanded downstream regulatory network of the floral B-class gene APETALA3 (AP3) may contribute to the highly specialized floral features in A. fimbriata. Our study not only elucidates the unique centromeric organization and three-dimensional epigenomic architecture of A. fimbriata, but also provides valuable genomic resources for investigating how regulatory network evolution drives phenotypic innovation in flowering plants.
Li et al. (Fri,) studied this question.