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Cultivated chrysanthemum (Chrysanthemum× morifoliumRamat.) is a beloved ornamental crop due to the diverse capitula types among varieties, but the molecular mechanism of capitulum development remains unclear. Here, we report a 2.60 Gb chromosome-scale reference genome of C. lavandulifolium,a wild Chrysanthemumspecies found in China, Korea and Japan. The evolutionary analysis of the genome revealed that only recent tandem duplications occurred in the C. lavandulifoliumgenome after the shared whole genome triplication (WGT) in Asteraceae. Based on the transcriptomic profiling of six important developmental stages of the radiate capitulum in C. lavandulifolium, we found genes in the MADS-box, TCP, NACand LOBgene families that were involved in disc and ray floret primordia differentiation. Notably, NAMand LOB30homologs were specifically expressed in the radiate capitulum, suggesting their pivotal roles in the genetic network of disc and ray floret primordia differentiation in chrysanthemum. The present study not only provides a high-quality reference genome of chrysanthemum but also provides insight into the molecular mechanism underlying the diverse capitulum types in chrysanthemum.

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Brassica rapacomprises several important cultivated vegetables and oil crops. Current reference genome assemblies of Brassica rapaare quite fragmented and not highly contiguous, thereby limiting extensive genetic and genomic analyses. Here, we report an improved assembly of the B. rapagenome (v3.0) using single-molecule sequencing, optical mapping, and chromosome conformation capture technologies (Hi-C). Relative to the previous reference genomes, our assembly features a contig N50 size of 1.45 Mb, representing a ~30-fold improvement. We also identified a new event that occurred in the B. rapagenome ~1.2 million years ago, when a long terminal repeat retrotransposon (LTR-RT) expanded. Further analysis refined the relationship of genome blocks and accurately located the centromeres in the B. rapagenome. The B. rapagenome v3.0 will serve as an important community resource for future genetic and genomic studies in B. rapa. This resource will facilitate breeding efforts in B. rapa, as well as comparative genomic analysis with other Brassicaspecies.