The Chrysanthemum nankingense Genome Provides Insights into the Evolution and Diversification of Chrysanthemum Flowers and Medicinal Traits

The Asteraceae (Compositae),a large plant family of approximately 24 000-35 000 species,accounts for^10% of all angiosperm species and contributes a lot to plant diversity.The most representative members of the Asteraceae are the economically important chrysanthemums (Chrysanthemum L.)that diversified through reticulate evolution.Biodiversity is typically created by multiple evolutionary mechanisms such as wholegenome duplication 0NGD)or polyploidization and locally repetitive genome expansion.However,the lack of genomic data from chrysanthemum species has prevented an in-depth analysis of the evolutionary mechanisms involved in their diversification.Here,we used Oxford Nanopore long-read technologyto sequence the diploid Chrysanthemum nankingense genome,which represents one of the progenitor genomes of domesticated chrysanthemums.Our analysis revealed that the evolution of the C.nankingense genome was driven by bursts of repetitive element expansion and WGD events including a recentWGD that distinguishes chrysanthemum from sunflower,which diverged from chrysanthemum approximately 38.8 million years ago.Variations of ornamental and medicinal traits in chrysanthemums are linked to the expansion of candidate gene families by duplication events including paralogous gene duplication.Collectively,our study of the assembled reference genome offers new knowledge and resources to dissect the history and pattern of evolution and diversification of chrysanthemum plants,and also to accelerate their breeding and improvement.

The genome sequencing and comparative analysis of a wild kiwifruit Actinidia eriantha

The current kiwifruit industry is mainly based on the cultivars derived from the species Actinidia chinensis(Ac)which may bring risks such as canker disease.Introgression of desired traits from wild relatives is an important method for improving kiwifruit cultivars.Actinidia eriantha(Ae)is a particularly important taxon used for hybridization or introgressive breeding of new kiwifruit cultivars because of its valued species-specific traits.Here,we assembled a chromosome-scale high-quality genome of a Ae sample which was directly collected from its wild populations.Our analysis revealed that 41.3%of the genome consists of repetitive elements,comparable to the percentage in Ac and Ae cultivar“White”genomes.The genomic structural variation,including the presence/absence-variation(PAV)of genes,is distinct between Ae and Ac,despite both sharing the same two kiwifruit-specific whole genome duplication(WGD)events.This suggests that a post-WGD divergence mechanism occurred during their evolution.We further investigated genes involved in ascorbic acid biosynthesis and disease-resistance of Ae,and we found introgressive genome could contribute to the complex relationship between Ae and other representative kiwifruit taxa.Collectively,the Ae genome offers valuable genetic resource to accelerate kiwifruit breeding applications.