Abstract
BackgroundWintersweet (Chimonanthus praecox), an important ornamental plant, has evolved unique fragrant aroma and winter-flowering properties, which are critical for its successful sexual reproduction. However, the molecular mechanisms underlying these traits are largely unknown in this species. In addition, wintersweet is also a typical representative species of the magnoliids, where the phylogenetic position of which relative to eudicots and monocots has not been conclusively resolved.ResultsHere, we present a chromosome-level wintersweet genome assembly with a total size of 695.36 Mb and a draft genome assembly of Calycanthus chinensis. Phylogenetic analyses of 17 representative angiosperm genomes suggest that Magnoliids and eudicots are sister to monocots. Whole-genome duplication signatures reveal two major duplication events in the evolutionary history of the wintersweet genome, with an ancient one shared by Laurales, and a more recent one shared by the Calycantaceae. Whole-genome duplication and tandem duplication events have significant impacts on copy numbers of genes related to terpene and benzenoid/phenylpropanoid (the main floral scent volatiles) biosynthesis, which may contribute to the characteristic aroma formation. An integrative analysis combining cytology with genomic and transcriptomic data reveals biological characteristics of wintersweet, such as floral transition in spring, floral organ specification, low temperature-mediated floral bud break, early blooming in winter, and strong cold tolerance.ConclusionsThese findings provide insights into the evolutionary history of wintersweet and the relationships among the Magnoliids, monocots, and eudicots; the molecular basis underlying floral scent biosynthesis; and winter flowering, and highlight the utility of multi-omics data in deciphering important ornamental traits in wintersweet.
Highlights
Wintersweet (Chimonanthus praecox), an important ornamental plant, has evolved unique fragrant aroma and winter-flowering properties, which are critical for its successful sexual reproduction
A total of 76.96 Gb of Pacific Biosciences (PacBio) long reads were achieved (Additional file 1: Table S1), approximately 98.83-fold highquality sequence coverage of the 778.71 Mb genome (Additional file 2: Fig. S1a and Additional file 1: Table S2)
The final assembly consists of 1259 scaffolds totalling 695.31 Mb with a scaffold N50 size of 4.49 Mb, covering 89.2% of the genome size estimated by genome survey (Table 1 and Additional file 1: Table S3)
Summary
Wintersweet (Chimonanthus praecox), an important ornamental plant, has evolved unique fragrant aroma and winter-flowering properties, which are critical for its successful sexual reproduction. Chimonanthus praecox (Chinese name “La Mei,” commonly known as wintersweet, 2n = 22), is a perennial deciduous shrub that belongs to the Calycantaceae family [3] It originates in China and has been cultivated for over a thousand years. Wintersweet flowers possess an intense fragrance that is endowed by a combination of volatile terpenoids (monoterpenes and sesquiterpenes) and benzenoids [5] which are emitted from nectaries distributed on the adaxial of inner petals [6]. These essential oils derived from its flower are widely used as components in perfume, cosmetics, and various flavor industries [7, 8]. Genetic resources are limited for wintersweet, which impedes progress on understanding floral scent biosynthesis and metabolism in wintersweet [10]
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