Abstract
Wintersweet (Chimonanthus praecox) is familiar as a garden plant and woody ornamental flower. On account of its unique flowering time and strong fragrance, it has a high ornamental and economic value. Despite a long history of human cultivation, our understanding of wintersweet genetics and molecular biology remains scant, reflecting a lack of basic genomic and transcriptomic data. In this study, we assembled three cDNA libraries, from three successive stages in flower development, designated as the flower bud with displayed petal, open flower and senescing flower stages. Using the Illumina RNA-Seq method, we obtained 21,412,928, 26,950,404, 24,912,954 qualified Illumina reads, respectively, for the three successive stages. The pooled reads from all three libraries were then assembled into 106,995 transcripts, 51,793 of which were annotated in the NCBI non-redundant protein database. Of these annotated sequences, 32,649 and 21,893 transcripts were assigned to gene ontology categories and clusters of orthologous groups, respectively. We could map 15,587 transcripts onto 312 pathways using the Kyoto Encyclopedia of Genes and Genomes pathway database. Based on these transcriptomic data, we obtained a large number of candidate genes that were differentially expressed at the open flower and senescing flower stages. An analysis of differentially expressed genes involved in plant hormone signal transduction pathways indicated that although flower opening and senescence may be independent of the ethylene signaling pathway in wintersweet, salicylic acid may be involved in the regulation of flower senescence. We also succeeded in isolating key genes of floral scent biosynthesis and proposed a biosynthetic pathway for monoterpenes and sesquiterpenes in wintersweet flowers, based on the annotated sequences. This comprehensive transcriptomic analysis presents fundamental information on the genes and pathways which are involved in flower development in wintersweet. And our data provided a useful database for further research of wintersweet and other Calycanthaceae family plants.
Highlights
The small, evolutionarily ancient Calycanthaceae family comprises four genera, namely Calycanthus L., in North America, Idiospermum Blake, in Australia, and Sinocalycanthus Cheng & S
Our work provides an excellent platform for future genetic and functional genomics research in wintersweet and provides an invaluable resource for genomics studies in other members of the Calycanthaceae family
Using Illumina sequencing-based gene analysis for the identification of Differentially Expressed Genes (DEGs), we identified a large number of candidate genes that were regulated either at the open flower stage (OF) stage or at the SF stage, or at both, and we were able to identify a number of regulated pathways
Summary
The small, evolutionarily ancient Calycanthaceae family comprises four genera, namely Calycanthus L., in North America, Idiospermum Blake, in Australia, and Sinocalycanthus Cheng & S. Wintersweet (Chimonanthus praecox), known as the ‘wax shrub’, is a hardy, fastgrowing perennial shrub, native to China; it is dichogamous and diploid (2n = 22) [2]. Its unique flowering time and strong fragrance make it one of the most popular ornamental plants in China; it is appreciated as a pot plant and for cut flowers and it has a high ornamental and economic value. It has been introduced into Korea, Japan, Europe, America, and Australia [2]. Wintersweet flowers are used in traditional Chinese medicinal preparations to treat heatstroke, vomiting, coughs and measles [4]
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