TPS genes expression pattern and terpenoids content in the leaves and flowers of Chimonanthus praecox and C. salicifolius

Chimonanthus spp. has attracted much attention due to its great ornamental value and potential medicinal value. The flowers of Chimonanthus praecox and C. salicifolius exude a strong aroma. Terpenoids are the main components of the floral volatile organic compounds (VOCs), and the synthesis of these compounds is closely related to the terpene synthase (TPS) gene. In this study, headspace-solid phase microextraction combined with gas chromatography-mass spectrometry (HS-SPME-GC-MS) was used to identify the floral components of C. praecox and C. salicifolius. 25 and 31 floral VOCs were identified from C. praecox and C. salicifolius, respectively. Combined with the published VOCs of Chimonanthus leaf, we found that monoterpenoids take most relative content of volatile in flowers while in leaves, both monoterpenoids and sesquiterpenoids have high relative content. We identified 63 and 48 TPS genes from the genomes of C. praecox and C. salicifolius. Transcriptome analysis showed that TPS-b subfamily genes (related to monoterpene synthesis) showed high expression levels in flowers and leaves, while TPS-a subfamily genes (related to sesquiterpene synthesis) showed strong expression in leaves. The TPS genes with high expression in leaves mainly evolved through tandem duplication, suggesting that tandem duplication of TPS genes may promote the synthesis of terpenoids in leaves. This study revealed the expression pattern of TPS genes in Chimonanthus plants, and proposed that the tandem duplication of TPS gene family may play an important role in the synthesis of monoterpenes in the leaves of Chimonanthus species.