Study on molecular mechanism of volatiles variation during Bupleurum scorzonerifolium root development based on metabolome and transcriptome analysis

Bupleurum scorzonerifolium Willd. is a medicinal herb. Its root has a high content of volatile oil (BSVO), which shows a variety of biological activities. Currently, BSVO in the injectable form is used for treating fever in humans and livestock. The yield and quality of volatile oils depends on the developmental stages of plants. However, the changes in BSVO yield and quality during root development in Bupleurum scorzonerifolium and the underlying molecular regulatory mechanisms remain unclear. This knowledge gap is limiting the improvement in the quality of BSVO. In the present study, B. scorzonerifolium root was collected at germinative, vegetative, florescence, fruiting and defoliating stages. The yield of BSVO, metabolic profile of volatile components and transcriptome of root samples at various developmental stages were comprehensively determined and compared. BSVO continuously accumulated from the germinative to fruiting stages, and its level slightly decreased from the fruiting to defoliating stages. A total of 82 volatile components were detected from B. scorzonerifolium root, of which 22 volatiles were identified as differentially accumulated metabolites (DAMs) during the root development. Of these volatiles, fatty acids and their derivatives accounted for the largest proportion. The contents of most major volatiles were highest at the fruiting stage. A large number of differentially expressed genes (DEGs) were detected during B. scorzonerifolium root development, of which 65 DEGs encoded various enzymes and transcription factors regulating the biosynthesis of fatty acids and their derivatives. In further analysis, 42 DEGs were identified to be significantly correlated with DAMs, and these DEGs may be the key genes for the biosynthesis of volatiles. To the best of our knowledge, this is the first study to comprehensively report the changes in the composition and content of volatiles and underlying mechanism during B. scorzonerifolium root development. This study provided important reference for future studies to determine the harvest time of B. scorzonerifolium roots and improve the quality of BSVO.