Transcriptomic analysis and dynamic expression of genes revealed flavonoid synthesis in Scutellaria viscidula

Scutellaria viscidula Bunge (Labiatae), a perennial herb, is an important medicinal plant that possesses broad pharmacological actions. S. viscidula contains flavonoids with good bioactivities (e.g. baicalin, wogonoside, baicalein and wogonin) mainly in its dry root, which is used as alternative to Scutellaria baicalensis in the north of China. Furthermore, S. viscidula also has flavones with interesting diverged structures such as panicolin, viscidulin I, viscidulin II and viscidulin III. Tracing the dynamic process of gene expression will help reveal the mechanism of flavonoid synthesis in S. viscidula, as well as the 4'-deoxyflavone biosynthesis in S. baicalensis. One way is to generate and analyze the expressed sequence tags (ESTs). However, little is known on the transcriptome information of S. viscidula, particularly the key genes involved in flavonoid biosynthesis. In this study, we conducted de novo transcriptome analysis of S. viscidula and obtained 42,310,834 reads and 40,052 unigenes, respectively. We revealed 177 genes relating to flavonoid biosynthesis, where 23 key enzyme encoding genes including CHS, CHI, F3H, PAL and 4CL were annotated. Furthermore, we investigated the dynamic expression of CHS, CHI, F3H, MYB2, and bHLH of stem, root and leaf of S. viscidula in May, July and September. Our results showed that these key genes had important regulatory function and exhibited positive correlation with total flavonoid content in different growth stages of S. viscidula. Collectively, this study provides high-quality transcriptome data of S. viscidula, and further gives significant information for understanding the molecular mechanism of gene expression and active ingredients in Scutellaria plants. Root mRNA profiles of Scutellaria viscidula Bunge collected in June were generated by deep sequencing, in a mixture of three samples, using Illumina® Hiseq 2000 platform.qRT–PCR validation was performed using SYBR Green assays.