Inter-specific differences of medicinal bioactive products are correlated with differential expressions of key enzyme genes in Scutellaria baicalensis and Scutellaria viscidula

Revealing the dynamic accumulation and synthesizing mechanism of medicinal bioactive products is critical for the evaluation and utilization of crops in medicinal industry. Huangqin (Scutellaria baicalensis Georgi) and Nianmao-Huangqin (Scutellaria viscidula Bge) are important medicinal crops containing flavonoids with good bioactivities. Previous studies have found significant differences of flavonoid contents between the two species. Nevertheless, the dynamic changes of bioactive products and related differential synthesizing mechanism remains unknown. In this study, an inter-specific comparative study was reported on the dynamic accumulation of eight bioactive products (scutellarin, scutellarein, baicalin, wogonoside, apigenin, baicalein, wogonin, and chrysin) and the expression of seven key enzyme genes in different organs (root, stem, and leaf) during different growth stages (May, June, July, August, September, and October) of S. baicalensis and S. viscidula. The results showed that the eight bioactive products were differentially accumulated in different growth stages for the two species. Specifically, the contents of five ingredients (except wogonoside, scutellarein and apigenin) in roots of S. baicalensis were significantly higher than those in S. viscidula in harvest stage (October). Meanwhile, the relative expression of seven key enzyme genes in baicalin synthesizing pathway showed significant spatio-temporal specificities. The expression of UBGAT in downstream baicalin synthesis was significantly higher in roots of S. baicalensis than that of S. viscidula (P < 0.05). Moreover, there exist significant correlations between the content of bioactive products and the expression of key enzyme genes. The expression of upstream (CLL-7, FNSII-1, FNSII-2) and downstream (F6H and UBGAT) key enzyme genes were significantly positively correlated with the contents of baicalin in both S. baicalensis and S. viscidula. On the contrary, the expression of GUS was significantly negatively correlated with the content of baicalin in the two species. Collectively, these results give clear evidences that the expression of key enzyme genes (e.g., FNSII-2, GUS, and UBGAT) in baicalin synthesis is probably the main reason for the difference of bioactive products, suggesting that S. viscidula can be used as an alternative to S. baicalensis in pharmaceutical industry. Furthermore, these findings will provide a theoretical basis for exploring the inter-specific differences of bioactive products in medicinal crops within the same genus, thereby revealing the molecular mechanism of quality formation of Chinese medicinal materials.