Oleanolic acid glucuronosyltransferase (OAGT) genes synthesizing the direct precursor of oleanane-type ginsenosides were discovered. The four recombinant proteins of OAGT were able to transfer glucuronic acid at C-3 of oleanolic acid that yields oleanolic acid 3-O-β-glucuronide. Ginsenosides are the primary active components in the genus Panax, and great efforts have been made to elucidate the mechanisms underlying dammarane-type ginsenoside biosynthesis. However, there is limited information on oleanane-type ginsenosides. Here, high-performance liquid chromatography analysis demonstrated that oleanane-type ginsenosides (particularly ginsenoside Ro and chikusetsusaponin IV and IVa) are the abundant ginsenosides in Panax zingiberensis, an extremely endangered Panax species in southwest China. These ginsenosides are derived from oleanolic acid 3-O-β-glucuronide, which may be formed from oleanolic acid catalyzed by an unknown oleanolic acid glucuronosyltransferase (OAGT). Transcriptomic analysis of leaves, stems, main roots, and fibrous roots of P. zingiberensis was performed, and a total of 46,098 unigenes were obtained, including all the identified homologous genes involved in ginsenoside biosynthesis. The most upstream genes were highly expressed in the leaves, and the UDP-glucosyltransferase genes were highly expressed in the roots. This finding indicated that the precursors of ginsenosides are mainly synthesized in the leaves and transported to different parts for the formation of particular ginsenosides. For the first time, enzyme activity assay characterized four genes (three from P. zingiberensis and one from P. japonicus var. major, another Panax species with oleanane-type ginsenosides) encoding OAGT, which particularly transfer glucuronic acid at C-3 of oleanolic acid to form oleanolic acid 3-O-β-glucuronide. Taken together, our study provides valuable genetic information for P. zingiberensis and the genes responsible for synthesizing the direct precursor of oleanane-type ginsenosides.

BackgroundTaproot thickening is a complex biological process that is dependent on the coordinated expression of genes controlled by both environmental and developmental factors. Panax notoginseng is an important Chinese medicinal herb that is characterized by an enlarged taproot as the main organ of saponin accumulation. However, the molecular mechanisms of taproot enlargement are poorly understood.ResultsA total of 29,957 differentially expressed genes (DEGs) were identified during the thickening process in the taproots of P. notoginseng. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment revealed that DEGs associated with “plant hormone signal transduction,” “starch and sucrose metabolism,” and “phenylpropanoid biosynthesis” were predominantly enriched. Further analysis identified some critical genes (e.g., RNase-like major storage protein, DA1-related protein, and Starch branching enzyme I) and metabolites (e.g., sucrose, glucose, fructose, malate, and arginine) that potentially control taproot thickening. Several aspects including hormone crosstalk, transcriptional regulation, homeostatic regulation between sugar and starch, and cell wall metabolism, were identified as important for the thickening process in the taproot of P. notoginseng.ConclusionThe results provide a molecular regulatory network of taproot thickening in P. notoginseng and facilitate the further characterization of the genes responsible for taproot formation in root medicinal plants or crops.

Ultrasonic-assisted extraction of flavonoids from Camellia fascicularis leaves was optimized using response surface methodology. The optimal extracting conditions of flavonoids were determined to be the ratio of liquid to raw material of 60 mL/g, ethanol concentration of 40%, extraction temperature of 72.3°C, and extraction time of 1.6 h, which contributed to the highest flavonoids yield of 4.765%. The crude flavonoids were purified through an AB-8 macroporous adsorption resin column, eluted with ethanol concentration of 40%, and purified flavonoids were obtained. In vitro antioxidant assay demonstrated that purified flavonoids showed significant antioxidant capacities in a concentration-dependent manner for scavenging hydroxyl radical, superoxide anion radical, 2,2-diphenyl-1-picrylhydrazyl radical, and azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt radical. Overall, ultrasonic-assisted extraction was found to be an effective method of extracting flavonoids from C. fascicularis leaves, which might be explored as potential natural antioxidant.Capacidad antioxidante de flavonoides obtenidos de hojas de Camellia fascicularis mediante su extracción asistida por ultrasonido RESUMEN Mediante el uso de la metodología de superficies de respuesta (MSR) se optimizó la extracción de flavonoides obtenidos de hojas de Camellia fascicularis asistida por ultrasonido. Al respecto, se estableció que las condiciones óptimas para la extracción de flavonoides son: ratio de líquido a materia prima de 60 mL/g, concentración de etanol de 40%, temperatura de extracción de 72,3°C y tiempo de extracción de 1,6 horas; a partir de estas condiciones se determinó que el máximo rendimiento de los flavonoides es 4,765%. Empleando una columna de resina de adsorción macroporosa AB-8 se purificaron los flavonoides crudos, siendo posteriormente eluidos con etanol en una concentración de 40%. El ensayo mediante antioxidante in vitro demostró que, dependiendo de su concentración, los flavonoides purificados tienen capacidades antioxidantes significativas para eliminar radicales de hidroxilo, anión superóxido, DPPH y ABTS. En general, se constató que la extracción asistida por ultrasonido constituye un método eficaz para la extracción de flavonoides de hojas de C. fascicularis, los cuales pueden ser sometidos a investigación como un potente antioxidante natural.

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