Regulation and differential expression of protopanaxadiol synthase in Asian and American ginseng ginsenoside biosynthesis by RNA interferences

Asian ginseng (Panax ginseng) and American ginseng (Panax quinquefolium), are thought to be representative plant of Panax species, have important commercial value and are used in worldwide. Panax species produces triterpene saponins called ginsenosides, which are classified into two groups by the skeleton of aglycones, namely dammarane-type and oleanane-type. Dammarane-type ginsenosides dominate over oleanane-type not only in amount but also in structural varieties. Researches shows that the saponins content in American ginseng is higher than that in Asian ginseng, the higher part of ginsenosides is from dammarane-type biosynthesis. It has been proposed that protopanaxadiol derived from dammarenediol-II, is a key hydroxylation by cytochrome P450 for the biosynthesis of ginsenosides, and the gene number of protopanaxadiol synthase has been published independent in Asian ginseng (PgCYP716A47). However, little is known about genes involved in hydroxylation and glycosylation in American ginseng ginsenoside biosynthesis. Here, we first cloned and identified a P450 gene named PqD12H encoding enzymes catalyzed dammarenediol-II to protopanaxadiol by RT-PCR using degenerate primers designed based on sequence homology. In vitro, the ectopic expression of PqD12H in recombinant WAT21 yeast resulted in protopanaxadiol production after dammarenediol-II was added to the culture medium. In vivo, we established both PgCYP716A47 and PqD12H RNAi transgenic. The RT-PCR and HPLC analysis of the final products of protopanaxadiol and protopanaxatriol showed a result that declined level of protopanaxadiol-type and protopanaxatriol-type ginsenosides. It suggested that the P450 synthase content or expression in American ginseng exceed than in Asian ginseng. The result elucidated the evolution relationship of P450s and the reason of different saponins content among Panax species.     

Molluscicidal saponins from Swartzia simplex

One monodesmosidic saponin and six bidesmosidic saponins have been isolated from the methanolic extract of the leaves of Swartzia simplex. They were shown to be glucuronides of oleanolic acid, gypsogenin and gypsogenic acid by chemical and spectral means. The monodesmosidic saponins exhibit various molluscicidal activities against the schistosomiasis-transmitting snail Biomphalaria glabrata.     

Molluscicidal saponins from Gundelia tournefortii

From the roots of Gundelia tournefortii seven saponins have been isolated mainly by DCCC. The main saponins (A and B) were characterized, mainly by ¹³C and ¹H NMR spectroscopy, as oleanolic acid 3-O-(2-[α-l-arabinopyranosyl(1 → 3) -β-d-gentiotriosyl(1 → 6) -β-d-glucopyranosyl]gb-d-xylopyranoside) (saponin A) and oleanolic acid 3-O-(2-[α-l-arabinopyranosyl] (1 → 3)-β-d-gentiobiosyl (1 → 6)-β-d-glucopyranosyl β-d-xylopyranoside) (saponin B). The other saponins are also derived from oleanolic acid and contain more sugar units. The saponin mixture and the saponins A and B possess strong molluscicidal activity against the schistosomiasis transmitting snail Biomphalaria glabrata.     

A Genome-Wide Compilation of the Two-Component Systems in Lotus japonicus

The two-component systems (TCS), or histidine-to-aspartate phosphorelays, are evolutionarily conserved common signal transduction mechanisms that are implicated in a wide variety of cellular responses to environmental stimuli in both prokaryotes and eukaryotes including plants. Among higher plants, legumes including Lotus japonicus have a unique ability to engage in beneficial symbiosis with nitrogen-fixing bacteria. We previously presented a genome-wide compiled list of TCS-associated components of Mesorhizobium loti, which is a symbiont specific to L. japonicus (Hagiwara et al. 2004, DNA Res., 11, 57–65). To gain both general and specific insights into TCS of this currently attractive model legume, here we compiled TCS-associated components as many as possible from a genome-wide viewpoint by taking advantage that the efforts of whole genome sequencing of L. japonicus are almost at final stage. In the current database (http://www.kazusa.or.jp/lotus/index.html), it was found that L. japonicus has, at least, 14 genes each encoding a histidine kinase, 7 histidine-containing phosphotransmitter-related genes, 7 type-A response regulator (RR)-related genes, 11 type-B RR-related genes, and also 5 circadian clock-associated pseudo-RR genes. These results suggested that most of the L. japonicus TCS-associated genes have already been uncovered in this genome-wide analysis, if not all. Here, characteristics of these TCS-associated components of L. japonicus were inspected, one by one, in comparison with those of Arabidopsis thaliana. In addition, some critical experiments were also done to gain further insights into the functions of L. japonicus TCS-associated genes with special reference to cytokinin-mediated signal transduction and circadian clock.     

SIRT1 activator isolated from artificial gastric juice incubate of total saponins in stems and leaves of Panax ginseng

Panax ginseng as a traditional Chinese medicine has been extensively used for the treatment of many diseases, especially in prolonging life and anti-tumor. Dammarane-type triterpenoids from P. ginseng have diverse beneficial effects and their chemical structures can be modified in the gastrointestinal tract after oral administration. In this paper, the dammarane-type triterpenoids were isolated from artificial gastric juice incubate of total saponins in the stems and leaves of P. ginseng through column chromatographic methods and their chemical structures were determined based on spectral data. Two new dammarane-type triterpenoids named ginsenotransmetins B (1) and C (2), along with twenty-nine known compounds (3–31), were obtained. All 31 compounds isolated were investigated for their activities of SIRT1 using SIRT1 fluorometric drug discovery assay kit. Among them, compounds 11, 17, 18, 20, 23, 24, 28, and 29, which were found to be potential as SIRT1 activators, exhibited significant stimulation of SIRT1 activity. The results showed that these compounds may be considered to be a useful medicinal resource for prolonging life and anti-tumor. In addition, the results were helpful to explain the longevity effect of ginseng from the new field of view.