Triterpenoid saponins from the root barks ofAralia elata

Identification and analysis of CYP450 and UGT supergene family members from the transcriptome of Aralia elata (Miq.) seem reveal candidate genes for triterpenoid saponin biosynthesis

BACKGROUND

Members of the cytochrome P450 (CYP450) and UDP-glycosyltransferase (UGT) gene superfamily have been shown to play essential roles in regulating secondary metabolite biosynthesis. However, the systematic identification of CYP450s and UGTs has not been reported in Aralia elata (Miq.) Seem, a highly valued medicinal plant.

RESULTS

In the present study, we conducted the RNA-sequencing (RNA-seq) analysis of the leaves, stems, and roots of A. elata, yielding 66,713 total unigenes. Following annotation and KEGG pathway analysis, we were able to identify 64 unigenes related to triterpenoid skeleton biosynthesis, 254 CYP450s and 122 UGTs, respectively. A total of 150 CYP450s and 92 UGTs encoding > 300 amino acid proteins were utilized for phylogenetic and tissue-specific expression analyses. This allowed us to cluster 150 CYP450s into 9 clans and 40 families, and then these CYP450 proteins were further grouped into two primary branches: A-type (53%) and non-A-type (47%). A phylogenetic analysis of 92 UGTs and other plant UGTs led to clustering into 16 groups (A-P). We further assessed the expression patterns of these CYP450 and UGT genes across A. elata tissues, with 23 CYP450 and 16 UGT members being selected for qRT-PCR validation, respectively. From these data, we identified CYP716A295 and CYP716A296 as the candidate genes most likely to be associated with oleanolic acid synthesis, while CYP72A763 and CYP72A776 were identified as being the most likely to play roles in hederagenin biosynthesis. We also selected five unigenes as the best candidates for oleanolic acid 3-O-glucosyltransferase. Finally, we assessed the subcellular localization of three CYP450 proteins within Arabidopsis protoplasts, highlighting the fact that they localize to the endoplasmic reticulum.

CONCLUSIONS

This study presents a systematic analysis of the CYP450 and UGT gene family in A. elata and provides a foundation for further functional characterization of these two multigene families.

Araloside A, an Antiulcer Constituent from the Root Bark of Aralia elata

Araloside A, a potent inhibitor of gastric lesion and ulcer formation in rats, was isolated from the root bark of Aralia elata through a bioassay-guided separation procedure. The compound exhibited significant reduction of HCl.ethanol-induced gastric lesions and aspirin-induced gastric ulcers at oral doses of 50 and 100 mg/kg, respectively. These activities are comparable to those of cimetidine.

Saponins and Other Constituents from the Leaves of Aralia elata

A new triterpenoid saponin, together with five known saponins, were isolated from the nonpolar n-hexane fraction of the leaves of Aralia elata. The structure of the new saponin, durupcoside C, was elucidated as hederagenin 3-O-beta-D-glucopyranosyl(1-->3)-beta-D-glucopyranosyl(1-->3)-alpha-L-arabinopyranoside on the basis of spectroscopic analysis. The known saponins were characterized as 3-O-alpha-L-rhamnopyranosyl(1-->2)-alpha-L-arabinopyranosyl hederagenin 28-O-beta-D-xylopyranosyl(1-->6)-beta-D-glucopyranosyl ester, hederagenin 3-O-beta-D-glucopyranosyl(1-->3)-alpha-L-rhamnopyranosyl(1-->2)-alpha-L-arabinopyranoside, oleanolic acid 3-O-beta-D-glucopyranosyl(1-->3)-alpha-L-rhamnopyranosyl(1-->2)-alpha-L-arabinopyranoside, hederagenin 3-O-alpha-L-rhamnopyranosyl(1-->2)-alpha-L-arabinopyranoside (alpha-hederin), and hederagenin 3-O-beta-D-glucopyranosyl(1-->3)-alpha-L-arabinopyranoside (collinsonidin). In addition, two known lipids, Arisaema glyceride 3 and ceramide mixtures were also isolated and characterized. Collinsonidin and two known lipids were isolated for the first time from this plant.