The genome of Dioscorea zingiberensis sheds light on the biosynthesis, origin and evolution of the medicinally important diosgenin saponins.

Diosgenin saponins isolated from Dioscorea species such as D. zingiberensis exhibit a broad spectrum of pharmacological activities. Diosgenin, the aglycone of diosgenin saponins, is an important starting material for the production of steroidal drugs. However, how plants produce diosgenin saponins and the origin and evolution of the diosgenin saponin biosynthetic pathway remain a mystery. Here we report a high-quality, 629-Mb genome of D. zingiberensis anchored on 10 chromosomes with 30 322 protein-coding genes. We reveal that diosgenin is synthesized in leaves ('source'), then converted into diosgenin saponins, and finally transported to rhizomes ('sink') for storage in plants. By evaluating the distribution and evolutionary patterns of diosgenin saponins in Dioscorea species, we find that diosgenin saponin-containing may be an ancestral trait in Dioscorea and is selectively retained. The results of comparative genomic analysis indicate that tandem duplication coupled with a whole-genome duplication event provided key evolutionary resources for the diosgenin saponin biosynthetic pathway in the D. zingiberensis genome. Furthermore, comparative transcriptome and metabolite analysis among 13 Dioscorea species suggests that specific gene expression patterns of pathway genes promote the differential evolution of the diosgenin saponin biosynthetic pathway in Dioscorea species. Our study provides important insights and valuable resources for further understanding the biosynthesis, evolution, and utilization of plant specialized metabolites such as diosgenin saponins.

[The comparative study on morphology and polysaccharides content of Dendrobium loddigesii from different habits].

The morphological characters and the polysaccharides content of Dendrobiam loddigesii from different habits were studied in this paper. The results showed that there were remarkable differences in morphology from five areas, such as stem height and diameter, laminae sizes and figures, amount of lateral bud, and texture of stem. The content of polysaccharides from sample of Xingyi and Anlong, Guizhou Province, respectively 22. 62% and 20. 96% , were higher than that of other areas. It can be preferentially choosed as good materal on commareial production.