Transcriptome Analysis Provides Insights into Catalpol Biosynthesis in the Medicinal Plant Rehmannia glutinosa and the Functional Characterization of RgGES Genes.

Rehmannia glutinosa, a member of the Scrophulariaceae family, has been widely used in traditional Chinese medicine since ancient times. The main bioactive component of R. glutinosa is catalpol. However, the biogenesis of catalpol, especially its downstream pathway, remains unclear. To identify candidate genes involved in the biosynthesis of catalpol, transcriptomes were constructed from R. glutinosa using the young leaves of three cultivars, Beijing No. 3, Huaifeng, and Jin No. 9, as well as the tuberous roots and adventitious roots of the Jin No. 9 cultivar. As a result, 71,142 unigenes with functional annotations were generated. A comparative analysis of the R. glutinosa transcriptomes identified over 200 unigenes of 13 enzymes potentially involved in the downstream steps of catalpol formation, including 9 genes encoding UGTs, 13 for aldehyde dehydrogenases, 70 for oxidoreductases, 44 for CYP450s, 22 for dehydratases, 30 for decarboxylases, 19 for hydroxylases, and 10 for epoxidases. Moreover, two novel genes encoding geraniol synthase (RgGES), which is the first committed enzyme in catalpol production, were cloned from R. glutinosa. The purified recombinant proteins of RgGESs effectively converted GPP to geraniol. This study is the first to discover putative genes coding the tailoring enzymes mentioned above in catalpol biosynthesis, and functionally characterize the enzyme-coding gene in this pathway in R. glutinosa. The results enrich genetic resources for engineering the biosynthetic pathway of catalpol and iridoids.

Identification and Functional Characterization of Tyrosine Decarboxylase from Rehmannia glutinosa.

Rehmannia glutinosa is an important medicinal plant that has long been used in Chinese traditional medicine. Acteoside, one of the bioactive components from R. glutinosa, possessed various pharmacological activities for human health; however, the molecular mechanism of acteoside formation is not fully understood. In the current study, a novel tyrosine decarboxylase (designated as RgTyDC2) was identified from the R. glutinosa transcriptome. Biochemical analysis of RgTyDC2 showed RgTyDC2 uses tyrosine and dopa as the substrate to produce tyramine and dopamine, respectively, and it displays higher catalytic efficiency toward tyrosine than dopa. Moreover, the transcript level of RgTyDC2 was consistent with the accumulation pattern of acteoside in R. glutinosa, supporting its possible role in the biosynthesis of acteoside in vivo.

A CONSTANS-LIKE gene of Nelumbo nucifera could promote potato tuberization.

MAIN CONCLUSION: CONSTANS-LIKE 5 of Nelumbo nucifera is capable of promoting potato tuberization through CONSTANS-FLOWERING LOCUS T and gibberellin signaling pathways with a probable association with lotus rhizome enlargement. Lotus (Nelumbo nucifera) is an aquatic plant that is affiliated to the Nelumbonaceace family. It is widely used as an ornamental, vegetable, and medicinal herb with its rhizome being a popular vegetable. To explore the molecular mechanism underlying its rhizome enlargement, we conducted a systematic analysis on the CONSTANS-LIKE (COL) gene family, with the results, indicating that this gene plays a role in regulating potato tuber expansion. These analyses included phylogenetic relationships, gene structure, and expressional patterns of lotus COL family genes. Based on these analyses, NnCOL5 was selected for further study on its potential function in lotus rhizome formation. NnCOL5 was shown to be located in the nucleus, and its expression was positively associated with the enlargement of lotus rhizome. Besides, the overexpression of NnCOL5 in potato led to increased tuber weight and starch content under short-day conditions without changing the number of tubers. Further analysis suggested that the observed tuber changes might be mediated by affecting the expression of genes in CO-FT and GA signaling pathways. These results provide valuable insight in understanding the functions of COL gene as well as the enlargement of lotus rhizome.