Date Published: April 18, 2016
Publisher: Springer Berlin Heidelberg
Author(s): Varun Kumar, Nikhil Malhotra, Tarun Pal, Rajinder Singh Chauhan.
Aconitum heterophyllum is an important component for various herbal drug formulations due to the occurrence of non-toxic aconites including marker compound, atisine. Despite huge pharmacological potential, the reprogramming of aconites production is limited due to lack of understanding on their biosynthesis. To address this problem, we have proposed here the complete atisine biosynthetic pathway for the first time connecting glycolysis, MVA/MEP, serine biosynthesis and diterpene biosynthetic pathways. The transcript profiling revealed phosphorylated pathway as a major contributor towards serine production in addition to repertoire of genes in glycolysis (G6PI, PFK, ALD and ENO), serine biosynthesis (PGDH and PSAT) and diterpene biosynthesis (KO and KH) sharing a similar pattern of expression (2-4-folds) in roots compared to shoots vis-à-vis atisine content (0–0.37 %). Quantification of steviol and comparative analysis of shortlisted genes between roots of high (0.37 %) vs low (0.14 %) atisine content accessions further confirmed the route of atisine biosynthesis. The results showed 6-fold increase in steviol content and 3–62-fold up-regulation of all the selected genes in roots of high content accession ascertaining their association towards atisine production. Moreover, significant positive correlations were observed between selected genes suggesting their co-expression and crucial role in atisine biosynthesis. This study, thus, offers unprecedented opportunities to explore the selected candidate genes for enhanced production of atisine in cultivated plant cells.
Medicinal plants are the prolific repositories of specialized metabolites having great commercial value as drugs used in the treatment of various disorders. Traditionally, they have been used as a major source of medication for the treatment of various ailments. Later on, with the advent of chromatographic separations and advancement in organic chemistry, efforts began to isolate and identify the bioactive compounds in plants and strive to synthesize the compounds in vitro. Owing to the sophisticated structures of most natural products, it became a formidable task to synthesize them, and thus, the natural products remain gleaned from the native medicinal plants (Barnes and Prasain 2005). Further, the rising demand of natural products facilitated over-harvesting of several medicinal plants and as a result the reckless collection reduced their populations in natural habitats, thus falling into the category of endangered plant species.
The goal of present study was to fill a gap in our knowledge of atisine biosynthesis and encoded genes. We have used the bio-retrobiosynthetic approach for formal interpretation of atisine biosynthesis pattern and integrated molecular layers to tap the detailed role of genes related to different feeder pathways for atisine biosynthesis in A. heterophyllum. Atisine biosynthesis involved seven interlinking metabolic processes, including glycolysis, phosphorylated, glycolate, glycerate, mevalonate, non-mevalonate and diterpene biosynthetic pathways. It is, however, clear that the dovetails of the genes to atisine biosynthesis remain murky.
The complete biosynthetic pathway of atisine has been elucidated for the first time in A. heterophyllum. This work highlights the candidate genes in glycolysis (G6PI, PFK, ALD and ENO), serine biosynthesis (PGDH and PSAT) and diterpene biosynthesis (KO and KH) and showed that phosphorylated pathway is a major contributor of serine for atisine production. The quantification of steviol in roots of high vs low content accessions revealed that atisine biosynthesis is regulated by two core modules, viz. atisenol and steviol in A. heterophyllum. This study provides a snapshot of atisine biosynthesis and associated bottlenecks in A. heterophyllum but actual realization necessitates a next level investigation to get a robust overview of exact mechanism behind atisine biosynthesis by elucidating missing enzymes and gene function analysis.