Biotechnological interventions and genetic diversity assessment in Swertia sp.: a myriad source of valuable secondary metabolites

The genus Swertia (Family: Gentianaceae) has cosmopolitan distribution which is present in almost all the continents except South America and Australia. Swertia genus has been renowned as one of the potent herbal drugs in the British, American, and Chinese Pharmacopeias as well as well-documented in the Indian traditional medicinal systems, viz. Ayurveda, Siddha, and Unani. Many species of this genus have therapeutic properties and have been used traditionally in the treatment of a number of health ailments viz. hepatitis, diabetes, inflammation, bacillary dysentery, cancer, malaria, fever etc. This genus is industrially important medicinal plant that has been used as a principal component in numerous marketed herbal/ polyherbal formulations. Medicinal usage of Swertia is endorsed to the miscellaneous compounds viz. xanthones, irridoids, seco-irridoids, and triterpenoids. A chain of systematic isolation of bio-active compounds and their diverse range of pharmacological effects during last 15-20 years proved this genus as industrially important plant. Due to the various practices of the Swertia species, annual demand is more than 100 tons per year for this important herb which is continuously increasing 10% annually. The market value rises 10% by the year as there is increased demand in national and international market resulted in adulteration of many Swertia spp. due to paucity of agricultural practices, exomorphological, phytochemical, and molecular characterization. Thus, efficient biotechnology methods are prerequisite for the mass production of authentic species, sustainable production of bio-active compounds and ex situ conservation. A chain of systematic biotechnological interventions in Swertia herb during last 20 years cover the assessment of genetic diversity, in vitro sustainable production of bio-active compounds and mass propagation of elite genotypes via direct and indirect organogenesis. This review attempts to present the comprehensive assessment on biotechnological process made in Swertia over the past few years. KEY POINTS: • Critical and updated assessment on biotechnological aspects of Swertia spp. • In vitro propagation and genetic diversity assessment in Swertia spp. • Biosynthesis and sustainable production of secondary metabolites in Swertia spp.

Production from both wild harvest and cultivation: The cross-border Swertia chirayita (Gentianaceae) trade

ETHNOPHARMACOLOGICAL RELEVANCE

Swertia chirayita is the most widely traded species in a genus of 150 species, many of which are used in traditional medicine. S. chirayita is used mainly in Ayurvedic and Tibetan systems of medicine and the homoeopathic system of medicine as well as in regional folk medicine. Primarily wild collected, with some cultivation. S. chirayita is traded as a medicinal substance and exported in the forms of dried whole plant or extract of whole plant individually and/or as active ingredients of Ayurvedic medicines. S. chirayita export valuations continue to make S. chirayita one of Nepal's highest foreign exchange earning medicinal plant species.

AIMS OF THE REVIEW

The aims of this review were first, to assess the scale of the global trade in S. chirayita, second, to review evidence from plant population biology and from studies on the impacts of wild harvest on S. chirayita populations and cultivation as an alternative source of supply.

METHODS

The taxonomy and trade names for S. chirayita were reviewed, followed by a synthesis of published information on Swertia population biology and studies on impacts of wild S. chirayita harvest from across the geographic range of this species. Data on the prices paid for S. chirayita were then compiled for the period 2001-2017, followed by an analysis of global trade data for S. chirayita.

RESULTS AND CONCLUSIONS

Based on India import data and assuming an estimate in an earlier study that 60% of Nepal's S. chirayita production goes to India and 35% to Tibet, then Nepal's 2013 annual production was about 711 metric tonnes (MT) of which about 675.6 MT would be exported (India + Tibet). Nepal's 2014 annual production would be an estimated 503.25 MT of which about 478 MT would be exported. Declines in S. chirayita populations have been widely noted across its range. In India, since 2004, a ban was placed on the export of wild harvested S. chirayita by the Government of India, where the Director General of Foreign Trade prohibited export of S. chirayita plants, plant portions and their derivatives and extracts obtained from the wild with the exception of 'formulations'. Cultivation of S. chirayita to meet commercial demand has been an important part of a solution to over-exploitation of wild stocks in eastern Nepal for 25 years, producing significant quantities that enter the export trade to India and Tibet. In Sankhuwasabha district, for example, 53.1 MT of S. chirayita were produced in 2013/014, just over half of which (27 MT) were exported to India, with the remainder exported to Tibet. Based on value-chain analysis and cost-benefit assessments, S. chirayita cultivation has been shown to be profitable in Nepal. However, since the first cost-benefit assessment was done (2013), prices dropped from NRs750/kg in April 2013 to a low of 250 NRs/kg in December 2017). Taking inflation into account further highlights the steep decline in the profitability for local farmers, who have limited options for value-adding. Consequently, farmers prefer to grow more profitable alternative crops, such as Nepal cardamom (Amomum subulatum Roxb.).

High-throughput sequencing and de novo transcriptome assembly of Swertia japonica to identify genes involved in the biosynthesis of therapeutic metabolites

Here, we report potential transcripts involved in the biosynthesis of therapeutic metabolites in Swertia japonica , the first report of transcriptome assembly, and characterization of the medicinal plant from Swertia genus. Swertia genus, representing over 170 plant species including herbs such as S. chirata, S. hookeri, S. longifolia, S. japonica, among others, have been used as the traditional medicine in China, India, Korea, and Japan for thousands of years. Due to the lack of genomic and transcriptomic resources, little is known about the molecular basis involved in the biosynthesis of characteristic key bioactive metabolites. Here, we performed deep-transcriptome sequencing for the aerial tissues and the roots of S. japonica, generating over 2 billion raw reads with an average length of 101 bps. Using a combined approach of three popular assemblers, de novo transcriptome assembly for S. japonica was obtained, yielding 81,729 unigenes having an average length of 884 bps and N50 value of 1452 bps, of which 46,963 unigenes were annotated based on the sequence similarity against NCBI-nr protein database. Annotation of transcriptome assembly resulted in the identification of putative genes encoding all enzymes from the key therapeutic metabolite biosynthesis pathways. Transcript abundance analysis, gene ontology enrichment analysis, and KEGG pathway enrichment analysis revealed metabolic processes being up-regulated in the aerial tissues with respect to the roots of S. japonica. We also identified 37 unigenes as potential candidates involved in the glycosylation of bioactive metabolites. Being the first report of transcriptome assembly and annotation for any of the Swertia species, this study will be a valuable resource for future investigations on the biosynthetic pathways of therapeutic metabolites and their regulations.

Authentication of medicinal plants by DNA markers

Medicinal plants have been used worldwide for centuries to maintain health and to treat diseases, more so chronic diseases. However, adulteration and use of spurious materials as substitutes have become a major concern for users and industry for reasons of safety and efficacy. Therefore, authentication of medicinal plants is of utmost importance. Morphological, anatomical, chemical and DNA markers solve the problem by differentiating the genuine material from the adulterants, substitutes and spurious drugs. DNA markers use nucleotide sequences to identify species; it takes preference over the other two markers being not age dependent, tissue specific and having a higher discriminating power. Therefore, characterization of plants with such markers is an ideal approach for identification of medicinal plant species and populations/varieties of the same species. Availability of certified taxonomic specimens in herbaria is certainly required for unambiguous confirmation through final visual comparison and analysis.

Lack of genetic diversity of a critically endangered important medicinal plant Chlorophytum borivilianum in Central India revealed by AFLP markers

Chlorophytum borivilianum is a traditional medicinal plant distributed throughout the tropics and subtropics. In the present investigation, AFLP analysis was used to assess the genetic similarity among 34 accessions. Nine primer sets of AFLP amplified 612 fragments, of which 246 fragments were found to be polymorphic. The average number of polymorphic bands per AFLP primer pair was 27.33. The amplified fragments ranged from 50 base pairs to 600 base pairs. Significant correlation was observed between total number of amplified fragments and polymorphic bands (p > 0.05) per primers. Cluster analysis based on AFLP data revealed limited genetic variation within the thirty four accessions collected from various parts of Central Indian forests.

Genetic diversity of Aquilegia (Ranunculaceae) species and cultivars assessed by AFLPs

Species of the genus Aquilegia are exceptionally diverse in their floral morphology and color, commonly known as columbine. They are widely planted ornamentals and are highly attractive for hummingbirds. However, little is known about their genetic diversity. We examined the genetic diversity of the species and cultivars using amplified fragment length polymorphism (AFLP) markers. Sixteen EcoRI/MseI AFLP primer combinations produced 327 informative polymorphic bands, with a mean of 20.4 bands scored per primer. Jaccard's coefficient of similarity varied from 0.61 to 0.93, indicative of high levels of genetic variation. Cluster analysis using the unweighted pair group method with arithmetic mean algorithm placed the 64 accessions into two main clusters, each divided into two sub-clusters. The AFLP variability was significantly associated with the geographic origins, as the Asian species and the North American species grouped into two distinct clusters. The genetic diversity found among Aquilegia demonstrated the potential value of Chinese germplasm for cultivar improvement and for widening the genetic basis of breeding programs and breeding material selection. We concluded that AFLPs are informative and can provide significant insights for genetic diversity research in columbine species.

Species-specific AFLP markers for identification of Zingiber officinale, Z. montanum and Z. zerumbet (Zingiberaceae)

The Zingiber genus, which includes the herbs known as gingers, commonly used in cooking, is well known for its medicinal properties, as described in the Indian pharmacopoeia. Different members of this genus, although somewhat similar in morphology, differ widely in their pharmacological and therapeutic properties. The most important species of this genus, with maximal therapeutic properties, is Zingiber officinale (garden ginger), which is often adulterated with other less-potent Zingiber sp. There is an existing demand in the herbal drug industry for an authentication system for the Zingiber sp in order to facilitate their commercial use as genuine phytoceuticals. To this end, we used amplified fragment length polymorphism (AFLP) to produce DNA fingerprints for three Zingiber species. Sixteen collections (six of Z. officinale, five of Z. montanum, and five of Z. zerumbet) were used in the study. Seven selective primer pairs were found to be useful for all the accessions. A total of 837 fragments were produced by these primer pairs. Species-specific markers were identified for all three Zingiber species (91 for Z. officinale, 82 for Z. montanum, and 55 for Z. zerumbet). The dendogram analysis generated from AFLP patterns showed that Z. montanum and Z. zerumbet are phylogenetically closer to each other than to Z. officinale. The AFLP fingerprints of the Zingiber species could be used to authenticate Zingiber sp-derived drugs and to resolve adulteration-related problems faced by the commercial users of these herbs.