The production of hypericins in two selected Hypericum perforatum shoot cultures is related to differences in black gland structure

Low temperature modifies seedling leaf anatomy and gene expression in Hypericum perforatum

Hypericum perforatum, commonly known as St John's wort, is a perennial herb that produces the anti-depression compounds hypericin (Hyp) and hyperforin. While cool temperatures increase plant growth, Hyp accumulation as well as changes transcript profiles, alterations in leaf structure and genes expression specifically related to Hyp biosynthesis are still unresolved. Here, leaf micro- and ultra-structure is examined, and candidate genes encoding for photosynthesis, energy metabolism and Hyp biosynthesis are reported based on transcriptomic data collected from H. perforatum seedlings grown at 15 and 22°C. Plants grown at a cooler temperature exhibited changes in macro- and micro-leaf anatomy including thicker leaves, an increased number of secretory cell, chloroplasts, mitochondria, starch grains, thylakoid grana, osmiophilic granules and hemispherical droplets. Moreover, genes encoding for photosynthesis (64-genes) and energy (35-genes) as well as Hyp biosynthesis (29-genes) were differentially regulated with an altered growing temperature. The anatomical changes and genes expression are consistent with the plant's ability to accumulate enhanced Hyp levels at low temperatures.

Elicitation as a tool to improve the profiles of high-value secondary metabolites and pharmacological properties of Hypericum perforatum

OBJECTIVES

In this review, we aim at updating the available information on the improvement of the Hypericum perforatum L. (Hypericaceae) phytochemical profile and pharmacological properties via elicitation.

KEY FINDINGS

Hypericum perforatum seedlings, shoots, roots, calli and cell suspension cultures were treated with diverse elicitors to induce the formation of secondary metabolites. The extracts of the elicitor-treated plant material containing naphthodianthrones, phloroglucinols, xanthones, flavonoids and other new compounds were quantitatively analysed and tested for their bioactivities. While hypericins were mainly produced in H. perforatum cultures containing dark nodules, namely shoots and seedlings, other classes of compounds such as xanthones, phloroglucinols and flavonoids were formed in all types of cultures. The extracts obtained from elicitor-treated samples generally possessed better bioactivities compared to the extract of control biomass.

SUMMARY

Although elicitation is an excellent tool for the production of valuable secondary metabolites in H. perforatum cell and tissue cultures, its exploitation is still in its infancy mainly due to the lack of reproducibility and difficulties in scaling up biomass production.

Biotechnological production of hyperforin for pharmaceutical formulation

Hyperforin is a major active constituent of Hypericum perforatum (St. John's wort). It has amazing pharmacological activities, such as antidepressant properties, but it is labile and difficult to synthesize. Its sensitivity and lipophilicity are challenges for processing and formulation. Its chemical complexity provokes approaches of biotechnological production and modification. Dedifferentiated H. perforatum cell cultures lack appropriate storage sites and hence appreciable hyperforin levels. Shoot cultures are capable of forming hyperforin but less suitable for biomass up-scaling in bioreactors. Roots commonly lack hyperforin but a recently established adventitious root line has been demonstrated to produce hyperforin and derivatives at promising levels. The roots also contained lupulones, the typical constituents of hop (Humulus lupulus). Although shear-sensitive, these root cultures provide a potential production platform for both individual compounds and extracts with novel combinations of constituents and pharmacological activities. Besides in vitro cultivation techniques, the reconstruction of hyperforin biosynthesis in microorganisms is a promising alternative for biotechnological production. The biosynthetic pathway is under study, with omics-technologies being increasingly implemented. These biotechnological approaches may not only yield hyperforin at reasonable productivity but also allow for modifications of its chemical structure and pharmacological profile.

Construction of Hypericin Gland-Specific cDNA Library via Suppression Subtractive Hybridization

Hypericin, an important determinant of the pharmacological properties of the genus Hypericum, is considered as a major molecule for drug development. However, biosynthesis and accumulation of hypericin is not well understood. Identification of genes differentially expressed in tissues with and without hypericin accumulation is a useful strategy to elucidate the mechanisms underlying the development of the dark glands and hypericin biosynthesis. Suppression Subtractive Hybridization (SSH) is a unique method for PCR-based amplification of specific cDNA fragments that differ between a control (driver) and experimental (tester) transcriptome. This technique relies on the removal of dsDNA formed by hybridization between a control and test sample, thus eliminating cDNAs of similar abundance, and retaining differentially expressed or variable in sequence cDNAs. In our laboratory we applied this method to identify the genes involved in the development of dark glands and accumulation of hypericin in Hypericum perforatum. Here we describe the complete procedure for the construction of hypericin gland-specific subtracted cDNA library.

Molecular Cloning and Expression Analysis of hyp-1 Type PR-10 Family Genes in Hypericum perforatum

Hypericum perforatum L. is an important medicinal plant for the treatment of depression. The plant contains bioactive hypericins that accumulate in dark glands present especially in reproductive parts of the plant. In this study, pathogenesis-related class 10 (PR-10) family genes were identified in H. perforatum, including three previously unidentified members with sequence homology to hyp-1, a phenolic coupling protein that has earlier been suggested to participate in biosynthesis and binding/transportation of hypericin. The PR-10 genes showed constitutive but variable expression patterns in different H. perforatum tissues. They were all expressed at relatively high levels in leaves, variably in roots and low levels in stem and reproductive parts of the plant with no specific association with dark glands. The gene expression was up-regulated in leaves after salicylic acid, abscisic acid and wounding treatments but with variable levels. To study exact location of the gene expression, in situ hybridization of hyp-1 transcripts was performed and the accumulation of the Hyp-1 protein was examined in various tissues. The presence of Hyp-1 protein in H. perforatum tissues mostly paralleled with the mRNA levels. In situ RNA hybridization localized the hyp-1 transcripts predominantly in vascular tissues in root and stem, while in leaf the mRNA levels were high also in mesophyll cells in addition to vasculature. Our results indicate that the studied PR-10 genes are likely to contribute to the defense responses in H. perforatum. Furthermore, despite the location of the hyp-1 transcripts in vasculature, no support for the transportation of the Hyp-1 protein to dark glands was found in the current study. The present results together with earlier data question the role of the hyp-1 as a key gene responsible for the hypericin biosynthesis in dark glands of H. perforatum.

Hypericins: biotechnological production from cell and organ cultures

Hypericum perforatum L. (St. John's wort), a perennial flowering plant native to Europe, is widely used as a medicinal plant and has a long history of its use in the treatment of various ailments. Currently, H. perforatum is widely used as an herbal remedy for the treatment of mild to moderate depression. Hypericins are natural napthodianthrone compounds produced from H. perforatum (St. John's wort) which are having antitumor, antiviral (i.e., against human immunodeficiency and hepatitis C virus), antineoplastic, and antidepressant properties. Currently, field-grown plant materials are generally used for the commercial production of hypericins. It has been reported that hypericin accumulation in natural plants is influenced by different ecological and environmental conditions including light intensity, nitrogen availability, temperature, seasons, and growing regions. Therefore, up to 17-fold and 13-fold differences in hypericin and pseudohypericin amounts, respectively, are reported in different phytopharmaceutical preparations. Plant cell and organ cultures are effective systems for producing natural products, and attempts were made for the production of biomass and stable concentrations of hypericins through in vitro cultures of H. perforatum. Cell, callus, shoot, plantlet, and adventitious root cultures have been established and various chemical and physical factors which influence the biomass and secondary metabolite accumulation have been investigated. Large-scale plantlet and adventitious root cultures have also been attempted in H. perforatum in bioreactors, and various strategies have been applied for the production of higher biomass and secondary products. This review describes the biotechnological approaches employed for the production of hypericins and focuses upon the challenges and future prospects.

Direct HPLC detection of benzodilactones and quinones in glands of Lysimachia fordiana

The gland cells were successfully collected from the stems of Lysimachia fordiana Oliver, and the homologous pigments of fordianin A, fordianin B, fordianaquinone A and fordianaquinone B were firstly detected in the glands by HPLC. This indicated that the stem was an ideal material for the preparation of the glands, and the gland was a center for the polycyclic pigments accumulation in this species.

Factors affecting polyphenol biosynthesis in wild and field grown St. John's Wort (Hypericum perforatum L. Hypericaceae/Guttiferae)

The increasing diffusion of herbal products is posing new questions: why are products so often different in their composition and efficacy? Which approach is more suitable to increase the biochemical productivity of medicinal plants with large-scale, low-cost solutions? Can the phytochemical profile of a medicinal plant be modulated in order to increase the accumulation of its most valuable constituents? Will polyphenol-rich medicinal crops ever be traded as commodities? Providing a proactive answer to such questions is an extremely hard task, due to the large number of variables involved: intraspecific chemodiversity, plant breeding, ontogenetic stage, post-harvest handling, biotic and abiotic factors, to name but a few. An ideal path in this direction should include the definition of optimum pre-harvesting and post-harvesting conditions and the availability of specific Good Agricultural Practices centered on secondary metabolism enhancement. The first steps to be taken are undoubtedly the evaluation and the organization of scattered data regarding the diverse factors involved in the optimization of medicinal plant cultivation, in order to provide an interdisciplinary overview of main possibilities, weaknesses and drawbacks. This review is intended to be a synopsis of the knowledge on this regard focused on Hypericum perforatum L. (Hypericaceae/Guttiferae) secondary metabolites of phenolic origin, with the aim to provide a reference and suggest an evolution towards the maximization of St. John's Wort bioactive constituents. Factors considered emerged not only from in-field agronomic results, but also from physiological, genetical, biotic, abiotic and phytochemical data that could be scaled up to the application level. To increase quality for final beneficiaries, growers' profits and ultimately transform phenolic-rich medicinal crops into commodities, the emerging trend suggests an integrated and synergic approach. Agronomy and genetics will need to develop their breeding strategies taking account of the suggestions of phytochemistry, biochemistry, pharmacognosy and pharmacology, without losing sight of the economic balance of the production.

Octaketide-producing type III polyketide synthase from Hypericum perforatum is expressed in dark glands accumulating hypericins

Hypericins are biologically active constituents of Hypericum perforatum (St John's wort). It is likely that emodin anthrone, an anthraquinone precursor of hypericins, is biosynthesized via the polyketide pathway by type III polyketide synthase (PKS). A PKS from H. perforatum, HpPKS2, was investigated for its possible involvement in the biosynthesis of hypericins. Phylogenetic tree analysis revealed that HpPKS2 groups with functionally divergent non-chalcone-producing plant-specific type III PKSs, but it is not particularly closely related to any of the currently known type III PKSs. A recombinant HpPKS2 expressed in Escherichia coli resulted in an enzyme of approximately 43 kDa. The purified enzyme catalysed the condensation of acetyl-CoA with two to seven malonyl-CoA to yield tri- to octaketide products, including octaketides SEK4 and SEK4b, as well as heptaketide aloesone. Although HpPKS2 was found to have octaketide synthase activity, production of emodin anthrone, a supposed octaketide precursor of hypericins, was not detected. The enzyme also accepted isobutyryl-CoA, benzoyl-CoA and hexanoyl-CoA as starter substrates producing a variety of tri- to heptaketide products. In situ RNA hybridization localized the HpPKS2 transcripts in H. perforatum leaf margins, flower petals and stamens, specifically in multicellular dark glands accumulating hypericins. Based on our results, HpPKS2 may have a role in the biosynthesis of hypericins in H. perforatum but some additional factors are possibly required for the production of emodin anthrone in vivo.

Bioactive constituent production in St. John's Wort in vitro hairy roots. Regenerated plant lines

A wild strain of Agrobacterium rhizogenes was used to regenerate twelve in vitro plant lines from different hairy roots of H. perforatum (St. John's Wort). The production of the main bioactive constituents was observed even though their yields varied in the different plant lines. Two lines were selected for the hyperoside production (4.9-4.6 mg/gdw) while nine were characterized by significant yields of chlorogenic acid (ranged from 0.47 to 1.09 mg/gdw). Furthermore, one out of twelve lines showed a 10-fold higher hypericin content (0.25 mg/gdw) than that reported for the in vitro shoots in the literature. Morphological and phytochemical features were determined in order to select H. perforatum genotypes enriched in valuable bioactive compounds.