Does phenotyping of Hypericum secondary metabolism reveal a tolerance to biotic/abiotic stressors?

In this review we summarize the current knowledge about the changes in Hypericum secondary metabolism induced by biotic/abiotic stressors. It is known that the extreme environmental conditions activate signaling pathways leading to triggering of enzymatic and non-enzymatic defense systems, which stimulate production of secondary metabolites with antioxidant and protective effects. Due to several groups of bioactive compounds including naphthodianthrones, acylphloroglucinols, flavonoids, and phenylpropanes, the world-wide Hypericum perforatum represents a high-value medicinal crop of Hypericum genus, which belongs to the most diverse genera within flowering plants. The summary of the up-to-date knowledge reveals a relationship between the level of defense-related phenolic compounds and interspecific differences in the stress tolerance. The chlorogenic acid, and flavonoids, namely the amentoflavone, quercetin or kaempferol glycosides have been reported as the most defense-related metabolites associated with plant tolerance against stressful environment including temperature, light, and drought, in association with the biotic stimuli resulting from plant-microbe interactions. As an example, the species-specific cold-induced phenolics profiles of 10 Hypericum representatives of different provenances cultured in vitro are illustrated in the case-study. Principal component analysis revealed a relationship between the level of defense-related phenolic compounds and interspecific differences in the stress tolerance indicating a link between the provenance of Hypericum species and inherent mechanisms of cold tolerance. The underlying metabolome alterations along with the changes in the activities of ROS-scavenging enzymes, and non-enzymatic physiological markers are discussed. Given these data it can be anticipated that some Hypericum species native to divergent habitats, with interesting high-value secondary metabolite composition and predicted high tolerance to biotic/abiotic stresses would attract the attention as valuable sources of bioactive compounds for many medicinal purposes.

Phytochemical profiling of several Hypericum species identified using genetic markers.

In the present study, we performed phytochemical profiling of several under-exploited Hypericum representatives taxonomically belonging to the sections Ascyreia, Androsaemum, Inodora, Hypericum, Coridium, Myriandra, and Adenosepalum. The authenticity of the starting plant material was confirmed using the nuclear ribosomal internal transcribed spacer as a molecular marker, DNA content and chromosome number. Phenolic constituents were analyzed using high-performance liquid chromatography to complement species-specific metabolic profiles. In several Hypericum representatives, the pharmacologically important compounds, including naphthodianthrones; phloroglucinol derivatives; chlorogenic acid; and some classes of flavonoids, particularly the flavonols rutin and hyperoside, flavanol catechin, and flavanones naringenin and naringin, were reported for the first time. Comparative multivariate analysis of chemometric data for seedlings cultured in vitro and acclimated to the outdoor conditions revealed a strong genetically predetermined interspecific variability in phenolic compound content. In addition to hypericins, which are the most abundant chemomarkers for the genus Hypericum, rarely employed phenolic metabolites, including phloroglucinol derivatives, chlorogenic acid, catechin, naringenin, naringin, and kaempferol-3-O-glucoside, were shown to be useful for discriminating between closely related species. Given the increasing interest in natural products of the genus Hypericum, knowledge of the spectrum of phenolic compounds in shoot cultures is a prerequisite for future biotechnological applications. In addition, phytochemical profiling should be considered as an additional part of the integrated plant authentication system, which predominantly relies upon genetic markers.

MALDI-HRMS Imaging Maps the Localization of Skyrin, the Precursor of Hypericin, and Pathway Intermediates in Leaves of Hypericum Species.

Hypericum perforatum and related species (Hypericaceae) are a reservoir of pharmacologically important secondary metabolites, including the well-known naphthodianthrone hypericin. However, the exact biosynthetic steps in the hypericin biosynthetic pathway, vis-à-vis the essential precursors and their localization in plants, remain unestablished. Recently, we proposed a novel biosynthetic pathway of hypericin, not through emodin and emodin anthrone, but skyrin. However, the localization of skyrin and its precursors in Hypericum plants, as well as the correlation between their spatial distribution with the hypericin pathway intermediates and the produced naphthodianthrones, are not known. Herein, we report the spatial distribution of skyrin and its precursors in leaves of five in vitro cultivated Hypericum plant species concomitant to hypericin, its analogs, as well as its previously proposed precursors emodin and emodin anthrone, using MALDI-HRMS imaging. Firstly, we employed HPLC-HRMS to confirm the presence of skyrin in all analyzed species, namely H. humifusum, H. bupleuroides, H. annulatum, H. tetrapterum, and H. rumeliacum. Thereafter, MALDI-HRMS imaging of the skyrin-containing leaves revealed a species-specific distribution and localization pattern of skyrin. Skyrin is localized in the dark glands in H. humifusum and H. tetrapterum leaves together with hypericin but remains scattered throughout the leaves in H. annulatum, H. bupleuroides, and H. rumeliacum. The distribution and localization of related compounds were also mapped and are discussed concomitant to the incidence of skyrin. Taken together, our study establishes and correlates for the first time, the high spatial distribution of skyrin and its precursors, as well as of hypericin, its analogs, and previously proposed precursors emodin and emodin anthrone in the leaves of Hypericum plants.

Targeted metabolomic profiling reveals interspecific variation in the genus Hypericum in response to biotic elicitors.

Shoot cultures of eight Hypericum species belonging to the sections Hypericum, Oligostema, Ascyreia and Webbia were evaluated for their phytochemical profiles by high-performance liquid chromatography. In total, 17 secondary metabolites assigned to the groups of anthraquinones, phloroglucinols, hydroxycinnamic acids and flavonoids were detected. Furthermore, the elicitation potential of 18 biotic factors derived from saccharides, endophytic fungi and Agrobacterium rhizogenes was examined and statistically analysed with the paired two-sample t-test and principal component analysis. The production of naphthodianthrones and emodin was predominantly stimulated by elicitors derived from Fusarium oxysporum and Trichoderma crassum, while Piriformospora indica promoted the phloroglucinols production. Among flavonoids, the aglycone amentoflavone was readily increased by several elicitors up to 15.7-fold in H. humifusum treated by potato-dextrose broth. However, the chlorogenic acid proved to be the most susceptible metabolite to elicitation, when 31.7-times increase was detected in H. maculatum shoots upon D-glucose treatment. In spite of several biotic factors have been tested, no metabolite was commonly induced in all Hypericum spp. as a response to elicitor treatments.

Chemometric evaluation of hypericin and related phytochemicals in 17 in vitro cultured Hypericum species, hairy root cultures and hairy root-derived transgenic plants.

OBJECTIVES: The objective of this study was to ascertain the presence and correlations among eight important secondary metabolites viz. hypericin, pseudohypericin, emodin, hyperforin, rutin, hyperoside, quercetin and quercitrin in different organs of 17 in vitro cultured Hypericum species, along with H. tomentosum and H. tetrapterum hairy root cultures, and hairy root-derived transgenic plants of H. tomentosum. METHODS: Samples were extracted and analysed by LC-MS. The LC-MS data were subjected to chemometric evaluations for metabolite profiling and correlating the phytochemical compositions in different samples. KEY FINDINGS: Hypericin, pseudohypericin and their proposed precursor emodin were detected in various levels in the leaves of eight Hypericum species. The highest content of hypericins and emodin was found in H. tetrapterum, which contains the studied secondary metabolites in all plant organs. A significant positive correlation between hypericins and emodin was observed both by principal component analysis (PCA) and multidimensional scaling (MDS), indicating the role of emodin as a possible precursor in the biosynthetic pathway of hypericins. Flavonoids were found in all tested plant organs except roots of H. pulchrum. The hairy roots lacked hypericin, pseudohypericin, emodin, hyperforin and rutin. However, the hairy root-derived transgenic plants showed a significant increase in flavonoids. CONCLUSIONS: This study broadens knowledge about the phytochemical composition of selected in vitro cultured Hypericum species, compared to that of hairy root cultures and hairy root-derived transgenic plants.