Functional iridoid synthases from iridoid producing and non-producing Nepeta species (subfam. Nepetoidae, fam. Lamiaceae)

Iridoids, a class of atypical monoterpenes, exhibit exceptional diversity within the Nepeta genus (subfam. Nepetoidae, fam. Lamiaceae).The majority of these plants produce iridoids of the unique stereochemistry, with nepetalactones (NLs) predominating; however, a few Nepeta species lack these compounds. By comparatively analyzing metabolomics, transcriptomics, gene co-expression, and phylogenetic data of the iridoid-producing N. rtanjensis Diklić & Milojević and iridoid-lacking N. nervosa Royle & Bentham, we presumed that one of the factors responsible for the absence of these compounds in N. nervosa is iridoid synthase (ISY). Two orthologues of ISY were mined from leaves transcriptome of N. rtanjensis (NrPRISE1 and NrPRISE2), while in N. nervosa only one (NnPRISE) was identified, and it was phylogenetically closer to the representatives of the Family 1 isoforms, designated as P5βRs. Organ-specific and MeJA-elicited profiling of iridoid content and co-expression analysis of IBG candidates, highlighted NrPRISE2 and NnPRISE as promising candidates for ISY orthologues, and their function was confirmed using in vitro assays with recombinant proteins, after heterologous expression of recombinant proteins in E. coli and their His-tag affinity purification. NrPRISE2 demonstrated ISY activity both in vitro and likely in planta, which was supported by the 3D modeling and molecular docking analysis, thus reclassification of NrPRISE2 to NrISY is accordingly recommended. NnPRISE also displays in vitro ISY-like activity, while its role under in vivo conditions was not here unambiguously confirmed. Most probably under in vivo conditions the NnPRISE lacks substrates to act upon, as a result of the loss of function of some of the upstream enzymes of the iridoid pathway. Our ongoing work is conducted towards re-establishing the biosynthesis of iridoids in N. nervosa.

Mixed elicitation with salicylic acid and hydrogen peroxide modulates the phenolic and iridoid pathways in Castilleja tenuiflora plants

MAIN CONCLUSION

SA and H₂O₂, in single and mixed elicitation stimulate specialized metabolism and activate oxidative stress in C. tenuiflora plants. Single elicitation with salicylic acid (SA at 75 µM) and, hydrogen peroxide (at 150 µM), and mixed elicitation (75 µM SA + 150 µM H₂O₂) were evaluated on specialized metabolism in Castilleja tenuiflora Benth. plants. Total phenolic content (TPC), phenylalanine ammonia-lyase (PAL) activity, antioxidant enzymes and specialized metabolite profiles, as well as the expression levels of eight genes involved in phenolic (Cte-TyrDC, Cte-GOT2, Cte-ADD, Cte-AO3, Cte-PAL1, Cte-CHS1) and terpene pathways (Cte-DXS1 and Cte-G10H) and their correlation with major metabolite (verbascoside and aucubin) concentrations were investigated. TPC content (three-fold) and PAL activity (11.5-fold) increased with mixed elicitation, as well as catalase and peroxidase activity (11.3-fold and 10.8-fold, respectively), compared to single elicitation. Phenylethanoid accumulation was greatest under mixed elicitation, followed by SA and H₂O₂. Lignan accumulation was differential, depending on the plant part and the elicitor. Flavonoids only appeared after mixed elicitation. The high concentration of verbascoside under mixed elicitation was related to a high gene expression. Single elicitation induced iridoid accumulation in specific parts (H₂O₂ in aerial parts and SA in roots), whereas under mixed elicitation, it accumulated in both parts. A high concentration of aucubin in the aerial part was related to a high expression level of genes of the terpene pathway Cte-DXS1 and Cte-G10H, and in the root with Cte-G10H, while Cte-DXS1 was downregulated in this tissue in all treatments. Mixed elicitation with SA and H₂O₂ represents an interesting tool to increase the production of specialized metabolites in plants.

Biotic Elicitors in Adventitious and Hairy Root Cultures: A Review from 2010 to 2022

One of the aims of plant in vitro culture is to produce secondary plant metabolites using plant cells and organ cultures, such as cell suspensions, adventitious, and hairy roots (among others). In cases where the biosynthesis of a compound in the plant is restricted to a specific organ, unorganized systems, such as plant cell cultures, are sometimes unsuitable for biosynthesis. Then, its production is based on the establishment of organ cultures such as roots or aerial shoots. To increase the production in these biotechnological systems, elicitors have been used for years as a useful tool since they activate secondary biosynthetic pathways that control the flow of carbon to obtain different plant compounds. One important biotechnological system for the production of plant secondary metabolites or phytochemicals is root culture. Plant roots have a very active metabolism and can biosynthesize a large number of secondary compounds in an exclusive way. Some of these compounds, such as tropane alkaloids, ajmalicine, ginsenosides, etc., can also be biosynthesized in undifferentiated systems, such as cell cultures. In some cases, cell differentiation and organ formation is necessary to produce the bioactive compounds. This review analyses the biotic elicitors most frequently used in adventitious and hairy root cultures from 2010 to 2022, focusing on the plant species, the target secondary metabolite, the elicitor and its concentration, and the yield/productivity of the target compounds obtained. With this overview, it may be easier to work with elicitors in in vitro root cultures and help understand why some are more effective than others.

Phenylpropanoid Glycoside and Phenolic Acid Profiles and Biological Activities of Biomass Extracts from Different Types of Verbena officinalis Microshoot Cultures and Soil-Grown Plant

Different types of microshoot cultures (agar, stationary liquid, agitated, and bioreactors) of Verbena officinalis were optimized for biomass growth and the production of phenylpropanoid glycosides and phenolic acids. Using ultra-high performance liquid chromatography with high-resolution time-of-flight mass spectrometry, the presence of verbascoside, isoverbascoside, leucoseptoside A/isomers, and cistanoside D/isomer was confirmed in the methanolic extracts obtained from all types of in vitro cultures. The compound’s content was determined by ultra-high-performance liquid chromatography. The main metabolites in biomass extracts were verbascoside and isoverbascoside (maximum 4881.61 and 451.80 mg/100 g dry weight (DW)). In the soil-grown plant extract, verbascoside was also dominated (1728.97 mg/100 g DW). The content of phenolic acids in the analyzed extracts was below 24 mg/100 g DW. The highest radical scavenging activity was found in the biomass extract from agitated cultures, the most effective reducing power in agar culture extract, and the highest chelating activity in extract from bioreactor cultures. The extracts showed significantly stronger bacteriostatic and bactericidal activity against Gram-positive bacteria (minimum inhibitory concentration (MIC) of 0.3–2.2 mg/mL and minimum bactericidal concentration (MBC) of 0.6–9 mg/mL) than against Gram-negative bacteria (MIC 0.6–9 mg/mL, MBC of 0.6–18 mg/mL). The biomass extract from liquid stationary culture showed the strongest antibacterial activity, while the extract from soil-grown herb had the lowest.

Gentianella lutescens subsp. carpatica J. Holub.: Shoot Propagation In Vitro and Effect of Sucrose and Elicitors on Xanthones Production

In vitro shoot culture of the endangered medicinal plant Gentianella lutescens was established from epicotyl explants cultured on MS basal medium with 0.2 mg L⁻¹ 6-benzylaminopurine (BA) and evaluated for xanthones content for the first time. Five shoot lines were obtained and no significant variations in multiplication rate, shoot elongation, and xanthones profile were found among them. The highest rooting rate (33.3%) was achieved by shoots treated for 2 days with 5 mg L⁻¹ indole-3-butyric acid (IBA) followed by cultivation in liquid PGR-free ½ MS medium for 60 days. HPLC analysis revealed the lower content of xanthones—mangiferin, bellidifolin, demethylbellidifolin, demethylbellidifolin-8-O-glucoside and bellidifolin-8-O-glucoside—in in vitro cultured shoots compared to wild growing plants. The increasing concentration of sucrose, sorbitol and abiotic elicitors salicylic acid (SA), jasmonic acid (JA) and methyl jasmonate (MeJA) altered shoot growth and xanthone production. Sucrose and sorbitol applied at the highest concentration of 233.6 mM increased dry matter percentage, while SA at 100 μM promoted shoot growth 2-fold. The increased sucrose concentration enhanced accumulation of xanthones in shoot cultures 2–3-fold compared to the control shoots. Elicitors at 100–300 μM increased the accumulation of mangiferin, demethylbellidifolin-8-O-glucoside, and bellidifolin-8-O-glucoside almost equally, while MeJA at the highest concentration of 500 μM enhanced amount of aglycones demethylbellidifolin and bellidifolin 7-fold compared to the control. The obtained results facilitate conservation of G. lutescens and pave the way for further research on large-scale shoot propagation and production of pharmacologically active xanthones.

The roles of methyl jasmonate to stress in plants

Plants are constantly exposed to various stresses, which can degrade their health. The stresses can be alleviated by the application of methyl jasmonate (MeJA), which is a hormone involved in plant signalling. MeJA induces synthesis of defensive compounds and initiates the expression of pathogenesis-related genes involved in systemic acquired resistance and local resistance. Thus, MeJA may be used against pathogens, salt stress, drought stress, low temperature, heavy metal stress and toxicities of other elements. The application of MeJA improves growth, induces the accumulation of active compounds, and affects endogenous hormones levels, and other physiological and biochemical characteristics in stressed plants. Furthermore, MeJA antagonises the adverse effects of osmotic stress by regulating inorganic penetrating ions or organic penetrants to suppress the absorption of toxic ions. MeJA also mitigates oxidative stress by activating antioxidant systems to scavenge reactive oxygen species (ROS) in stressed plants. For these reasons, we reviewed the use of exogenous MeJA in alleviating biotic (pathogens and insects) and abiotic stresses in plants.