The biological and structural similarity between lunularic acid and abscisic acid

Reversible Glc-conjugation/hydrolysis modulates the homeostasis of lunularic acid in Marchantia polymorpha growth

The circadian clock efficiently coordinates growth regulators and plant growth in the temporal regulation of physiological processes. The involvement of the growth-regulator-clock in governing the spatio-temporal regulation of plant growth and development remains unexplained in the nonvascular liverworts. In this study, we aimed to assess the relationship between the putative liverwort growth regulator lunularic acid (LA) levels and the growth variation of Marchantia polymorpha according to the circadian clock. LA level exhibited a similar circadian rhythm as gemmalings' accelerated growth during the light phase, and UV-B stress experiments implied that the surge in LA levels at the start of the light phase could serve as a circadian rhythm-based prediction for preempting UV-B injury, with LA serving as a protective shield against UV-B irradiation. Notably, Glc-conjugation/hydrolysis, buffering the anabolism-catabolism of endogenous LA, was rhythmically regulated. Furthermore, the reversible conversion between LA and LA-4'-O-glucoside (mediated by glucosyltransferases MpUGT744A1 and β-glucosidases MpBGLU2/3) was characterized both in vitro and in vivo and evidenced to be relevant to diurnal variation in LA level. Interaction between MpUGT744A1 and MpBGLU2 ensures the efficient metabolic flux between LA and LA-GE. These findings shed light on the regulatory mechanisms that govern LA metabolism and the importance of understanding the temporal aspects of LA for Marchantia's adaptive response to environmental stressors such as UV-B radiation.

The evolution of plant responses underlying specialized metabolism in host-pathogen interactions

In the course of plant evolution from aquatic to terrestrial environments, land plants (embryophytes) acquired a diverse array of specialized metabolites, including phenylpropanoids, flavonoids and cuticle components, enabling adaptation to various environmental stresses. While embryophytes and their closest algal relatives share candidate enzymes responsible for producing some of these compounds, the complete genetic network for their biosynthesis emerged in embryophytes. In this review, we analysed genomic data from chlorophytes, charophytes and embryophytes to identify genes related to phenylpropanoid, flavonoid and cuticle biosynthesis. By integrating published research, transcriptomic data and metabolite studies, we provide a comprehensive overview on how these specialized metabolic pathways have contributed to plant defence responses to pathogens in non-vascular bryophytes and vascular plants throughout evolution. The evidence suggests that these biosynthetic pathways have provided land plants with a repertoire of conserved and lineage-specific compounds, which have shaped immunity against invading pathogens. The discovery of additional enzymes and metabolites involved in bryophyte responses to pathogen infection will provide evolutionary insights into these versatile pathways and their impact on environmental terrestrial challenges.This article is part of the theme issue 'The evolution of plant metabolism'.

Inspired by Nature: Isostere Concepts in Plant Hormone Chemistry

Chemical concepts such as isosteres and scaffold hopping have proven to be powerful tools in agrochemical innovation processes. They offer opportunities to modify known molecular lead structures with the aim to improve a range of parameters, including biological efficacy and spectrum, physicochemical properties, stability, and toxicity. While recent biochemical insights into plant-specific receptors and signaling pathways trigger the discovery of the first lead structures, the disclosure of such a new chemical structure sparks a broad range of synthesis activities giving rise to diverse chemical innovation and often a considerable boost in biological activity. Herein, recent examples of isostere concepts in plant-hormone chemistry will be discussed, outlining how synthetic creativity can broaden the scope of natural product chemistry and giving rise to new opportunities in research fields such as abiotic stress tolerance and growth promotion.

Spatial Distribution, Antioxidant Capacity, and Spore Germination-Promoting Effect of Bibenzyls from Marchantia polymorpha

Liverworts, considered to be the first plant type to successfully make the transition from water to land, can resist different oxidative stress. As characteristic constituents of liverworts, the bibenzyls are efficient antioxidants. In this study, spatial distributions of the bibenzyls within Marchantia polymorpha L., the model species of liverworts, were mapped using airflow-assisted desorption electrospray ionization imaging mass spectrometry. Bibenzyls were found to largely exist in the female receptacle of M. polymorpha, where lunularic acid was found to focus in the central region and bisbibenzyls were enriched in the periphery. The region-specific gene expression and antioxidant activities were characterized. In line with the spatial feature of bibenzyls, higher MpSTCS1A and Mp4CL expression levels and antioxidant ability were exhibited in the archegoniophore. The expression level of MpSTCS1A, and the content of total phenolic acid was increased after UV-B irradiation, suggesting bibenzyls play an important role in UV-B tolerance. Moreover, lunularic acid and extract of archegoniophore at a certain concentration can stimulate the spore germination under normal conditions and UV-B stress. These works broaden our understanding of the significance of bibenzyls in spore propagation and environmental adaptation.

An Overview of the Medicinally Important Plant Type III PKS Derived Polyketides

Plants produce interesting secondary metabolites that are a valuable source of both medicines for human use, along with significant advantages for the manufacturer species. The active compounds which lead to these instrumental effects are generally secondary metabolites produced during various plant growth phases, which provide the host survival advantages while affecting human health inadvertently. Different chemical classes of secondary metabolites are biosynthesized by the plant type III polyketide synthases (PKSs). They are simple homodimeric proteins with the unique mechanistic potential to produce a broad array of secondary metabolites by utilizing simpler starter and extender units. These PKS derived products are majorly the precursors of some important secondary metabolite pathways leading to products such as flavonoids, stilbenes, benzalacetones, chromones, acridones, xanthones, cannabinoids, aliphatic waxes, alkaloids, anthrones, and pyrones. These secondary metabolites have various pharmaceutical, medicinal and industrial applications which make biosynthesizing type III PKSs an important tool for bioengineering purposes. Because of their structural simplicity and ease of manipulation, these enzymes have garnered interest in recent years due to their application in the generation of unnatural natural polyketides and modified products in the search for newer drugs for a variety of health problems. The following review covers the biosynthesis of a variety of type III PKS-derived secondary metabolites, their biological relevance, the associated enzymes, and recent research.

One-Pot Synthesis of Metastable 2,5-Dihydrooxepines through Retro-Claisen Rearrangements: Method and Applications

A one-pot methodology to synthesize metastable bicyclic 2,5-dihydrooxepines from cyclic 1,3-diketones and 1,4-dibromo-2-butenes through the retro-Claisen rearrangement of syn-2-vinylcyclopropyl diketone intermediates is reported. DFT calculations were performed to understand the reaction selectivity and mechanisms towards [1,3]- or [3,3]-sigmatropic rearrangements, highlighting the crucial influence of the temperature. The reaction was successfully applied to a short protecting group-free total synthesis of radulanin A, a natural 2,5-dihydrobenzoxepine. Moreover, the strong herbicidal potential of this natural product is demonstrated for the first time.

Chemotypes and Biomarkers of Seven Species of New Caledonian Liverworts from the Bazzanioideae Subfamily

Volatile components of seven species of the Bazzanioideae sub-family (Lepidoziaceae) native to New Caledonia, including three endemic species (Bazzania marginata, Acromastigum caledonicum and A. tenax), were analyzed by GC-FID-MS in order to index these plants to known or new chemotypes. Detected volatile constituents in studied species were constituted mainly by sesquiterpene, as well as diterpene compounds. All so-established compositions cannot successfully index some of them to known chemotypes but afforded the discovery of new chemotypes such as cuparane/fusicoccane. The major component of B. francana was isolated and characterized as a new zierane-type sesquiterpene called ziera-12(13),10(14)-dien-5-ol (23). In addition, qualitative intraspecies variations of chemical composition were very important particularly for B. francana which possessed three clearly defined different compositions. We report here also the first phytochemical investigation of Acromastigum species. Moreover, crude diethyl ether extract of B. vitatta afforded a new bis(bibenzyl) called vittatin (51), for which a putative biosynthesis was suggested.

Chemical Constituents of Bryophytes: Structures and Biological Activity

Comparatively little attention has been paid to the bryophytes for use in the human diet or medicine in spite of the presence of 23 000 species globally. Several hundred new compounds have been isolated from the liverworts (Marchantiophyta), and more than 40 new carbon skeletons of terpenoids and aromatic compounds were found. Most of the liverworts studied elaborate characteristic odiferous, pungent, and bitter-tasting compounds, of which many show antimicrobial, antifungal, antiviral, allergic contact dermatitis, cytotoxic, insecticidal, anti-HIV, plant growth regulatory, neurotrophic, NO production and superoxide anion radical release inhibitory, muscle relaxing, antiobesity, piscicidal, and nematocidal activities. The biological effects ascribed to the liverworts are mainly due to lipophilic sesqui- and diterpenoids, phenolic compounds, and polyketides, which are the principal constituents of their oil bodies. Some mosses and liverworts produce significant levels of vitamin B₂ and tocopherols, as well as prostaglandin-like highly unsaturated fatty acids. The most characteristic chemical phenomenon of the liverworts is that most of the sesqui- and diterpenoids are enantiomers of those found in higher plants. In this review, the chemical constituents and potential medicinal uses of bryophytes are discussed.

Abscisic acid-induced gene expression in the liverwort Marchantia polymorpha is mediated by evolutionarily conserved promoter elements

Abscisic acid (ABA) is a phytohormone widely distributed among members of the land plant lineage (Embryophyta), regulating dormancy, stomata closure and tolerance to environmental stresses. In angiosperms (Magnoliophyta), ABA-induced gene expression is mediated by promoter elements such as the G-box-like ACGT-core motifs recognized by bZIP transcription factors. In contrast, the mode of regulation by ABA of gene expression in liverworts (Marchantiophyta), representing one of the earliest diverging land plant groups, has not been elucidated. In this study, we used promoters of the liverwort Marchantia polymorpha dehydrin and the wheat Em genes fused to the β-glucuronidase (GUS) reporter gene to investigate ABA-induced gene expression in liverworts. Transient assays of cultured cells of Marchantia indicated that ACGT-core motifs proximal to the transcription initiation site play a role in the ABA-induced gene expression. The RY sequence recognized by B3 transcriptional regulators was also shown to be responsible for the ABA-induced gene expression. In transgenic Marchantia plants, ABA treatment elicited an increase in GUS expression in young gemmalings, which was abolished by simultaneous disruption of the ACGT-core and RY elements. ABA-induced GUS expression was less obvious in mature thalli than in young gemmalings, associated with reductions in sensitivity to exogenous ABA during gametophyte growth. In contrast, lunularic acid, which had been suggested to function as an ABA-like substance, had no effect on GUS expression. The results demonstrate the presence of ABA-specific response mechanisms mediated by conserved cis-regulatory elements in liverworts, implying that the mechanisms had been acquired in the common ancestors of embryophytes.

Phytotoxic cis-clerodane diterpenoids from the Chinese liverwort Scapania stephanii

Five cis-clerodane diterpenoids, stephanialides A-E, along with seven known cis-clerodanes, scaparvins A-C, parvitexins B and C, 3-chloro-4-hydroxy-parvitexin A, and scapanialide B, were isolated from the Chinese liverwort Scapania stephanii. Their structures were established unequivocally on the basis of spectroscopic data. The absolute configuration of stephanialide A was determined by analysis of CD data using the octant rule. Phytotoxic activity evaluation showed that this type of diterpenoids can significantly inhibit root elongation of the seeds of Arabidopsis thaliana, Lepidium sativum and Brassica pekinensis.

Phytochemical and biological studies of bryophytes

The bryophytes contain the Marchantiophyta (liverworts), Bryophyta (mosses) and Anthocerotophyta (hornworts). Of these, the Marchantiophyta have a cellular oil body which produce a number of mono-, sesqui- and di-terpenoids, aromatic compounds like bibenzyl, bis-bibenzyls and acetogenins. Most sesqui- and di-terpenoids obtained from liverworts are enantiomers of those found in higher plants. Many of these compounds display a characteristic odor, and can have interesting biological activities. These include: allergenic contact dermatitis, antimicrobial, antifungal and antiviral, cytotoxic, insecticidal, insect antifeedant, superoxide anion radical release, 5-lipoxygenase, calmodulin, hyaluronidase, cyclooxygenase, DNA polymerase β, and α-glucosidase and NO production inhibitory, antioxidant, piscicidal, neurotrophic and muscle relaxing activities among others. Each liverwort biosynthesizes unique components, which are valuable for their chemotaxonomic classification. Typical chemical structures and biological activity of the selected liverwort constituents as well as the hemi- and total synthesis of some biologically active compounds are summarized.

ABA in bryophytes: how a universal growth regulator in life became a plant hormone?

Abscisic acid (ABA) is not a plant-specific compound but one found in organisms across kingdoms from bacteria to animals, suggesting that it is a ubiquitous and versatile substance that can modulate physiological functions of various organisms. Recent studies have shown that plants developed an elegant system for ABA sensing and early signal transduction mechanisms to modulate responses to environmental stresses for survival in terrestrial conditions. ABA-induced increase in stress tolerance has been reported not only in vascular plants but also in non-vascular bryophytes. Since bryophytes are the key group of organisms in the context of plant evolution, clarification of their ABA-dependent processes is important for understanding evolutionary adaptation of land plants. Molecular approaches using Physcomitrella patens have revealed that ABA plays a role in dehydration stress tolerance in mosses, which comprise a major group of bryophytes. Furthermore, we recently reported that signaling machinery for ABA responses is also conserved in liverworts, representing the most basal members of extant land plant lineage. Conservation of the mechanism for ABA sensing and responses in angiosperms and basal land plants suggests that acquisition of this mechanism for stress tolerance in vegetative tissues was one of the critical evolutionary events for adaptation to the land. This review describes the role of ABA in basal land plants as well as non-land plant organisms and further elaborates on recent progress in molecular studies of model bryophytes by comparative and functional genomic approaches.

Monocyclic phenolic acids; hydroxy- and polyhydroxybenzoic acids: occurrence and recent bioactivity studies

Among the wide diversity of naturally occurring phenolic acids, at least 30 hydroxy- and polyhydroxybenzoic acids have been reported in the last 10 years to have biological activities. The chemical structures, natural occurrence throughout the plant, algal, bacterial, fungal and animal kingdoms, and recently described bioactivities of these phenolic and polyphenolic acids are reviewed to illustrate their wide distribution, biological and ecological importance, and potential as new leads for the development of pharmaceutical and agricultural products to improve human health and nutrition.

Jasmonic acid, protein phosphatase inhibitor, metals and UV-irradiation increased momilactone A and B concentrations in the moss Hypnum plumaeforme

Momilactone A and B have been found only in rice and the moss, Hypnum plumaeforme, although both plants are taxonomically quite distinct. The endogenous concentrations of momilactone A and B in H. plumaeforme were 58.7 and 24.3 microg/g dry weight, respectively. UV-irradiation increased the concentrations of momilactone A and B. The concentrations of momilactone A and B, respectively, became 14- and 15-fold greater than those of non-UV-irradiated control. CuCl2 and FeCl2 (1 mmol/L) treatments also increased momilactone A and B concentrations by 2.7- to 6.1-fold and 2.9- to 6.3-fold, respectively. In addition, the protein phosphatase inhibitor, cantharidin, and jasmonic acid increased momilactone A and B concentrations in H. plumaeforme. Cantharidin acts as an elicitor and jasmonic acid is an important signaling molecule regulating inducible defense genes against the pathogen infection. Momilactone A and B, respectively, were increased 12- and 11-fold by 200 micromol/L cantharidin, and 14- and 15-fold by 100 micromol/L jasmonic acid compared with non-treated controls. As momilactone A and B are phytoalexins, these compounds may play an important role in defense responses against biotic and abiotic stress conditions in H. plumaeforme.

HIGH-THROUGHPUT SCREENING TECHNOLOGY FOR MONITORING PHYTOHORMONE PRODUCTION IN MICROALGAE(1)

New miniaturized techniques for multiplying microalgae and estimating their phytohormone production were developed; in these methods, the strains to be tested are cultivated in microtitre plates, and the phytohormones in suspensions of the cultures are measured by direct ELISAs. Specific and sensitive ELISAs for determining abscisic acid (ABA), indole-3-acetic acid (IAA), cis- and trans-zeatin riboside, isopentenyladenosine (iPR), and other less common cytokinins were developed for this purpose. Polyclonal antibodies used in the ABA and IAA assays were raised against C1- and C1'- conjugates of the compounds with BSA, respectively, and thus were specific for the free acids and their respective C1-derivatives. The use of cytokinin ribosides coupled via their sugar residues to BSA as haptens generally led to antibodies that bound free bases, 9-glycosides and nucleotides, but with high specificity for the corresponding N(6) -side chains. Using internal standards, dilution assays, and authentic [(2) H] and [(3) H] recovery markers, it was shown that the ELISAs could be used to estimate contents of the selected phytohormones in the cultures. The ELISAs provided reliable and very fast estimates of the selected phytohormones, at concentrations ranging from 0.01 to 10 pmol · mL(-1) in various microalgal strains. In addition, a recently developed HPLC selected ion monitoring mass spectrometry (HPLC-SIM-MS) method was used to calibrate and validate the ELISA results and confirm the presence of the detected phytohormones in immunoaffinity-purified extracts. Where independent validation of results is deemed necessary, the use of quantitative HPLC-MS is recommended for each new microalgal strain to be tested.