Secondary metabolites from Marchantia paleacea calluses and their allelopathic effects on Arabidopsis seed growth

One-Pot Tandem Coupling Method for the Short-Step Formal Synthesis of Riccardin C

One-pot reactions reduce reagent amounts and circumvent process treatments, such as work-up and purifications in multi-step reactions. In this study, we achieved the formal total synthesis of riccardin C through a one-pot reaction by simultaneously linking four units through two Sonogashira coupling reactions and one Suzuki coupling reaction, followed by reduction and deprotection. Thus, this one-pot method comprised five steps and did not require the purification of intermediate reaction mixtures, which saves resources, such as reagents and solvents, and expedites the work process.

Tissue Culture of Plagiochasma appendiculatum and the Effect of Callus Differentiation on Types and Content of Bisbibenzyls

Plagiochasma appendiculatum, a thalloid liverwort, contains high levels of bisbibenzyls, aromatic compounds with potent antitumor as well as antifungal activities. In the present study, rapid growth callus was induced from the thallus of P. appendiculatum, and optimal culture conditions, including medium, temperature, pH, and plant growth regulators for callus production were evaluated. Under optimal culture conditions, the biomass of the callus doubled with a sigmoidal growth curve after 15 days. Differentiation and plant regeneration were studied on a medium supplemented with different plant hormones (α-naphthaleneacetic acid [NAA], 6-benzyladenine [6-BA], and 2,4-dichlorophenoxyacetic acid [2,4-D]). NAA and 6-BA stimulated rhizoid and thallus differentiation, respectively, whereas 2,4-D inhibited the differentiation of thallus and rhizoid. Different metabolic profiles of callus, differentiated thallus, and thallus in the soil were studied by high-performance liquid chromatography. The results showed that both the callus and thallus could synthesize bisbibenzyls. In addition, the kinds and content of bisbibenzyl differed significantly between the callus and thallus. In conclusion, P. appendiculatum thallus cultured in vitro possesses the ability to biosynthesize bisbibenzyl, and it may be utilized for the mass production of specific bisbibenzyls in an appropriate growth environment.

Stress, senescence, and specialized metabolites in bryophytes

Life on land exposes plants to varied abiotic and biotic environmental stresses. These environmental drivers contributed to a large expansion of metabolic capabilities during land plant evolution and species diversification. In this review we summarize knowledge on how the specialized metabolite pathways of bryophytes may contribute to stress tolerance capabilities. Bryophytes are the non-tracheophyte land plant group (comprising the hornworts, liverworts, and mosses) and rapidly diversified following the colonization of land. Mosses and liverworts have as wide a distribution as flowering plants with regard to available environments, able to grow in polar regions through to hot desert landscapes. Yet in contrast to flowering plants, for which the biosynthetic pathways, transcriptional regulation, and compound function of stress tolerance-related metabolite pathways have been extensively characterized, it is only recently that similar data have become available for bryophytes. The bryophyte data are compared with those available for angiosperms, including examining how the differing plant forms of bryophytes and angiosperms may influence specialized metabolite diversity and function. The involvement of stress-induced specialized metabolites in senescence and nutrient response pathways is also discussed.

Roles of the 2-Oxoglutarate-Dependent Dioxygenase Superfamily in the Flavonoid Pathway: A Review of the Functional Diversity of F3H, FNS I, FLS, and LDOX/ANS

The 2-oxoglutarate-dependent dioxygenase (2-OGD) superfamily is one of the largest protein families in plants. The main oxidation reactions they catalyze in plants are hydroxylation, desaturation, demethylation, epimerization, and halogenation. Four members of the 2-OGD superfamily, i.e., flavonone 3β-hydroxylase (F3H), flavones synthase I (FNS I), flavonol synthase (FLS), and anthocyanidin synthase (ANS)/leucoanthocyanidin dioxygenase (LDOX), are present in the flavonoid pathway, catalyzing hydroxylation and desaturation reactions. In this review, we summarize the recent research progress on these proteins, from the discovery of their enzymatic activity, to their functional verification, to the analysis of the response they mediate in plants towards adversity. Substrate diversity analysis indicated that F3H, FNS Ⅰ, ANS/LDOX, and FLS perform their respective dominant functions in the flavonoid pathway, despite the presence of functional redundancy among them. The phylogenetic tree classified two types of FNS Ⅰ, one mainly performing FNS activity, and the other, a new type of FNS present in angiosperms, mainly involved in C-5 hydroxylation of SA. Additionally, a new class of LDOXs is highlighted, which can catalyze the conversion of (+)-catechin to cyanidin, further influencing the starter and extension unit composition of proanthocyanidins (PAs). The systematical description of the functional diversity and evolutionary relationship among these enzymes can facilitate the understanding of their impacts on plant metabolism. On the other hand, it provides molecular genetic evidence of the chemical evolution of flavonoids from lower to higher plants, promoting plant adaptation to harsh environments.

Structural and biochemical characterization of the plant type III polyketide synthases of the liverwort Marchantia paleacea

Chalcone synthases (CHSs) of the type III polyketide synthases (PKSs), catalyze the formation of a tetraketide intermediate from a CoA-tethered starter and malonyl-CoA but use different cyclization mechanisms to produce distinct chemical scaffolds. Herein, we characterized CHS and CHS-like enzymes (designated MpCHS and MpCHSL1, 2 and 3) from Marchantia paleacea and determined the crystal structure of MpCHSL1. MpCHS catalyzed a Claisen condensation to form chalcone, while MpCHSLs catalyzed the formation of lactonized α-pyrones in vitro. Based on the structural, mutational and in vitro biochemical analyses, we established that MpCHSL1 is structurally and functionally closer to prototype CHS than stilbene synthase, and characterized the structural basis for the functional diversity of the type III PKSs. A chalcone-forming mutant of MpCHSL1 was build directed by the structural information. These findings pave the way for future studies to elucidate the functional diversity of type III PKSs in liverwort.

Identification of chalcone isomerase in the basal land plants reveals an ancient evolution of enzymatic cyclization activity for synthesis of flavonoids

Flavonoids ubiquitously distribute to the terrestrial plants and chalcone isomerase (CHI)-catalyzed intramolecular and stereospecific cyclization of chalcones is a committed step in the production of flavonoids. However, so far the bona fide CHIs are found only in vascular plants, and their origin and evolution remains elusive. We conducted transcriptomic and/or genomic sequence search, subsequent phylogenetic analysis, and detailed biochemical and genetic characterization to explore the potential existence of CHI proteins in the basal bryophyte liverwort species and the lycophyte Selaginella moellendorffii. We found that both liverwort and Selaginella species possess canonical CHI-fold proteins that cluster with their corresponding higher plant counterparts. Among them, some members exhibited bona fide CHI activity, which catalyze stereospecific cyclization of both 6'-hydroxychalcone and 6'-deoxychalcone, yielding corresponding 5-hydroxy and 5-deoxyflavanones, resembling the typical type II CHIs currently known to be 'specific' for legume plants. Expressing those primitive bona fide CHIs in the Arabidopsis chi mutant restores the seed coat transparent testa phenotype and the accumulation of flavonoids. These findings, in contrast to our current understanding of the evolution of enzymatic CHIs, suggest that emergence of the bona fide type II CHIs is an ancient evolution event that occurred before the divergence of liverwort lineages.

Functional characterization of a chalcone synthase from the liverwort Plagiochasma appendiculatum

A chalcone synthase gene ( PaCHS ) was isolated and functionally characterized from liverwort. The ectopic expression of PaCHS in Marchantia paleacea callus raised the flavonoids content. Chalcone synthase (CHS; EC 2.3.1.74) is pivotal for the biosynthesis of flavonoid and anthocyanin pigments in plants. It produces naringenin chalcone by condensing one p-coumaroyl- and three malonyl-coenzyme A thioesters through a polyketide intermediate that is cyclized by intramolecular Claisen condensation. Although CHSs of higher plants have been extensively studied, enzyme properties of the CHSs in liverworts have been scarcely characterized. In this study, we report the cloning and characterization of CHS (designated as PaCHS) from the liverwort Plagiochasma appendiculatum. The gene product was 60-70 % identical with chalcone synthases from other species, and contained the characteristic conserved Cys-His-Asn catalytic triad. The recombinant PaCHS was able to catalyze p-coumaroyl-CoA and malonyl-CoA to generate naringenin in vitro. Heterologously expressed PaCHS protein showed similar kinetic properties to those of higher plant CHS. The ectopic expression of PaCHS in Marchantia paleacea callus raised the content of the total flavonoids. These results suggested that PaCHS played a key role in the flavonoids biosynthesis in liverworts. Furthermore, when the thallus of P. appendiculatum was treated with abiotic stress inducers methyl jasmonate, salicylic acid and abscisic acid, PaCHS expression was enhanced. This is the first time that a CHS in liverworts has been functionally characterized.