Plant Lignans Research Articles

Plasmid-free production of the plant lignan pinoresinol in growing Escherichia coli cells

BackgroundThe high-value aryl tetralin lignan (+)-pinoresinol is the main precursor of many plant lignans including (-)-podophyllotoxin, which is used for the synthesis of chemotherapeutics. As (-)-podophyllotoxin is traditionally isolated from endangered and therefore limited natural sources, there is a particular need for biotechnological production. Recently, we developed a reconstituted biosynthetic pathway from (+)-pinoresinol to (-)-deoxypodophyllotoxin, the direct precursor of (-)-podophyllotoxin, in the recombinant host Escherichia coli. However, the use of the expensive substrate (+)-pinoresinol limits its application from the economic viewpoint. In addition, the simultaneous expression of multiple heterologous genes from different plasmids for a multi-enzyme cascade can be challenging and limits large-scale use.ResultsIn this study, recombinant plasmid-free E. coli strains for the multi-step synthesis of pinoresinol from ferulic acid were constructed. To this end, a simple and versatile plasmid toolbox for CRISPR/Cas9-assisted chromosomal integration has been developed, which allows the easy transfer of genes from the pET vector series into the E. coli chromosome. Two versions of the developed toolbox enable the efficient integration of either one or two genes into intergenic high expression loci in both E. coli K-12 and B strains. After evaluation of this toolbox using the fluorescent reporter mCherry, genes from Petroselinum crispum and Zea mays for the synthesis of the monolignol coniferyl alcohol were integrated into different E. coli strains. The product titers achieved with plasmid-free E. coli W3110(T7) were comparable to those of the plasmid-based expression system. For the subsequent oxidative coupling of coniferyl alcohol to pinoresinol, a laccase from Corynebacterium glutamicum was selected. Testing of different culture media as well as optimization of gene copy number and copper availability for laccase activity resulted in the synthesis of 100 mg/L pinoresinol using growing E. coli cells.ConclusionsFor efficient and simple transfer of genes from pET vectors into the E. coli chromosome, an easy-to-handle molecular toolbox was developed and successfully tested on several E. coli strains. By combining heterologous and endogenous enzymes of the host, a plasmid-free recombinant E. coli growing cell system has been established that enables the synthesis of the key lignan pinoresinol.

Unveiling the Power of Flax Lignans: From Plant Biosynthesis to Human Health Benefits.

Flax (Linum usitatissimum L.) is the richest plant source of lignin secondary metabolites. Lignans from flax have been applied in the fields of food, medicine, and health due to their significant physiological activities. The most abundant lignan is secoisolariciresinol, which exists in a glycosylated form in plants. After ingestion, it is converted by human intestinal flora into enterodiol and enterolactone, which both have physiological roles. Here, the basic structures, contents, synthesis, regulatory, and metabolic pathways, as well as extraction and isolation methods, of flax lignans were reviewed. Additionally, the physiological activity-related mechanisms and their impacts on human health, from the biosynthesis of lignans in plants to the physiological activity effects observed in animal metabolites, were examined. The review elucidates that lignans, as phenolic compounds, not only function as active substances in plants but also offer significant nutritional values and health benefits when flax is consumed.

Cloning and functional characterization of the pinoresinol-lariciresinol reductase gene IiPLR2 in Isatis indigotica

The pinoresinol-lariciresinol reductase (PLR), a crucial enzyme in the biosynthesis of lignans in plants, catalyzes a two-step reaction to produce lariciresinol and secoisolariciresinol. Lignans such as lariciresinol are the effective components of traditional Chinese medicine Radix Isatidis in exerting antiviral activity. In order to study the function of the key enzyme PLR in the biosynthesis of lariciresinol in Isatis indigotica, the original plant of Radix Isatidis, IiPLR2 was cloned from I. indigotica, with a full length of 954 bp, encoding 317 amino acids. Multiple sequence alignment showed that IiPLR2 contained a conserved nicotinamide adenine dinucleotide phosphate (NADPH)-binding motif. The phylogenetic tree showcased that IiPLR2 shared the same clade with AtPrR1 from Arabidopsis thaliana. The prokaryotic expression vector pET32a-IiPLR2 was constructed and then transformed into Escherichia coli BL21(DE3) competent cells for protein expression. The purified enzyme IiPLR2 could catalyze the conversion of pinoresinol to lariciresinol and the conversion of lariciresinol to secoisolariciresinol. The cloning, sequencing, and catalytic functional analysis of IiPLR2 in this study enrich the understanding of this kind of functional proteins in I. indigotica and supplement the biosynthesis pathways of lignans. Moreover, this study provides a functional module for further research on metabolic regulation and synthetic biology and lays a foundation for comprehensively revealing the relationship between the spatial structures and catalytic functions of such proteins.

Novel systems biology experimental pipeline reveals matairesinol's antimetastatic potential in prostate cancer: an integrated approach of network pharmacology, bioinformatics, and experimental validation.

Matairesinol (MAT), a plant lignan renowned for its anticancer properties in hormone-sensitive cancers like breast and prostate cancers, presents a promising yet underexplored avenue in the treatment of metastatic prostate cancer (mPC). To elucidate its specific therapeutic targets and mechanisms, our study adopted an integrative approach, amalgamating network pharmacology (NP), bioinformatics, GeneMANIA-based functional association (GMFA), and experimental validation. By mining online databases, we identified 27 common targets of mPC and MAT, constructing a MAT-mPC protein-protein interaction network via STRING and pinpointing 11 hub targets such as EGFR, AKT1, ERBB2, MET, IGF1, CASP3, HSP90AA1, HIF1A, MMP2, HGF, and MMP9 with CytoHuba. Utilizing DAVID, Gene Ontology (GO) analysis highlighted metastasis-related processes such as epithelial-mesenchymal transition, positive regulation of cell migration, and key Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, including cancer, prostate cancer, PI3K-Akt, and MAPK signaling, while the web resources such as UALCAN and GEPIA2 affirmed the clinical significance of the top 11 hub targets in mPC patient survival analysis and gene expression patterns. Our innovative GMFA enrichment method further enriched network pharmacology findings. Molecular docking analyses demonstrated substantial interactions between MAT and 11 hub targets. Simulation studies confirmed the stable interactions of MAT with selected targets. Experimental validation in PC3 cells, employing quantitative real-time reverse-transcription PCR and various cell-based assays, corroborated MAT's antimetastatic effects on mPC. Thus, this exhaustive NP analysis, complemented by GMFA, molecular docking, molecular dynamics simulations, and experimental validations, underscores MAT's multifaceted role in targeting mPC through diverse therapeutic avenues. Nevertheless, comprehensive in vitro validation is imperative to solidify these findings.

Sesaminol alters phospholipid metabolism and alleviates obesity-induced NAFLD.

The prevalence of obesity-induced non-alcoholic fatty liver disease (NAFLD) and insulin resistance is increasing worldwide. We previously demonstrated that sesaminol increases thermogenesis in adipocytes, improves insulin sensitivity, and mitigates obesity in mice. In this study, we demonstrated that sesaminol increased mitochondrial activity and reduced ROS production in hepatocytes. Therefore, we delve into the metabolic action of sesaminol in obesity-induced NAFLD or metabolic dysfunction-associated liver disease (MAFLD). Here, we report that sesaminol induces OXPHOS proteins and mitochondrial function invivo. Further, our data suggest that sesaminol administration reduces hepatic triacylglycerol accumulation and LDL-C levels. Prominently, the lipidomics analyses revealed that sesaminol administration decreased the major phospholipids such as PC, PE, PI, CL, and PS to maintain membrane lipid homeostasis in the liver upon HFD challenge. Besides, SML reduced ePC and SM molecular species and increased PA levels in the HFD-fed mice. Also, sesaminol renders anti-inflammatory properties and dampens fibrosis markers in the liver. Remarkably, SML lowers the hepatic levels of ALT and AST enzymes and alleviates NAFLD in diet-induced obese mice. The molecular docking analysis identifies peroxisome proliferator-activated receptors as potential endogenous receptors for sesaminol. Together, our study demonstrates plant lignan sesaminol as a potential small molecule that alters the molecular species of major phospholipids, including sphingomyelin and ether-linked PCs in the liver tissue, improves metabolic parameters, and alleviates obesity-induced fatty liver disease in mice.

Genome-Wide Identification, Evolution, and Expression Analysis of the DIR Gene Family in Schima superba.

Schima superba, commonly known as the Chinese guger tree, is highly adaptable and tolerant of poor soil conditions. It is one of the primary species forming the evergreen broad-leaved forests in southern China. Dirigent proteins (DIRs) play crucial roles in the synthesis of plant lignin and lignans, secondary metabolism, and response to adversity stress. However, research on the DIR gene family in S. superba is currently limited. This study identified 24 SsDIR genes, categorizing them into three subfamilies. These genes are unevenly distributed across 13 chromosomes, with 83% being intronless. Collinearity analysis indicated that tandem duplication played a more significant role in the expansion of the gene family compared to segmental duplication. Additionally, we analyzed the expression patterns of SsDIRs in different tissues of S. superba. The SsDIR genes exhibited distinct expression patterns across various tissues, with most being specifically expressed in the roots. Further screening identified SsDIR genes that may regulate drought stress, with many showing differential expression under drought stress conditions. In the promoter regions of SsDIRs, various cis-regulatory elements involved in developmental regulation, hormone response, and stress response were identified, which may be closely related to their diverse regulatory functions. This study will contribute to the further functional identification of SsDIR genes, providing insights into the biosynthetic pathways of lignin and lignans and the mechanisms of plant stress resistance.

Construction of lignan glycosides biosynthetic network in Escherichia coli using mutltienzyme modules

BackgroundDue to the complexity of the metabolic pathway network of active ingredients, precise targeted synthesis of any active ingredient on a synthetic network is a huge challenge. Based on a complete analysis of the active ingredient pathway in a species, this goal can be achieved by elucidating the functional differences of each enzyme in the pathway and achieving this goal through different combinations. Lignans are a class of phytoestrogens that are present abundantly in plants and play a role in various physiological activities of plants due to their structural diversity. In addition, lignans offer various medicinal benefits to humans. Despite their value, the low concentration of lignans in plants limits their extraction and utilization. Recently, synthetic biology approaches have been explored for lignan production, but achieving the synthesis of most lignans, especially the more valuable lignan glycosides, across the entire synthetic network remains incomplete.ResultsBy evaluating various gene construction methods and sequences, we determined that the pCDF-Duet-Prx02-PsVAO gene construction was the most effective for the production of (+)-pinoresinol, yielding up to 698.9 mg/L after shake-flask fermentation. Based on the stable production of (+)-pinoresinol, we synthesized downstream metabolites in vivo. By comparing different fermentation methods, including “one-cell, one-pot” and “multicellular one-pot”, we determined that the “multicellular one-pot” method was more effective for producing (+)-lariciresinol, (-)-secoisolariciresinol, (-)-matairesinol, and their glycoside products. The “multicellular one-pot” fermentation yielded 434.08 mg/L of (+)-lariciresinol, 96.81 mg/L of (-)-secoisolariciresinol, and 45.14 mg/L of (-)-matairesinol. Subsequently, ultilizing the strict substrate recognition pecificities of UDP-glycosyltransferase (UGT) incorporating the native uridine diphosphate glucose (UDPG) Module for in vivo synthesis of glycoside products resulted in the following yields: (+)-pinoresinol glucoside: 1.71 mg/L, (+)-lariciresinol-4-O-d-glucopyranoside: 1.3 mg/L, (+)-lariciresinol-4’-O-d-glucopyranoside: 836 µg/L, (-)-secoisolariciresinol monoglucoside: 103.77 µg/L, (-)-matairesinol-4-O-d-glucopyranoside: 86.79 µg/L, and (-)-matairesinol-4’-O-d-glucopyranoside: 74.5 µg/L.ConclusionsBy using various construction and fermentation methods, we successfully synthesized 10 products of the lignan pathway in Isatis indigotica Fort in Escherichia coli, with eugenol as substrate. Additionally, we obtained a diverse range of lignan products by combining different modules, setting a foundation for future high-yield lignan production.

Phytochemical and Gene Network Analysis Elucidating the Key Genes Involved in the Biosynthesis of Gomisin J in Schisandra sphenanthera

The biosynthesis and distribution of lignans in medicinal plants, particularly in Schisandra sphenanthera, hold significant pharmacological importance. This study bridges the knowledge gap in understanding the tissue-specific biosynthesis and distribution of these compounds, with a focus on Gomisin J. Our phytochemical analysis revealed a distinct accumulation pattern of Gomisin J, predominantly in the roots, contrasting with the distribution of Pregomisin and Dihydroguaiaretic acid. This finding highlights the roots’ unique role in lignan storage and biosynthesis. Further, differential gene expression analysis across various tissues illuminated the biosynthetic pathways and regulatory mechanisms of these lignans. Utilizing Weighted Gene Co-expression Network Analysis (WGCNA), we identified the MEtan module as a key player, strongly correlated with Gomisin J levels. This module’s in-depth examination revealed the crucial involvement of four cytochrome P450 (CYP) enzymes and eight transcription factors. Notably, the CYP genes DN6828 and DN2874-i3 exhibited up-regulation in roots across both male and female plants, while DN51746 was specifically up-regulated in male roots, indicating a potential gender-specific aspect in Gomisin J biosynthesis. Comparative analysis with functionally characterized CYP71A homologs suggests these CYP genes might be involved in distinct biosynthetic pathways, including terpenoids, alkaloids, and phenylpropanoids, and potentially in lignan biosynthesis. This hypothesis, supported by their more than 55% identity with CYP71As and strong correlation with Gomisin J concentration, opens avenues for novel discoveries in lignan biosynthesis, pending further functional characterization. Our research provides a comprehensive understanding of the genetic and metabolic mechanisms underlying the tissue-specific distribution of lignans in Schisandra sphenanthera, offering valuable insights for their pharmacological exploitation.

Effect of pinoresinol-lariciresinol reductases on biosynthesis of lignans with substrate selectivity in Schisandra chinensis

Schisandra lignans are the main bioactive compounds found in Schisandra chinensis fruits, such as schisandrol lignans and schisandrin lignans, which play important roles in organ protection or other clinical roles. Pinoresinol-lariciresinol reductase (PLR) plays a pivotal role in plant lignan biosynthesis, however, limited research has been conducted on S. chinensis PLR to date. This study identified five genes as ScPLR, successfully cloned their coding sequences, and elucidated their catalytic capabilities. ScPLR3-5 could recognize both pinoresinol and lariciresinol as substrates, and convert them into lariciresinol and secoisolariciresinol, respectively, while ScPLR2 exclusively catalyzed the conversion of (+)-pinoresinol into (+)-lariciresinol. Transcript-metabolite correlation analysis indicated that ScPLR2 exhibited unique properties that differed from the other members. Molecular docking and site-directed mutagenesis revealed that Phe271 and Leu40 in the substrate binding motif were crucial for the catalytic activity of ScPLR2. This study serves as a foundation for understanding the essential enzymes involved in schisandra lignan biosynthesis.

In Vitro Comparative Study on Antineoplastic Effects of Pinoresinol and Lariciresinol on Healthy Cells and Breast Cancer-Derived Human Cells.

Herbal medicines are the preferred anticancer agents due to their lower cytotoxic effects on healthy cells. Plant lignans play an important role in treating various diseases, especially cancer. The present study aimed to evaluate the effect of podophyllotoxin, pinoresinol, and lariciresinol on cellular toxicity and inducing apoptosis in fibroblasts, HEK-293, and SkBr3 cell lines. An in vitro study was conducted from 2017 to 2019 at the Faculty of Biological Sciences, Tarbiat Modares University (Tehran, Iran). The cell lines were treated for 24 and 48 hours with different concentrations of lignans. Cell viability and apoptosis were examined using MTT and flow cytometry, respectively. Expression levels of cell cycle and apoptosis regulator genes were determined using quantitative real-time polymerase chain reaction. Data were analyzed using a two-way analysis of variance followed by Tukey's HSD test. P<0.05 was considered statistically significant. Podophyllotoxin significantly increased apoptosis in fibroblast cells compared to pinoresinol and lariciresinol (P<0.001). The percentage of cell viability of fibroblast cells treated for 48 hours with pinoresinol, lariciresinol, and podophyllotoxin was reduced by 49%, 47%, and 36%, respectively. Treatment with pinoresinol and lariciresinol significantly overexpressed pro-apoptotic genes and underexpressed anti-apoptotic genes in SkBr3 cells (P<0.001). SkBr3 cells treated with lariciresinol significantly reduced gene expression (P<0.001). Pinoresinol and lariciresinol can potentially be used as new therapeutic agents for the treatment of breast cancer.

Functional analysis of a dirigent protein AtsDIR23 in Acorustatarinowii

Acorus tatarinowii (A. tatarinowii) is a medicinal plant of the Araceae family. Currently, pharmacology focuses on the study of volatile oils, but there are few reports of another important secondary metabolite, lignan. Dirigent protein is thought to play an important role in plant secondary metabolism and responds to a variety of biotic and abiotic stresses. However, the DIR gene family of A. tatarinowii has not been systematically analyzed, and it is unknown whether it affects lignan synthesis. In this study, a total of 27 AtsDIRs were identified by comprehensive analysis of the genome of the medicinal plant A. tatarinowii, and the candidate gene AtsDIR23 that may be involved in lignan synthesis was screened through bioinformatics and transcriptome analysis. It is worth noting that AtsDIR23 is significantly expressed in rhizomes and is a member of the DIR-a subfamily. Subsequently, subcellular localization revealed that AtsDIR23 was localized in chloroplasts. The functional verification of AtsDIR23 b y the transient transformation of A. tatarinowii and the stable transformation of Arabidopsis thaliana showed that the content of lignans in overexpressed plants increased. Co-expression analysis screening revealed the MYB transcription factor (AtsMYB91) that is highly correlated with AtsDIR23 expression, while yeast one-hybrid assays and double luciferase experiments showed that AtsMYB91 negatively regulated the expression of AtsDIR23 b y binding to the AtsDIR23 promoter. In conclusion, AtsDIR23 can promote the accumulation of lignans, which provides a reference for further research on the regulation of lignans by DIR genes.

The ERF transcription factor LTF1 activates DIR1 to control stereoselective synthesis of antiviral lignans and stress defense in Isatis indigotica roots

Lignans are a powerful weapon for plants to resist stresses and have diverse bioactive functions to protect human health. Elucidating the mechanisms of stereoselective biosynthesis and response to stresses of lignans is important for the guidance of plant improvement. Here, we identified the complete pathway to stereoselectively synthesize antiviral (−)-lariciresinol glucosides in Isatis indigotica roots, which consists of three-step sequential stereoselective enzymes DIR1/2, PLR, and UGT71B2. DIR1 was further identified as the key gene in respoJanuary 2024nse to stresses and was able to trigger stress defenses by mediating the elevation in lignan content. Mechanistically, the phytohormone-responsive ERF transcription factor LTF1 colocalized with DIR1 in the cell periphery of the vascular regions in mature roots and helped resist biotic and abiotic stresses by directly regulating the expression of DIR1. These systematic results suggest that DIR1 as the first common step of the lignan pathway cooperates with PLR and UGT71B2 to stereoselectively synthesize (−)-lariciresinol derived antiviral lignans in I. indigotica roots and is also a part of the LTF1-mediated regulatory network to resist stresses. In conclusion, the LTF1-DIR1 module is an ideal engineering target to improve plant Defenses while increasing the content of valuable lignans in plants.

An analysis of the nutritional effects of Schisandra chinensis components based on mass spectrometry technology.

Schisandra chinensis (Turcz.) Baill. (S. chinensis) is a Traditional Chinese medicinal herb that can be used both for medicinal purposes and as a food ingredient due to its beneficial properties, and it is enriched with a wide of natural plant nutrients, including flavonoids, phenolic acids, anthocyanins, lignans, triterpenes, organic acids, and sugars. At present, there is lack of comprehensive study or systemic characterization of nutritional and active ingredients of S. chinensis using innovative mass spectrometry techniques. The comprehensive review was conducted by searching the PubMed databases for relevant literature of various mass spectrometry techniques employed in the analysis of nutritional components in S. chinensis, as well as their main nutritional effects. The literature search covered the past 5 years until March 15, 2023. The potential nutritional effects of S. chinensis are discussed, including its ability to enhance immunity, function as an antioxidant, anti-allergen, antidepressant, and anti-anxiety agent, as well as its ability to act as a sedative-hypnotic and improve memory, cognitive function, and metabolic imbalances. Meanwhile, the use of advanced mass spectrometry detection technologies have the potential to enable the discovery of new nutritional components of S. chinensis, and to verify the effects of different extraction methods on these components. The contents of anthocyanins, lignans, organic acids, and polysaccharides, the main nutritional components in S. chinensis, are also closely associated to its quality. This review will provide guidelines for an in-depth study on the nutritional value of S. chinensis and for the development of healthy food products with effective components.

Proliferative response of ERα-positive breast cancer cells to 10 μM enterolactone, and the associated alteration in the transcriptomic landscape

Enterolactone (EL) is a product of gut-microbial metabolism of dietary plant lignans. Studies linking EL with breast cancer risk have bolstered investigations into its effects on the mammary epithelial cells, and the mechanisms thereof. While it binds to the estrogen receptor α (ERα), its effect on the proliferation of mammary tumor cell lines is reportedly ambivalent; depending on its concentration. The genomic correlates of EL actions also remain unexplored. Here we have elaborately studied the effect of EL on proliferation of ERα-positive, and ERα-negative cell lines. 10 µM EL significantly enhanced the growth of the ERα-positive MCF-7 or T47D breast cancer cells, but not the ERα-negative MDA-MB-231 or MDA-MB-453 cells. In MCF-7 cells, it significantly increased the expression of TFF1 mRNA, an estrogen-induced transcript. The binding of ERα to the estrogen response element within the TFF1 locus further demonstrated the pro-estrogenic effect of 10 µM EL. We further explored the genome-wide transcriptomic effect of 10 µM EL using the next generation sequencing technology (RNA-seq). Analysis of RNA-seq data obtained from vehicle (0.1% DMSO)- or 10 µM EL-treated MCF-7 cells revealed modulation of expression of diverse sets of functionally related genes, which reflected cell cycle progression. The manner in which 10 µM EL regulated the hallmark G2/M checkpoint, and estrogen-response-late genes correlated with proliferation inducing, and estrogen-like effects of EL on MCF-7 cells.

Exploiting Underutilised crops

Exploiting Underutilised crops

Identification of Human Gut Microbiome Associated with Enterolignan Production.

Dietary plant lignans are converted inside the gut to enterolignans enterodiol (ED) and enterolactone (EL), which have several biological functions, and health benefits. In this study, we characterized the gut microbiome composition associated with enterolignan production using data from a cross-sectional study in the Japanese population. We identified enterolignan producers by measuring ED and EL levels in subject's serum using liquid chromatography-tandem mass spectrometry. Enterolignan producers show more abundant proportion of Ruminococcaceae and Lachnospiraceae than non-enterolignan producers. In particular, subjects with EL in their serum had a highly diverse gut microbiome that was rich in Ruminococcaceae and Rikenellaceae. Moreover, we built a random forest classification model to classify subjects to either EL producers or not using three characteristic bacteria. In conclusion, our analysis revealed the composition of gut microbiome that is associated with lignan metabolism. We also confirmed that it can be used to classify the microbiome ability to metabolize lignan using machine learning approach.

Production of beneficial lignans in heterologous host plants.

Production of beneficial lignans in heterologous host plants.

Distribution, biosynthesis and therapeutic potential of lignans.

Lignans have long been known for their abundant therapeutic properties due to their polyphenolic structure. Linseed is the richest plant source of lignans and has been studied widely for their properties. The most prevalent lignan, secoisolariciresinol diglucoside (SDG), is consumed with linseed and converted into mammalian lignans, enterodiol (END) and enterolactone (ENL), by the gut microbiota. SDG can easily be assessed using HPLC and its deglycosylated form viz secoisolariciresinol can be asses using GC-MS techniques. Variety of extraction and analysis methods has been reported for plant lignans. SDG is known to have therapeutic properties including anti-oxidant, anti-cancerous, anti-inflammatory, modulation of gene expression, anti-diabetic, estrogenic and anti-estrogenic. Despite a large number of bioactivities, strong evidences for the underlying mechanisms for most of the properties are still unknown. SDG is most studied for its anti-cancerous properties. But the use of lignans as anti-carcinogenic agent is limited and commercially not reported due to challenges of purification at commercial level, rapid metabolism, untargeted delivery and toxic compounds associated with lignans. Exploration of more prominent and active derivatives of SDG and their targeted drug delivery should be an important research toward the use of bioactive lignans of linseed.

The Involvement of microRNAs in Plant Lignan Biosynthesis-Current View.

Lignans, as secondary metabolites synthesized within a phenylpropanoid pathway, play various roles in plants, including their involvement in growth and plant defense processes. The health and nutritional benefits of lignans are unquestionable, and many studies have been devoted to these attributes. Although the regulatory role of miRNAs in the biosynthesis of secondary metabolites has been widely reported, there is no systematic review available on the miRNA-based regulatory mechanism of lignans biosynthesis. However, the genetic background of lignan biosynthesis in plants is well characterized. We attempted to put together a regulatory mosaic based on current knowledge describing miRNA-mediated regulation of genes, enzymes, or transcription factors involved in this biosynthesis process. At the same time, we would like to underline the fact that further research is necessary to improve our understanding of the miRNAs regulating plant lignan biosynthesis by exploitation of current approaches for functional identification of miRNAs.

Advances in plant caffeic acid-O-methyltransferase

Monolignin alcohols (type H, type G and type S) are the basic units of lignin and lignans in plants, and their composition differences directly determine the chemical diversity and biological activity of lignin and lignans. Caffeic acid O-methyltransferase (COMT) catalyzes the methylation of oxygen atoms on the hydroxyl groups of phenylpropanoids, playing a critical role in the composition of different types of monolignin alcohols, and thus acting as a key enzyme involved in the biosynthesis pathway of lignin and lignans. A previous review published in 2010 mainly introduced the gene characteristics of COMT and its regulatory role in lignin biosynthesis. This article summarized the latest research progress of COMT in the past decade, including the gene characteristics, expression characteristics, structural characteristics of COMT and its regulatory effects, and prospected future research and application of COMT.