Lignin Biosynthetic Pathway Research Articles

Investigating the Variation between Lignin Content and the Fracture Characteristics in Capsicum annuum Mutant Stems

The cultivation of horticultural plants in controlled greenhouse environments is a pivotal practice in modern agriculture, offering the potential to enhance crop productivity and mitigate climate change effects. This study investigates the biomechanical properties and lignin content of various Capsicum annuum mutant lines—‘fragile-plant’ (frx), ‘tortuous internodi’ (tti), and ‘puffy-structured stem’ (pfi)—in comparison to a commercially established variety, ‘Garai Fehér’. We employed the acetyl bromide method to quantify lignin content and conducted three-point bending tests to assess rigidity in three distinct regions of the stem. Gene expression analysis of key lignin biosynthetic pathway genes (PAL, C4H, 4CL, CCoAOMT, CAD) was performed using qRT-PCR. The results revealed significant differences in lignin content and breaking force among the genotypes and stem regions. The tti mutants exhibited similar lignin content to the control but lower breaking strength, likely due to elongated internodes. The frx mutants showed uniformly reduced lignin content, correlating with their fragile stems. The pfi mutants displayed abnormally high lignin content in the top region yet demonstrated the lowest stem rigidity in every region. Overexpression of CAD and CCoAOMT was detected in the mutants in specific regions of the stem, suggesting alterations in lignin biosynthesis; however, we could not confirm the correlation between them. Our findings indicate that while lignin content generally correlates with stem rigidity, this trait is complex and influenced by more factors.

Herbicidal Sorbicillinoid Analogs Cause Lignin Accumulation in Aspergillus aculeatus TE-65L.

Five new sorbicillinoid derivatives, including (±)-aspersorbicillin A [(±)-1], a pair of enantiomers at C-9, and aspersorbicillins B-D (2-4), together with two known analogs (5 and 6) were isolated from the endophytic fungus Aspergillus aculeatus TE-65L. Their structures including absolute configurations were determined by detailed spectroscopic analyses and electronic circular dichroism calculations. The herbicidal activity of sorbicillinoids on the germ and radicle elongation of various weed types was reported for the first time. Compound 1 displayed significant herbicidal activity against Eleusine indica germ elongation (IC50 = 28.8 μg/mL), while compound 6 inhibited radicle elongation (IC50 = 25.6 μg/mL). Both were stronger than those of glyphosate (66.2 and 30.9 μg/mL, respectively). Further transcriptomic and LC-MS/MS metabolomic analysis indicated that 6 induced the transcriptional expressions of genes related to the lignin biosynthetic pathway, resulting in lignin accumulation. Transmission electron microscopy confirmed the cell wall thickening of seeds treated with 6, suggesting weed growth inhibition. This study reveals new lead compounds for fabricating natural herbicides and expands the agricultural use of sorbicillinoid analogs.

Lr34/Yr18/Sr57/Pm38 confers broad-spectrum resistance to fungal diseases via sinapyl alcohol transport for cell wall lignification in wheat

The widely recognized pleiotropic adult plant resistance gene Lr34 encodes an ATP-binding cassette transporter and plays an important role in breeding wheat for enhanced resistance to multiple fungal diseases. Despite its significance, the mechanisms underlying Lr34-mediated pathogen defense remain largely unknown. Our study demonstrates that wheat lines carrying the Lr34res allele exhibit thicker cell walls and enhanced resistance to fungal penetration compared to those without Lr34res. Transcriptome and metabolite profiling revealed that the lignin biosynthetic pathway is suppressed in lr34 mutants, indicating a disruption in cell wall lignification. Additionally, we discovered that lr34 mutant lines are hypersensitive to sinapyl alcohol, a major monolignol crucial for cell wall lignification. Yeast accumulation and efflux assays confirmed that the LR34 protein functions as a sinapyl alcohol transporter. Both genetic and virus-induced gene silencing experiments demonstrated that the disease resistance conferred by Lr34 can be enhanced by incorporating the TaCOMT-3B gene, which is responsible for the biosynthesis of sinapyl alcohol. Collectively, our findings provide novel insights into the role of Lr34 in disease resistance through mediating sinapyl alcohol transport and cell wall deposition, and highlight the synergistic effect of TaCOMT-3B and Lr34 against multiple fungal pathogens by mediating cell wall lignification in adult wheat plants.

How lignin biosynthesis responds to nitrogen in plants: ascoping review.

Nitrogen (N) plays a critical role in the functioning of key amino acids and synthetic enzymes responsible for the various stages of lignin biosynthesis. However, the precise mechanisms through which N influences lignin biosynthesis have not been fully elucidated. This scoping review explores how lignin biosynthesis responds to N in plants. A systematic search of the literature in several databases was conducted using relevant keywords. Only 44 of the 1842 selected studies contained a range of plant species, experimental conditions, and research approaches. Lignin content, structure, and biosynthetic pathways in response to N are discussed, and possible response mechanisms of lignin under low N are proposed. Among the selected studies, 64.52% of the studies reter to lignin content found a negative correlation between N availability and lignin content. Usually, high N decreases the lignin content, delays cell lignification, increases p-hydroxyphenyl propane (H) monomer content, and regulates lignin synthesis through the expression of key genes (PAL, 4CL, CCR, CAD, COMT, LAC, and POD) encoding miRNAs and transcription factors (e.g., MYB, bHLH). N deficiency enhances lignin synthesis through the accumulation of phenylpropanoids, phenolics, and soluble carbohydrates, and indirect changes in phytohormones, secondary metabolites, etc. This review provides new insights and important references for future studies on the regulation of lignin biosynthesis.

GhWRKY55 as a negative regulator of cotton resistance to Verticillium dahliae via lignin biosynthetic and jasmonic acid signaling pathways

Verticillium wilt, caused by Verticillium dahliae, is a major threat to cotton yield and quality. While the WRKY gene family has been shown to be involved in plant defense against V. dahliae, the underlying mechanisms remain unclear. In this study, we found that Gossypium hirsutum WRKY DNA binding protein 55 (GhWRKY55) negatively regulates cotton defense against V. dahliae. GhWRKY55 expression was suppressed in resistant cotton cultivars following V. dahliae inoculation, and the overexpression of GhWRKY55 in Arabidopsis decreased the resistance to V. dahliae. Silencing of GhWRKY55 enhanced the resistance of susceptible cotton to V. dahliae by increasing salicylic acid (SA) accumulation, decreasing jasmonic acid (JA) levels, and altering lignin content and monomer G/S ratio. Yeast one-hybrid and dual-luciferase assays revealed that GhWRKY55 protein interacts with the promoters of lignin biosynthesis-related gene GhHCT_D10 and JA signaling pathway gene GhPR3_D01–1. Our findings suggest that GhWRKY55 negatively regulates cotton resistance to V. dahliae by affecting lignin biosynthesis and JA signaling pathway. These results provide new insights into the relationship between GhWRKY55, SA/JA, and lignin in defense against V. dahliae.

Profiling of the gene expression and alternative splicing landscapes of Eucalyptus grandis.

Eucalyptus is a widely planted hardwood tree speciesdue to its fast growth, superior wood properties and adaptability. However, the post-transcriptional regulatory mechanisms controlling tissue development and stress responses in Eucalyptus remain poorly understood. In this study, we performed a comprehensive analysis of the gene expression profile and the alternative splicing (AS) landscape of E. grandis using strand-specific RNA-Seq, which encompassed 201 libraries including different organs, developmental stages, and environmental stresses. We identified 10 416 genes (33.49%) that underwent AS, and numerous differentially expressed and/or differential AS genes involved in critical biological processes, such as primary-to-secondary growth transition of stems, adventitious root formation, aging and responses to phosphorus- or boron-deficiency. Co-expression analysis of AS events and gene expression patterns highlighted the potential upstream regulatory role of AS events in multiple processes. Additionally, we highlighted the lignin biosynthetic pathway to showcase the potential regulatory functions of AS events in the KNAT3 and IRL3 genes within this pathway. Our high-quality expression atlas and AS landscape serve as valuable resources for unravelling the genetic control of woody plant development, long-term adaptation, and understanding transcriptional diversity in Eucalyptus. Researchers can conveniently access these resources through the interactive ePlant browser (https://bar.utoronto.ca/eplant_eucalyptus).

Lignin biosynthesis pathway repressors in gymnosperms: differential repressor domains as compared to angiosperms.

Lignin is a polyphenolic polymer present in the cell walls of specialized plant cell types in vascular plants that provides structural support and plays a major role in plant protection. The lignin biosynthesis pathway is regulated by transcription factors from the MYB (myeloblastosis) family. While several MYB members positively regulate lignin synthesis, only a few negatively regulate lignin synthesis. These lignin suppressors are well characterized in model plant species; however, their role has not been fully explored in gymnosperms. Lignin forms one of the major hurdles for the forest-based industry e.g. paper, pulp, and biofuel production. Therefore, the detailed mechanisms involved in the regulation of lignin synthesis are valuable, especially in conifers that form the major source of softwood for timber and paper production. In this review, the potential and differential domains present in the MYB suppressors in gymnosperms are discussed, along with their phylogenetic analysis. Sequence analysis revealed that the N-terminal regions of the MYB suppressor members were found to be conserved among the gymnosperms and angiosperms containing the R2, R3, and bHLH domains, while the C-terminal regions were found to be highly variable. The typical repressor motifs like the LxLxL-type EAR motif and the TLLLFR motif were absent from the C-terminal regions of MYB suppressors from most gymnosperms. However, although the gymnosperms lacked the characteristic repressor domains, a R2R3-type MYB member from Ginkgo was reported to repress the lignin biosynthetic pathway. It is proposed that gymnosperms possess unique kinds of repressors that need further functional validation.

Genetic control of pod morphological traits and pod edibility in a common bean RIL population

Key messageQTL mapping, association analysis, and colocation study with previously reported QTL revealed three main regions controlling pod morphological traits and two loci for edible pod characteristics on the common bean chromosomes Pv01 and Pv06.Bean pod phenotype is a complex characteristic defined by the combination of different traits that determine the potential use of a genotype as a snap bean. In this study, the TUM RIL population derived from a cross between ‘TU’ (dry) and ‘Musica’ (snap) was used to investigate the genetic control of pod phenotype. The character was dissected into pod morphological traits (PMTs) and edible pod characteristics (EPC). The results revealed 35 QTL for PMTs located on seven chromosomes, suggesting a strong QTL colocation on chromosomes Pv01 and Pv06. Some QTL were colocated with previously reported QTL, leading to the mapping of 15 consensus regions associated with bean PMTs. Analysis of EPC of cooked beans revealed that two major loci with epistatic effect, located on chromosomes Pv01 and Pv06, are involved in the genetic control of this trait. An association study using a subset of the Spanish Diversity Panel (snap vs. non-snap) detected 23 genomic regions, with three regions being mapped at a position similar to those of two loci identified in the TUM population. The results demonstrated the relevant roles of Pv01 and Pv06 in the modulation of bean pod phenotype. Gene ontology enrichment analysis revealed a significant overrepresentation of genes regulating the phenylpropanoid metabolic process and auxin response in regions associated with PMTs and EPC, respectively. Both biological functions converged in the lignin biosynthetic pathway, suggesting the key role of the pathway in the genetic control of bean pod phenotype.

Silicon inhibits cadmium uptake by regulating the genes associated with the lignin biosynthetic pathway and plant hormone signal transduction in maize plants.

Cadmium (Cd) contamination in soil poses a severe threat to plant growth and development. In contrast, silicon (Si) has shown promise in enhancing plant resilience under Cd-induced stress. In this study, we conducted an integrated investigation employing morphological studies, gene expression analysis, and metabolomics to unravel the molecular mechanisms underlying Cd tolerance in maize plants. Our results demonstrate that Si biofortification significantly mitigated Cd stress by reducing Cd accumulation in plant tissues, increasing Si content, and enhancing maize biomass in Cd-stressed plants resulted in a substantial enhancement in shoot dry weight (+ 75%) and root dry weight (+ 30%). Notably, Si treatment upregulated key lignin-related genes (TaPAL, TaCAD, Ta4CL, and TaCOMT) and promoted the accumulation of metabolites (sinapyl alcohol, phenylalanine, p-coumaryl alcohol, cafeyl alcohol, and coniferaldehyde) essential for cell wall strength, particularly under Cd stress conditions. Si application enriched the signal transduction by hormones and increased resistance by induction of biosynthesis genes (TaBZR1, TaLOX3, and TaNCDE1) and metabolites (brassinolide, abscisic acid, and jasmonate) in the roots and leaves under Cd stress. Furthermore, our study provides a comprehensive view of the intricate molecular crosstalk between Si, Cd stress, and plant hormonal responses. We unveil a network of genetic and metabolic interactions that culminate in a multifaceted defense system, enabling maize plants to thrive even in the presence of Cd-contaminated soil. This knowledge not only advances our understanding of the protective role of Si but also highlights the broader implications for sustainable agricultural practices. By harnessing the insights gained from this research, we may pave the way for innovative strategies to fortify crops against environmental stressors, ultimately contributing to the goal of food security in an ever-changing world. In summary, our research offers valuable insights into the protective mechanisms facilitated by Si, which enhance plants' ability to withstand environmental stress, and holds promise for future applications in sustainable agriculture.

Characterization of caffeoyl shikimate esterase gene family identifies CsCSE5 as a positive regulator of Podosphaera xanthii and Corynespora cassiicola pathogen resistance in cucumber.

CsCSE genes might be involved in the tolerance of cucumber to pathogens. Silencing of the CsCSE5 gene resulted in attenuated resistance of cucumber to Podosphaera xanthii and Corynespora cassiicola. Caffeoyl shikimate esterase (CSE), a key enzyme in the lignin biosynthetic pathway, has recently been characterized to play a key role in defense against pathogenic infection in plants. However, a systematic analysis of the CSE gene family in cucumber (Cucumis sativus) has not yet been conducted. Here, we identified eight CsCSE genes from the cucumber genome via bioinformatic analyses, and these genes were unevenly distributed on chromosomes 1, 3, 4, and 5. Results from multiple sequence alignment indicated that the CsCSE proteins had domains required for CSE activity. Phylogenetic analysis of gene structure and protein motifs revealed the conservation and diversity of the CsCSE gene family. Collinearity analysis showed that CsCSE genes had high homology with CSE genes in wax gourd (Benincasa hispida). Cis-acting element analysis of the promoters suggested that CsCSE genes might play important roles in growth, development, and stress tolerance. Expression pattern analysis indicated that CsCSE5 might be involved in regulating the resistance of cucumber to pathogens. Functional verification data confirmed that CsCSE5 positively regulates the resistance of cucumber to powdery mildew pathogen Podosphaera xanthii and target leaf spot pathogen Corynespora cassiicola. The results of our study provide information that will aid the genetic improvement of resistant cucumber varieties.

Comprehensive Time-Course Transcriptome Reveals the Crucial Biological Pathways Involved in the Seasonal Branch Growth in Siberian Elm (Ulmus pumila).

Timber, the most prevalent organic material on this planet, is the result of a secondary xylem emerging from vascular cambium. Yet, the intricate processes governing its seasonal generation are largely a mystery. To better understand the cyclic growth of vascular tissues in elm, we undertook an extensive study examining the anatomy, physiology, and genetic expressions in Ulmus pumila. We chose three robust 15-year-old elm trees for our study. The cultivars used in this study were collected from the Inner Mongolia Autonomous Region in China and nurtured in the tree farm of Shandong Normal University. Monthly samples of 2-year-old elm branches were taken from the tree from February to September. Marked seasonal shifts in elm branch vascular tissues were observed by phenotypic observation: In February, the cambium of the branch emerged from dormancy, spurring growth. By May, elms began generating secondary xylem, or latewood, recognized by its tiny pores and dense cell structure. From June to August, there was a marked increase in the thickness of the secondary xylem. Transcriptome sequencing provides a potential molecular mechanism for the thickening of elm branches and their response to stress. In February, the tree enhanced its genetic responses to cold and drought stress. The amplified expression of CDKB, CYCB, WOX4, and ARF5 in the months of February and March reinforced their essential role in the development of the vascular cambium in elm. Starting in May, the elm deployed carbohydrates as a carbon resource to synthesize the abundant cellulose and lignin necessary for the formation of the secondary wall. Major genes participating in cellulose (SUC and CESA homologs), xylan (UGD, UXS, IRX9, IRX10, and IRX14), and lignin (PAL, C4H, 4CL, HCT, C3H, COMT, and CAD) biosynthetic pathways for secondary wall formation were up-regulated by May or/and June. In conclusion, our findings provided a foundation for an in-depth exploration of the molecular processes dictating the seasonal growth of elm timber.

Cotton 4-coumarate-CoA ligase 3 enhanced plant resistance to Verticillium dahliae by promoting jasmonic acid signaling-mediated vascular lignification and metabolic flux.

Lignins and their antimicrobial-related polymers cooperatively enhance plant resistance to pathogens. Several isoforms of 4-coumarate-coenzyme A ligases (4CLs) have been identified as indispensable enzymes involved in lignin and flavonoid biosynthetic pathways. However, their roles in plant-pathogen interaction are still poorly understood. This study uncovers the role of Gh4CL3 in cotton resistance to the vascular pathogen Verticillium dahliae. The cotton 4CL3-CRISPR/Cas9 mutant (CR4cl) exhibited high susceptibility to V. dahliae. This susceptibility was most probably due to the reduction in the total lignin content and the biosynthesis of several phenolic metabolites, e.g., rutin, catechin, scopoletin glucoside, and chlorogenic acid, along with jasmonic acid (JA) attenuation. These changes were coupled with a significant reduction in 4CL activity toward p-coumaric acid substrate, and it is likely that recombinant Gh4CL3 could specifically catalyze p-coumaric acid to form p-coumaroyl-coenzyme A. Thus, overexpression of Gh4CL3 (OE4CL) showed increasing 4CL activity that augmented phenolic precursors, cinnamic, p-coumaric, and sinapic acids, channeling into lignin and flavonoid biosyntheses and enhanced resistance to V. dahliae. Besides, Gh4CL3 overexpression activated JA signaling that instantly stimulated lignin deposition and metabolic flux in response to pathogen, which all established an efficient plant defense response system, and inhibited V. dahliae mycelium growth. Our results propose that Gh4CL3 acts as a positive regulator for cotton resistance against V. dahliae by promoting JA signaling-mediated enhanced cell wall rigidity and metabolic flux.

Modulation of lignin biosynthesis for drought tolerance in plants.

Lignin is a complex polymer that is embedded in plant cell walls to provide physical support and water protection. For these reasons, the production of lignin is closely linked with plant adaptation to terrestrial regions. In response to developmental cues and external environmental conditions, plants use an elaborate regulatory network to determine the timing and location of lignin biosynthesis. In this review, we summarize the canonical lignin biosynthetic pathway and transcriptional regulatory network of lignin biosynthesis, consisting of NAC and MYB transcription factors, to explain how plants regulate lignin deposition under drought stress. Moreover, we discuss how the transcriptional network can be applied to the development of drought tolerant plants.

Transcriptional networks orchestrating red and pink testa color in peanut

BackgroundTesta color is an important trait of peanut (Arachis hypogaea L.) which is closely related with the nutritional and commercial value. Pink and red are main color of peanut testa. However, the genetic mechanism of testa color regulation in peanut is not fully understood. To elucidate a clear picture of peanut testa regulatory model, samples of pink cultivar (Y9102), red cultivar (ZH12), and two RNA pools (bulk red and bulk pink) constructed from F4 lines of Y9102 x ZH12 were compared through a bulk RNA-seq approach.ResultsA total of 2992 differential expressed genes (DEGs) were identified among which 317 and 1334 were up-regulated and 225 and 1116 were down-regulated in the bulk red-vs-bulk pink RNA pools and Y9102-vs-ZH12, respectively. KEGG analysis indicates that these genes were divided into significantly enriched metabolic pathways including phenylpropanoid, flavonoid/anthocyanin, isoflavonoid and lignin biosynthetic pathways. Notably, the expression of the anthocyanin upstream regulatory genes PAL, CHS, and CHI was upregulated in pink and red testa peanuts, indicating that their regulation may occur before to the advent of testa pigmentation. However, the differential expression of down-stream regulatory genes including F3H, DFR, and ANS revealed that deepening of testa color not only depends on their gene expression bias, but also linked with FLS inhibition. In addition, the down-regulation of HCT, IFS, HID, 7-IOMT, and I2’H genes provided an alternative mechanism for promoting anthocyanin accumulation via perturbation of lignin and isoflavone pathways. Furthermore, the co-expression module of MYB, bHLH, and WRKY transcription factors also suggested a fascinating transcriptional activation complex, where MYB-bHLH could utilize WRKY as a co-option during the testa color regulation by augmenting anthocyanin biosynthesis in peanut.ConclusionsThese findings reveal candidate functional genes and potential strategies for the manipulation of anthocyanin biosynthesis to improve peanut varieties with desirable testa color.

Downregulation of barley ferulate 5-hydroxylase dramatically alters straw lignin structure without impact on mechanical properties.

Barley is a major cereal crop for temperate climates, and a diploid genetic model for polyploid wheat. Cereal straw biomass is an attractive source of feedstock for green technologies but lignin, a key determinant of feedstock recalcitrance, complicates bio-conversion processes. However, manipulating lignin content to improve the conversion process could negatively affect agronomic traits. An alternative approach is to manipulate lignin composition which influences the physical and chemical properties of straw. This study validates the function of a barley ferulate 5-hydroxylase gene and demonstrates that its downregulation using the RNA-interference approach substantially impacts lignin composition. We identified five barley genes having putative ferulate 5-hydroxylase activity. Downregulation of HvF5H1 substantially reduced the lignin syringyl/guaiacyl (S/G) ratio in straw while the lignin content, straw mechanical properties, plant growth habit, and grain characteristics all remained unaffected. Metabolic profiling revealed significant changes in the abundance of 173 features in the HvF5H1-RNAi lines. The drastic changes in the lignin polymer of transgenic lines highlight the plasticity of barley lignification processes and the associated potential for manipulating and improving lignocellulosic biomass as a feedstock for green technologies. On the other hand, our results highlight some differences between the lignin biosynthetic pathway in barley, a temperate climate grass, and the warm climate grass, rice, and underscore potential diversity in the lignin biosynthetic pathways in grasses.

Water Deficit-Induced Changes in Phenolic Acid Content in Maize Leaves Is Associated with Altered Expression of Cinnamate 4-Hydroxylase and p-Coumaric Acid 3-Hydroxylase

The amino acid phenylalanine is a precursor to phenolic acids that constitute the lignin biosynthetic pathway. Although there is evidence of a role of some phenolic acids in plant responses to pathogens and salinity, characterization of the involvement of phenolic acids in plant responses to drought is limited. Drought reduces water content in plant tissue and can lead to decreased cell viability and increased cell death. We thus subjected maize seedlings to water deficit and evaluated relative water content and cell viability together with p-coumaric acid, caffeic acid and ferulic acid contents in the leaves. Furthermore, we measured the enzymatic activity of cinnamate 4-hydroxylase (EC 1.14.13.11) and p-coumarate 3-hydroxylase (EC 1.14.17.2) and associated these with the expression of genes encoding cinnamate 4-hydroxylase and p-coumarate-3 hydroxylase in response to water deficit. Water deficit reduced relative water content and cell viability in maize leaves. This corresponded with decreased p-coumaric acid but increased caffeic and ferulic acid content in the leaves. Changes in the phenolic acid content of the maize leaves were associated with increased enzymatic activities of cinnamate 4-hydroxylase and p-coumarate hydroxylase. The increased enzymatic activity of p-coumarate 3-hydroxylase was associated with increased expression of a gene encoding p-coumarate 3-hydroxylase. We thus conclude that metabolic pathways involving phenolic acids may contribute to the regulation of drought responses in maize, and we propose that further work to elucidate this regulation may contribute to the development of new maize varieties with improved drought tolerance. This can be achieved by marker-assisted selection to select maize lines with high levels of expression of genes encoding cinnamate 4-hydroxylase and/or p-coumarate 3-hydroxylase for use in breeding programs aimed and improving drought tolerance, or by overexpression of these genes via genetic engineering to confer drought tolerance.

Mutation of Os4BGlu18, monolignol β-glucosidase, improves salinity insensitivity in a rice

Rice is a salt-sensitive crop, and its development and yield are greatly affected by salinity. Using a forward genetics approach, the salt-insensitive line, sitl2, was selected from a core population (M 10 ) induced by gamma-ray irradiation. Under salt treatment, the sitl2 mutant showed greater fresh weight, chlorophyll content, and lower hydrogen peroxide (H 2 O 2 ) levels than the wild type (WT). In addition, the sitl2 mutant showed a lower Na+ content in the shoots and roots under salinity stress. A single-base guanine deletion of Os4BGlu18 , which hydrolyzes monolignol-glucoside by monolignol β-glucosidase, was found by whole genome re-sequencing. Subcellular localization of Os4BGlu18 and the mutant form (Os4BGlu18p.Gly115fs) GFP-tagged proteins were found in the cytosol of rice protoplasts. The expression levels of Os4BGlu18 and most UDP-glucosyltransferase genes examined were lower in the mutant than in the WT. Monolignols were extracted in higher amounts from WT shoots and roots than from the sitl2 mutant; however, monolignol glucoside was extracted in higher amounts in sitl2 . Phloroglucinol-HCl staining showed that sitl2 had more intense and higher lignin content than WT. These results suggest that sitl2 might confer salt tolerance caused by the mutation of Os4BGlu 18 and could be used as a new resource for breeding programs to enhance salt tolerance in rice. • Using a forward genetics approach, a salt-insensitive TILLING line ( sitl2 ) was selected, which could be useful as a new resource for breeding programs. • The sitl2 mutant exhibited a single-base guanine deletion in Os4BGlu18 and a frameshift with a premature stop. • Mutation of Os4BGlu18 affected the expression of lignin biosynthetic pathway genes and UDP-glucosyltransferase genes, and caused high accumulation of lignin in the vascular bundles of shoots and roots in sit2.

Physcomitrium patens CAD1 has distinct roles in growth and resistance to biotic stress

BackgroundPhyscomitrium patens provides an evolutionary link between green algae and vascular plants. Although the genome of P. patens includes orthologs of all the core lignin biosynthetic enzymes, the occurrence of lignin in moss is very controversial. Besides, little information is available about the lignin enzymes in moss to date. For example, cinnamyl alcohol dehydrogenase (CAD) is a crucial enzyme that catalyzes the last step of the lignin biosynthetic pathway, suggesting an ideal way to study the evolutionary process. By investigating the functions of CAD in evolution, this study will elucidate the evolutionary roles of lignin-like in the early stage of land colonization.ResultsCAD multigene family in P. patens is composed of four genes. The PpCADs contain a conserved glycine-rich domain to catalyze NADPH-dependent reduction to their corresponding alcohols, indicating that PpCADs have the potential to synthesize monolignols by bioinformatics analysis. Even though PpCAD1 could produce lignin in theory, no conventional monomer was detected in the cell wall or cytoplasm of PpCAD1_OE plants. However, the phenylpropanoids were promoted in PpCAD1_OE transformants to modify gametophore architecture and development, making the distribution of phyllids more scarcity and the moss colony more giant, possibly due to the enhanced expression of the AUX-IAA family. The transcripts of at least one gene encoding the enzyme in the lignin biosynthetic pathway were increased in PpCAD1_OE plants. In addition, the PpCAD1_OE gametophore inhibited the Botrytis cinerea assault mainly by enhanced phenylpropanoids in the cell wall instead of influencing transcripts of defense genes pathogenesis-related 10 (PR10) and nonexpresser of PR genes 1 (NPR1). Likewise, ectopic expression of PpCAD1 in Arabidopsis led to a significant increase in lignin content, exhibiting chunky roots, robust seedlings, advanced flowering, and efficient resistance against pathogens.ConclusionPpCAD occurs in more than one copy, suggesting functional divergence in the ancestral plant. PpCAD1 catalyzes monolignol biosynthesis and has homologous functions with vascular plants. Despite no detected conventional monolignol, the increased phenylpropanoids in the PpCAD1_OE gametophore, possibly intermediate metabolites in the lignin pathway, had conserved functions during the evolution of terrestrial plants. The results inferred that the lignin enzyme of the early non-vascular plant played roles in stem elongation and resistance against pathogens of P. patens during the conquest of land.

Transcriptome and metabolome analyses provide insights into the relevance of pericarp thickness variations in Camellia drupifera and Camellia oleifera

Camellia fruit is a woody edible oil source with a recalcitrant pericarp, which increases processing costs. However, the relevance of pericarp thickness variations in Camellia species remains unclear. Therefore, this study aimed to identify pericarp differences at the metabolic and transcription levels between thick-pericarp Camellia drupifera BG and thin-pericarp Camellia oleifera SG. Forty differentially accumulated metabolites were screened through non-targeted UHPLC-Q-TOF MS-based metabolite profiling. S-lignin was prominently upregulated in BG compared with SG, contributing to the thick pericarp of BG. KEGG enrichment and coexpression network analysis showed 29 differentially expressed genes associated with the lignin biosynthetic pathway, including 21 genes encoding catalysts and 8 encoding transcription factors. Nine upregulated genes encoding catalysts potentially led to S-lignin accumulation in BG pericarp, and transcription factors NAC and MYB were possibly involved in major transcriptional regulatory mechanisms. Conventional growth-related factors WRKYs and AP2/ERFs were positively associated while pathogenesis-related proteins MLP328 and NCS2 were negatively associated with S-lignin content. Thus, Camellia balances growth and defense possibly by altering lignin biosynthesis. The results of this study may guide the genetic modifications of C. drupifera to optimize its growth-defense balance and improve seed accessibility.

Modulation of phenylpropanoid and lignin biosynthetic pathway is crucial for conferring resistance in pigeon pea against Fusarium wilt

To elucidate the role of the phenylpropanoid pathway in the expression of resistance during compatible and incompatible interactions between pigeon pea and wilt-causing vascular pathogen Fusarium udum, we estimated the total phenol content, lignin, phenolic acids and activity of enzymes involved in lignin polymerization of monolignols and examined the expression pattern of lignin biosynthesis genes. Our results demonstrated a higher accumulation of free and cell wall-bound phenolics and total lignin content in the highly resistant pigeon pea genotype ICP 14623 as compared to susceptible genotype ICP 14166. An increased activity of phenylpropanoid pathway-associated defense enzymes such as Phenylalanine ammonia-lyase, polyphenol oxidase, ascorbate and guaiacol- dependent peroxidases in resistant pigeon pea genotypes suggests their role in resistance. Moreover, analysis of lignin biosynthesis genes revealed their differential expression during resistant and susceptible interactions, revealed their crucial role in imparting resistance against wilt. Overall, our results indicated the role of physical and biochemical components of the phenylpropanoid pathway in the expression of resistance in pigeon pea against Fusarium wilt.