Artificial miRNA-mediated down-regulation of two monolignoid biosynthetic genes (C3H and F5H) cause reduction in lignin content in jute

Two monolignoid biosynthetic genes 4-coumarate:coenzyme A ligase (4CL) and p-coumaric acid 3-hdroxylase (C3H) involved in lignin accumulation in pear fruits

One of the most important factors impacting the quality of pear fruit is the presence of stone cells and lignin. Lignin is the main component of stone cells in pear fruits. Two monolignoid biosynthetic genes 4-coumarate:coenzyme A ligase (4CL) and p-coumaric acid 3-hdroxylase (C3H) are involved in lignin accumulation in pear fruits. However, the functions of these genes in lignin biosynthesis were excluded in pear. In our study, we isolated and cloned Pb4CL11 (GenBank: KM455955.1) and PbC3H1 (GenBank: KM373790.1) from pear, which contained 1644 bp encoded 54 amino acids (AA), and 1539 bp encoded 513 AA, respectively. The expression of Pb4CL11 and PbC3H1 in Arabidopsis thaliana led to an increase in cell wall thickness for intervascular fibers and xylem cells and lignin content. Overexpression of Pb4CL11 and PbC3H1 in A. thaliana can significantly increase the expression of AtPAL, AtC4H, AtHCT, AtC3H, AtCCOMT, AtCCR, AtF5H, AtCOMT, AtCAD4 and AtCAD5 with promotion of lignin biosynthesis. Taken together, our study's findings not only demonstrated the probable function of Pb4CL11 and PbC3H1 in lignin biosynthesis but also laid the groundwork for future studies using molecular biological methods to control lignin production and the formation of stone cells in pear fruits.

Overexpression of PtoMYB115 improves lignocellulose recalcitrance to enhance biomass digestibility and bioethanol yield by specifically regulating lignin biosynthesis in transgenic poplar

Background

Woody plants provide the most abundant biomass resource that is convertible for biofuels. Since lignin is a crucial recalcitrant factor against lignocellulose hydrolysis, genetic engineering of lignin biosynthesis is considered as a promising solution. Many MYB transcription factors have been identified to involve in the regulation of cell wall formation or phenylpropanoid pathway. In a previous study, we identified that PtoMYB115 contributes to the regulation of proanthocyanidin pathway, however, little is known about its role in lignocellulose biosynthesis and biomass saccharification in poplar.

Results

Here, we detected the changes of cell wall features and examined biomass enzymatic saccharification for bioethanol production under various chemical pretreatments in PtoMYB115 transgenic plants. We reported that PtoMYB115 might specifically regulate lignin biosynthesis to affect xylem development. Overexpression of PtoMYB115 altered lignin biosynthetic gene expression, resulting in reduced lignin deposition, raised S/G and beta-O-4 linkage, resulting in a significant reduction in cellulase adsorption with lignin and an increment in cellulose accessibility. These alterations consequently improved lignocellulose recalcitrance for significantly enhanced biomass saccharification and bioethanol yield in the PtoMYB115-OE transgenic lines. In contrast, the knockout of PtoMYB115 by CRISPR/Cas9 showed reduced woody utilization under various chemical pretreatments.

Conclusions

This study shows that PtoMYB115 plays an important role in specifically regulating lignin biosynthesis and improving lignocellulose features. The enhanced biomass saccharification and bioethanol yield in the PtoMYB115-OE lines suggests that PtoMYB115 is a candidate gene for genetic modification to facilitate the utilization of biomass.

May phytophenolics alleviate aflatoxins-induced health challenges? A holistic insight on current landscape and future prospects

The future GCC-connected environmental risk factors expedited the progression of nCDs. Indeed, the emergence of AFs is becoming a global food security concern. AFs are lethal carcinogenic mycotoxins, causing damage to the liver, kidney, and gastrointestinal organs. Long-term exposure to AFs leads to liver cancer. Almost a variety of food commodities, crops, spices, herbaceous materials, nuts, and processed foods can be contaminated with AFs. In this regard, the primary sections of this review aim to cover influencing factors in the occurrence of AFs, the role of AFs in progression of nCDs, links between GCC/nCDs and exposure to AFs, frequency of AFs-based academic investigations, and world distribution of AFs. Next, the current trends in the application of PPs to alleviate AFs toxicity are discussed. Nearly, more than 20,000 published records indexed in scientific databases have been screened to find recent trends on AFs and application of PPs in AFs therapy. Accordingly, shifts in world climate, improper infrastructures for production/storage of food commodities, inconsistency of global polices on AFs permissible concentration in food/feed, and lack of the public awareness are accounting for a considerable proportion of AFs damages. AFs exhibited their toxic effects by triggering the progression of inflammation and oxidative/nitrosative stress, in turn, leading to the onset of nCDs. PPs could decrease AFs-associated oxidative stress, genotoxic, mutagenic, and carcinogenic effects by improving cellular antioxidant balance, regulation of signaling pathways, alleviating inflammatory responses, and modification of gene expression profile in a dose/time-reliant fashion. The administration of PPs alone displayed lower biological properties compared to co-treatment of these metabolites with AFs. This issue might highlight the therapeutic application of PPs than their preventative content. Flavonoids such as quercetin and oxidized tea phenolics, curcumin and resveratrol were the most studied anti-AFs PPs. Our literature review clearly disclosed that considering PPs in antioxidant therapies to alleviate complications of AFs requires improvement in their bioavailability, pharmacokinetics, tissue clearance, and off-target mode of action. Due to the emergencies in the elimination of AFs in food/feedstuffs, further large-scale clinical assessment of PPs to decrease the consequences of AFs is highly required.

An insight into microRNA biogenesis and its regulatory role in plant secondary metabolism

The present review highlights the regulatory roles of microRNAs in plant secondary metabolism and focuses on different bioengineering strategies to modulate secondary metabolite content in plants. MicroRNAs (miRNAs) are the class of small endogenous, essential, non-coding RNAs that riboregulate the gene expression involved in various biological processes in most eukaryotes. MiRNAs has emerged as important regulators in plants that function by silencing target genes through cleavage or translational inhibition. These miRNAs plays an important role in a wide range of plant biological and metabolic processes, including plant development and various environmental response controls. Several important plant secondary metabolites like alkaloids, terpenoids, and phenolics are well studied for their function in plant defense against different types of pests and herbivores. Due to the presence of a wide range of biological and pharmaceutical properties of plant secondary metabolites, it is important to study the regulation of their biosynthetic pathways. The contribution of miRNAs in regulating plant secondary metabolism is not well explored. Recent advancements in molecular techniques have improved our knowledge in understanding the molecular function of genes, proteins, enzymes, and small RNAs involved in different steps of secondary metabolic pathways. In the present review, we have discussed the recent progress made on miRNA biogenesis, its regulation, and highlighted the current research developed in the field of identification, analysis, and characterizations of various miRNAs that regulate plant secondary metabolism. We have also discussed how different bioengineering strategies such as artificial miRNA (amiRNA), endogenous target mimicry, and CRISPR/Cas9 could be utilized to enhance the secondary metabolite production in plants.

A regulatory network driving shoot lignification in rapidly growing bamboo

Woody bamboo is environmentally friendly, abundant, and an alternative to conventional timber. Degree of lignification and lignin content and deposition affect timber properties. However, the lignification regulatory network in monocots is poorly understood. To elucidate the regulatory mechanism of lignification in moso bamboo (Phyllostachys edulis), we conducted integrated analyses using transcriptome, small RNA, and degradome sequencing followed by experimental verification. The lignification degree and lignin content increased with increased bamboo shoot height, whereas phenylalanine ammonia-lyase and Laccase activities first increased and then decreased with shoot growth. Moreover, we identified 11,504 differentially expressed genes (DEGs) in different portions of the 13th internodes of different height shoots; most DEGs associated with cell wall and lignin biosynthesis were upregulated, whereas some DEGs related to cell growth were downregulated. We identified a total of 1,502 miRNAs, of which 687 were differentially expressed. Additionally, in silico and degradome analyses indicated that 5,756 genes were targeted by 691 miRNAs. We constructed a regulatory network of lignification, including 11 miRNAs, 22 transcription factors, and 36 enzyme genes, in moso bamboo. Furthermore, PeLAC20 overexpression increased lignin content in transgenic Arabidopsis (Arabidopsis thaliana) plants. Finally, we proposed a reliable miRNA-mediated "MYB-PeLAC20" module for lignin monomer polymerization. Our findings provide definite insights into the genetic regulation of bamboo lignification. In addition to providing a platform for understanding related mechanisms in other monocots, these insights could be used to develop strategies to improve bamboo timber properties.

Bm-miR172c-5p Regulates Lignin Biosynthesis and Secondary Xylem Thickness by Altering the Ferulate 5 Hydroxylase Gene in Bacopa monnieri

MicroRNAs (miRNAs) are small non-coding, endogenous RNAs containing 20-24 nucleotides that regulate the expression of target genes involved in various plant processes. A total of 1,429 conserved miRNAs belonging to 95 conserved miRNA families and 12 novel miRNAs were identified from Bacopa monnieri using small RNA sequencing. The Bm-miRNA target transcripts related to the secondary metabolism were further selected for validation. The Bm-miRNA expression in shoot and root tissues was negatively correlated with their target transcripts. The Bm-miRNA cleavage sites were mapped within the coding or untranslated region as depicted by the modified RLM-RACE. In the present study, we validate three miRNA targets, including asparagine synthetase, cycloartenol synthase and ferulate 5 hydroxylase (F5H) and elucidate the regulatory role of Bm-miR172c-5p, which cleaves the F5H gene involved in the lignin biosynthesis. Overexpression (OE) of Bm-miR172c-5p precursor in B. monnieri suppresses F5H gene, leading to reduced lignification and secondary xylem thickness under control and drought stress. By contrast, OE of endogenous target mimics (eTMs) showed enhanced lignification and secondary xylem thickness leading to better physiological response under drought stress. Taken together, we suggest that Bm-miRNA172c-5p might be a key player in maintaining the native phenotype of B. monnieri under control and different environmental conditions.

Multi-omics analyses on Kandelia obovata reveal its response to transplanting and genetic differentiation among populations

BACKGROUND

Restoration through planting is the dominant strategy to conserve mangrove ecosystems. However, many of the plantations fail to survive. Site and seeding selection matters for planting. The process of afforestation, where individuals were planted in a novel environment, is essentially human-controlled transplanting events. Trying to deepen and expand the understanding of the effects of transplanting on plants, we have performed a seven-year-long reciprocal transplant experiment on Kandelia obovata along a latitudinal gradient.

RESULTS

Combined phenotypic analyses and next-generation sequencing, we found phenotypic discrepancies among individuals from different populations in the common garden and genetic differentiation among populations. The central population with abundant genetic diversity and high phenotypic plasticity had a wide plantable range. But its biomass was reduced after being transferred to other latitudes. The suppressed expression of lignin biosynthesis genes revealed by RNA-seq was responsible for the biomass reduction. Moreover, using whole-genome bisulfite sequencing, we observed modification of DNA methylation in MADS-box genes that involved in the regulation of flowering time, which might contribute to the adaptation to new environments.

CONCLUSIONS

Taking advantage of classical ecological experiments as well as multi-omics analyses, our work observed morphology differences and genetic differentiation among different populations of K. obovata, offering scientific advice for the development of restoration strategy with long-term efficacy, also explored phenotypic, transcript, and epigenetic responses of plants to transplanting events between latitudes.

Value addition to jute: assessing the effect of artificial reduction of lignin on jute diversification

In the backdrop of an abundance of lignin in jute, the main focus of the present study was to conduct a quality assessment of four delignified jute lines (in which four lignin biosynthetic genes were individually downregulated) across advanced generations for industrial applications. To this end, the transgenic lines were advanced to 7^th (COMT and C4H lines) and 5^th (C3H and F5H lines) transformed generations. The results exhibit approximately 16–25% reduction in acid-insoluble lignin for the whole stem and 13–14% reduction in fiber lignin content for all four transgenic lines compared to the control. The altered lignin composition led to a 3–6% increase in the cellulose content and a small improvement in the enzymatic release of glucose. Lignin reduction led to an exposure of the underlying fibrils in transgenic lines as observed through a scanning electron microscope whereas, it was undiscernible in the control fiber. Furthermore, an analysis of the mechanical properties appears almost similar to that of the control with no morphological deformities. Jute fibers from the transgenic lines offer tremendous cost-effective implications from an economic perspective.

Comparative gene expression analysis reveals that multiple mechanisms regulate the weeping trait in Prunus mume

Prunus mume (also known as Mei) is an important ornamental plant that is popular with Asians. The weeping trait in P. mume has attracted the attention of researchers for its high ornamental value. However, the formation of the weeping trait of woody plants is a complex process and the molecular basis of weeping stem development is unclear. Here, the morphological and histochemical characteristics and transcriptome profiles of upright and weeping stems from P. mume were studied. Significant alterations in the histochemical characteristics of upright and weeping stems were observed, and the absence of phloem fibres and less xylem in weeping stems might be responsible for their inability to resist gravity and to grow downward. Transcriptome analysis showed that differentially expressed genes (DEGs) were enriched in phenylpropanoid biosynthesis and phytohormone signal transduction pathways. To investigate the differential responses to hormones, upright and weeping stems were treated with IAA (auxin) and GA₃ (gibberellin A3), respectively, and the results revealed that weeping stems had a weaker IAA response ability and reduced upward bending angles than upright stems. On the contrary, weeping stems had increased upward bending angles than upright stems with GA₃ treatment. Compared to upright stems, interestingly, DEGs associated with diterpenoid biosynthesis and phenylpropanoid biosynthesis were significantly enriched after being treated with IAA, and expression levels of genes associated with phenylpropanoid biosynthesis, ABC transporters, glycosylphosphatidylinositol (GPI)—anchor biosynthesis were altered after being treated with GA₃ in weeping stems. Those results reveal that multiple molecular mechanisms regulate the formation of weeping trait in P. mume, which lays a theoretical foundation for the cultivation of new varieties.

CmMYB8 encodes an R2R3 MYB transcription factor which represses lignin and flavonoid synthesis in chrysanthemum

R2R3-MYB transcription factors are important regulators of the growth and development of plants. Here, CmMYB8 a chrysanthemum gene encoding an R2R3-MYB transcription factor, was isolated and functionally characterized. The gene was transcribed throughout the plant, but most strongly in the stem. When CmMYB8 was over-expressed, a number of genes encoding components of lignin synthesis were down-regulated, and the plants' lignin content was reduced. The composition of the lignin in the transgenic plants was also altered, and its S/G ratio was reduced. A further consequence of the over-expression of CmMYB8 was to lessen the transcript abundance of key genes involved in flavonoid synthesis, resulting in a reduced accumulation of flavonoids. The indication is that the CmMYB8 protein participates in the negative regulation of both lignin and flavonoid synthesis.

Jasmonate responsive transcription factor WsMYC2 regulates the biosynthesis of triterpenoid withanolides and phytosterol via key pathway genes in Withania somnifera (L.) Dunal

Functional characterization of WsMYC2 via artificial microRNA mediated silencing and transient over-expression displayed significant regulatory role vis-à-vis withanolides and stigmasterol biosyntheses in Withania somnifera. Further, metabolic intensification corroborated well with higher expression levels of putative pathway genes. Additionally, copious expression of WsMYC2 in response to exogenous elicitors resulted in enhanced withanolides production. Withania somnifera, a high value multipurpose medicinal plant, is a rich reservoir of structurally diverse and biologically active triterpenoids known as withanolides. W. somnifera has been extensively pursued vis-à-vis pharmacological and chemical studies. Nonetheless, there exists fragmentary knowledge regarding the metabolic pathway and the regulatory aspects of withanolides biosynthesis. Against this backdrop, a jasmonate-responsive MYC2 transcription factor was identified and functionally characterized from W. somnifera. In planta transient over-expression of WsMYC2 showed significant enhancement of mRNA transcript levels which corroborated well with the enhanced content of withanolides and stigmasterol. Further, a comparative analysis of expression levels of some of the genes of triterpenoid pathway viz. WsCAS, WsCYP85A, WsCYP90B and WsCYP710A in corroboration with the over-expression and silencing of WsMYC2 suggested its positive influence on their regulation. These corroboratory approaches suggest that WsMYC2 has cascading effect on over-expression of multiple pathway genes leading to the increased triterpenoid biosynthesis in infiltered plants. Further, the functional validation of WsMYC2 was carried out by artificial micro-RNA mediated silencing. It resulted in significant reduction of withanolides and stigmasterol levels, indicative of crucial role of WsMYC2 in the regulation of their biosyntheses. Taken together, these non-complementary approaches provided unambiguous understanding of the regulatory role of WsMYC2 in context to withanolides and stigmasterol biosyntheses. Furthermore, the upstream promoter of WsMYC2 presented several cis-regulatory elements primarily related to phytohormone responsiveness. WsMYC2 displayed inducible nature in response to MeJA. It had substantial influence on the higher expression of WsMYC2 which was in consonance with enhanced accumulation of withanolides.

Integration of renewable deep eutectic solvents with engineered biomass to achieve a closed-loop biorefinery

Despite the enormous potential shown by recent biorefineries, the current bioeconomy still encounters multifaceted challenges. To develop a sustainable biorefinery in the future, multidisciplinary research will be essential to tackle technical difficulties. Herein, we leveraged a known plant genetic engineering approach that results in aldehyde-rich lignin via down-regulation of cinnamyl alcohol dehydrogenase (CAD) and disruption of monolignol biosynthesis. We also report on renewable deep eutectic solvents (DESs) synthesized from phenolic aldehydes that can be obtained from CAD mutant biomass. The transgenic Arabidopsis thaliana CAD mutant was pretreated with the DESs and showed a twofold increase in the yield of fermentable sugars compared with wild type (WT) upon enzymatic saccharification. Integrated use of low-recalcitrance engineered biomass, characterized by its aldehyde-type lignin subunits, in combination with a DES-based pretreatment, was found to be an effective approach for producing a high yield of sugars typically used for cellulosic biofuels and biobased chemicals. This study demonstrates that integration of renewable DES with plant genetic engineering is a promising strategy in developing a closed-loop process.

Aluminum induced physiological and proteomic responses in tea (Camellia sinensis) roots and leaves

Tea (Camellia sinensis (L.) O. Kuntze), is an aluminum (Al) hyperaccumulator and grows well in acid soils. Although Al-induced growth of tea plant has been studied, the proteomic profiles of tea plants in response to Al are unclear. In the present study, the proteomic profiles in tea roots and leaves under Al stress were investigated using iTRAQ proteomics approach. In total, 755 and 1059 differentially expressed proteins were identified in tea roots and leaves, respectively. KEGG enrichment analysis showed that the differentially expressed proteins in roots were mainly involved in 11 pathways whereas those from leaves were mainly involved in 9 pathways. Abundance of most protein functions in glycolytic metabolism were enhanced in tea roots, and proteins involved in photosynthesis were stimulated in tea leaves. The protein ferulate-5-hydroxylase (F5H) in lignin biosynthetic pathway was down-regulated in both roots and leaves. Furthermore, antioxidant enzymes (ascorbate peroxidase, catalase and glutathione S-transferase) and citrate synthesis were accumulated in tea roots in response to Al. The results indicated that active photosynthesis and glycolysis as well as increased activities of antioxidant enzymes can be considered as a possible reason for the stimulatory effects of Al on the growth of tea plants. Additionally, the down-regulation of F5H and the binding of Al and phenolic acids may reduce the accumulation of lignin.

Modification of Monolignol Biosynthetic Pathway in Jute: Different Gene, Different Consequence

Lignin, a cross-linked macromolecule of hydrophobic aromatic structure, provides additional rigidity to a plant cell wall. Although it is an integral part of the plant cell, presence of lignin considerably reduces the quality of the fiber of fiber-yielding plants. Decreasing lignin in such plants holds significant commercial and environmental potential. This study aimed at reducing the lignin content in jute-a fiber crop, by introducing hpRNA-based vectors for downregulation of two monolignoid biosynthetic genes- cinnamate 4-hydroxylase (C4H) and caffeic acid O-methyltransferase (COMT). Transgenic generations, analyzed through Southern, RT-PCR and northern assays showed downregulation of the selected genes. Transgenic lines exhibited reduced level of gene expression with ~ 16-25% reduction in acid insoluble lignin for the whole stem and ~13-14% reduction in fiber lignin content compared to the control lines. Among the two transgenic plant types one exhibited an increase in cellulose content and concomitant improvement of glucose release. Composition of the lignin building blocks was found to alter and this alteration resulted in a pattern, different from other plants where the same genes were manipulated. It is expected that successful COMT-hpRNA and C4H-hpRNA transgenesis in jute will have far-reaching commercial implications leading to product diversification and value addition.