Introducing curcumin biosynthesis in Arabidopsis enhances lignocellulosic biomass processing

Lignin hydrogenolysis: Tuning the reaction by lignin chemistry

Replacing fossil resource with biomass is one of the promising approaches to reduce our carbon footprint. Lignin is one of the three major components of lignocellulosic biomass, accounting for 10-35 wt% of dried weight of the biomass. Hydrogenolytic depolymerization of lignin is attracting increasing attention because of its capacity of utilizing lignin in its uncondensed form and compatibility with the biomass fractionation processes. Lignin is a natural aromatic polymer composed of a variety of monolignols associated with a series of lignin linkage motifs. Hydrogenolysis cleaves various ether bonds in lignin and releases phenolic monomers which can be further upgraded into valuable products, i.e., drugs, terephthalic acid, phenol. This review provides an overview of the state-of-the-art advances of the reagent (lignin), products (hydrol lignin), mass balance, and mechanism of the lignin hydrogenolysis reaction. The chemical structure of lignin is reviewed associated with the free radical coupling of monolignols and the chemical reactions of lignin upon isolation processes. The reactions of lignin linkages upon hydrogenolysis are discussed. The components of hydrol lignin and the selectivity production of phenolic monomers are reviewed. Future challenges on hydrogenolysis of lignin are proposed. This article provides an overview of lignin hydrogenolysis reaction which shows light on the generation of optimized lignin ready for hydrogenolytic depolymerization.

Enhancing monolignol ferulate conjugate levels in poplar lignin via OsFMT1

BACKGROUND

The phenolic polymer lignin is one of the primary chemical constituents of the plant secondary cell wall. Due to the inherent plasticity of lignin biosynthesis, several phenolic monomers have been shown to be incorporated into the polymer, as long as the monomer can undergo radicalization so it can participate in coupling reactions. In this study, we significantly enhance the level of incorporation of monolignol ferulate conjugates into the lignin polymer to improve the digestibility of lignocellulosic biomass.

RESULTS

Overexpression of a rice Feruloyl-CoA Monolignol Transferase (FMT), OsFMT1, in hybrid poplar (Populus alba x grandidentata) produced transgenic trees clearly displaying increased cell wall-bound ester-linked ferulate, p-hydroxybenzoate, and p-coumarate, all of which are in the lignin cell wall fraction, as shown by NMR and DFRC. We also demonstrate the use of a novel UV-Vis spectroscopic technique to rapidly screen plants for the presence of both ferulate and p-hydroxybenzoate esters. Lastly we show, via saccharification assays, that the OsFMT1 transgenic p oplars have significantly improved processing efficiency compared to wild-type and Angelica sinensis-FMT-expressing poplars.

CONCLUSIONS

The findings demonstrate that OsFMT1 has a broad substrate specificity and a higher catalytic efficiency compared to the previously published FMT from Angelica sinensis (AsFMT). Importantly, enhanced wood processability makes OsFMT1 a promising gene to optimize the composition of lignocellulosic biomass.

Social and biological innovations are essential to deliver transformative forest biotechnologies

Forests make immense contributions to societies in the form of ecological services and sustainable industrial products. However, they face major challenges to their viability and economic use due to climate change and growing biotic and economic threats, for which recombinant DNA (rDNA) technology can sometimes provide solutions. But the application of rDNA technologies to forest trees faces major social and biological obstacles that make its societal acceptance a 'wicked' problem without straightforward solutions. We discuss the nature of these problems, and the social and biological innovations that we consider essential for progress. As case studies of biological challenges, we focus on studies of modifications in wood chemistry and transformation efficiency. We call for major innovations in regulations, and the dissolution of method-based market barriers, that together could lead to greater research investments, enable wide use of field studies, and facilitate the integration of rDNA-modified trees into conventional breeding programs. Without near-term adoption of such innovations, rDNA-based solutions will be largely unavailable to help forests adapt to the growing stresses from climate change and the proliferation of forest pests, nor will they be available to provide economic and environmental benefits from expanded use of wood and related bioproducts as part of an expanding bioeconomy.

Enabling Lignin Valorization Through Integrated Advances in Plant Biology and Biorefining

Despite lignin having long been viewed as an impediment to the processing of biomass for the production of paper, biofuels, and high-value chemicals, the valorization of lignin to fuels, chemicals, and materials is now clearly recognized as a critical element for the lignocellulosic bioeconomy. However, the intended application for lignin will likely require a preferred lignin composition and form. To that end, effective lignin valorization will require the integration of plant biology, providing optimal feedstocks, with chemical process engineering, providing efficient lignin transformations. Recent advances in our understanding of lignin biosynthesis have shown that lignin structure is extremely diverse and potentially tunable, while simultaneous developments in lignin refining have resulted in the development of several processes that are more agnostic to lignin composition. Here, we review the interface between in planta lignin design and lignin processing and discuss the advances necessary for lignin valorization to become a feature of advanced biorefining.

The plant cell wall-dynamic, strong, and adaptable-is a natural shapeshifter

Mythology is replete with good and evil shapeshifters, who, by definition, display great adaptability and assume many different forms-with several even turning themselves into trees. Cell walls certainly fit this definition as they can undergo subtle or dramatic changes in structure, assume many shapes, and perform many functions. In this review, we cover the evolution of knowledge of the structures, biosynthesis, and functions of the 5 major cell wall polymer types that range from deceptively simple to fiendishly complex. Along the way, we recognize some of the colorful historical figures who shaped cell wall research over the past 100 years. The shapeshifter analogy emerges more clearly as we examine the evolving proposals for how cell walls are constructed to allow growth while remaining strong, the complex signaling involved in maintaining cell wall integrity and defense against disease, and the ways cell walls adapt as they progress from birth, through growth to maturation, and in the end, often function long after cell death. We predict the next century of progress will include deciphering cell type-specific wall polymers; regulation at all levels of polymer production, crosslinks, and architecture; and how walls respond to developmental and environmental signals to drive plant success in diverse environments.

Diarylheptanoid Derivatives (Musellins A-F) and Dimeric Phenylphenalenones from Seed Coats of Musella lasiocarpa, the Chinese Dwarf Banana

Phenylphenalenones (PPs) are phytoalexins protecting banana plants (Musaceae) against various pathogens. However, how plants synthesize PPs is still poorly understood. In this work, we investigated the major secondary metabolites of developing seed coats of Musella lasiocarpa to determine if this species might be a good model system to study the biosynthesis of PPs. We found that PPs are major components of M. lasiocarpa seed coats at middle and late developmental stages. Two previously undescribed PP dimers (M-4 and M-6) and a group of unreported diarylheptanoid (DH) derivatives named musellins A-F (B-7, B-9, B-10, B-12, B-14, and B-15) were isolated along with 14 known compounds. Musellin D (B-12) and musellin F (B-15) contain the first reported furo[3,2-c]pyran ring and represent a previously undescribed carbon skeleton. The chemical structures of all new compounds were characterized by spectroscopic data, including NMR, HRESIMS, and ECD analysis. Plausible biosynthetic pathways for the formation of PPs and DHs are proposed.

The impact of curcumin on livestock and poultry animal's performance and management of insect pests

Plant-based natural products are alternative to antibiotics that can be employed as growth promoters in livestock and poultry production and attractive alternatives to synthetic chemical insecticides for insect pest management. Curcumin is a natural polyphenol compound from the rhizomes of turmeric (Curcuma spp.) and has been suggested to have a number of therapeutic benefits in the treatment of human diseases. It is also credited for its nutritional and pesticide properties improving livestock and poultry production performances and controlling insect pests. Recent studies reported that curcumin is an excellent feed additive contributing to poultry and livestock animal growth and disease resistance. Also, they detailed the curcumin's growth-inhibiting and insecticidal activity for reducing agricultural insect pests and insect vector-borne human diseases. This review aims to highlight the role of curcumin in increasing the growth and development of poultry and livestock animals and in controlling insect pests. We also discuss the challenges and knowledge gaps concerning curcumin use and commercialization as a feed additive and insect repellent.

High value valorization of lignin as environmental benign antimicrobial

Lignin is a natural aromatic polymer of p-hydroxyphenylpropanoids with various biological activities. Noticeably, plants have made use of lignin as biocides to defend themselves from pathogen microbial invasions. Thus, the use of isolated lignin as environmentally benign antimicrobial is believed to be a promising high value approach for lignin valorization. On the other hand, as green and sustainable product of plant photosynthesis, lignin should be beneficial to reduce the carbon footprint of antimicrobial industry. There have been many reports that make use of lignin to prepare antimicrobials for different applications. However, lignin is highly heterogeneous polymers different in their monomers, linkages, molecular weight, and functional groups. The structure and property relationship, and the mechanism of action of lignin as antimicrobial remains ambiguous. To show light on these issues, we reviewed the publications on lignin chemistry, antimicrobial activity of lignin models and isolated lignin and associated mechanism of actions, approaches in synthesis of lignin with improved antimicrobial activity, and the applications of lignin as antimicrobial in different fields. Hopefully, this review will help and inspire researchers in the preparation of lignin antimicrobial for their applications.

Making small molecules in plants: A chassis for synthetic biology-based production of plant natural products

Plant natural products have been extensively exploited in food, medicine, flavor, cosmetic, renewable fuel, and other industrial sectors. Synthetic biology has recently emerged as a promising means for the cost-effective and sustainable production of natural products. Compared with engineering microbes for the production of plant natural products, the potential of plants as chassis for producing these compounds is underestimated, largely due to challenges encountered in engineering plants. Knowledge in plant engineering is instrumental for enabling the effective and efficient production of valuable phytochemicals in plants, and also paves the way for a more sustainable future agriculture. In this manuscript, we briefly recap the biosynthesis of plant natural products, focusing primarily on industrially important terpenoids, alkaloids, and phenylpropanoids. We further summarize the plant hosts and strategies that have been used to engineer the production of natural products. The challenges and opportunities of using plant synthetic biology to achieve rapid and scalable production of high-value plant natural products are also discussed.

Field and saccharification performances of poplars severely downregulated in CAD1

Lignin is one of the main factors causing lignocellulosic biomass recalcitrance to enzymatic hydrolysis. Glasshouse-grown poplars severely downregulated for CINNAMYL ALCOHOL DEHYDROGENASE 1 (CAD1), the enzyme catalysing the last step in the monolignol-specific branch of lignin biosynthesis, have increased saccharification yields and normal growth. Here, we assess the performance of these hpCAD poplars in the field under short rotation coppice culture for two consecutive rotations of 1 yr and 3 yr. While 1-yr-old hpCAD wood had 10% less lignin, 3-yr-old hpCAD wood had wild-type lignin levels. Because of their altered cell wall composition, including elevated levels of cinnamaldehydes, both 1-yr-old and 3-yr-old hpCAD wood showed enhanced saccharification yields upon harsh alkaline pretreatments (up to +85% and +77%, respectively). In contrast with previous field trials with poplars less severely downregulated for CINNAMYL ALCOHOL DEHYDROGENASE (CAD), the hpCAD poplars displayed leaning phenotypes, early bud set, early flowering and yield penalties. Moreover, hpCAD wood had enlarged vessels, decreased wood density and reduced relative and free water contents. Our data show that the phenotypes of CAD-deficient poplars are strongly dependent on the environment and underpin the importance of field trials in translating basic research towards applications.

Lignin engineering in forest trees: From gene discovery to field trials

Wood is an abundant and renewable feedstock for the production of pulp, fuels, and biobased materials. However, wood is recalcitrant toward deconstruction into cellulose and simple sugars, mainly because of the presence of lignin, an aromatic polymer that shields cell-wall polysaccharides. Hence, numerous research efforts have focused on engineering lignin amount and composition to improve wood processability. Here, we focus on results that have been obtained by engineering the lignin biosynthesis and branching pathways in forest trees to reduce cell-wall recalcitrance, including the introduction of exotic lignin monomers. In addition, we draw general conclusions from over 20 years of field trial research with trees engineered to produce less or altered lignin. We discuss possible causes and solutions for the yield penalty that is often associated with lignin engineering in trees. Finally, we discuss how conventional and new breeding strategies can be combined to develop elite clones with desired lignin properties. We conclude this review with priorities for the development of commercially relevant lignin-engineered trees.

Selecting Endophytes for Rhizome Production, Curcumin Content, Biocontrol Potential, and Antioxidant Activities of Turmeric (Curcuma longa)

Beneficial endophytes may enhance plant growth and stress tolerance. Yet, the plant health benefits of endophytes can be altered by biotic and abiotic factors and, thus, favour the inhibition of turmeric growth and curcumin production. The double petri dish method and greenhouse pot experiments were conducted to assess the biocontrol potential and impact of endophytes on the output, curcumin levels, and antioxidant activities of turmeric (Curcuma longa L.). The results showed that endophytes could control some disease-causing plant pathogens: 52% of all isolates have an antagonistic action against Fusarium oxysporum, 43% against Pythium myriotylum, 35% against Phytophthora megakarya, and 56% against Ralstonia solanacearum in vitro. Eight months after sowing, most endophyte isolates can increase the yield of turmeric rhizomes on a sterile substrate after inoculation, with yields ranging from 42 to 105% higher than the control and 3 to 50% higher than the urea treatment. In addition, 52% endophytes isolate significantly raised curcumin levels after 8 months of culture (from 2.1 to 3.1%) compared to control (1.7%) and urea treatment (1.8%). These endophytes promote an increase in the levels of reduced glutathione (22%), total thiols (26%), and carotenoids (91%) in turmeric. The study concludes that, in general, the endophytes-turmeric association can stimulate turmeric rhizome production, curcumin, and the antioxidant activities of the plant. They can also be used as biocontrol agents for plant pathogens.

Overexpression of the scopoletin biosynthetic pathway enhances lignocellulosic biomass processing

Lignin is the main factor limiting the enzymatic conversion of lignocellulosic biomass into fermentable sugars. To reduce the recalcitrance engendered by the lignin polymer, the coumarin scopoletin was incorporated into the lignin polymer through the simultaneous expression of FERULOYL-CoA 6'-HYDROXYLASE 1 (F6'H1) and COUMARIN SYNTHASE (COSY) in lignifying cells in Arabidopsis. The transgenic lines overproduced scopoletin and incorporated it into the lignin polymer, without adversely affecting plant growth. About 3.3% of the lignin units in the transgenic lines were derived from scopoletin, thereby exceeding the levels of the traditional p-hydroxyphenyl units. Saccharification efficiency of alkali-pretreated scopoletin-overproducing lines was 40% higher than for wild type.

Engineering Curcumin Biosynthesis in Poplar Affects Lignification and Biomass Yield

Lignocellulosic biomass is recalcitrant toward deconstruction into simple sugars mainly due to the presence of lignin. By engineering plants to partially replace traditional lignin monomers with alternative ones, lignin degradability and extractability can be enhanced. Previously, the alternative monomer curcumin has been successfully produced and incorporated into lignified cell walls of Arabidopsis by the heterologous expression of DIKETIDE-CoA SYNTHASE (DCS) and CURCUMIN SYNTHASE2 (CURS2). The resulting transgenic plants did not suffer from yield penalties and had an increased saccharification yield after alkaline pretreatment. Here, we translated this strategy into the bio-energy crop poplar. Via the heterologous expression of DCS and CURS2 under the control of the secondary cell wall CELLULOSE SYNTHASE A8-B promoter (ProCesA8-B), curcumin was also produced and incorporated into the lignified cell walls of poplar. ProCesA8-B:DCS_CURS2 transgenic poplars, however, suffered from shoot-tip necrosis and yield penalties. Compared to that of the wild-type (WT), the wood of transgenic poplars had 21% less cellulose, 28% more matrix polysaccharides, 23% more lignin and a significantly altered lignin composition. More specifically, ProCesA8-B:DCS_CURS2 lignin had a reduced syringyl/guaiacyl unit (S/G) ratio, an increased frequency of p-hydroxyphenyl (H) units, a decreased frequency of p-hydroxybenzoates and a higher fraction of phenylcoumaran units. Without, or with alkaline or hot water pretreatment, the saccharification efficiency of the transgenic lines was equal to that of the WT. These differences in (growth) phenotype illustrate that translational research in crops is essential to assess the value of an engineering strategy for applications. Further fine-tuning of this research strategy (e.g., by using more specific promoters or by translating this strategy to other crops such as maize) might lead to transgenic bio-energy crops with cell walls more amenable to deconstruction without settling in yield.

Crystal structure of the plant feruloyl-coenzyme A monolignol transferase provides insights into the formation of monolignol ferulate conjugates

Lignin is a highly complex phenolic polymer which is essential for plants, but also makes it difficult for industrial processing. Engineering lignin by introducing relatively labile linkages into the lignin backbone can render it more amenable to chemical depolymerization. It has been reported that introducing a feruloyl-coenzyme A monolignol transferase from Angelica sinensis (AsFMT) into poplar could incorporate monolignol ferulate conjugates (ML-FAs) into lignin polymers, suggesting a promising way to manipulate plants for readily deconstructing. FMT catalyzes a reaction between monolignols and feruloyl-CoA to produce ML-FAs and free CoA-SH. However, the mechanisms of substrate specificity and catalytic process of FMT remains poorly understood. Here we report the structure of AsFMT, which adopts a typical fold of BAHD acyltransferase family. Structural comparisons with other BAHD homologs reveal several unique structural features of AsFMT, different from those of the BAHD homologs. Further molecular docking studies showed that T375 in AsFMT may function as an oxyanion hole to stabilize the reaction intermediate and also proposed a role of H278 in the binding of the nucleophilic hydroxyl group of monolignols. Together, this study provides important structural insights into the reactions catalyzed by AsFMT and will shed light on its future application in lignin engineering.

pHBMT1, a BAHD-family monolignol acyltransferase, mediates lignin acylation in poplar

Poplar (Populus) lignin is naturally acylated with p-hydroxybenzoate ester moieties. However, the enzyme(s) involved in the biosynthesis of the monolignol-p-hydroxybenzoates have remained largely unknown. Here, we performed an in vitro screen of the Populus trichocarpa BAHD acyltransferase superfamily (116 genes) using a wheatgerm cell-free translation system and found five enzymes capable of producing monolignol-p-hydroxybenzoates. We then compared the transcript abundance of the five corresponding genes with p-hydroxybenzoate concentrations using naturally occurring unrelated genotypes of P. trichocarpa and revealed a positive correlation between the expression of p-hydroxybenzoyl-CoA monolig-nol transferase (pHBMT1, Potri.001G448000) and p-hydroxybenzoate levels. To test whether pHBMT1 is responsible for the biosynthesis of monolignol-p-hydroxybenzoates, we overexpressed pHBMT1 in hybrid poplar (Populus alba × P. grandidentata) (35S::pHBMT1 and C4H::pHBMT1). Using three complementary analytical methods, we showed that there was an increase in soluble monolignol-p-hydroxybenzoates and cell-wall-bound monolignol-p-hydroxybenzoates in the poplar transgenics. As these pendent groups are ester-linked, saponification releases p-hydroxybenzoate, a precursor to parabens that are used in pharmaceuticals and cosmetics. This identified gene could therefore be used to engineer lignocellulosic biomass with increased value for emerging biorefinery strategies.

In Planta Cell Wall Engineering: From Mutants to Artificial Cell Walls

To mitigate the effects of global warming and to preserve the limited fossil fuel resources, an increased exploitation of plant-based materials and fuels is required, which would be one of the most important innovations related to sustainable development. Cell walls account for the majority of plant dry biomass and so is the target of such innovations. In this review, we discuss recent advances in in planta cell wall engineering through genetic manipulations, with a focus on wild-type-based and mutant-based approaches. The long history of using a wild-type-based approach has resulted in the development of many strategies for manipulating lignin, hemicellulose and pectin to decrease cell wall recalcitrance. In addition to enzyme-encoding genes, many transcription factor genes important for changing relevant cell wall characteristics have been identified. Although mutant-based cell wall engineering is relatively new, it has become feasible due to the rapid development of genome-editing technologies and systems biology-related research; we will soon enter an age of designed artificial wood production via complex genetic manipulations of many industrially important trees and crops.

Vessel- and ray-specific monolignol biosynthesis as an approach to engineer fiber-hypolignification and enhanced saccharification in poplar

Lignin is one of the main factors determining recalcitrance to processing of lignocellulosic biomass towards bio-based materials and fuels. Consequently, wood of plants engineered for low lignin content is typically more amenable to processing. However, lignin-modified plants often exhibit collapsed vessels and associated growth defects. Vessel-specific reintroduction of lignin biosynthesis in dwarfed low-lignin cinnamoyl-CoA reductase1 (ccr1) Arabidopsis mutants using the ProSNBE:AtCCR1 construct overcame the yield penalty while maintaining high saccharification yields, and showed that monolignols can be transported between the different xylem cells acting as 'good neighbors' in Arabidopsis. Here, we translated this research into the bio-energy crop poplar. By expressing ProSNBE:AtCCR1 into CRISPR/Cas9-generated ccr2 poplars, we aimed for vessel-specific lignin biosynthesis to: (i) achieve growth restoration while maintaining high saccharification yields; and (ii) study the existence of 'good neighbors' in poplar wood. Analyzing the resulting ccr2 ProSNBE:AtCCR1 poplars showed that vessels and rays act as good neighbors for lignification in poplar. If sufficient monolignols are produced by these cells, monolignols migrate over multiple cell layers, resulting in a restoration of the lignin amount to wild-type levels. If the supply of monolignols is limited, the monolignols are incorporated into the cell walls of the vessels and rays producing them and their adjoining cells resulting in fiber hypolignification. One such fiber-hypolignified line had 18% less lignin and, despite its small yield penalty, had an increase of up to 71% in sugar release on a plant base upon saccharification.

Tailoring renewable materials via plant biotechnology

Plants inherently display a rich diversity in cell wall chemistry, as they synthesize an array of polysaccharides along with lignin, a polyphenolic that can vary dramatically in subunit composition and interunit linkage complexity. These same cell wall chemical constituents play essential roles in our society, having been isolated by a variety of evolving industrial processes and employed in the production of an array of commodity products to which humans are reliant. However, these polymers are inherently synthesized and intricately packaged into complex structures that facilitate plant survival and adaptation to local biogeoclimatic regions and stresses, not for ease of deconstruction and commercial product development. Herein, we describe evolving techniques and strategies for altering the metabolic pathways related to plant cell wall biosynthesis, and highlight the resulting impact on chemistry, architecture, and polymer interactions. Furthermore, this review illustrates how these unique targeted cell wall modifications could significantly extend the number, diversity, and value of products generated in existing and emerging biorefineries. These modifications can further target the ability for processing of engineered wood into advanced high performance materials. In doing so, we attempt to illuminate the complex connection on how polymer chemistry and structure can be tailored to advance renewable material applications, using all the chemical constituents of plant-derived biopolymers, including pectins, hemicelluloses, cellulose, and lignins.

Modified lignocellulose and rich starch for complete saccharification to maximize bioethanol in distinct polyploidy potato straw

Potato is a major food crop with enormous biomass straw, but lignocellulose recalcitrance causes a costly bioethanol conversion. Here, we selected the cytochimera (Cyt) potato samples showing significantly-modified lignocellulose and much increased soluble sugars and starch by 2-4 folds in mature straws. Under two pretreatments (8 min liquid hot water; 5% CaO) at minimized conditions, the potato Cyt straw showed complete enzymatic saccharification. Further performing yeast fermentation with all hexoses released from soluble sugars, starch and lignocellulose in the Cyt straw, this study achieved a maximum bioethanol yield of 24 % (% dry matter), being higher than those of other bioenergy crops as previously reported. Hence, this study has proposed a novel mechanism model on the reduction of major lignocellulose recalcitrance and regulation of carbon assimilation to achieve cost-effective bioethanol production under optimal pretreatments. This work also provides a sustainable strategy for utilization of potato straws with minimum waste release.

Natural Products for Regulating Macrophages M2 Polarization

Macrophages M2 polarization have been taken as an anti-inflammatory progression during inflammation. Natural plant-derived products, with potential therapeutic and preventive activities against inflammatory diseases, have received increasing attention in recent years because of their whole regulative effects and specific pharmacological activities. However, the molecular mechanisms about how different kinds of natural compounds regulate macrophages polarization still unclear. Therefore, in the current review, we summarized the detailed research progress on the active compounds derived from herbal plants with regulating effects on macrophages, especially M2 polarization. These natural occurring compounds including flavonoids, terpenoids, glycosides, lignans, coumarins, alkaloids, polyphenols and quinones. In addition, we extensively discussed the cellular mechanisms underlying the M2 polarization for each compound, which could provide potential therapeutic strategies aiming macrophages M2 polarization.

Rewired phenolic metabolism and improved saccharification efficiency of a Zea mays cinnamyl alcohol dehydrogenase 2 (zmcad2) mutant

Lignocellulosic biomass is an abundant byproduct from cereal crops that can potentially be valorized as a feedstock to produce biomaterials. Zea mays CINNAMYL ALCOHOL DEHYDROGENASE 2 (ZmCAD2) is involved in lignification, and is a promising target to improve the cellulose-to-glucose conversion of maize stover. Here, we analyzed a field-grown zmcad2 Mutator transposon insertional mutant. Zmcad2 mutant plants had an 18% lower Klason lignin content, whereas their cellulose content was similar to that of control lines. The lignin in zmcad2 mutants contained increased levels of hydroxycinnamaldehydes, i.e. the substrates of ZmCAD2, ferulic acid and tricin. Ferulates decorating hemicelluloses were not altered. Phenolic profiling further revealed that hydroxycinnamaldehydes are partly converted into (dihydro)ferulic acid and sinapic acid and their derivatives in zmcad2 mutants. Syringyl lactic acid hexoside, a metabolic sink in CAD-deficient dicot trees, appeared not to be a sink in zmcad2 maize. The enzymatic cellulose-to-glucose conversion efficiency was determined after 10 different thermochemical pre-treatments. Zmcad2 yielded significantly higher conversions compared with controls for almost every pre-treatment. However, the relative increase in glucose yields after alkaline pre-treatment was not higher than the relative increase when no pre-treatment was applied, suggesting that the positive effect of the incorporation of hydroxycinnamaldehydes was leveled off by the negative effect of reduced p-coumarate levels in the cell wall. Taken together, our results reveal how phenolic metabolism is affected in CAD-deficient maize, and further support mutating CAD genes in cereal crops as a promising strategy to improve lignocellulosic biomass for sugar-platform biorefineries.

Biosynthesis and heterologous production of furanocoumarins: perspectives and current challenges

Covering: up to October 2020 Furanocoumarins are plant secondary metabolites used to treat several skin disorders, such as psoriasis and vitiligo, and also with other potential therapeutic activities. Furanocoumarins are extracted from plants where they accumulate in low amounts over long growth periods. In addition, their extraction and purification are difficult in an environmentally unfriendly and expensive process. Hence, new sustainable and greener production schemes able to overcome such limitations ought to be developed. While the heterologous production of simple coumarins has been demonstrated, the biosynthesis of more complex furanocoumarins remains greatly unexplored. Although several important steps of the pathway have been elucidated in the last decade, the complete pathway has not been completely unravelled. In this paper, we review the natural conversion of amino acids into furanocoumarins, as well as the heterologous expression of each enzyme of the pathway. We also explore the challenges that need to be addressed so that their heterologous production can become a viable alternative.

Reductive catalytic fractionation of pine wood: elucidating and quantifying the molecular structures in the lignin oil

In-depth structural analysis of biorefined lignin is imperative to understand its physicochemical properties, essential for its efficient valorization to renewable materials and chemicals. Up to now, research on Reductive Catalytic Fractionation (RCF) of lignocellulose biomass, an emerging biorefinery technology, has strongly focused on the formation, separation and quantitative analysis of the abundant lignin-derived phenolic monomers. However, detailed structural information on the linkages in RCF lignin oligomers, constituting up to 50 wt% of RCF lignin, and their quantification, is currently lacking. This study discloses new detailed insights into the pine wood RCF lignin oil's molecular structure through the combination of fractionation and systematic analysis, resulting in the first assignment of the major RCF-derived structural units in the 1H-13C HSQC NMR spectrum of the RCF oligomers. Specifically, β-5 γ-OH, β-5 ethyl, β-1 γ-OH, β-1 ethyl, β-β 2x γ-OH, β-β THF, and 5-5 inter-unit linkages were assigned unambiguously, resulting in the quantification of over 80% of the lignin inter-unit linkages and end-units. Detailed inspection of the native lignin inter-unit linkages and their conversion reveals the occurring hydrogenolysis chemistry and the unambiguous proof of absence of lignin fragment condensation during proper RCF processing. Overall, the study offers an advanced analytical toolbox for future RCF lignin conversion and lignin structural analysis research, and valuable insights for lignin oil valorization purposes.

Mesoscale Reaction-Diffusion Phenomena Governing Lignin-First Biomass Fractionation

Lignin solvolysis from the plant cell wall is the critical first step in lignin depolymerization processes involving whole biomass feedstocks. However, little is known about the coupled reaction kinetics and transport phenomena that govern the effective rates of lignin extraction. Here, we report a validated simulation framework that determines intrinsic, transport-independent kinetic parameters for the solvolysis of lignin, hemicellulose, and cellulose upon incorporation of feedstock characteristics for the methanol-based extraction of poplar as an example fractionation process. Lignin fragment diffusion is predicted to compete on the same time and length scales as reactions of lignin within cell walls and longitudinal pores of typical milled particle sizes, and mass transfer resistances are predicted to dominate the solvolysis of poplar particles that exceed approximately 2 mm in length. Beyond the approximately 2 mm threshold, effectiveness factors are predicted to be below 0.25, which implies that pore diffusion resistances may attenuate observable kinetic rate measurements by at least 75 % in such cases. Thus, researchers are recommended to conduct kinetic evaluations of lignin-first catalysts using biomass particles smaller than approximately 0.2 mm in length to avoid feedstock-specific mass transfer limitations in lignin conversion studies. Overall, this work highlights opportunities to improve lignin solvolysis by genetic engineering and provides actionable kinetic information to guide the design and scale-up of emerging biorefinery strategies.

Transgenic Poplar Designed for Biofuels

Members of the genus Populus (i.e., cottonwood, hybrid poplar) represent a promising source of lignocellulosic biomass for biofuels. However, one of the major factors negatively affecting poplar's efficient conversion to biofuel is the inherent recalcitrance to enzymatic saccharification due to cell wall components such as lignin. To this effect, there have been efforts to modify gene expression to reduce biomass recalcitrance by changing cell wall properties. Here, we review recent genetic modifications of poplar that led to change cell wall properties and the resulting effects on subsequent pretreatment efficacy and saccharification. Although genetic engineering's impacts on cell wall properties are not fully predictable, recent studies have shown promising improvement in the biological conversion of transgenic poplar to biofuels.

Brønsted Acid Catalyzed Tandem Defunctionalization of Biorenewable Ferulic acid and Derivates into Bio-Catechol

An efficient conversion of biorenewable ferulic acid into bio-catechol has been developed. The transformation comprises two consecutive defunctionalizations of the substrate, that is, C-O (demethylation) and C-C (de-2-carboxyvinylation) bond cleavage, occurring in one step. The process only requires heating of ferulic acid with HCl (or H₂ SO₄ ) as catalyst in pressurized hot water (250 °C, 50 bar N₂ ). The versatility is shown on a variety of other (biorenewable) substrates yielding up to 84 % di- (catechol, resorcinol, hydroquinone) and trihydroxybenzenes (pyrogallol, hydroxyquinol), in most cases just requiring simple extraction as work-up.

Identification of enzymatic genes with the potential to reduce biomass recalcitrance through lignin manipulation in Arabidopsis

BACKGROUND

During the chemical and biochemical decomposition of lignocellulosic biomasses, lignin is highly recalcitrant. Genetic transformation of plants to qualitatively and/or quantitatively modify lignin may reduce these recalcitrant properties. Efficient discovery of genes to achieve lignin manipulation is thus required.

RESULTS

To screen for new genes to reduce lignin recalcitrance, we heterologously expressed 50 enzymatic genes under the control of a cinnamate 4-hydroxylase (C4H) gene promoter, derived from a hybrid aspen, which is preferentially active in tissues with lignified cell walls in Arabidopsis plants. These genes encode enzymes that act on metabolites in shikimate, general phenylpropanoid, flavonoid, or monolignol biosynthetic pathways. Among these genes, 30, 18, and 2 originated from plants, bacteria, and fungi, respectively. In our first screening step, 296 independent transgenic plants (T₁ generation) harboring single or multiple transgenes were generated from pools of seven Agrobacterium strains used for conventional floral-dip transformation. Wiesner and Mäule staining patterns in the stems of the resultant plants revealed seven and nine plants with apparent abnormalities in the two respective staining analyses. According to genomic PCR and subsequent direct sequencing, each of these 16 plants possessed a gene encoding either coniferaldehyde dehydrogenase (calB), feruloyl-CoA 6'-hydroxylase (F6H1), hydroxycinnamoyl-CoA hydratase/lyase (couA), or ferulate 5-hydroxylase (F5H), with one transgenic plant carrying both calB and F6H1. The effects of these genes on lignin manipulation were confirmed in individually re-created T₁ transgenic Arabidopsis plants. While no difference in lignin content was detected in the transgenic lines compared with the wild type, lignin monomeric composition was changed in the transgenic lines. The observed compositional change in the transgenic plants carrying calB, couA, and F5H led to improved sugar release from cell walls after alkaline pretreatment.

CONCLUSIONS

Simple colorimetric characterization of stem lignin is useful for simultaneous screening of many genes with the potential to reduce lignin recalcitrance. In addition to F5H, the positive control, we identified three enzyme-coding genes that can function as genetic tools for lignin manipulation. Two of these genes (calB and couA) accelerate sugar release from transgenic lignocelluloses.

Effect of curcumin on hippocampus dentate gyrus injury induced by nicotine in rats

Introduction: Nicotine is the most important alkaloid compound in tobacco and is a major risk factor in the development of functional disorder of several organ systems. Some plants produce Curcumin, which has antioxidant and neuroprotective properties. This study was designed to evaluate the therapeutic effects of curcumin against nicotine injury on the hippocampus CA1 region of rats. Methods: In this study, 48 male Wistar rats were randomly assigned to eight groups: Normal control (saline) group, Nicotine control group (0.5 mg/kg); Curcumin groups (10, 30, and 60 mg/kg) and Nicotine + Curcumin groups (10, 30, and 60 mg/kg). Treatments were administered intraperitoneally daily for 28 days. Golgi staining technique investigated the number of dendritic spines. Cresyl violet staining method was used to determine the number of neurons in hippocampal region CA1. Griess technique was assessed to determine serum nitrite oxide level. Also, the Ferric reducing/antioxidant power (FRAP) method was applied to determine the total antioxidant capacity. Results: Nicotine administration significantly increased nitrite oxide level and decreased total antioxidant capacity as well as the number of neuronal dendritic spines and neurons compared to the normal control group (P < 0.01). In all Curcumin and Nicotine + Curcumin groups, the number of neurons, neuronal dendritic spines, and total antioxidant capacity increased significantly compared to the nicotine control group, while nitrite oxide level decreased significantly compared to the nicotine control group (P < 0.01). Conclusion: Curcumin administration can improve hippocampal CA1 region injury induced by nicotine.

Lignin biosynthesis and its integration into metabolism

Lignin is a principal structural component of cell walls in higher terrestrial plants. It reinforces the cell walls, facilitates water transport, and acts as a physical barrier to pathogens. Lignin is typically described as being composed of p-hydroxyphenyl (H), guaiacyl (G), and syringyl (S) units that derive from the polymerization of the hydroxycinnamyl alcohols, p-coumaryl, coniferyl, and sinapyl alcohol, respectively. However, lignin also derives from various other aromatic monomers. Here, we review the biosynthetic pathway to the lignin monomers, and how flux through the pathway is regulated. Upon perturbation of the phenylpropanoid pathway, pathway intermediates may successfully incorporate into the lignin polymer, thereby affecting its physicochemical properties, or may remain soluble as such or as derivatized molecules that might interfere with physiological processes.

Pretreatment of sweet sorghum straw and its enzymatic digestion: insight into the structural changes and visualization of hydrolysis process

BACKGROUND

The efficient utilization of lignocellulosic biomass for biofuel production has received increasing attention. Previous studies have investigated the pretreatment process of biomass, but the detailed enzymatic hydrolysis process of pretreated biomass remains largely unclear. Thus, this study investigated the pretreatment efficiency of dilute alkali, acid, hydrogen peroxide and its ultimate effects on enzymatic hydrolysis. Furthermore, to better understand the enzymatic digestion process of alkali-pretreated sweet sorghum straw (SSS), multimodal microscopy techniques were used to visualize the enzymatic hydrolysis process.

RESULT

After pretreatment with alkali, an enzymatic hydrolysis efficiency of 86.44% was obtained, which increased by 99.54% compared to the untreated straw (43.23%). The FTIR, XRD and SEM characterization revealed a sequence of microstructural changes occurring in plant cell walls after pretreatment, including the destruction of lignin-polysaccharide interactions, the increase of porosity and crystallinity, and reduction of recalcitrance. During the course of hydrolysis, the cellulase dissolved the cell walls in the same manner and the digestion firstly occurred from the middle of cell walls and then toward the cell wall corners. The CLSM coupled with fluorescent labeling demonstrated that the sclerenchyma cells and vascular bundles in natural SSS were highly lignified, which caused the nonproductive bindings of cellulase on lignin. However, the efficient delignification significantly increased the accessibility and digestibility of cellulase to biomass, thereby improving the saccharification efficiency.

CONCLUSION

This work will be helpful in investigating the biomass pretreatment and its structural characterization. In addition, the visualization results of the enzymatic hydrolysis process of pretreated lignocellulose could be used for guidance to explore the lignocellulosic biomass processing and large-scale biofuel production.