Potential transgenic routes to increase tree biomass

Quality trait improvement in horticultural crops: OMICS and modern biotechnological approaches

Horticultural crops are an essential part of food and nutritional security. Moreover, these form an integral part of the agricultural economy and have enormous economic potential. They are a rich source of nutrients that are beneficial to human health. Plant breeding of horticultural crops has focussed primarily on increasing the productivity and related traits of these crops. However, fruit and vegetable quality is paramount to their perishability, marketability, and consumer acceptance. The improved nutritional value is beneficial to underprivileged and undernourished communities. Due to a declining genetic base, conventional plant breeding does not contribute much to quality improvement as the existing natural allelic variations and crossing barriers between cultivated and wild species limit it. Over the past two decades, 'omics' and modern biotechnological approaches have made it possible to decode the complex genomes of crop plants, assign functions to the otherwise many unknown genes, and develop genome-wide DNA markers. Genetic engineering has enabled the validation of these genes and the introduction of crucial agronomic traits influencing various quality parameters directly or indirectly. This review discusses the significant advances in the quality improvement of horticultural crops, including shelf life, aroma, browning, nutritional value, colour, and many other related traits.

Effects of Pb(II) and Zn(II) Contamination on Adsorption, Desorption and Degradation of Cry1Ac Toxin Identical to Bt Transgenic Poplar in Black Soil

Bt transgenic white poplar has been commercially planted in China since 2002, and it showed obvious insect resistance in the field. However, the ecological risk of planting Bt transgenic poplar in a field contaminated with heavy metals has received little attention. The effects of Pb(II) and Zn(II) contamination on the adsorption, desorption and degradation of Bt toxin identical to Bt transgenic poplar in black soil were studied. The results showed that the adsorption of Bt toxin was enhanced and the desorption of Bt toxin was inhibited in black soil by Pb(II) and Zn(II) at concentrations between 0 and 1 mmol/L, and the effect of Pb(II) on Bt toxin was greater than that of Zn(II). In the presence of heavy metal ions, the Cry1Ac toxin molecules are oriented with domain I toward soil particles through the metal ion bridge. The promoting mechanism of Bt toxin adsorption by heavy metal ions in black soil is mainly attributed to cation-controlled electrostatic attraction (CCEA), which is different from patch-controlled electrostatic attraction (PCEA). With the increase in soil concentration from 1 to 4 mg/mL, the adsorption amount of Bt toxin showed a downward trend, and both Pb(II) and Zn(II) had the maximal promotion effect when the soil concentration was 2 mg/mL. The promoting effect of Zn(II) on the adsorption of Bt toxin increased with the increased temperature (5-45 °C), but the promoting effect of Pb(II) was maximal at 25 °C. Both Pb(II) and Zn(II) affected the degradation characteristics of Bt toxin in black soil. For the lead-contaminated black soil, the residual amount of Bt toxin increased in the early stage but decreased in the later stage compared to the control soil. For the zinc-contaminated black soil, the residual amount of Bt toxin decreased compared to the control soil except between the second and tenth days. In this study, it was observed that Bt toxin was degraded rapidly in the early stage, followed by a large amount of released Bt toxin and slow degradation in the middle and late stages.

From residue to resource: new insights into the synthesis of functionalized lignin micro/nanospheres by self-assembly technology for waste resource utilization

Among the most abundant biopolymers in the biosphere, lignin is a renewable aromatic compound that represents an untapped opportunity to create new biological products. However, the complex interlacing structures of cellulose, hemicellulose and lignin, as well as the unique properties of lignin, limit the utilization of value-added lignin. Lignin-based nanomaterials open the door for lignin applications in environmental pollutant remediation, biofuel production, biomedicine, and other fields. Herein, we present various factors influencing the formation of micro-nanospheres by self-assembly techniques through a review of previous literature, and emphasize the simple and green synthesis of lignin micro/nanospheres (LMNPs) under non-modified conditions. More importantly, we discuss the mechanism of the formation of nanospheres. Considering the heterogeneity of lignin and the polarity of different solvents, we propose that self-assembly techniques should focus more on the influence brought by lignin itself or the solvent, so that the external conditions can be controlled to prepare LMNPs, which can be used in specific fields. A brief overview of the contribution of lignin-based nanomaterials in various fields is also presented. This review could provide insight for the development of lignin-based nanomaterials.

Bioengineering and Molecular Biology of Miscanthus

Miscanthus is a perennial wild plant that is vital for the production of paper and roofing, as well as horticulture and the development of new high-yielding crops in temperate climates. Chromosome-level assembly of the ancient tetraploid genome of miscanthus chromosomes is reported to provide resources that can link its chromosomes to related diploid sorghum and complex polyploid sugarcane. Analysis of Miscanthus sinensis and Miscanthus sacchariflorus showed intense mixing and interspecific hybridization and documented the origin of a high-yielding triploid bioenergetic plant, Miscanthus × giganteus. The Miscanthus genome expands comparative genomics functions to better understand the main abilities of Andropogoneae herbs. Miscanthus × giganteus is widely regarded as a promising lignocellulosic biomass crop due to its high-biomass yield, which does not emit toxic compounds into the environment, and ability to grow in depleted lands. The high production cost of lignocellulosic bioethanol limits its commercialization. The main components that inhibit the enzymatic reactions of fermentation and saccharification are lignin in the cell wall and its by-products released during the pre-treatment stage. One approach to overcoming this barrier could be to genetically modify the genes involved in lignin biosynthesis, manipulating the lignin content and composition of miscanthus.

Overexpression of Plasma Membrane H+-ATPase in Guard Cells Enhances Light-Induced Stomatal Opening, Photosynthesis, and Plant Growth in Hybrid Aspen

Stomata in the plant epidermis open in response to light and regulate CO₂ uptake for photosynthesis and transpiration for uptake of water and nutrients from roots. Light-induced stomatal opening is mediated by activation of the plasma membrane (PM) H⁺-ATPase in guard cells. Overexpression of PM H⁺-ATPase in guard cells promotes light-induced stomatal opening, enhancing photosynthesis and growth in Arabidopsis thaliana. In this study, transgenic hybrid aspens overexpressing Arabidopsis PM H⁺-ATPase (AHA2) in guard cells under the strong guard cell promoter Arabidopsis GC1 (AtGC1) showed enhanced light-induced stomatal opening, photosynthesis, and growth. First, we confirmed that AtGC1 induces GUS expression specifically in guard cells in hybrid aspens. Thus, we produced AtGC1::AHA2 transgenic hybrid aspens and confirmed expression of AHA2 in AtGC1::AHA2 transgenic plants. In addition, AtGC1::AHA2 transgenic plants showed a higher PM H⁺-ATPase protein level in guard cells. Analysis using a gas exchange system revealed that transpiration and the photosynthetic rate were significantly increased in AtGC1::AHA2 transgenic aspen plants. AtGC1::AHA2 transgenic plants showed a>20% higher stem elongation rate than the wild type (WT). Therefore, overexpression of PM H⁺-ATPase in guard cells promotes the growth of perennial woody plants.

A Label-Free Proteomic and Complementary Metabolomic Analysis of Leaves of the Resurrection Plant Xerophytaschlechteri during Dehydration

Vegetative desiccation tolerance, or the ability to survive the loss of ~95% relative water content (RWC), is rare in angiosperms, with these being commonly called resurrection plants. It is a complex multigenic and multi-factorial trait, with its understanding requiring a comprehensive systems biology approach. The aim of the current study was to conduct a label-free proteomic analysis of leaves of the resurrection plant Xerophyta schlechteri in response to desiccation. A targeted metabolomics approach was validated and correlated to the proteomics, contributing the missing link in studies on this species. Three physiological stages were identified: an early response to drying, during which the leaf tissues declined from full turgor to a RWC of ~80–70%, a mid-response in which the RWC declined to 40% and a late response where the tissues declined to 10% RWC. We identified 517 distinct proteins that were differentially expressed, of which 253 proteins were upregulated and 264 were downregulated in response to the three drying stages. Metabolomics analyses, which included monitoring the levels of a selection of phytohormones, amino acids, sugars, sugar alcohols, fatty acids and organic acids in response to dehydration, correlated with some of the proteomic differences, giving insight into the biological processes apparently involved in desiccation tolerance in this species.

Metabolic engineering in woody plants: challenges, advances, and opportunities

Woody plant species represent an invaluable reserve of biochemical diversity to which metabolic engineering can be applied to satisfy the need for commodity and specialty chemicals, pharmaceuticals, and renewable energy. Woody plants are particularly promising for this application due to their low input needs, high biomass, and immeasurable ecosystem services. However, existing challenges have hindered their widespread adoption in metabolic engineering efforts, such as long generation times, large and highly heterozygous genomes, and difficulties in transformation and regeneration. Recent advances in omics approaches, systems biology modeling, and plant transformation and regeneration methods provide effective approaches in overcoming these outstanding challenges. Promises brought by developments in this space are steadily opening the door to widespread metabolic engineering of woody plants to meet the global need for a wide range of sustainably sourced chemicals and materials.

Multivariate linear mixed model enhanced the power of identifying genome-wide association to poplar tree heights in a randomized complete block design

With the advances in high-throughput sequencing technologies, it is not difficult to extract tens of thousands of single-nucleotide polymorphisms (SNPs) across many individuals in a fast and cheap way, making it possible to perform genome-wide association studies (GWAS) of quantitative traits in outbred forest trees. It is very valuable to apply traditional breeding experiments in GWAS for identifying genome variants associated with ecologically and economically important traits in Populus. Here, we reported a GWAS of tree height measured at multiple time points from a randomized complete block design (RCBD), which was established with clones from an F₁ hybrid population of Populus deltoides and Populus simonii. A total of 22,670 SNPs across 172 clones in the RCBD were obtained with restriction site-associated DNA sequencing (RADseq) technology. The multivariate mixed linear model was applied by incorporating the pedigree relationship matrix of individuals to test the association of each SNP to the tree heights over 8 time points. Consequently, 41 SNPs were identified significantly associated with the tree height under the P-value threshold determined by Bonferroni correction at the significant level of 0.01. These SNPs were distributed on all but two chromosomes (Chr02 and Chr18) and explained the phenotypic variance ranged from 0.26% to 2.64%, amounting to 63.68% in total. Comparison with previous mapping studies for poplar height as well as the candidate genes of these detected SNPs were also investigated. We therefore showed that the application of multivariate linear mixed model to the longitudinal phenotypic data from the traditional breeding experimental design facilitated to identify far more genome-wide variants for tree height in poplar. The significant SNPs identified in this study would enhance understanding of molecular mechanism for growth traits and would accelerate marker-assisted breeding programs in Populus.

Sucrose synthase determines carbon allocation in developing wood and alters carbon flow at the whole tree level in aspen

Despite the ecological and industrial importance of biomass accumulation in wood, the control of carbon (C) allocation to this tissue and to other tree tissues remain poorly understood. We studied sucrose synthase (SUS) to clarify its role in biomass formation and C metabolism at the whole tree level in hybrid aspen (Populus tremula × tremuloides). To this end, we analysed source leaves, phloem, developing wood, and roots of SUSRNAi trees using a combination of metabolite profiling, ¹³ CO₂ pulse labelling experiments, and long-term field experiments. The glasshouse grown SUSRNAi trees exhibited a mild stem phenotype together with a reduction in wood total C. The ¹³ CO₂ pulse labelling experiments showed an alteration in the C flow in all the analysed tissues, indicating that SUS affects C metabolism at the whole tree level. This was confirmed when the SUSRNAi trees were grown in the field over a 5-yr period; their stem height, diameter and biomass were substantially reduced. These results establish that SUS influences C allocation to developing wood, and that it affects C metabolism at the whole tree level.

High-Quality SNP Linkage Maps Improved QTL Mapping and Genome Assembly in Populus

With the advances in high-throughput sequencing technologies and the development of new software for extracting single nucleotide polymorphisms (SNPs) across a mapping population, it is possible to construct high-quality genetic maps with thousands of SNPs in outbred forest trees. Two parent-specific linkage maps were constructed with restriction site-associated DNA sequencing data from an F₁ hybrid population derived from Populus deltoides and Populus simonii, and applied in QTL mapping and genome assembly. The female P. deltoides map contained 4018 SNPs, which were divided into 19 linkage groups under a wide range of LOD thresholds from 7 to 55. The male P. simonii map showed similar characteristics, consisting of 2097 SNPs, which also belonged to 19 linkage groups under LOD thresholds of 7 to 29. The SNP order of each linkage group was optimal among different ordering results from several available software. Moreover, the linkage maps allowed the detection of 39 QTLs underlying tree height and 47 for diameter at breast height. In addition, the linkage maps improved the anchoring of 689 contigs of P. simonii to chromosomes. The 2 parental genetic maps of Populus are of high quality, especially in terms of SNP data quality, the SNP order within linkage groups, and the perfect match between the number of linkage groups and the karyotype of Populus, as well as the excellent performances in QTL mapping and genome assembly. Both approaches for extracting and ordering SNPs could be applied to other species for constructing high-quality genetic maps.

Overexpression of MADS-box Gene AGAMOUS-LIKE 12 Activates Root Development in Juglans sp. and Arabidopsis thaliana

Until recently, the roles of plant MADS-box genes have mainly been characterized during inflorescence and flower differentiation. In order to precise the roles of AGAMOUS-LIKE 12, one of the few MADS-box genes preferentially expressed in roots, we placed its cDNA under the control of the double 35S CaMV promoter to produce transgenic walnut tree and Arabidopsis plants. In Juglans sp., transgenic somatic embryos showed significantly higher germination rates but abnormal development of their shoot apex prevented their conversion into plants. In addition, a wide range of developmental abnormalities corresponding to ectopic root-like structures affected the transgenic lines suggesting partial reorientations of the embryonic program toward root differentiation. In Arabidopsis, AtAGL12 overexpression lead to the production of faster growing plants presenting dramatically wider and shorter root phenotypes linked to increased meristematic cell numbers within the root apex. In the upper part of the roots, abnormal cell divisions patterns within the pericycle layer generated large ectopic cell masses that did not prevent plants to grow. Taken together, our results confirm in both species that AGL12 positively regulates root meristem cell division and promotes overall root vascular tissue formation. Genetic engineering of AGL12 expression levels could be useful to modulate root architecture and development.

Marginal Lands to Grow Novel Bio-Based Crops: A Plant Breeding Perspective

The biomass demand to fuel a growing global bio-based economy is expected to tremendously increase over the next decades, and projections indicate that dedicated biomass crops will satisfy a large portion of it. The establishment of dedicated biomass crops raises huge concerns, as they can subtract land that is required for food production, undermining food security. In this context, perennial biomass crops suitable for cultivation on marginal lands (MALs) raise attraction, as they could supply biomass without competing for land with food supply. While these crops withstand marginal conditions well, their biomass yield and quality do not ensure acceptable economic returns to farmers and cost-effective biomass conversion into bio-based products, claiming genetic improvement. However, this is constrained by the lack of genetic resources for most of these crops. Here we first review the advantages of cultivating novel perennial biomass crops on MALs, highlighting management practices to enhance the environmental and economic sustainability of these agro-systems. Subsequently, we discuss the preeminent breeding targets to improve the yield and quality of the biomass obtainable from these crops, as well as the stability of biomass production under MALs conditions. These targets include crop architecture and phenology, efficiency in the use of resources, lignocellulose composition in relation to bio-based applications, and tolerance to abiotic stresses. For each target trait, we outline optimal ideotypes, discuss the available breeding resources in the context of (orphan) biomass crops, and provide meaningful examples of genetic improvement. Finally, we discuss the available tools to breed novel perennial biomass crops. These comprise conventional breeding methods (recurrent selection and hybridization), molecular techniques to dissect the genetics of complex traits, speed up selection, and perform transgenic modification (genetic mapping, QTL and GWAS analysis, marker-assisted selection, genomic selection, transformation protocols), and novel high-throughput phenotyping platforms. Furthermore, novel tools to transfer genetic knowledge from model to orphan crops (i.e., universal markers) are also conceptualized, with the belief that their development will enhance the efficiency of plant breeding in orphan biomass crops, enabling a sustainable use of MALs for biomass provision.

Plant cell wall sugars: sweeteners for a bio-based economy

Global warming and the consequent climate change is one of the major environmental challenges we are facing today. The driving force behind the rise in temperature is our fossil-based economy, which releases massive amounts of the greenhouse gas carbon dioxide into the atmosphere. In order to reduce greenhouse gas emission, we need to scale down our dependency on fossil resources, implying that we need other sources for energy and chemicals to feed our economy. Here, plants have an important role to play; by means of photosynthesis, plants capture solar energy to split water and fix carbon derived from atmospheric carbon dioxide. A significant fraction of the fixed carbon ends up as polysaccharides in the plant cell wall. Fermentable sugars derived from cell wall polysaccharides form an ideal carbon source for the production of bio-platform molecules. However, a major limiting factor in the use of plant biomass as feedstock for the bio-based economy is the complexity of the plant cell wall and its recalcitrance towards deconstruction. To facilitate the release of fermentable sugars during downstream biomass processing, the composition and structure of the cell wall can be engineered. Different strategies to reduce cell wall recalcitrance will be described in this review. The ultimate goal is to obtain a tailor-made biomass, derived from plants with a cell wall optimized for particular industrial or agricultural applications, without affecting plant growth and development.

MVQTLCIM: composite interval mapping of multivariate traits in a hybrid F1 population of outbred species

Background

With the plummeting cost of the next-generation sequencing technologies, high-density genetic linkage maps could be constructed in a forest hybrid F₁ population. However, based on such genetic maps, quantitative trait loci (QTL) mapping cannot be directly conducted with traditional statistical methods or tools because the linkage phase and segregation pattern of molecular markers are not always fixed as in inbred lines.

Results

We implemented the traditional composite interval mapping (CIM) method to multivariate trait data in forest trees and developed the corresponding software, mvqtlcim. Our method not only incorporated the various segregations and linkage phases of molecular markers, but also applied Takeuchi’s information criterion (TIC) to discriminate the QTL segregation type among several possible alternatives. QTL mapping was performed in a hybrid F₁ population of Populus deltoides and P. simonii, and 12 QTLs were detected for tree height over 6 time points. The software package allowed many options for parameters as well as parallel computing for permutation tests. The features of the software were demonstrated with the real data analysis and a large number of Monte Carlo simulations.

Conclusions

We provided a powerful tool for QTL mapping of multiple or longitudinal traits in an outbred F₁ population, in which the traditional software for QTL mapping cannot be used. This tool will facilitate studying of QTL mapping and thus will accelerate molecular breeding programs especially in forest trees. The tool package is freely available from https://github.com/tongchf /mvqtlcim.

Electronic supplementary material

The online version of this article (10.1186/s12859-017-1908-1) contains supplementary material, which is available to authorized users.

Impact of RAV1-engineering on poplar biomass production: a short-rotation coppice field trial

BACKGROUND

Early branching or syllepsis has been positively correlated with high biomass yields in short-rotation coppice (SRC) poplar plantations, which could represent an important lignocellulosic feedstock for the production of second-generation bioenergy. In prior work, we generated hybrid poplars overexpressing the chestnut gene RELATED TO ABI3/VP1 1 (CsRAV1), which featured c. 80% more sylleptic branches than non-modified trees in growth chambers. Given the high plasticity of syllepsis, we established a field trial to monitor the performance of these trees under outdoor conditions and a SRC management.

RESULTS

We examined two CsRAV1-overexpression poplar events for their ability to maintain syllepsis and their potential to enhance biomass production. Two poplar events with reduced expression of the CsRAV1 homologous poplar genes PtaRAV1 and PtaRAV2 were also included in the trial. Under our culture conditions, CsRAV1-overexpression poplars continued developing syllepsis over two cultivation cycles. Biomass production increased on completion of the first cycle for one of the overexpression events, showing unaltered structural, chemical, or combustion wood properties. On completion of the second cycle, aerial growth and biomass yields of both overexpression events were reduced as compared to the control.

CONCLUSIONS

These findings support the potential application of CsRAV1-overexpression to increase syllepsis in commercial elite trees without changing their wood quality. However, the syllepsis triggered by the introduction of this genetic modification appeared not to be sufficient to sustain and enhance biomass production.

Biotechnology for bioenergy dedicated trees: meeting future energy demands

With the increase in human demands for energy, purpose-grown woody crops could be part of the global renewable energy solution, especially in geographical regions where plantation forestry is feasible and economically important. In addition, efficient utilization of woody feedstocks would engage in mitigating greenhouse gas emissions, decreasing the challenge of food and energy security, and resolving the conflict between land use for food or biofuel production. This review compiles existing knowledge on biotechnological and genomics-aided improvements of biomass performance of purpose-grown poplar, willow, eucalyptus and pine species, and their relative hybrids, for efficient and sustainable bioenergy applications. This includes advancements in tree in vitro regeneration, and stable expression or modification of selected genes encoding desirable traits, which enhanced growth and yield, wood properties, site adaptability, and biotic and abiotic stress tolerance. Genetic modifications used to alter lignin/cellulose/hemicelluloses ratio and lignin composition, towards effective lignocellulosic feedstock conversion into cellulosic ethanol, are also examined. Biotech-trees still need to pass challengeable regulatory authorities’ processes, including biosafety and risk assessment analyses prior to their commercialization release. Hence, strategies developed to contain transgenes, or to mitigate potential transgene flow risks, are discussed.

Overexpression of a pine Dof transcription factor in hybrid poplars: A comparative study in trees growing under controlled and natural conditions

In this work, the role of the pine transcriptional regulator Dof 5 in carbon and nitrogen metabolism has been examined in poplar trees. The overexpression of the gene and potential effects on growth and biomass production were compared between trees growing in a growth chamber under controlled conditions and trees growing in a field trial during two growth seasons. Ten-week-old transgenic poplars exhibited higher growth than untransformed controls and exhibited enhanced capacity for inorganic nitrogen uptake in the form of nitrate. Furthermore, the transgenic trees accumulated significantly more carbohydrates such as glucose, fructose, sucrose and starch. Lignin content increased in the basal part of the stem likely due to the thicker stem of the transformed plants. The enhanced levels of lignin were correlated with higher expression of the PAL1 and GS1.3 genes, which encode key enzymes involved in the phenylalanine deamination required for lignin biosynthesis. However, the results in the field trial experiment diverged from those observed in the chamber system. The lines overexpressing PpDof5 showed attenuated growth during the two growing seasons and no modification of carbon or nitrogen metabolism. These results were not associated with a decrease in the expression of the transgene, but they can be ascribed to the nitrogen available in the field soil compared to that available for growth under controlled conditions. This work highlights the paramount importance of testing transgenic lines in field trials.

The response of marigold (Tagetes erecta Linn.) to ozone: impacts on plant growth and leaf physiology

Progressively increasing ozone (O₃) concentrations pose a potential threat to the value of marigold (Tagetes erecta Linn.), a plant widely used in urban landscaping. The response of marigold to elevated O₃ has been reported earlier, but the mechanisms underlying the O₃ effect have not been clearly elucidated. In the present study, we exposed marigold "Moonsong Deep Orange" plants to elevated O₃, including ambient non-filtered air (NF) plus 60 ppb (NF+60) and 120 ppb (NF+120) O₃, to assess visible injury and the possible physiological consequences of this pollutant. Yellow lesions appeared after 4 days under NF+120 treatment and 12 days under NF+60 treatment, with 85.6% and 36.8% of the leaves being injured at harvest time, respectively. Compared with NF, NF+60 inhibited leaf photosynthesis, stem-diameter growth, and biomass production significantly, while the parameters were decreased more by NF+120. Although the stomatal conductance decreased under elevated O₃ exposure, the O₃ flux into leaves increased by 28.0-104.8% under NF+60 treatment and 57.5-145.6% under NF+120 treatment. The total ascorbic acid (ASA) content increased due to elevated O₃ exposure, while the reduced ASA content did not, resulting in a decreased ratio of reduced to total ASA. A lower level of jasmonic acid (JA) was observed under elevated O₃ exposure. In conclusion, the impacts of elevated O₃ on marigold plants may be ascribed to increased O₃ flux into leaves and reduced protective capacity of leaves to convert oxidized to reduced ASA and synthesize endogenous JA.

Modification of plant cell wall structure accompanied by enhancement of saccharification efficiency using a chemical, lasalocid sodium

The cell wall is one major determinant of plant cell morphology, and is an attractive bioresource. Here, we report a novel strategy to modify plant cell wall property by small molecules. Lasalocid sodium (LS) was isolated by chemical screening to identify molecules that affect the cell morphology of tobacco BY-2 cells. LS treatment led to an increase in cell wall thickness, whilst the quantity and sugar composition of the cell wall remained unchanged in BY-2 cells. The chemical also disordered the cellular arrangement of hypocotyls of Arabidopsis plants, resulting in a decrease in hypocotyl length. LS treatment enhanced enzymatic saccharification efficiency in both BY-2 cells and Arabidopsis plants. Microarray analysis on Arabidopsis showed that exposure to LS upregulated type III peroxidase genes, of which some are involved in lignin biogenesis, and jasmonic acid response genes, and phloroglucinol staining supported the activation of lignification by the LS treatment. As jasmonic acid-mediated lignification is a typical reaction to cell wall damage, it is possible that LS induces cell wall loosening, which can trigger cell wall damage response. Thus, LS is a unique chemical for modification of cell wall and morphology through changes in cell wall architecture.

Plant Fibre: Molecular Structure and Biomechanical Properties, of a Complex Living Material, Influencing Its Deconstruction towards a Biobased Composite

Plant cell walls form an organic complex composite material that fulfils various functions. The hierarchical structure of this material is generated from the integration of its elementary components. This review provides an overview of wood as a composite material followed by its deconstruction into fibres that can then be incorporated into biobased composites. Firstly, the fibres are defined, and their various origins are discussed. Then, the organisation of cell walls and their components are described. The emphasis is on the molecular interactions of the cellulose microfibrils, lignin and hemicelluloses in planta. Hemicelluloses of diverse species and cell walls are described. Details of their organisation in the primary cell wall are provided, as understanding of the role of hemicellulose has recently evolved and is likely to affect our perception and future study of their secondary cell wall homologs. The importance of the presence of water on wood mechanical properties is also discussed. These sections provide the basis for understanding the molecular arrangements and interactions of the components and how they influence changes in fibre properties once isolated. A range of pulping processes can be used to individualise wood fibres, but these can cause damage to the fibres. Therefore, issues relating to fibre production are discussed along with the dispersion of wood fibres during extrusion. The final section explores various ways to improve fibres obtained from wood.

Paving the Way for Lignin Valorisation: Recent Advances in Bioengineering, Biorefining and Catalysis

Lignin is an abundant biopolymer with a high carbon content and high aromaticity. Despite its potential as a raw material for the fuel and chemical industries, lignin remains the most poorly utilised of the lignocellulosic biopolymers. Effective valorisation of lignin requires careful fine-tuning of multiple "upstream" (i.e., lignin bioengineering, lignin isolation and "early-stage catalytic conversion of lignin") and "downstream" (i.e., lignin depolymerisation and upgrading) process stages, demanding input and understanding from a broad array of scientific disciplines. This review provides a "beginning-to-end" analysis of the recent advances reported in lignin valorisation. Particular emphasis is placed on the improved understanding of lignin's biosynthesis and structure, differences in structure and chemical bonding between native and technical lignins, emerging catalytic valorisation strategies, and the relationships between lignin structure and catalyst performance.

Overexpression of GA20-OXIDASE1 impacts plant height, biomass allocation and saccharification efficiency in maize

Increased biomass yield and quality are of great importance for the improvement of feedstock for the biorefinery. For the production of bioethanol, both stem biomass yield and the conversion efficiency of the polysaccharides in the cell wall to fermentable sugars are of relevance. Increasing the endogenous levels of gibberellic acid (GA) by ectopic expression of GA20-OXIDASE1 (GA20-OX1), the rate-limiting step in GA biosynthesis, is known to affect cell division and cell expansion, resulting in larger plants and organs in several plant species. In this study, we examined biomass yield and quality traits of maize plants overexpressing GA20-OX1 (GA20-OX1). GA20-OX1 plants accumulated more vegetative biomass than control plants in greenhouse experiments, but not consistently over two years of field trials. The stems of these plants were longer but also more slender. Investigation of GA20-OX1 biomass quality using biochemical analyses showed the presence of more cellulose, lignin and cell wall residue. Cell wall analysis as well as expression analysis of lignin biosynthetic genes in developing stems revealed that cellulose and lignin were deposited earlier in development. Pretreatment of GA20-OX1 biomass with NaOH resulted in a higher saccharification efficiency per unit of dry weight, in agreement with the higher cellulose content. On the other hand, the cellulose-to-glucose conversion was slower upon HCl or hot-water pretreatment, presumably due to the higher lignin content. This study showed that biomass yield and quality traits can be interconnected, which is important for the development of future breeding strategies to improve lignocellulosic feedstock for bioethanol production.

WD40-Repeat Proteins in Plant Cell Wall Formation: Current Evidence and Research Prospects

The metabolic complexity of living organisms relies on supramolecular protein structures which ensure vital processes, such as signal transduction, transcription, translation and cell wall synthesis. In eukaryotes WD40-repeat (WDR) proteins often function as molecular "hubs" mediating supramolecular interactions. WDR proteins may display a variety of interacting partners and participate in the assembly of complexes involved in distinct cellular functions. In plants, the formation of lignocellulosic biomass involves extensive synthesis of cell wall polysaccharides, a process that requires the assembly of large transmembrane enzyme complexes, intensive vesicle trafficking, interactions with the cytoskeleton, and coordinated gene expression. Because of their function as supramolecular hubs, WDR proteins could participate in each or any of these steps, although to date only few WDR proteins have been linked to the cell wall by experimental evidence. Nevertheless, several potential cell wall-related WDR proteins were recently identified using in silico approaches, such as analyses of co-expression, interactome and conserved gene neighborhood. Notably, some WDR genes are frequently genomic neighbors of genes coding for GT2-family polysaccharide synthases in eukaryotes, and this WDR-GT2 collinear microsynteny is detected in diverse taxa. In angiosperms, two WDR genes are collinear to cellulose synthase genes, CesAs, whereas in ascomycetous fungi several WDR genes are adjacent to chitin synthase genes, chs. In this Perspective we summarize and discuss experimental and in silico studies on the possible involvement of WDR proteins in plant cell wall formation. The prospects of biotechnological engineering for enhanced biomass production are discussed.

Wood biosynthesis and typologies: a molecular rhapsody

Wood represents one of the most important renewable commodities for humanity and plays a crucial role in terrestrial ecosystem carbon-cycling. Wood formation is the result of a multitude of events that require the concerted action of endogenous and exogenous factors under the influence of photoperiod, for instance genes and plant growth regulators. Beyond providing mechanical support and being responsible for the increase in stem radial diameter, woody tissues constitute the vascular system of trees and are capable of reacting to environmental stimuli, and as such are therefore quite plastic and responsive. Despite the ecological and economic importance of wood, not all aspects of its formation have been unveiled. Many gaps in our knowledge are still present, which hinder the maximal exploitation of this precious bioresource. This review aims at surveying the current knowledge of wood formation and the available molecular data addressing the relationship between wood production and environmental factors, which have crucial influences on the rhythmic regulation of cambial activity and exert profound effects on tree stem growth, wood yield and properties. We will here go beyond wood sensu stricto, i.e., secondary xylem, and extend our survey to other tissues, namely vascular cambium, phloem and fibres. The purpose is to provide the reader with an overview of the complexity of the topic and to highlight the importance of progressing in the future towards an integrated knowledge on the subject.

Current challenges in commercially producing biofuels from lignocellulosic biomass

Biofuels that are produced from biobased materials are a good alternative to petroleum based fuels. They offer several benefits to society and the environment. Producing second generation biofuels is even more challenging than producing first generation biofuels due the complexity of the biomass and issues related to producing, harvesting, and transporting less dense biomass to centralized biorefineries. In addition to this logistic challenge, other challenges with respect to processing steps in converting biomass to liquid transportation fuel like pretreatment, hydrolysis, microbial fermentation, and fuel separation still exist and are discussed in this review. The possible coproducts that could be produced in the biorefinery and their importance to reduce the processing cost of biofuel are discussed. About $1 billion was spent in the year 2012 by the government agencies in US to meet the mandate to replace 30% existing liquid transportation fuels by 2022 which is 36 billion gallons/year. Other countries in the world have set their own targets to replace petroleum fuel by biofuels. Because of the challenges listed in this review and lack of government policies to create the demand for biofuels, it may take more time for the lignocellulosic biofuels to hit the market place than previously projected.