Cellulose synthesis in higher plants

Cell twisting during desiccation reveals axial asymmetry in wall organization

Plant cell size and shape are tuned to their function and specified primarily by cellulose microfibril (CMF) patterning of the cell wall. Arabidopsis thaliana leaf trichomes are unicellular structures that act as a physical defense to deter insect feeding. This highly polarized cell type employs a strongly anisotropic cellulose wall to extend and taper, generating sharply pointed branches. During elongation, the mechanisms by which shifts in fiber orientation generate cells with predictable sizes and shapes are unknown. Specifically, the axisymmetric growth of trichome branches is often thought to result from axisymmetric CMF patterning. Here, we analyzed the direction and degree of twist of branches after desiccation to reveal the presence of an asymmetric cell wall organization with a left-hand bias. CMF organization, quantified using computational modeling, suggests a limited reorientation of microfibrils during growth and a maximum branch length limited by the wall axial stiffness. The model provides a mechanism for CMF asymmetry, which occurs after the branch bending stiffness becomes low enough that ambient bending affects the principal stresses. After this stage, the CMF synthesis results in a constant bending stiffness for longer branches. The bending vibration natural frequencies of branches with respect to their length are also discussed.

Mutation of CESA1 phosphorylation site influences pectin synthesis and methylesterification with a role in seed development

Cell wall biogenesis is required for the production of seeds of higher plants. However, little is known about regulatory mechanisms underlying cell wall biogenesis during seed formation. Here we show a role for the phosphorylation of Arabidopsis cellulose synthase 1 (AtCESA1) in modulating pectin synthesis and methylesterification in seed coat mucilage. A phosphor-null mutant of AtCESA1 on T166 (AtCESA1^T166A) was constructed and introduced into a null mutant of AtCESA1 (Atcesa1-1). The resulting transgenic lines showed a slight but significant decrease in cellulose contents in mature seeds. Defects in cellulosic ray architecture along with reduced levels of non-adherent and adherent mucilage were observed on the seeds of the AtCESA1^T166A mutant. Reduced mucilage pectin synthesis was also reflected by a decrease in the level of uronic acid. Meanwhile, an increase in the degree of pectin methylesterification was also observed in the seed coat mucilage of AtCESA1^T166A mutant. Change in seed development was further reflected by a delayed germination and about 50% increase in the accumulation of proanthocyanidins, which is known to bind pectin and inhibit seed germination as revealed by previous studies. Taken together, the results suggest a role of AtCESA1 phosphorylation on T166 in modulating mucilage pectin synthesis and methylesterification as well as cellulose synthesis with a role in seed development.

Proteome-wide identification of non-histone lysine methylation in tomato during fruit ripening

INTRODUCTION

Histone and non-histone methylations are important post-translational modifications in plants. Histone methylation plays a crucial role in regulating chromatin structure and gene expression. However, the involvement of non-histone methylation in plant biological processes remains largely unknown.

METHODS

The methylated substrates and methylation sites during tomato fruit ripening were identified by LC-MS/MS. Bioinformatics of lysine methylated proteins was conducted to analyze the possible role of methylated proteins. The effects of methylation modification on protein functions were preliminarily investigated by site-directed mutation simulation.

RESULTS

A total of 241 lysine methylation (mono-, di- and trimethylation) sites in 176 proteins were identified with two conserved methylation motifs: xxxxxxExxx_K_xxxExxxxxx and xxxxxxExxx_K_xxxxxxxxxx. These methylated proteins were mainly related to fruit ripening and senescence, oxidation reduction process, signal transduction, stimulus and stress responses, and energy metabolism. Three representative proteins, thioredoxin (Trx), glutathione S-transferase T1 (GST T1), and NADH dehydrogenase (NOX), were selected to investigate the effect of methylation modifications on protein activity. Mimicking demethylation led to decreased Trx activity but increased GST T1 and NOX activities. In addition, RT-qPCR exhibited that the expression of many genes that encode proteins subjected to methylation was upregulated during fruit ripening.

CONCLUSION

Our study suggests that tomato fruit ripening undergo non-histone lysine methylation, which may participate in the regulation of fruit ripening. It is the first report of methyl proteome profiling of non-histone lysine in horticultural crops.

Identification of the CesA Subfamily and Functional Analysis of GhMCesA35 in Gossypium Hirsutum L

The cellulose synthase genes control the biosynthesis of cellulose in plants. Nonetheless, the gene family members of CesA have not been identified in the newly assembled genome of Gossypiumhirsutum (AD1, HEBAU_NDM8). We identified 38 CesA genes in G. hirsutum (NDM8) and found that the protein sequence of GhMCesA35 is 100% identical to CelA1 in a previous study. It is already known that CelA1 is involved in cellulose biosynthesis in vitro. However, the function of this gene in vivo has not been validated. In this study, we verified the function of GhMCesA35 in vivo based on overexpressed Arabidopsis thaliana. In addition, we found that it interacted with GhCesA7 through the yeast two-hybrid assay. This study provides new insights for studying the biological functions of CesA genes in G. hirsutum, thereby improving cotton fiber quality and yield.

How salt stress-responsive proteins regulate plant adaptation to saline conditions

An overview is presented of recent advances in our knowledge of candidate proteins that regulate various physiological and biochemical processes underpinning plant adaptation to saline conditions. Salt stress is one of the environmental constraints that restrict plant distribution, growth and yield in many parts of the world. Increased world population surely elevates food demands all over the globe, which anticipates to add a great challenge to humanity. These concerns have necessitated the scientists to understand and unmask the puzzle of plant salt tolerance mechanisms in order to utilize various strategies to develop salt tolerant crop plants. Salt tolerance is a complex trait involving alterations in physiological, biochemical, and molecular processes. These alterations are a result of genomic and proteomic complement readjustments that lead to tolerance mechanisms. Proteomics is a crucial molecular tool that indicates proteins expressed by the genome, and also identifies the functions of proteins accumulated in response to salt stress. Recently, proteomic studies have shed more light on a range of promising candidate proteins that regulate various processes rendering salt tolerance to plants. These proteins have been shown to be involved in photosynthesis and energy metabolism, ion homeostasis, gene transcription and protein biosynthesis, compatible solute production, hormone modulation, cell wall structure modification, cellular detoxification, membrane stabilization, and signal transduction. These candidate salt responsive proteins can be therefore used in biotechnological approaches to improve tolerance of crop plants to salt conditions. In this review, we provided comprehensive updated information on the proteomic data of plants/genotypes contrasting in salt tolerance in response to salt stress. The roles of salt responsive proteins that are potential determinants for plant salt adaptation are discussed. The relationship between changes in proteome composition and abundance, and alterations observed in physiological and biochemical features associated with salt tolerance are also addressed.

Structural snapshot of a glycoside hydrolase family 8 endo-β-1,4-glucanase capturing the state after cleavage of the scissile bond

Bacterial cellulose (BC), which is produced by bacteria, is a biodegradable and biocompatible natural resource. Because of its remarkable physicochemical properties, BC has attracted attention for the development and manufacture of biomedical and industrial materials. In the BC production system, the enzyme endo-β-1,4-glucanase, which belongs to glycoside hydrolase family 8 (GH8), acts as a cleaner by trimming disordered cellulose fibers to produce high-quality BC. Understanding the molecular mechanism of the endo-β-1,4-glucanase would help in developing a reasonable biosynthesis of BC. Nevertheless, all of the steps in the reaction of this endo-β-1,4-glucanase are not clear. This study confirms the BC hydrolytic activity of the endo-β-1,4-glucanase from the BC-producing bacterium Enterobacter sp. CJF-002 (EbBcsZ) and reports crystal structures of EbBcsZ. Unlike in previously reported GH8 endo-β-1,4-glucanase structures, here the base catalyst was mutated (D242A) and the structure of this mutant bound to cellooligosaccharide [EbBcsZ(D242A)CPT] was analyzed. The EbBcsZ(D242A)CPT structure showed two cellooligosaccharides individually bound to the plus and minus subsites of EbBcsZ. The glucosyl unit in subsite −1 presented a distorted 5 S 1 conformation, a novel snapshot of a state immediately after scissile-bond cleavage. In combination with previous studies, the reaction process of endo-β-1,4-glucanase is described and the β-1,4-glucan-trimming mechanism of EbBcsZ is proposed. The EbBcsZ(D242A)CPT structure also showed an additional β-1,4-glucan binding site on the EbBcsZ surface, which may help to accept the substrate.

Dietary Fiber in Plant Cell Walls—The Healthy Carbohydrates

Dietary fiber (DF) is one of the major classes of nutrients for humans. It is widely distributed in the edible parts of natural plants, with the cell wall being the main DF-containing structure. The DF content varies significantly in different plant species and organs, and the processing procedure can have a dramatic effect on the DF composition of plant-based foods. Given the considerable nutritional value of DF, a deeper understanding of DF in food plants, including its composition and biosynthesis, is fundamental to the establishment of a daily intake reference of DF and is also critical to molecular breeding programs for modifying DF content. In the past decades, plant cell wall biology has seen dramatic progress, and such knowledge is of great potential to be translated into DF-related food science research and may provide future research directions for improving the health benefits of food crops. In this review, to spark interdisciplinary discussions between food science researchers and plant cell wall biologists, we focus on a specific category of DF—cell wall carbohydrates. We first summarize the content and composition of carbohydrate DF in various plant-based foods, and then discuss the structure and biosynthesis mechanism of each carbohydrate DF category, in particular the respective biosynthetic enzymes. Health impacts of DF are highlighted, and finally, future directions of DF research are also briefly outlined.

Identification and Fine Mapping of the Recessive Gene BK-5, Which Affects Cell Wall Biosynthesis and Plant Brittleness in Maize

The cellulose of the plant cell wall indirectly affects the cell shape and straw stiffness of the plant. Here, the novel brittleness mutant brittle stalk-5 (bk-5) of the maize inbred line RP125 was characterized. We found that the mutant displayed brittleness of the stalk and even the whole plant, and that the brittleness phenotype existed during the whole growth period from germination to senescence. The compressive strength was reduced, the cell wall was thinner, and the cellulose content was decreased compared to that of the wild type. Genetic analysis and map-based cloning indicated that bk-5 was controlled by a single recessive nuclear gene and that it was located in a 90.2-Kb region on chromosome 3 that covers three open reading frames (ORFs). Sequence analysis revealed a single non-synonymous missense mutation, T-to-A, in the last exon of Zm00001d043477 (B73: version 4, named BK-5) that caused the 951th amino acid to go from leucine to histidine. BK-5 encodes a cellulose synthase catalytic subunit (CesA), which is involved with cellulose synthesis. We found that BK-5 was constitutively expressed in all tissues of the germinating stage and silking stage, and highly expressed in the leaf, auricula, and root of the silking stage and the 2-cm root and bud of the germinating stage. We found that BK-5 mainly localized to the Golgi apparatus, suggesting that the protein might move to the plasma membrane with the aid of Golgi in maize. According to RNA-seq data, bk-5 had more downregulated genes than upregulated genes, and many of the downregulated genes were enzymes and transcription factors related to cellulose, hemicellulose, and lignin biosynthesis of the secondary cell wall. The other differentially expressed genes were related to metabolic and cellular processes, and were significantly enriched in hormone signal transduction, starch and sucrose metabolism, and the plant-pathogen interaction pathway. Taken together, we propose that the mutation of gene BK-5 causes the brittle stalk phenotype and provides important insights into the regulatory mechanism of cellulose biosynthesis and cell wall development in maize.

Temperature-induced dynamics of plant carbohydrate metabolism

Carbohydrates are direct products of photosynthetic CO₂ assimilation. Within a changing temperature regime, both photosynthesis and carbohydrate metabolism need tight regulation to prevent irreversible damage of plant tissue and to sustain energy metabolism, growth and development. Due to climate change, plants are and will be exposed to both long-term and short-term temperature changes with increasing amplitude. Particularly sudden fluctuations, which might comprise a large temperature amplitude from low to high temperature, pose a challenge for plants from the cellular to the ecosystem level. A detailed understanding of fundamental regulatory processes, which link photosynthesis and carbohydrate metabolism under such fluctuating environmental conditions, is essential for an estimate of climate change consequences. Further, understanding these processes is important for biotechnological application, breeding and engineering. Environmental light and temperature regimes are sensed by a molecular network that comprises photoreceptors and molecular components of the circadian clock. Photosynthetic efficiency and plant productivity then critically depend on enzymatic regulation and regulatory circuits connecting plant cells with their environment and re-stabilising photosynthetic efficiency and carbohydrate metabolism after temperature-induced deflection. This review summarises and integrates current knowledge about re-stabilisation of photosynthesis and carbohydrate metabolism after perturbation by changing temperature (heat and cold).

Down-regulation of OsMYB103L distinctively alters beta-1,4-glucan polymerization and cellulose microfibers assembly for enhanced biomass enzymatic saccharification in rice

BACKGROUND

As a major component of plant cell walls, cellulose provides the most abundant biomass resource convertible for biofuels. Since cellulose crystallinity and polymerization have been characterized as two major features accounting for lignocellulose recalcitrance against biomass enzymatic saccharification, genetic engineering of cellulose biosynthesis is increasingly considered as a promising solution in bioenergy crops. Although several transcription factors have been identified to regulate cellulose biosynthesis and plant cell wall formation, much remains unknown about its potential roles for genetic improvement of lignocellulose recalcitrance.

RESULTS

In this study, we identified a novel rice mutant (Osfc9/myb103) encoded a R2R3-MYB transcription factor, and meanwhile generated OsMYB103L-RNAi-silenced transgenic lines. We determined significantly reduced cellulose levels with other major wall polymers (hemicellulose, lignin) slightly altered in mature rice straws of the myb103 mutant and RNAi line, compared to their wild type (NPB). Notably, the rice mutant and RNAi line were of significantly reduced cellulose features (crystalline index/CrI, degree of polymerization/DP) and distinct cellulose nanofibers assembly. These alterations consequently improved lignocellulose recalcitrance for significantly enhanced biomass enzymatic saccharification by 10-28% at p < 0.01 levels (n = 3) after liquid hot water and chemical (1% H₂SO₄, 1% NaOH) pretreatments with mature rice straws. In addition, integrated RNA sequencing with DNA affinity purification sequencing (DAP-seq) analyses revealed that the OsMYB103L might specifically mediate cellulose biosynthesis and deposition by regulating OsCesAs and other genes associated with microfibril assembly.

CONCLUSIONS

This study has demonstrated that down-regulation of OsMYB103L could specifically improve cellulose features and cellulose nanofibers assembly to significantly enhance biomass enzymatic saccharification under green-like and mild chemical pretreatments in rice. It has not only indicated a powerful strategy for genetic modification of plant cell walls in bioenergy crops, but also provided insights into transcriptional regulation of cellulose biosynthesis in plants.

Solid-State NMR Investigations of Extracellular Matrixes and Cell Walls of Algae, Bacteria, Fungi, and Plants

Extracellular matrixes (ECMs), such as the cell walls and biofilms, are important for supporting cell integrity and function and regulating intercellular communication. These biomaterials are also of significant interest to the production of biofuels and the development of antimicrobial treatment. Solid-state nuclear magnetic resonance (ssNMR) and magic-angle spinning-dynamic nuclear polarization (MAS-DNP) are uniquely powerful for understanding the conformational structure, dynamical characteristics, and supramolecular assemblies of carbohydrates and other biomolecules in ECMs. This review highlights the recent high-resolution investigations of intact ECMs and native cells in many organisms spanning across plants, bacteria, fungi, and algae. We spotlight the structural principles identified in ECMs, discuss the current technical limitation and underexplored biochemical topics, and point out the promising opportunities enabled by the recent advances of the rapidly evolving ssNMR technology.

Rice Brittle Culm19 Encoding Cellulose Synthase Subunit CESA4 Causes Dominant Brittle Phenotype But has No Distinct Influence on Growth and Grain Yield

BACKGROUND

Mechanical strength is a crucial agronomic trait in rice (Oryza sativa), and brittle mutants are thought suitable materials to investigate the mechanism of cell wall formation. So far, almost all brittle mutants are recessive, and most of them are defected in multiple morphologies and/or grain yield, limiting their application in hybrid breeding and in rice straw recycling.

RESULTS

We identified a semi-dominant brittle mutant Brittle culm19 (Bc19) isolated from the japonica variety Nipponbare through chemical mutagenesis. The mutant showed the same apparent morphologies and grain yield to the wild type plant except for its weak mechanical strength. Its development of secondary cell wall in sclerenchyma cells was affected, along with reduced contents of cellulose, hemicellulose, lignin and sugars in culms and leaves. Positional cloning suggested that the Bc19 gene was allelic to OsCESA4, encoding one of the cellulose synthase A (CESA) catalytic subunits. In this mutant, a C-to-T substitution occurred in the coding sequence of BC19, causing the P507S missense mutation in its encoded product, which was located in the second cytoplasmic region of the OsCESA4 protein. Furthermore, introducing mutant gene Bc19 into the wild-type plant resulted in brittle plants, confirming that the P507S point mutation in OsCESA4 protein was responsible for the semi-dominant brittle phenotype of Bc19 mutant. Reverse correlation was revealed between cellulose contents and expression levels of mutant gene Bc19 among the homozygous mutant, the hybrid F₁ plant, and the Bc19 overexpression transgenic plants, implying that gene Bc19 might affect cellulose synthesis in a dosage-dependent manner.

CONCLUSIONS

Bc19, a semi-dominant brittle mutant allele of gene OsCESA4, was identified using map-based cloning approach. The mutated protein of Bc19 possessing the P507S missense mutation behaved in a dosage-dependent semi-dominant manner. Unique brittle effect on phenotype and semi-dominant genetic quality of gene Bc19 indicated its potential application in grain-straw dual-purpose hybrid rice breeding.

Plant cell adhesion and growth on artificial fibrous scaffolds as an in vitro model for plant development

Mechanistic studies of plant development would benefit from an in vitro model that mimics the endogenous physical interactions between cells and their microenvironment. Here, we present artificial scaffolds to which both solid- and liquid-cultured tobacco BY-2 cells adhere without perturbing cell morphology, division, and cortical microtubule organization. Scaffolds consisting of polyvinylidene tri-fluoroethylene (PVDF-TrFE) were prepared to mimic the cell wall’s fibrillar structure and its relative hydrophobicity and piezoelectric property. We found that cells adhered best to scaffolds consisting of nanosized aligned fibers. In addition, poling of PVDF-TrFE, which orients the fiber dipoles and renders the scaffold more piezoelectric, increased cell adhesion. Enzymatic treatments revealed that the plant cell wall polysaccharide, pectin, is largely responsible for cell adhesion to scaffolds, analogous to pectin-mediated cell adhesion in plant tissues. Together, this work establishes the first plant biomimetic scaffolds that will enable studies of how cell-cell and cell-matrix interactions affect plant developmental pathways.

Weaving of bacterial cellulose by the Bcs secretion systems

Cellulose is the most abundant biological compound on Earth and while it is the predominant building constituent of plants, it is also a key extracellular matrix component in many diverse bacterial species. While bacterial cellulose was first described in the 19th century, it was not until this last decade that a string of structural works provided insights into how the cellulose synthase BcsA, assisted by its inner-membrane partner BcsB, senses c-di-GMP to simultaneously polymerize its substrate and extrude the nascent polysaccharide across the inner bacterial membrane. It is now established that bacterial cellulose can be produced by several distinct types of cellulose secretion systems and that in addition to BcsAB, they can feature multiple accessory subunits, often indispensable for polysaccharide production. Importantly, the last years mark significant progress in our understanding not only of cellulose polymerization per se but also of the bigger picture of bacterial signaling, secretion system assembly, biofilm formation and host tissue colonization, as well as of structural and functional parallels of this dominant biosynthetic process between the bacterial and eukaryotic domains of life. Here, we review current mechanistic knowledge on bacterial cellulose secretion with focus on the structure, assembly and cooperativity of Bcs secretion system components.

Bph30 confers resistance to brown planthopper by fortifying sclerenchyma in rice leaf sheaths

Phloem-feeding insects cause massive losses in agriculture and horticulture. Host plant resistance to phloem-feeding insects is often mediated by changes in phloem composition, which deter insect settling and feeding and decrease viability. Here, we report that rice plant resistance to the phloem-feeding brown planthopper (BPH) is associated with fortification of the sclerenchyma tissue, which is located just beneath the epidermis and a cell layer or two away from the vascular bundle in the rice leaf sheath. We found that BPHs prefer to feed on the smooth and soft region on the surface of rice leaf sheaths called the long-cell block. We identified Bph30 as a rice BPH resistance gene that prevents BPH stylets from reaching the phloem due to the fortified sclerenchyma. Bph30 is strongly expressed in sclerenchyma cells and enhances cellulose and hemicellulose synthesis, making the cell walls stiffer and sclerenchyma thicker. The structurally fortified sclerenchyma is a formidable barrier preventing BPH stylets from penetrating the leaf sheath tissues and arriving at the phloem to feed. Bph30 belongs to a novel gene family, encoding a protein with two leucine-rich domains. Another member of the family, Bph40, also conferred resistance to BPH. Collectively, the fortified sclerenchyma-mediated resistance mechanism revealed in this study expands our understanding of plant-insect interactions and opens a new path for controlling planthoppers in rice.

Comparative transcriptome analysis reveals the molecular mechanism of salt tolerance in Apocynum venetum

Apocynum venetum is a traditional Chinese medicinal herb with tolerance to various abiotic stresses, especially, salinity. However, only a few studies have investigated the salt-tolerant mechanism of this non-halophyte under salt stress at phenotypic and physiological levels. To explore the molecular mechanism of salinity tolerance in A. venetum, the global transcriptome profiles of seedling leaves under different salt-stress durations, using 200 mM NaCl, were analyzed. De novo assembly of approximately 715 million high-quality reads and approximately 105.61 Gb sequence data was performed. In total, 2822 differentially expressed genes (DEGs) were identified. DEGs were significantly enriched in flavonoid metabolism-related pathways such as "flavonoid biosynthesis" and "phenylpropanoid biosynthesis". Most of these DEGs were downregulated under salt stress. However, genes encoding the non-selective cation channels and antioxidants were upregulated under salt stress, whereas most cell wall-related DEGs were downregulated. Consequently, the concentration of flavonoids decreased, whereas that of Na⁺ increased with exposure time. Thus, we hypothesized that the accumulation of Na⁺ in the leaves, which resulted in reduced flavonoid concentration under salt stress, directly led to a decrease in the salt tolerance of A. venetum. This was verified by overexpressing four flavonoid synthesis pathway genes in Arabidopsis. The transgenic plants showed higher salt tolerance than the wild-type plants due to the accumulation of total flavonoids. These physiological and transcriptome analyses of A. venetum revealed major molecular underpinnings contributing to the responses of A. venetum to salt stress, thereby improving our understanding of the molecular mechanisms underlying salt tolerance in A. venetum and plants in general. The findings serve as a basis for functional studies on and engineering strategies for plant salinity tolerance.

SWO1 modulates cell wall integrity under salt stress by interacting with importin ɑ in Arabidopsis

Maintenance of cell wall integrity is of great importance not only for plant growth and development, but also for the adaptation of plants to adverse environments. However, how the cell wall integrity is modulated under salt stress is still poorly understood. Here, we report that a nuclear-localized Agenet domain-containing protein SWO1 (SWOLLEN 1) is required for the maintenance of cell wall integrity in Arabidopsis under salt stress. Mutation in SWO1 gene results in swollen root tips, disordered root cell morphology, and root elongation inhibition under salt stress. The swo1 mutant accumulates less cellulose and pectin but more lignin under high salinity. RNA-seq and ChIP-seq assays reveal that SWO1 binds to the promoter of several cell wall-related genes and regulates their expression under saline conditions. Further study indicates that SWO1 interacts with importin ɑ IMPA1 and IMPA2, which are required for the import of nuclear-localized proteins. The impa1 impa2 double mutant also exhibits root growth inhibition under salt stress and mutations of these two genes aggravate the salt-hypersensitive phenotype of the swo1 mutant. Taken together, our data suggest that SWO1 functions together with importin ɑ to regulate the expression of cell wall-related genes, which enables plants to maintain cell wall integrity under high salinity.

From vesicles to materials: bioinspired strategies for fabricating hierarchically structured soft matter

Certain organisms including species of mollusks, polychaetes, onychophorans and arthropods produce exceptional polymeric materials outside their bodies under ambient conditions using concentrated fluid protein precursors. While much is understood about the structure-function relationships that define the properties of such materials, comparatively less is understood about how such materials are fabricated and specifically, how their defining hierarchical structures are achieved via bottom-up assembly. Yet this information holds great potential for inspiring sustainable manufacture of advanced polymeric materials with controlled multi-scale structure. In the present perspective, we first examine recent work elucidating the formation of the tough adhesive fibres of the mussel byssus via secretion of vesicles filled with condensed liquid protein phases (coacervates and liquid crystals)-highlighting which design principles are relevant for bio-inspiration. In the second part of the perspective, we examine the potential of recent advances in drops and additive manufacturing as a bioinspired platform for mimicking such processes to produce hierarchically structured materials. This article is part of the theme issue 'Bio-derived and bioinspired sustainable advanced materials for emerging technologies (part 1)'.

Cell wall associated immunity in plants

The plant cell wall is the first physical and defensive barrier against pathogens. The plant cell wall usually undergoes dynamic remodeling as an immune response to prevent infection by pathogens. In this review, we summarize advances on relationship between cell wall and immunity in plants. In particular, we outline current progresses regarding the regulation of the cell wall components, including cellulose, hemicellulose, pectin and lignin, on plant disease resistance. We also discuss the impacts of cell wall-derived cellodextrin, oligogalacturonic acid and xyloglucan/xylan oligosaccharides as potent elicitors or signal molecules to trigger plant immune response. We further propose future studies on dissecting the molecular regulation of cell wall on plant immunity, which have potentials in practical application of crop breeding aiming at improvement of plant disease resistance.

Structural insights into homotrimeric assembly of cellulose synthase CesA7 from Gossypium hirsutum

Cellulose is one of the most abundant organic polymers in nature. It contains multiple β-1,4-glucan chains synthesized by cellulose synthases (CesAs) on the plasma membrane of higher plants. CesA subunits assemble into a pseudo-sixfold symmetric cellulose synthase complex (CSC), known as a 'rosette complex'. The structure of CesA remains enigmatic. Here, we report the cryo-EM structure of the homotrimeric CesA7 from Gossypium hirsutum at 3.5-angstrom resolution. The GhCesA7 homotrimer shows a C3 symmetrical assembly. Each protomer contains seven transmembrane helices (TMs) which form a channel potentially facilitating the release of newly synthesized glucans. The cytoplasmic glycosyltransferase domain (GT domain) of GhCesA7 protrudes from the membrane, and its catalytic pocket is directed towards the TM pore. The homotrimer GhCesA7 is stabilized by the transmembrane helix 7 (TM7) and the plant-conserved region (PCR) domains. It represents the building block of CSCs and facilitates microfibril formation. This structure provides insight into how eukaryotic cellulose synthase assembles and provides a mechanistic basis for the improvement of cotton fibre quality in the future.

Functional understanding of secondary cell wall cellulose synthases in Populus trichocarpa via the Cas9/gRNA-induced gene knockouts

Plant cellulose is synthesized by a large plasma membrane-localized cellulose synthase (CesA) complex. However, an overall functional determination of secondary cell wall (SCW) CesAs is still lacking in trees, especially one based on gene knockouts. Here, the Cas9/gRNA-induced knockouts of PtrCesA4, 7A, 7B, 8A and 8B genes were produced in Populus trichocarpa. Based on anatomical, immunohistochemical and wood composition evidence, we gained a comprehensive understanding of five SCW PtrCesAs at the genetic level. Complete loss of PtrCesA4, 7A/B or 8A/B led to similar morphological abnormalities, indicating similar and nonredundant genetic functions. The absence of the gelatinous (G) layer, one-layer-walled fibres and a 90% decrease in cellulose in these mutant woods revealed that the three classes of SCW PtrCesAs are essential for multilayered SCW structure and wood G-fibre. In addition, the mutant primary and secondary phloem fibres lost the n(G + L)- and G-layers and retained the thicker S-layers (L, lignified; S, secondary). Together with polysaccharide immunolocalization data, these findings suggest differences in the role of SCW PtrCesAs-synthesized cellulose in wood and phloem fibre wall structures. Overall, this functional understanding of the SCW PtrCesAs provides further insights into the impact of lacking cellulose biosynthesis on growth, SCW, wood G-fibre and phloem fibre wall structures in the tree.

TRANVIA (TVA) facilitates cellulose synthase trafficking and delivery to the plasma membrane

Cellulose is synthesized at the plasma membrane by cellulose synthase (CESA) complexes (CSCs), which are assembled in the Golgi and secreted to the plasma membrane through the trans-Golgi network (TGN) compartment. However, the molecular mechanisms that guide CSCs through the secretory system and deliver them to the plasma membrane are poorly understood. Here, we identified an uncharacterized gene, TRANVIA (TVA), that is transcriptionally coregulated with the CESA genes required for primary cell wall synthesis. The tva mutant exhibits enhanced sensitivity to cellulose synthesis inhibitors; reduced cellulose content; and defective dynamics, density, and secretion of CSCs to the plasma membrane as compared to wild type. TVA is a plant-specific protein of unknown function that is detected in at least two different intracellular compartments: organelles labeled by markers for the TGN and smaller compartments that deliver CSCs to the plasma membrane. Together, our data suggest that TVA promotes trafficking of CSCs to the plasma membrane by facilitating exit from the TGN and/or interaction of CSC secretory vesicles with the plasma membrane.

Updating Insights into the Catalytic Domain Properties of Plant Cellulose synthase (CesA) and Cellulose synthase-like (Csl) Proteins

The wall is the last frontier of a plant cell involved in modulating growth, development and defense against biotic stresses. Cellulose and additional polysaccharides of plant cell walls are the most abundant biopolymers on earth, having increased in economic value and thereby attracted significant interest in biotechnology. Cellulose biosynthesis constitutes a highly complicated process relying on the formation of cellulose synthase complexes. Cellulose synthase (CesA) and Cellulose synthase-like (Csl) genes encode enzymes that synthesize cellulose and most hemicellulosic polysaccharides. Arabidopsis and rice are invaluable genetic models and reliable representatives of land plants to comprehend cell wall synthesis. During the past two decades, enormous research progress has been made to understand the mechanisms of cellulose synthesis and construction of the plant cell wall. A plethora of cesa and csl mutants have been characterized, providing functional insights into individual protein isoforms. Recent structural studies have uncovered the mode of CesA assembly and the dynamics of cellulose production. Genetics and structural biology have generated new knowledge and have accelerated the pace of discovery in this field, ultimately opening perspectives towards cellulose synthesis manipulation. This review provides an overview of the major breakthroughs gathering previous and recent genetic and structural advancements, focusing on the function of CesA and Csl catalytic domain in plants.

De novo transcriptome analysis of white teak (Gmelina arborea Roxb) wood reveals critical genes involved in xylem development and secondary metabolism

BACKGROUND

Gmelina arborea Roxb is a fast-growing tree species of commercial importance for tropical countries due to multiple industrial uses of its wood. Wood is primarily composed of thick secondary cell walls of xylem cells which imparts the strength to the wood. Identification of the genes involved in the secondary cell wall biosynthesis as well as their cognate regulators is crucial to understand how the production of wood occurs and serves as a starting point for developing breeding strategies to produce varieties with improved wood quality, better paper pulping or new potential uses such as biofuel production. In order to gain knowledge on the molecular mechanisms and gene regulation related with wood development in white teak, a de novo sequencing and transcriptome assembly approach was used employing secondary cell wall synthesizing cells from young white teak trees.

RESULTS

For generation of transcriptome, RNA-seq reads were assembled into 110,992 transcripts and 49,364 genes were functionally annotated using plant databases; 5071 GO terms and 25,460 SSR markers were identified within xylem transcripts and 10,256 unigenes were assigned to KEGG database in 130 pathways. Among transcription factor families, C2H2, C3H, bLHLH and MYB were the most represented in xylem. Differential gene expression analysis using leaves as a reference was carried out and a total of 20,954 differentially expressed genes were identified including monolignol biosynthetic pathway genes. The differential expression of selected genes (4CL, COMT, CCoAOMT, CCR and NST1) was validated using qPCR.

CONCLUSIONS

We report the very first de novo transcriptome of xylem-related genes in this tropical timber species of commercial importance and constitutes a valuable extension of the publicly available transcriptomic resource aimed at fostering both basic and breeding studies.

Cellulose accumulation in the secondary cell walls is negatively correlated with the tenderness of new shoots in Camellia sinensis

Tea, which is usually made from the new shoots of tea plants (Camellia sinensis), is one of the most popular and healthy beverages. The tenderness of new shoots plays a critical role in the production of high-quality tea; however, the factors affecting the tenderness of the new shoots of tea have not been extensively studied. Here, we show that cellulose accumulation is negatively correlated with the tenderness of new shoots, including leaves and stems, by characterizing the cellulose content and visualizing cellulose in the new shoots of two cultivars ("Huangjinya" and "Yujinxiang") via toluidine blue staining. We further found that the number of cells with secondary cell walls (SCWs) and the thickness of SCWs increased with the maturity degree of stems in both cultivars. Because cellulose is the most abundant polymer in SCW, we next identified three cellulose synthase CsCesAs, CsCesA4, 7, and 8A, through homologous alignment with Arabidopsis AtCesAs. Protein sequence analysis revealed that these proteins were closely related based on the phylogenetic analysis. We finally showed that the gene expression of the three CsCesAs was positively correlated with the maturity degree and cellulose content of the new shoots. Thus, our data suggest that cellulose accumulation, especially in the SCWs, is negatively correlated with the tenderness of new shoots in tea plants.

Doxorubicin Embedded into Nanofibrillated Bacterial Cellulose (NFBC) Produces a Promising Therapeutic Outcome for Peritoneally Metastatic Gastric Cancer in Mice Models via Intraperitoneal Direct Injection

Natural materials such as bacterial cellulose are gaining interest for their use as drug-delivery vehicles. Herein, the utility of nanofibrillated bacterial cellulose (NFBC), which is produced by culturing a cellulose-producing bacterium (Gluconacetobacter intermedius NEDO-01) in a medium supplemented with carboxymethylcellulose (CMC) that is referred to as CM-NFBC, is described. Recently, we demonstrated that intraperitoneal administration of paclitaxel (PTX)-containing CM-NFBC efficiently suppressed tumor growth in a peritoneally disseminated cancer xenograft model. In this study, to confirm the applicability of NFBC in cancer therapy, a chemotherapeutic agent, doxorubicin (DXR), embedded into CM-NFBC, was examined for its efficiency to treat a peritoneally disseminated gastric cancer via intraperitoneal administration. DXR was efficiently embedded into CM-NFBC (DXR/CM-NFBC). In an in vitro release experiment, 79.5% of DXR was released linearly into the peritoneal wash fluid over a period of 24 h. In the peritoneally disseminated gastric cancer xenograft model, intraperitoneal administration of DXR/CM-NFBC induced superior tumor growth inhibition (TGI = 85.5%) by day 35 post-tumor inoculation, compared to free DXR (TGI = 62.4%). In addition, compared with free DXR, the severe side effects that cause body weight loss were lessened via treatment with DXR/CM-NFBC. These results support the feasibility of CM-NFBC as a drug-delivery vehicle for various anticancer agents. This approach may lead to improved therapeutic outcomes for the treatment of intraperitoneally disseminated cancers.

Coffee cell walls—composition, influence on cup quality and opportunities for coffee improvements

The coffee beverage is the second most consumed drink worldwide after water. In coffee beans, cell wall storage polysaccharides (CWSPs) represent around 50 per cent of the seed dry mass, mainly consisting of galactomannans and arabinogalactans. These highly abundant structural components largely influence the organoleptic properties of the coffee beverage, mainly due to the complex changes they undergo during the roasting process. From a nutritional point of view, coffee CWSPs are soluble dietary fibers shown to provide numerous health benefits in reducing the risk of human diseases. Due to their influence on coffee quality and their health-promoting benefits, CWSPs have been attracting significant research attention. The importance of cell walls to the coffee industry is not restricted to beans used for beverage production, as several coffee by-products also present high concentrations of cell wall components. These by-products include cherry husks, cherry pulps, parchment skin, silver skin, and spent coffee grounds, which are currently used or have the potential to be utilized either as food ingredients or additives, or for the generation of downstream products such as enzymes, pharmaceuticals, and bioethanol. In addition to their functions during plant development, cell walls also play a role in the plant’s resistance to stresses. Here, we review several aspects of coffee cell walls, including chemical composition, biosynthesis, their function in coffee’s responses to stresses, and their influence on coffee quality. We also propose some potential cell wall–related biotechnological strategies envisaged for coffee improvements.

Inhibition of cell expansion enhances cortical microtubule stability in the root apex of Arabidopsis thaliana

Background

Cortical microtubules regulate cell expansion by determining cellulose microfibril orientation in the root apex of Arabidopsis thaliana. While the regulation of cell wall properties by cortical microtubules is well studied, the data on the influence of cell wall to cortical microtubule organization and stability remain scarce. Studies on cellulose biosynthesis mutants revealed that cortical microtubules depend on Cellulose Synthase A (CESA) function and/or cell expansion. Furthermore, it has been reported that cortical microtubules in cellulose-deficient mutants are hypersensitive to oryzalin. In this work, the persistence of cortical microtubules against anti-microtubule treatment was thoroughly studied in the roots of several cesa mutants, namely thanatos, mre1, any1, prc1-1 and rsw1, and the Cellulose Synthase Interacting 1 protein (csi1) mutant pom2-4. In addition, various treatments with drugs affecting cell expansion were performed on wild-type roots. Whole mount tubulin immunolabeling was applied in the above roots and observations were performed by confocal microscopy.

Results

Cortical microtubules in all mutants showed statistically significant increased persistence against anti-microtubule drugs, compared to those of the wild-type. Furthermore, to examine if the enhanced stability of cortical microtubules was due to reduced cellulose biosynthesis or to suppression of cell expansion, treatments of wild-type roots with 2,6-dichlorobenzonitrile (DCB) and Congo red were performed. After these treatments, cortical microtubules appeared more resistant to oryzalin, than in the control.

Conclusions

According to these findings, it may be concluded that inhibition of cell expansion, irrespective of the cause, results in increased microtubule stability in A. thaliana root. In addition, cell expansion does not only rely on cortical microtubule orientation but also plays a regulatory role in microtubule dynamics, as well. Various hypotheses may explain the increased cortical microtubule stability under decreased cell expansion such as the role of cell wall sensors and the presence of less dynamic cortical microtubules.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40709-021-00143-8.

Elucidating compositional factors of maize cell walls contributing to stalk strength and lodging resistance

Lodging is one of the causes of maize (Zea mays L.) production losses worldwide and, at least, the resistance to stalk lodging has been positively correlated with stalk strength. In order to elucidate the putative relationship between cell wall, stalk strength and lodging resistance, twelve maize inbreds varying in rind penetration strength and lodging resistance were characterized for cell wall composition and structure. Stepwise multiple regression indicates that H lignin subunits confer a greater rind penetration strength. Besides, the predictive model for lodging showed that a high ferulic acid content increases the resistance to lodging, whereas those of diferulates decrease it. These outcomes highlight that the strength and lodging susceptibility of maize stems may be conditioned by structural features of cell wall rather than by the net amount of cellulose, hemicelluloses and lignin. The results presented here provide biotechnological targets in breeding programs aimed at improving lodging in maize.

Nucleotide-sugar metabolism in plants: the legacy of Luis F. Leloir

This review commemorates the 50th anniversary of the Nobel Prize in Chemistry awarded to Luis F. Leloir 'for his discovery of sugar-nucleotides and their role in the biosynthesis of carbohydrates'. He and his co-workers discovered that activated forms of simple sugars, such as UDP-glucose and UDP-galactose, are essential intermediates in the interconversion of sugars. They elucidated the biosynthetic pathways for sucrose and starch, which are the major end-products of photosynthesis, and for trehalose. Trehalose 6-phosphate, the intermediate of trehalose biosynthesis that they discovered, is now a molecule of great interest due to its function as a sugar signalling metabolite that regulates many aspects of plant metabolism and development. The work of the Leloir group also opened the doors to an understanding of the biosynthesis of cellulose and other structural cell wall polysaccharides (hemicelluloses and pectins), and ascorbic acid (vitamin C). Nucleotide-sugars also serve as sugar donors for a myriad of glycosyltransferases that conjugate sugars to other molecules, including lipids, phytohormones, secondary metabolites, and proteins, thereby modifying their biological activity. In this review, we highlight the diversity of nucleotide-sugars and their functions in plants, in recognition of Leloir's rich and enduring legacy to plant science.

MicroRNA775 regulates intrinsic leaf size and reduces cell wall pectin levels by targeting a galactosyltransferase gene in Arabidopsis

Plants possess unique primary cell walls made of complex polysaccharides that play critical roles in determining intrinsic cell and organ size. How genes responsible for synthesizing and modifying the polysaccharides in the cell wall are regulated by microRNAs (miRNAs) to control plant size remains largely unexplored. Here we identified 23 putative cell wall-related miRNAs, termed as CW-miRNAs, in Arabidopsis thaliana and characterized miR775 as an example. We showed that miR775 post-transcriptionally silences GALT9, which encodes an endomembrane-located galactosyltransferase belonging to the glycosyltransferase 31 family. Over-expression of miR775 and deletion of GALT9 led to significantly enlarged leaf-related organs, primarily due to increased cell size. Monosaccharide quantification, confocal Raman imaging, and immunolabeling combined with atomic force microscopy revealed that the MIR775A-GALT9 circuit modulates pectin levels and the elastic modulus of the cell wall. We also showed that MIR775A is directly repressed by the transcription factor ELONGATED HYPOCOTYL5 (HY5). Genetic analysis confirmed that HY5 is a negative regulator of leaf size that acts through the HY5-MIR775A-GALT9 repression cascade to control pectin levels. These findings demonstrate that miR775-regulated cell wall remodeling is an integral determinant of intrinsic leaf size in A. thaliana. Studying other CW-miRNAs would provide more insights into cell wall biology.

Activating the MYB51 and MYB122 to upregulate the transcription of glucosinolates biosynthesis genes by copper ions in Arabidopsis

Copper ions (Cu²⁺) are key constituents of copper-based antimicrobial compounds (CBACs), which are extensively used in agriculture. Previously, we demonstrated that a low concentration of Cu²⁺ induced plant defenses associated with callose deposition in Arabidopsis as well as flg22, a microbe-associated molecular pattern (MAMP) peptide. However, the details and differences of the mechanisms between Cu²⁺- and flg22-mediated callose deposition remain unclear. Here, we reported that Cu²⁺- and flg22-induced defense responses and callose deposition are dependent on AtACS8 and AtACS2/AtACS6, respectively. After the RNA sequencing data were mined, the expression of MYB51, MYB122, CYP79B2/B3 and CYP83B1 implied that a conserved downstream indole glucosinolate (IGS) metabolic pathway is regulated by Cu²⁺. In the Cu²⁺-induced response, the ethylene biosynthesis rate-limiting gene AtACS8 and the signal transduction pathway were found to be required for Cu²⁺-activated MYB51 and MYB122 transcription. Functional redundancy of MYB51 and MYB122, the key regulators of the IGS metabolic pathway, was identified in the Cu²⁺-mediated regulation of IGS gene transcription, promotion of callose deposition, and increase in Arabidopsis resistance to bacterial pathogens. Furthermore, IGS genes such as CYP79B2, CYP81F2 and PAD2 were required for Cu²⁺-induced callose deposition and defense responses. Our results demonstrate that Cu²⁺ activates MYB51 and MYB122 through distinct ethylene signal transduction to regulate the IGS metabolic pathway, resulting in an enhanced defense response in Arabidopsis.

On the orientation of the chains in the mercerized cellulose

The cold alkaline treatment or mercerization of cellulose is widely used in industry to enrich the cellulose raw with high-molecular-weight [Formula: see text]-cellulose. Washing out of hemicelluloses by alkalies is accompanied by the rearrangement of the cellulose chains' packing, well known as a transition between cellulose I and cellulose II. Cellulose II can also be produced by the precipitation of the cellulose solutions (regeneration). The currently accepted theory implies that in cellulose II, both mercerized and regenerated, the macromolecules are arranged antiparallelly. However, forming such a structure in the course of the mercerization seems to be significantly hindered, while it seems to be quite possible in the regeneration process. In this work, we discuss the sticking points in the theory on the antiparallel structure of mercerized cellulose from a theoretical point of view summarizing all of the available experimental data in the field.

FASCICLIN-LIKE 18 Is a New Player Regulating Root Elongation in Arabidopsis thaliana

The plasticity of root development represents a key trait that enables plants to adapt to diverse environmental cues. The pattern of cell wall deposition, alongside other parameters, affects the extent, and direction of root growth. In this study, we report that FASCICLIN-LIKE ARABINOGALACTAN PROTEIN 18 (FLA18) plays a role during root elongation in Arabidopsis thaliana. Using root-specific co-expression analysis, we identified FLA18 to be co-expressed with a sub-set of genes required for root elongation. FLA18 encodes for a putative extra-cellular arabinogalactan protein from the FLA-gene family. Two independent T-DNA insertion lines, named fla18-1 and fla18-2, display short and swollen lateral roots (LRs) when grown on sensitizing condition of high-sucrose containing medium. Unlike fla4/salt overly sensitive 5 (sos5), previously shown to display short and swollen primary root (PR) and LRs under these conditions, the PR of the fla18 mutants is slightly longer compared to the wild-type. Overexpression of the FLA18 CDS complemented the fla18 root phenotype. Genetic interaction between either of the fla18 alleles and sos5 reveals a more severe perturbation of anisotropic growth in both PR and LRs, as compared to the single mutants and the wild-type under restrictive conditions of high sucrose or high-salt containing medium. Additionally, under salt-stress conditions, fla18sos5 had a small, chlorotic shoot phenotype, that was not observed in any of the single mutants or the wild type. As previously shown for sos5, the fla18-1 and fla18-1sos5 root-elongation phenotype is suppressed by abscisic acid (ABA) and display hypersensitivity to the ABA synthesis inhibitor, Fluridon. Last, similar to other cell wall mutants, fla18 root elongation is hypersensitive to the cellulose synthase inhibitor, Isoxaben. Altogether, the presented data assign a new role for FLA18 in the regulation of root elongation. Future studies of the unique vs. redundant roles of FLA proteins during root elongation is anticipated to shed a new light on the regulation of root architecture during plant adaptation to different growth conditions.

A gene that underwent adaptive evolution, LAC2 (LACCASE), in Populus euphratica improves drought tolerance by improving water transport capacity

Drought severely limits plant development and growth; accordingly, plants have evolved strategies to prevent water loss and adapt to water deficit conditions. However, experimental cases that corroborate these evolutionary processes are limited. The LACCASEs (LACs) family is involved in various plant development and growth processes. Here, we performed an evolutionary analysis of LACs from Populus euphratica and characterized the functions of LACs in Arabidopsis and poplar. The results showed that in PeuLACs, multiple gene duplications led to apparent functional redundancy as the result of various selective pressures. Among them, PeuLAC2 underwent strong positive selection. Heterologous expression analyses showed that the overexpression of PeuLAC2 alters the xylem structure of plants, including thickening the secondary cell wall (SCW) and increasing the fiber cell length and stem tensile strength. Altogether, these changes improve the water transport capacity of plants. The analysis of the physiological experimental results showed that PeuLAC2-OE lines exhibited a stronger antioxidant response and greater drought tolerance than WT. Three genes screened by transcriptome analysis, NAC025, BG1, and UGT, that are associated with SCW synthesis and drought stress were all upregulated in the PeuLAC2-OE lines, implying that the overexpression of PeuLAC2 thickened the SCW, improved the water transport capacity of the plant, and further enhanced its drought tolerance. Our study highlights that genes that have undergone adaptive evolution may participate in the development of adaptive traits in P. euphratica and that PeuLAC2 could be a candidate gene for molecular genetic breeding in trees.

Re-routing of Sugar Catabolism Provides a Better Insight Into Fungal Flexibility in Using Plant Biomass-Derived Monomers as Substrates

The filamentous ascomycete Aspergillus niger has received increasing interest as a cell factory, being able to efficiently degrade plant cell wall polysaccharides as well as having an extensive metabolism to convert the released monosaccharides into value added compounds. The pentoses D-xylose and L-arabinose are the most abundant monosaccharides in plant biomass after the hexose D-glucose, being major constituents of xylan, pectin and xyloglucan. In this study, the influence of selected pentose catabolic pathway (PCP) deletion strains on growth on plant biomass and re-routing of sugar catabolism was addressed to gain a better understanding of the flexibility of this fungus in using plant biomass-derived monomers. The transcriptome, metabolome and proteome response of three PCP mutant strains, ΔlarAΔxyrAΔxyrB, ΔladAΔxdhAΔsdhA and ΔxkiA, grown on wheat bran (WB) and sugar beet pulp (SBP), was evaluated. Our results showed that despite the absolute impact of these PCP mutations on pure pentose sugars, they are not as critical for growth of A. niger on more complex biomass substrates, such as WB and SBP. However, significant phenotypic variation was observed between the two biomass substrates, but also between the different PCP mutants. This shows that the high sugar heterogeneity of these substrates in combination with the high complexity and adaptability of the fungal sugar metabolism allow for activation of alternative strategies to support growth.

A Semi-Dominant Mutation in OsCESA9 Improves Salt Tolerance and Favors Field Straw Decay Traits by Altering Cell Wall Properties in Rice

BACKGROUND

Cellulose synthase (CESA) mutants have potential use in straw processing due to their lower cellulose content, but almost all of the mutants exhibit defective phenotypes in plant growth and development. Balancing normal plant growth with reduced cellulose content remains a challenge, as cellulose content and normal plant growth are typically negatively correlated with one another.

RESULT

Here, the rice (Oryza sativa) semi-dominant brittle culm (sdbc) mutant Sdbc1, which harbors a substitution (D387N) at the first conserved aspartic acid residue of OsCESA9, exhibits lower cellulose content and reduced secondary wall thickness as well as enhanced biomass enzymatic saccharification compared with the wild type (WT). Further experiments indicated that the OsCESA9^D387N mutation may compete with the wild-type OsCESA9 for interacting with OsCESA4 and OsCESA7, further forming non-functional or partially functional CSCs. The OsCESA9/OsCESA9^D387N heterozygous plants increase salt tolerance through scavenging and detoxification of ROS and indirectly affecting related gene expression. They also improve rice straw return to the field due to their brittle culms and lower cellulose content without any negative effects in grain yield and lodging.

CONCLUSION

Hence, OsCESA9^D387N allele can improve rice salt tolerance and provide the prospect of the rice straw for biofuels and bioproducts due to its improved enzymatic saccharification.

Breeding Targets to Improve Biomass Quality in Miscanthus

Lignocellulosic crops are attractive bioresources for energy and chemicals production within a sustainable, carbon circular society. Miscanthus is one of the perennial grasses that exhibits great potential as a dedicated feedstock for conversion to biobased products in integrated biorefineries. The current biorefinery strategies are primarily focused on polysaccharide valorization and require severe pretreatments to overcome the lignin barrier. The need for such pretreatments represents an economic burden and impacts the overall sustainability of the biorefinery. Hence, increasing its efficiency has been a topic of great interest. Inversely, though pretreatment will remain an essential step, there is room to reduce its severity by optimizing the biomass composition rendering it more exploitable. Extensive studies have examined the miscanthus cell wall structures in great detail, and pinpointed those components that affect biomass digestibility under various pretreatments. Although lignin content has been identified as the most important factor limiting cell wall deconstruction, the effect of polysaccharides and interaction between the different constituents play an important role as well. The natural variation that is available within different miscanthus species and increased understanding of biosynthetic cell wall pathways have specified the potential to create novel accessions with improved digestibility through breeding or genetic modification. This review discusses the contribution of the main cell wall components on biomass degradation in relation to hydrothermal, dilute acid and alkaline pretreatments. Furthermore, traits worth advancing through breeding will be discussed in light of past, present and future breeding efforts.

Xylan Is Critical for Proper Bundling and Alignment of Cellulose Microfibrils in Plant Secondary Cell Walls

Plant biomass represents an abundant and increasingly important natural resource and it mainly consists of a number of cell types that have undergone extensive secondary cell wall (SCW) formation. These cell types are abundant in the stems of Arabidopsis, a well-studied model system for hardwood, the wood of eudicot plants. The main constituents of hardwood include cellulose, lignin, and xylan, the latter in the form of glucuronoxylan (GX). The binding of GX to cellulose in the eudicot SCW represents one of the best-understood molecular interactions within plant cell walls. The evenly spaced acetylation and 4-O-methyl glucuronic acid (MeGlcA) substitutions of the xylan polymer backbone facilitates binding in a linear two-fold screw conformation to the hydrophilic side of cellulose and signifies a high level of molecular specificity. However, the wider implications of GX-cellulose interactions for cellulose network formation and SCW architecture have remained less explored. In this study, we seek to expand our knowledge on this by characterizing the cellulose microfibril organization in three well-characterized GX mutants. The selected mutants display a range of GX deficiency from mild to severe, with findings indicating even the weakest mutant having significant perturbations of the cellulose network, as visualized by both scanning electron microscopy (SEM) and atomic force microscopy (AFM). We show by image analysis that microfibril width is increased by as much as three times in the severe mutants compared to the wild type and that the degree of directional dispersion of the fibrils is approximately doubled in all the three mutants. Further, we find that these changes correlate with both altered nanomechanical properties of the SCW, as observed by AFM, and with increases in enzymatic hydrolysis. Results from this study indicate the critical role that normal GX composition has on cellulose bundle formation and cellulose organization as a whole within the SCWs.

Polysaccharide Biosynthesis: Glycosyltransferases and Their Complexes

Glycosyltransferases (GTs) are enzymes that catalyze reactions attaching an activated sugar to an acceptor substrate, which may be a polysaccharide, peptide, lipid, or small molecule. In the past decade, notable progress has been made in revealing and cloning genes encoding polysaccharide-synthesizing GTs. However, the vast majority of GTs remain structurally and functionally uncharacterized. The mechanism by which they are organized in the Golgi membrane, where they synthesize complex, highly branched polysaccharide structures with high efficiency and fidelity, is also mostly unknown. This review will focus on current knowledge about plant polysaccharide-synthesizing GTs, specifically focusing on protein-protein interactions and the formation of multiprotein complexes.

Recent Advances in Food Emulsions and Engineering Foodstuffs Using Plant-Based Nanocelluloses

In this article, the application of nanocelluloses, especially cellulose nanofibrils and cellulose nanocrystals, as functional ingredients in foods is reviewed. These ingredients offer a sustainable and economic source of natural plant-based nanoparticles. Nanocelluloses are particularly suitable for altering the physicochemical, sensory, and nutritional properties of foods because of their ability to create novel structures. For instance, they can adsorb to air-water or oil-water interfaces and stabilize foams or emulsions, self-assemble in aqueous solutions to form gel networks, and act as fillers or fat replacers. The functionality of nanocelluloses can be extended by chemical functionalization of their surfaces or by using them in combination with other natural food ingredients, such as biosurfactants or biopolymers. As a result, it is possible to create stimuli-responsive, tailorable, and/or active functional biomaterials suitable for a range of foodapplications. In this article, we describe the chemistry, structure, and physicochemical properties of cellulose as well as their relevance for the application of nanocelluloses as functional ingredients in foods. Special emphasis is given to their use as particle stabilizers in Pickering emulsions, but we also discuss their potential application for creating innovative biomaterials with novel functional attributes, such as edible films and packaging. Finally, some of the challenges associated with using nanocelluloses in foods are critically evaluated, including their potential safety and consumer acceptance.

The Tetracentron genome provides insight into the early evolution of eudicots and the formation of vessel elements

Background

Tetracentron sinense is an endemic and endangered deciduous tree. It belongs to the Trochodendrales, one of four early diverging lineages of eudicots known for having vesselless secondary wood. Sequencing and resequencing of the T. sinense genome will help us understand eudicot evolution, the genetic basis of tracheary element development, and the genetic diversity of this relict species.

Results

Here, we report a chromosome-scale assembly of the T. sinense genome. We assemble the 1.07 Gb genome sequence into 24 chromosomes and annotate 32,690 protein-coding genes. Phylogenomic analyses verify that the Trochodendrales and core eudicots are sister lineages and showed that two whole-genome duplications occurred in the Trochodendrales approximately 82 and 59 million years ago. Synteny analyses suggest that the γ event, resulting in paleohexaploidy, may have only happened in core eudicots. Interestingly, we find that vessel elements are present in T. sinense, which has two orthologs of AtVND7, the master regulator of vessel formation. T. sinense also has several key genes regulated by or regulating TsVND7.2 and their regulatory relationship resembles that in Arabidopsis thaliana. Resequencing and population genomics reveals high levels of genetic diversity of T. sinense and identifies four refugia in China.

Conclusions

The T. sinense genome provides a unique reference for inferring the early evolution of eudicots and the mechanisms underlying vessel element formation. Population genomics analysis of T. sinense reveals its genetic diversity and geographic structure with implications for conservation.

Supplementary information

The online version contains supplementary material available at 10.1186/s13059-020-02198-7.

Exo- and endoglucanase production by Curvularia affinis using bean (Phaseolus vulgaris L.) waste biomass

Background

In many countries, agricultural residues are generated in large quantities, and most of these are underutilized and considered waste, especially in developing countries.

Result

In this study, Curvularia affinis was isolated from the leaves of Phaseolus vulgaris L. beans and identified using 18S rRNA sequencing. C. affinis was tested for exo- and endoglucanase production using biomass of bean waste compared with the use of microcrystalline cellulose (MCC) and carboxymethylcellulose (CMC) as its growth substrates. C. affinis was better able to produce exo- and endoglucanase enzymes on bean waste biomass than on MCC and CMC. The highest activities of exo- and endoglucanase were detected with substrate concentrations 2% using MCC or CMC and with 4% using bean waste. The optimum incubation period for enzymes activity was 6 days with MCC or CMC (activity was 5.90 and 2.99 U/g of exoglucanase and endoglucanase, respectively) and 8 days with bean waste where activity was 3.64 U/g and 0.92 U/g of exoglucanase and endoglucanase, respectively. Exo- and endoglucanase production showed the highest activity at pH 5–6. In process wherein surfactant (Tween 80) was used, the exoglucanase activity gradually increased from 5.92 U/g to 6.20 U/g and then decreased to 5.70 U/g at 0.50% compared with that using the MCC substrate. The exoglucanase activity gradually increased from 3.80 U/g at 0.0% to 4.12 U/g at 0.20% and then decreased to 3.01 U/g at 0.50% Tween 80 using bean waste. Pretreated bean biomass also yielded higher enzyme production than the non-pretreated biomass. Alkaline-pretreated biomass showed the highest enzyme production compared with acid-treated residues, followed by the H2O2-treated ones.

Conclusion

The study concluded that C. affinis produce exo- and endoglucanase enzymes using cheap and abundant biomass of beans. Moreover, optimization of enzymes indicated that pretreatment of biomass bean biomass is a good choice process for enhanced enzymes productivity.

Hydrogen sulfide promotes hypocotyl elongation via increasing cellulose content and changing the arrangement of cellulose fibrils in alfalfa

Hydrogen sulfide (H2S) is known to have positive physiological functions in plant growth, but limited data are available on its influence on cell walls. Here, we demonstrate a novel mechanism by which H2S regulates the biosynthesis and deposition of cell wall cellulose in alfalfa (Medicago sativa). Treatment with NaHS was found to increase the length of epidermal cells in the hypocotyl, and transcriptome analysis indicated that it caused the differential expression of numerous of cell wall-related genes. These differentially expressed genes were directly associated with the biosynthesis of cellulose and hemicellulose, and with the degradation of pectin. Analysis of cell wall composition showed that NaHS treatment increased the contents of cellulose and hemicellulose, but decreased the pectin content. Atomic force microscopy revealed that treatment with NaHS decreased the diameter of cellulose fibrils, altered the arrangement of the fibrillar bundles, and increased the spacing between the bundles. The dynamics of cellulose synthase complexes (CSCs) were closely related to cellulose synthesis, and NaHS increased the rate of mobility of the particles. Overall, our results suggest that the H2S signal enhances the plasticity of the cell wall by regulating the deposition of cellulose fibrils and by decreasing the pectin content. The resulting increases in cellulose and hemicellulose contents lead to cell wall expansion and cell elongation.

Comparative Transcriptomic Analysis of the Development of Sepal Morphology in Tomato (Solanum Lycopersicum L.)

Sepal is an important component of the tomato flower and fruit that typically protects the flower in bud and functions as a support for petals and fruits. Moreover, sepal appearance influences the commercial property of tomato nowadays. However, the phenotype information and development mechanism of the natural variation of sepal morphology in the tomato is still largely unexplored. To study the developmental mechanism and to determine key genes related to downward sepal in the tomato, we compared the transcriptomes of sepals between downward sepal (dsp) mutation and the wild-type by RNA sequencing and found that the differentially expressed genes were dominantly related to cell expansion, auxin, gibberellins and cytokinin. dsp mutation affected cell size and auxin, and gibberellins and cytokinin contents in sepals. The results showed that cell enlargement or abnormal cell expansion in the adaxial part of sepals in dsp. As reported, auxin, gibberellins and cytokinin were important factors for cell expansion. Hence, dsp mutation regulated cell expansion to control sepal morphology, and auxin, gibberellins and cytokinin may mediate this process. One ARF gene and nine SAUR genes were dramatically upregulated in the sepal of the dsp mutant, whereas seven AUX/IAA genes were significantly downregulated in the sepal of dsp mutant. Further bioinformatic analyses implied that seven AUX/IAA genes might function as negative regulators, while one ARF gene and nine SAUR genes might serve as positive regulators of auxin signal transduction, thereby contributing to cell expansion in dsp sepal. Thus, our data suggest that 17 auxin-responsive genes are involved in downward sepal formation in the tomato. This study provides valuable information for dissecting the molecular mechanism of sepal morphology control in the tomato.