Modification Of Plant Cell Walls Research Articles

Upgrading pectin methylation for consistently enhanced biomass enzymatic saccharification and cadmium phytoremediation in rice Ospmes site-mutants

Crop straws provide enormous biomass residues applicable for biofuel production and trace metal phytoremediation. However, as lignocellulose recalcitrance determines a costly process with potential secondary waste liberation, genetic modification of plant cell walls is deemed as a promising solution. Although pectin methylation plays an important role for plant cell wall construction and integrity, little is known about its regulation roles on lignocellulose hydrolysis and trace metal elimination. In this study, we initially performed a typical CRISPR/Cas9 gene-editing for site mutations of OsPME31, OsPME34 and OsPME79 in rice, and then determined significantly upgraded pectin methylation degrees in the young seedlings of three distinct site-mutants compared to their wild type. We then examined distinctively improved lignocellulose recalcitrance in three mutants including reduced cellulose levels, crystallinity and polymerization or raised hemicellulose deposition and cellulose accessibility, which led to specifically enlarged biomass porosity either for consistently enhanced biomass enzymatic saccharification under mild alkali pretreatments or for cadmium (Cd) accumulation up to 2.4-fold. Therefore, this study proposed a novel model to elucidate how pectin methylation could play a unique enhancement role for both lignocellulose enzymatic hydrolysis and Cd phytoremediation, providing insights into precise pectin modification for effective biomass utilization and efficient trace metal exclusion.

A comprehensive review on genetic modification of plant cell wall for improved saccharification efficiency.

The focus is now on harnessing energy from green sources through sustainable technology to minimize environmental pollution. Several crop residues including rice and wheat straw are having enormous potential to be used as lignocellulosic source material for bioenergy production. The lignocellulosic feedstock is primarily composed of cellulose, hemicellulose, and lignin cell wall polymers. The hemicellulose and lignin polymers induce crosslinks in the cell wall, by firmly associating with cellulose microfibrils, and thereby, denying considerable access of cellulose to cellulase enzymes. This issue has been addressed by various researchers through downregulating several genes associated in monolignol biosynthesis in Arabidopsis, Poplar, Rice and Switchgrass to increase ethanol recovery. Similarly, xylan biosynthetic genes are also targeted to genetically culminate its accumulation in the secondary cell walls. Regulation of cellulose synthases (CesA) proves to be an effective tool in addressing the negative impact of these two factors. Modification in the expression of cellulose synthase aids in reducing cellulose crystallinity as well as polymerisation degree which in turn increases ethanol recovery. The engineered bioenergy crops and various fungal strains with state of art biomass processing techniques presents the most recent integrative biotechnology model for cost effective green fuels generation along with production of key value-added products with minuscule disturbances in the environment. Plant breeding strategies utilizing the existing variability for biomass traits will be key in developing dual purpose varieties. For this purpose, reorientation of conventional breeding techniques for incorporating useful biomass traits will be effective.

Meloidogyne arenaria candidate effector MaMsp4 interacts with maize (Zea mays L.) proteins involved in host defense response and cell wall modifications

Background and aimsMeloidogyne arenaria is an economically important root-knot nematode species. Successful plant infection by nematode is facilitated by parasite effectors. This study aimed to characterize a candidate M. arenaria effector, indicate its molecular partners from maize, and analyze its role during infection.Material and methodsAt first, we performed EST database mining to find candidate effector protein from M. arenaria. The expression of its coding gene in nematode developmental stages was assessed using digital droplet PCR. Candidate effector molecular partners were determined using yeast two-hybrid screening of maize cDNA library and interactions were confirmed by co-immunoprecipitation after co-expression in Nicotiana benthamiana. Candidate effector and its molecular partners were GFP-fused and localization in N. benthamiana leaves was observed under confocal microscope. Then, expression level of genes encoding interacting proteins from maize was measured.ResultsMaMsp4 protein was evaluated as candidate effector in M. arenaria and the highest expression level of its coding gene was observed in stage J2. MaMsp4 maize molecular partners were indicated, interactions with beta-galactosidase 11, pectinesterase, S-adenosyl methionine decarboxylase 2, and ethanolamine-phosphate cytidylyltransferase were confirmed, and all proteins fused with GFP were detected in the apoplast and/or cytoplasm. Genes of beta-galactosidase 11 and pectinesterase, playing role in cell wall modifications, were overexpressed at 24 hpi followed by down-regulation at 7 dpi, while S-adenosyl methionine decarboxylase 2 and ethanolamine-phosphate cytidylyltransferase, involved in plant defense response, were suppressed at 7 dpi, without preceding up-regulation.ConclusionsWe have found that MaMsp4 interacts with plant proteins involved in plant cell wall modifications and defense mechanisms related to polyamines biosynthesis.

Deep into the Apoplast: Grapevine and Plasmopara viticola Proteomes Reveal the Secret Beneath Host and Pathogen Communication at 6 h After Contact.

The apoplast is the first hub of plant-pathogen communication where pathogen effectors are recognized by plant defensive proteins and cell receptors, thus activating signal transduction pathways. As a result of this first contact, the host triggers a defense response that involves the modulation of extra- and intracellular proteins. In grapevine-pathogen interactions, little is known about the trafficking between extra- and intracellular spaces. Grapevine is an economically important crop that relies on heavy fungicide use to control several diseases, and a deeper knowledge on the activation of its immune response is crucial to define new control strategies. In this study, we focused on the first 6 h postinoculation with Plasmopara viticola to evaluate grapevine proteome modulation in the apoplast. The in planta P. viticola proteome was also assessed to enable a deeper understanding of plant-pathogen communication. Our results showed that several plant mechanisms are triggered in the tolerant grapevine cultivar Regent after inoculation, such as oomycete recognition, plant cell wall modifications, reactive oxygen species signaling, and secretion of proteins to disrupt oomycete structures. On the other hand, P. viticola proteins related to development and virulence were the most predominant. This pioneer study highlights the early dynamics of cellular communication in grapevine defense that leads to the successful establishment of an incompatible interaction.

Modification of plant cell walls with hydroxycinnamic acids by BAHD acyltransferases.

In the last decade it has become clear that enzymes in the "BAHD" family of acyl-CoA transferases play important roles in the addition of phenolic acids to form ester-linked moieties on cell wall polymers. We focus here on the addition of two such phenolics-the hydroxycinnamates, ferulate and p-coumarate-to two cell wall polymers, glucuronoarabinoxylan and to lignin. The resulting ester-linked feruloyl and p-coumaroyl moities are key features of the cell walls of grasses and other commelinid monocots. The capacity of ferulate to participate in radical oxidative coupling means that its addition to glucuronoarabinoxylan or to lignin has profound implications for the properties of the cell wall - allowing respectively oxidative crosslinking to glucuronoarabinoxylan chains or introducing ester bonds into lignin polymers. A subclade of ~10 BAHD genes in grasses is now known to (1) contain genes strongly implicated in addition of p-coumarate or ferulate to glucuronoarabinoxylan (2) encode enzymes that add p-coumarate or ferulate to lignin precursors. Here, we review the evidence for functions of these genes and the biotechnological applications of manipulating them, discuss our understanding of mechanisms involved, and highlight outstanding questions for future research.

Functional characterization of ZmbHLH121, a bHLH transcription factor, focusing on Zea mays kernel development

Seed size is a result of the complex interactions among embryo, endosperm, seed coat and the mother plant. The final yield of maize depends on the kernel size and weight. Here we demonstrate that, ZmbHLH121, a maize bHLH transcription factor positively regulates kernel size and weight in maize. Over expression of ZmbHLH121 (ZmbHLH121-OE) produced larger and heavier kernels while ZmbHLH12-RNA interference (ZmbHLH121-RNAi) produced smaller and lighter kernels compared with non-transgenic plants. The biochemical studies suggested that, ZmbHLH121 is a transcriptional activator and binds to G-box cis-element ABA responsive element (ABRE). The expression analysis of ZmbHLH121indicated that, ZmbHLH121 expressed throughout the reproductive developmental stages of maize and higher expression was observed in the early kernel developmental stages. Transcriptome analysis revealed that, ZmbHLH121 regulated the transcription of downstream genes involved in plant cell death, cell differentiation and cell wall modifications. Therefore, our data established a molecular network of regulating kernel size and weight in maize and suggested ZmbHLH121 as a promising target of grain yield in maize.

Comparative genomics of plant pathogenic Diaporthe species and transcriptomics of Diaporthe caulivora during host infection reveal insights into pathogenic strategies of the genus

BackgroundDiaporthe caulivora is a fungal pathogen causing stem canker in soybean worldwide. The generation of genomic and transcriptomic information of this ascomycete, together with a comparative genomic approach with other pathogens of this genus, will contribute to get insights into the molecular basis of pathogenicity strategies used by D. caulivora and other Diaporthe species.ResultsIn the present work, the nuclear genome of D. caulivora isolate (D57) was resolved, and a comprehensive annotation based on gene expression and genomic analysis is provided. Diaporthe caulivora D57 has an estimated size of 57,86 Mb and contains 18,385 predicted protein-coding genes, from which 1501 encode predicted secreted proteins. A large array of D. caulivora genes encoding secreted pathogenicity-related proteins was identified, including carbohydrate-active enzymes (CAZymes), necrosis-inducing proteins, oxidoreductases, proteases and effector candidates. Comparative genomics with other plant pathogenic Diaporthe species revealed a core secretome present in all Diaporthe species as well as Diaporthe-specific and D. caulivora-specific secreted proteins. Transcriptional profiling during early soybean infection stages showed differential expression of 2659 D. caulivora genes. Expression patterns of upregulated genes and gene ontology enrichment analysis revealed that host infection strategies depends on plant cell wall degradation and modification, detoxification of compounds, transporter activities and toxin production. Increased expression of effectors candidates suggests that D. caulivora pathogenicity also rely on plant defense evasion. A high proportion of the upregulated genes correspond to the core secretome and are represented in the pathogen-host interaction (PHI) database, which is consistent with their potential roles in pathogenic strategies of the genus Diaporthe.ConclusionsOur findings give novel and relevant insights into the molecular traits involved in pathogenicity of D. caulivora towards soybean plants. Some of these traits are in common with other Diaporthe pathogens with different host specificity, while others are species-specific. Our analyses also highlight the importance to have a deeper understanding of pathogenicity functions among Diaporthe pathogens and their interference with plant defense activation.

Comparative Secretome Analyses of Trichoderma/Arabidopsis Co-cultures Identify Proteins for Salt Stress, Plant Growth Promotion, and Root Colonization

Numerous Trichoderma strains are beneficial for plants, promote their growth, and confer stress tolerance. A recently described novel Trichoderma strain strongly promotes the growth of Arabidopsis thaliana seedlings on media with 50 mM NaCl, while 150 mM NaCl strongly stimulated root colonization and induced salt-stress tolerance in the host without growth promotion. To understand the dynamics of plant-fungus interaction, we examined the secretome from both sides and revealed a substantial change under different salt regimes, and during co-cultivation. Stress-related proteins, such as a fungal cysteine-rich Kp4 domain-containing protein which inhibits plant cell growth, fungal WSC- and CFEM-domain-containing proteins, the plant calreticulin, and cell-wall modifying enzymes, disappear when the two symbionts are co-cultured under high salt concentrations. In contrast, the number of lytic polysaccharide monooxygenases increases, which indicates that the fungus degrades more plant lignocellulose under salt stress and its lifestyle becomes more saprophytic. Several plant proteins involved in plant and fungal cell wall modifications and root colonization are only found in the co-cultures under salt stress, while the number of plant antioxidant proteins decreased. We identified symbiosis- and salt concentration-specific proteins for both partners. The Arabidopsis PYK10 and a fungal prenylcysteine lyase are only found in the co-culture which promoted plant growth. The comparative analysis of the secretomes supports antioxidant enzyme assays and suggests that both partners profit from the interaction under salt stress but have to invest more in balancing the symbiosis. We discuss the role of the identified stage- and symbiosis-specific fungal and plant proteins for salt stress, and conditions promoting root colonization and plant growth.

Draft Genome Sequence of Oceanobacillus jordanicus Strain GSFE11, a Halotolerant Plant Growth-Promoting Bacterial Endophyte Isolated From the Jordan Valley.

The bacterium Oceanobacillus jordanicus strain GSFE11 is a halotolerant endophyte isolated from sterilized roots of Durum wheat (Triticum turgidum ssp. Durum) growing in hot and arid environments of Ghor Safi area in the Jordan Valley. The draft genome sequence and annotation of this plant growth-promoting endophytic bacterium are reported in this study. The draft genome sequence of Oceanobacillus jordanicus strain GSFE11 has 3 839 208 bp with a G + C content of 39.09%. A total of 3893 protein-coding genes and 68 RNA coding genes were predicted. Several putative genes that are involved in secretion and delivery systems, transport, adhesion, motility, membrane proteins, plant cell wall modification, and detoxification were identified, some are characteristics of endophytes lifestyle including genes that are involved in metabolism of carbohydrate, genes for xylose, fructose and chitin utilization, quinone cofactors biosynthesis, genes associated with nitrogen, sulfur, phosphate and iron acquisition, in addition to genes involved in the biosynthesis of plant hormone auxin. This study highlights the importance of using genome analysis and phylogenomic analysis to resolve the differences between closely related species, such analysis showed Oceanobacillus jordanicus strain GSFE11 to be a new species closely related to Oceanobacillus picturae (genome size 3.67 Mb), Oceanobacillus jordanicus has higher a number of predicted genes compared with Oceanobacillus picturae (3961 genes vs 3823 genes).

Lectin affinity-based glycoproteome analysis of the developing xylem in poplar

Glycosylation is a significant post-translational modification of the proteins, and some glycoproteins serve as the players in plant cell wall synthesis and modification. Wood is a highly developed cell wall organization, and protein glycosylation as a regulatory way might be involved in wood formation. Here, a lectin affinity-based glycoproteome was performed in stem developing xylem of poplar. After enrichment, trypsin digestion, LC-MS/MS analysis and peptide identification, we identified 154 glycoproteins from poplar developing xylem, which were classified into 9 functional groups mainly including protein acting on carbohydrates, oxido-reductase, proteases, and protein kinases. Further, N- and/or O-glycosylation sites of the identified proteins were analyzed by the bioinformatic tools, and deglycosylation experiments in the selected PtSOD and PtHAD proteins verified the reliability of the identified glycoproteins. Analysis of protein subcellular localization showed that total 63 percent of the identified glycoproteins were extracellular proteins or located in the plasma membrane. Poplar eFP and RT-qPCR data showed that a number of the genes encoding these glycoproteins such as laccase, peroxidase and cysteine protease, have highly preferential expression profiles in the developing xylem. Together with the literatures, most identified glycoproteins could be involved in wood cell wall synthesis and modification in poplar. Thus, our study provides some potential wood formation-related glycoproteins to be determined during tree stem development.

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

BackgroundAs 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.ResultsIn 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.ConclusionsThis 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.

The different root apex zones contribute to drought priming induced tolerance to a reoccurring drought stress in wheat

Drought priming is a promising approach to improve tolerance to further drought in wheat. The root apex plays important roles in drought however, its contribution to drought priming remains unknown. To provide mechanistic insights into this process, the transcriptomes and proteomes at three different zones along the root axis under drought stress were analyzed. Physiological assessment of root growth indicated that priming augmented roots growth in response to drought and also the levels of protective proline and glycine betaine. Scanning across the proximal to the distal zones of the root apex indicated increases the transcription of genes involved in primary and secondary metabolism. Conversely, genes related to translation, transcription, folding, sorting and degradation, replication and repair were increased in the apex compared to the proximal zone. A single drought episode suppressed their expression but prior drought priming served to maintain expression with recurrent drought stress. The differentially primed responses genes were mainly involved in the pathways related to plant hormone signaling, stress defense and cell wall modification. The prediction of regulatory hubs using Cytoscape implicated signaling components such as the ABA receptor PYL4 as influencing antioxidant status and the cell cycle. Based our integrative transcriptomic-proteomic assessments we present a model for drought priming protected plant hormone signaling transduction pathways to drive the cell cycle and cell wall loosening to confer beneficial effects on roots to counter the effects of drought. This model provides a theoretical basis for improvement of drought tolerance in wheat, via an increased understanding of drought priming induced drought tolerance.

Botrytis cinerea Transcriptome during the Infection Process of the Bryophyte Physcomitrium patens and Angiosperms.

Botrytis cinerea is a necrotrophic pathogen that causes grey mold in many plant species, including crops and model plants of angiosperms. B. cinerea also infects and colonizes the bryophyte Physcomitrium patens (previously Physcomitrella patens), which perceives the pathogen and activates defense mechanisms. However, these defenses are not sufficient to stop fungal invasion, leading finally to plant decay. To gain more insights into B. cinerea infection and virulence strategies displayed during moss colonization, we performed genome wide transcriptional profiling of B. cinerea during different infection stages. We show that, in total, 1015 B. cinerea genes were differentially expressed in moss tissues. Expression patterns of upregulated genes and gene ontology enrichment analysis revealed that infection of P. patens tissues by B. cinerea depends on reactive oxygen species generation and detoxification, transporter activities, plant cell wall degradation and modification, toxin production and probable plant defense evasion by effector proteins. Moreover, a comparison with available RNAseq data during angiosperm infection, including Arabidopsis thaliana, Solanum lycopersicum and Lactuca sativa, suggests that B. cinerea has virulence and infection functions used in all hosts, while others are more specific to P. patens or angiosperms.

Brassinosteroid overproduction improves lignocellulose quantity and quality to maximize bioethanol yield under green-like biomass process in transgenic poplar

BackgroundAs a leading biomass feedstock, poplar plants provide enormous lignocellulose resource convertible for biofuels and bio-chemicals. However, lignocellulose recalcitrance particularly in wood plants, basically causes a costly bioethanol production unacceptable for commercial marketing with potential secondary pollution to the environment. Therefore, it becomes important to reduce lignocellulose recalcitrance by genetic modification of plant cell walls, and meanwhile to establish advanced biomass process technology in woody plants. Brassinosteroids, plant-specific steroid hormones, are considered to participate in plant growth and development for biomass production, but little has been reported about brassinosteroids roles in plant cell wall assembly and modification. In this study, we generated transgenic poplar plant that overexpressed DEETIOLATED2 gene for brassinosteroids overproduction. We then detected cell wall feature alteration and examined biomass enzymatic saccharification for bioethanol production under various chemical pretreatments.ResultsCompared with wild type, the PtoDET2 overexpressed transgenic plants contained much higher brassinosteroids levels. The transgenic poplar also exhibited significantly enhanced plant growth rate and biomass yield by increasing xylem development and cell wall polymer deposition. Meanwhile, the transgenic plants showed significantly improved lignocellulose features such as reduced cellulose crystalline index and degree of polymerization values and decreased hemicellulose xylose/arabinose ratio for raised biomass porosity and accessibility, which led to integrated enhancement on biomass enzymatic saccharification and bioethanol yield under various chemical pretreatments. In contrast, the CRISPR/Cas9-generated mutation of PtoDET2 showed significantly lower brassinosteroids level for reduced biomass saccharification and bioethanol yield, compared to the wild type. Notably, the optimal green-like pretreatment could even achieve the highest bioethanol yield by effective lignin extraction in the transgenic plant. Hence, this study proposed a mechanistic model elucidating how brassinosteroid regulates cell wall modification for reduced lignocellulose recalcitrance and increased biomass porosity and accessibility for high bioethanol production.ConclusionsThis study has demonstrated a powerful strategy to enhance cellulosic bioethanol production by regulating brassinosteroid biosynthesis for reducing lignocellulose recalcitrance in the transgenic poplar plants. It has also provided a green-like process for biomass pretreatment and enzymatic saccharification in poplar and beyond.

Draft Genome Sequence of Pseudarthrobacter phenanthrenivorans Strain MHSD1, a Bacterial Endophyte Isolated From the Medicinal Plant Pellaea calomelanos.

Pseudarthrobacter phenanthrenivorans strain MHSD1 is a bacterial endophyte isolated from sterilized leaves of Pellaea calomelanos, a medicinal plant capable of growing in arid environments. Here, we report the draft genome sequence and annotation of this bacterial endophyte. The draft genome sequence of P. phenanthrenivorans strain MHSD1 has 4 450 468 bp with a G + C content of 65.30%. The National Center for Biotechnology Information Prokaryotic Genome Annotation Pipeline identified a total of 4004 protein-coding genes, 56 genes coding for RNAs, and 82 pseudogenes. Biosynthesis pathways for various phytohormones such as auxin, salicylic acid, ethylene, cytokinin, jasmonic acid, abscisic acid, and gibberellins were identified. Putative genes involved in various characteristics of bacterial endophyte lifestyle such as transport, motility, adhesion, membrane proteins, secretion and delivery systems, plant cell wall modification, and detoxification were identified. Phylogenomic analysis showed P. phenanthrenivorans strain MHSD1 to be a subspecies of P. phenanthrenivorans Sphe3.

Structural insights into the molecular mechanisms of pectinolytic enzymes

Pectinolytic enzymes produced by a large variety of organisms are well characterized concerning their physiological and pathological activities during modification or degradation of the complex plant cell wall. The exponential growth in structural information of these enzymes over past decades has rendered insights into functionally relevant residues, active sites and molecular basis of the enzymatic mechanism, which in turn, endorses its usage in industrial applications. This review highlights a comprehensive and up to date summary of structural information and the structure–function correlation of pectinolytic enzymes.

Distinct cellulose and callose accumulation for enhanced bioethanol production and biotic stress resistance in OsSUS3 transgenic rice

Genetic modification of plant cell walls is an effective approach to reduce lignocellulose recalcitrance in biofuel production, but it may affect plant stress response. Hence, it remains a challenge to reduce biomass recalcitrance and simultaneously enhance stress resistance. In this study, the OsSUS3-transgenic plants exhibited increased cell wall polysaccharides deposition and reduced cellulose crystallinity and xylose/arabinose proportion of hemicellulose, resulting in largely enhanced biomass saccharification and bioethanol production. Additionally, strengthening of the cell wall also contributed to plant biotic resistance. Notably, the transgenic plants increased stress-induced callose accumulation, and promoted the activation of innate immunity, leading to greatly improved multiple resistances to the most destructive diseases and a major pest. Hence, this study demonstrates a significant improvement both in bioethanol production and biotic stress resistance by regulating dynamic carbon partitioning for cellulose and callose biosynthesis in OsSUS3-transgenic plants. Meanwhile, it also provides a potential strategy for plant cell wall modification.

Genome-Wide Identification, Characterization and Expression Patterns of the Pectin Methylesterase Inhibitor Genes in Sorghum bicolor.

Cell walls are basically complex with dynamic structures that are being involved in several growth and developmental processes, as well as responses to environmental stresses and the defense mechanism. Pectin is secreted into the cell wall in a highly methylesterified form. It is able to perform function after the de-methylesterification by pectin methylesterase (PME). Whereas, the pectin methylesterase inhibitor (PMEI) plays a key role in plant cell wall modification through inhibiting the PME activity. It provides pectin with different levels of degree of methylesterification to affect the cell wall structures and properties. The PME activity was analyzed in six tissues of Sorghum bicolor, and found a high level in the leaf and leaf sheath. PMEI families have been identified in many plant species. Here, a total of 55 pectin methylesterase inhibitor genes (PMEIs) were identified from S. bicolor whole genome, a more detailed annotation of this crop plant as compared to the previous study. Chromosomal localization, gene structures and sequence characterization of the PMEI family were analyzed. Moreover, cis-acting elements analysis revealed that each PMEI gene was regulated by both internal and environmental factors. The expression patterns of each PMEI gene were also clustered according to expression pattern analyzed in 47 tissues under different developmental stages. Furthermore, some SbPMEIs were induced when treated with hormonal and abiotic stress. Taken together, these results laid a strong foundation for further study of the functions of SbPMEIs and pectin modification during plant growth and stress responses of cereal.

Overproduction of fungal endo-β-1,4-glucanase leads to characteristic lignocellulose modification for considerably enhanced biomass enzymatic saccharification and bioethanol production in transgenic rice straw

Genetic modification of plant cell walls has been considered to reduce lignocellulose recalcitrance for enhanced biomass enzymatic saccharification and biofuel production in bioenergy crops. Although endo-β-1,4-glucanase (EG II) secreted by fungi has been broadly applied for enzymatic hydrolysis of cellulose, it remains to explore its role in cellulose modification when the EG II gene is overexpressed in plant. In this study, we selected transgenic rice plants that overproduced Trichoderma reesei EG II enzyme specifically deposited into plant cell walls, and then examined much higher enzymatic activities by fourfold to fivefold in transgenic young seedlings than those of wild type in vitro. Notably, despite slightly altered cell wall compositions and polymer interlinkages relative to the wild type, the transgenic mature rice straw exhibited significantly reduced cellulose DP and CrI values and hemicellulosic Xyl/Ara ratio, leading to much increased biomass porosity. These should play integrated impact for enhanced biomass enzymatic saccharification and bioethanol production even under mild alkali pretreatment. Therefore, the results suggested that the EG II deposition should have enzymatic activity specific for minor-modification of cellulose microfibrils in transgenic rice plants. It has also provided a potential strategy for mild cell wall modification and optimal biomass process in rice and other bioenergy crops.

Quantitative proteomics analysis reveals resistance differences of banana cultivar ‘Brazilian’ to Fusarium oxysporum f. sp. cubense races 1 and 4

Banana Fusarium wilt, caused by Fusarium oxysporum f. sp. cubense (Foc), is one of the most devastating diseases in banana production. Foc is classified into three physiological races. However, the resistance mechanisms of banana against different Foc races are poorly understood. In this study, we performed a comparative proteomics analysis to investigate the resistance mechanisms of ‘Brazilian’ against Foc1 and Foc4. The proteomes of ‘Brazilian’ roots inoculated with Foc1 and Foc4 and mock inoculated control at 48 h were analyzed using TMT based quantitative analysis technique. A total of 7325 unique protein species were identified, of which 689, 744, and 1222 protein species were differentially accumulated in Foc1 vs. CK, Foc4 vs. CK, and Foc1 vs. Foc4, respectively. The differential accumulations of candidate protein species were further confirmed by RT-qPCR, PRM, and physiological and biochemical assays. Bioinformatics analysis revealed that the differentially abundance protein species (DAPS) related to pattern recognition receptors, plant cell wall modification, redox homeostasis, and defense responses were differentially accumulated after Foc1 and Foc4 infection, suggesting that ‘Brazilian’ differed in resistance to the two Foc races. Our study lay the foundation for an in-depth understanding of the interaction between bananas and Foc at the proteome level. SignificanceThe banana fusarium wilt disease is one of the most destructive disease of banana and is caused by Fusarium oxysporum f. sp. cubense (Foc). Foc is classified into three physiological races, namely, Foc1, Foc2, and Foc4. Among these races, Foc1 and Foc4 are widely distributed in south China and significantly lose yield. Although both physiological races (Foc1 and Foc4) can invade the Cavendish banana cultivar ‘Brazilian’, they have significant pathogenicity differences. Unfortunately, how the resistance differences are produced between two races is still largely unclear to date. In this study, we addressed this issue by performing TMT-based comparative quantitative proteomics analysis of ‘Brazilian’ roots after inoculation with Foc1 and Foc4 as well as sterile water as the control. We revealed that the series of protein species associated with pattern recognition receptors, plant cell wall modification, redox homeostasis, pathogenesis, phytohormones and signal transduction, plant secondary metabolites and programmed cell death etc. were involved in the response to Foc infection. Notably, the potential role of lipid signaling in banana defense against Foc are not reported previously but rather unveiled for the first time in this study. The current study represents the most extensive analysis of the protein profile of ‘Brazilian’ in response to Foc inoculation and includes for the first time the results from comparison quantitative proteomics analysis between plants inoculated with a pathogenic strain Foc4 and a nonpathogenic strain Foc1 of ‘Brazilian’, which will lay the foundation for an in-depth understanding of the interaction between bananas and Foc at the proteome level.