Biopolyester Membranes of Plants: Cutin and Suberin

Plant epithelia: What is the role of the mortar in the wall?

In a growing plant root, the inner vascular system is sealed off by an epithelium, the endodermis. The space between all of the cells in the endodermal layer is filled with an impermeable mass called the Casparian strip, which closes the spaces between cells in the endodermal layer. The role of the Casparian strip has been proposed to prevent backflow of water and nutrients into the soil, but as mutant plants lacking the Casparian strip only have weak phenotypes, the view that it serves an essential function in plants has been challenged. In an accompanying paper, it is shown that loss of the Casparian strip impacts the ability of the plant to take up ammonium and allocate it to the shoots.

What is the function of the Casparian strip, a plant structure first described in 1865? This Primer explores the implications of a new study which reports that loss of the Casparian strip in root endodermis affects the ability of the plant to take up ammonium and allocate it to the shoots.

Outstanding Toughness of Cherry Bark Achieved by Helical Spring Structure of Rigid Cellulose Fiber Combined with Flexible Layers of Lipid Polymers

Cellulose, a main component of cell walls, generally makes materials hard and brittle. However, an ultratough, cellulosic material is found in nature: cherry bark. Surprisingly, it elongates by more than twice of its initial length and behaves as a plastic film during stretching. This amazing mechanical property is achieved by a well-designed cell wall structure; cellulose fibers are folded like helical springs, covered by multiple flexible layers of lipid polymers.

QUANTIFICATION OF THE CONTRIBUTION OF FILLER CHARACTERISTICS TO NATURAL RUBBER REINFORCEMENT USING PRINCIPAL COMPONENT ANALYSIS

Practical statistical models were developed to quantify individual contributions from characteristics of conventional and non-conventional fillers and predict resulting mechanical properties of both hevea and guayule natural rubber composites. Carbon black N330 and four different agro-industrial residues, namely, eggshells, carbon fly ash, processing tomato peels, and guayule bagasse, were used in this study. Filler characteristics were used as explanatory variables in multiple linear regression analyses. Principal component analysis was used to evaluate correlations among explanatory variables based on their correlation matrices and to transform them into a new set of independent variables, which were then used to generate reliable regression models. Surface area, dispersive component of surface energy, carbon black, and waste-derived filler loading were found to have almost equal importance in the prediction of composite properties. However, models developed for ultimate elongation poorly explained variability, indicating the dependence of this property on other variables. Agro-industrial residues could potentially serve as more sustainable fillers for polymer composites than conventional fillers. This new modeling approach for polymer composites allows the performance of a wide range of different waste-derived fillers to be predicted with minimum laboratory work, facilitating the optimization of compound recipes to address specific product requirements.

Multifunctional Roles of Plant Cuticle During Plant-Pathogen Interactions

In land plants the cuticle is the outermost layer interacting with the environment. This lipophilic layer comprises the polyester cutin embedded in cuticular wax; and it forms a physical barrier to protect plants from desiccation as well as from diverse biotic and abiotic stresses. However, the cuticle is not merely a passive, mechanical shield. The increasing research on plant leaves has addressed the active roles of the plant cuticle in both local and systemic resistance against a variety of plant pathogens. Moreover, the fruit cuticle also serves as an important determinant of fruit defense and quality. It shares features with those of vegetative organs, but also exhibits specific characteristics, the functions of which gain increasing attention in recent years. This review describes multiple roles of plant cuticle during plant-pathogen interactions and its responses to both leaf and fruit pathogens. These include the dynamic changes of plant cuticle during pathogen infection; the crosstalk of cuticle with plant cell wall and diverse hormone signaling pathways for plant disease resistance; and the major biochemical, molecular, and cellular mechanisms that underlie the roles of cuticle during plant-pathogen interactions. Although research developments in the field have greatly advanced our understanding of the roles of plant cuticle in plant defense, there still remain large gaps in our knowledge. Therefore, the challenges thus presented, and future directions of research also are discussed in this review.

Mechanical properties of cuticles and their primary determinants

Cuticles envelope primary surfaces of the above-ground portion of plants. They function as barriers to water movement and to gas exchange, and in pathogen defense. To serve as a barrier on growing organs, cuticles must remain intact but at the same time must accommodate ongoing growth. Minimizing cuticle failure has stimulated significant research on the cuticle's mechanical properties. The objective here is to review the literature on the mechanical properties of isolated fruit and leaf cuticles. Cuticles are viscoelastic polymers. Viscoelasticity results mainly from the cutin matrix. Impregnation by waxes, flavonoids, and cutan increases stiffness and strength but decreases extensibility. On the inner side, the cutin matrix is impregnated by cell wall polysaccharides, which are responsible for its elastic behavior. Across species, the maximum forces sustainable by hydrated cuticles in uniaxial tensile tests averaged 0.82 N (range 0.15-1.63 N), the maximum stresses averaged 13.2 MPa (range 2.0-29.0 MPa), the maximum strains averaged 8.8% (range 1.6-28.0%), and the moduli of elasticity averaged 224 MPa (range 60-730 MPa). Among the environmental factors, high temperature and hydration both decreased stiffness. Therefore, the mechanical properties of cuticles in vivo depend largely on the relative proportions of their constituents. These proportions change during development and are also affected by environmental factors such as temperature.

Comparative Morphology, Transcription, and Proteomics Study Revealing the Key Molecular Mechanism of Camphor on the Potato Tuber Sprouting Effect

Sprouting regulation in potato tubers is important for improving commercial value and producing new plants. Camphor shows flexible inhibition of tuber sprouting and prolongs the storage period of potato, but its underlying mechanism remains unknown. The results of the present study suggest that camphor inhibition caused bud growth deformities and necrosis, but after moving to more ventilated conditions, new sprouts grew from the bud eye of the tuber. Subsequently, the sucrose and fructose contents as well as polyphenol oxidase (PPO) activity were assessed after camphor inhibition. Transcription and proteomics data from dormancy (D), sprouting (S), camphor inhibition (C), and recovery sprouting (R) samples showed changes in the expression levels of approximately 4000 transcripts, and 700 proteins showed different abundances. KEGG (Kyoto encyclopaedia of genes and genomes) pathway analysis of the transcription levels indicated that phytohormone synthesis and signal transduction play important roles in tuber sprouting. Camphor inhibited these processes, particularly for gibberellic acid, brassinosteroids, and ethylene, leading to dysregulation of physiological processes such as cutin, suberine and wax biosynthesis, fatty acid elongation, phenylpropanoid biosynthesis, and starch and sucrose metabolism, resulting in bud necrosis and prolonged storage periods. The KEGG pathway correlation between transcripts and proteins revealed that terpenoid backbone biosynthesis and plant-pathogen interaction pathways showed significant differences in D vs. S samples, but 13 pathways were remarkably different in the D vs. C groups, as camphor inhibition significantly increased both the transcription levels and protein abundance of pathogenesis-related protein PR-10a (or STH-2), the pathogenesis-related P2-like precursor protein, and the kirola-like protein as compared to sprouting. In recovery sprouting, these genes and proteins were decreased at both the transcriptional level and in protein abundance. It was important to find that the inhibitory effect of camphor on potato tuber sprout was reversible, revealing the action mechanism was similar to resistance to pathogen infection. The present study provides a theoretical basis for the application of camphor in prolonging seed potato storage.

Fine Mapping of a Gene (ER4.1) that Causes Epidermal Reticulation of Tomato Fruit and Characterization of the Associated Transcriptome

The hydrophobic cuticle that covers the surface of tomato (Solanum lycopersicum) fruit plays key roles in development and protection against biotic and abiotic stresses, including water loss, mechanical damage, UV radiation, pathogens, and pests. However, many details of the genes and regulatory mechanisms involved in cuticle biosynthesis in fleshy fruits are not well understood. In this study, we describe a novel tomato fruit phenotype, characterized by epidermal reticulation (ER) of green fruit and a higher water loss rate than wild type (WT) fruit. The ER phenotype is controlled by a single gene, ER4.1, derived from an introgressed chromosomal segment from the wild tomato species S. pennellii (LA0716). We performed fine mapping of the single dominant gene to an ~300 kb region and identified Solyc04g082540, Solyc04g082950, Solyc04g082630, and Solyc04g082910as potential candidate genes for the ER4.1 locus, based on comparative RNA-seq analysis of ER and WT fruit peels. In addition, the transcriptome analysis revealed that the expression levels of genes involved in cutin, wax and flavonoid biosynthesis were altered in the ER fruit compared with WT. This study provides new insights into the regulatory mechanisms and metabolism of the fruit cuticle.

Cuticular Waxes of Arabidopsis thaliana Shoots: Cell-Type-Specific Composition and Biosynthesis

It is generally assumed that all plant epidermis cells are covered with cuticles, and the distinct surface geometries of pavement cells, guard cells, and trichomes imply functional differences and possibly different wax compositions. However, experiments probing cell-type-specific wax compositions and biosynthesis have been lacking until recently. This review summarizes new evidence showing that Arabidopsis trichomes have fewer wax compound classes than pavement cells, and higher amounts of especially long-chain hydrocarbons. The biosynthesis machinery generating this characteristic surface coating is discussed. Interestingly, wax compounds with similar, long hydrocarbon chains had been identified previously in some unrelated species, not all of them bearing trichomes.

Suberin Fatty Acids from Outer Birch Bark: Isolation and Physical Material Characterization

The isolation and physical material properties of suberin fatty acids (SFAs) were investigated with special reference to their potential applications as novel pharmaceutical excipients. SFAs were isolated from outer birch bark (OBB) with a new extractive hydrolysis method. The present simplified isolation process resulted in a moderate batch yield and chemical purity of SFAs, but further development is needed for establishing batch-to-batch variation. Cryogenic milling was the method of choice for the particle size reduction of SFAs powder. The cryogenically milled SFAs powder exhibited a semicrystalline structure with apparent microcrystalline domains within an amorphous fatty acids matrix. The thermogravimetric analysis (TGA) of SFAs samples showed a good thermal stability up to 200 °C, followed by a progressive weight loss, reaching a plateau at about 95% volatilization at about 470 °C. The binary blends of SFAs and microcrystalline cellulose (MCC; Avicel PH 101) in a ratio of 25:75 (w/w) displayed good powder flow and tablet compression properties. The corresponding theophylline-containing tablets showed sustained or prolonged-release characteristics. The physicochemical and bulk powder properties of SFAs isolated from OBB are auspicious in terms of potential pharmaceutical excipient applications.

Molecular Features of Humic Acids and Fulvic Acids from Contrasting Environments

Insight in the molecular structure of humic acid (HA) and fulvic acid (FA) can contribute to identify relationships between their molecular properties, and further our quantitative abilities to model important organic matter functions such as metal complexation and association with mineral surfaces. Pyrolysis gas chromatography/mass spectrometry (Py-GC-MS) is used to compare the molecular composition of HA and FA. A systematic comparison was obtained by using samples from different environmental sources, including solid and aqueous samples from both natural and waste sources. The chemical signature of the pyrolysates was highly variable and no significant difference between HA and FA was found for major chemical groups, that is, carbohydrates, phenols, benzenes, and lignin phenols, together accounting for 62-96% of all quantified pyrolysis products. However, factor analysis showed that within each sample, FAs consistently differed from corresponding HAs in a larger contribution from mono- and polyaromatic hydrocarbons and heterocyclic hydrocarbons, together accounting for 3.9-44.5% of the quantified pyrolysis products. This consistent difference between FAs and corresponding HAs, suggests that their binding properties may, in addition to the carboxyl and phenolic groups, be influenced by the molecular architecture. Py-GC-MS may thus contribute to identify relationships between HA and FA binding- and molecular-properties.

Investigation of the Fusarium virguliforme Transcriptomes Induced during Infection of Soybean Roots Suggests that Enzymes with Hydrolytic Activities Could Play a Major Role in Root Necrosis

Sudden death syndrome (SDS) is caused by the fungal pathogen, Fusarium virguliforme, and is a major threat to soybean production in North America. There are two major components of this disease: (i) root necrosis and (ii) foliar SDS. Root symptoms consist of root necrosis with vascular discoloration. Foliar SDS is characterized by interveinal chlorosis and leaf necrosis, and in severe cases by flower and pod abscission. A major toxin involved in initiating foliar SDS has been identified. Nothing is known about how root necrosis develops. In order to unravel the mechanisms used by the pathogen to cause root necrosis, the transcriptome of the pathogen in infected soybean root tissues of a susceptible cultivar, 'Essex', was investigated. The transcriptomes of the germinating conidia and mycelia were also examined. Of the 14,845 predicted F. virguliforme genes, we observed that 12,017 (81%) were expressed in germinating conidia and 12,208 (82%) in mycelia and 10,626 (72%) in infected soybean roots. Of the 10,626 genes induced in infected roots, 224 were transcribed only following infection. Expression of several infection-induced genes encoding enzymes with oxidation-reduction properties suggests that degradation of antimicrobial compounds such as the phytoalexin, glyceollin, could be important in early stages of the root tissue infection. Enzymes with hydrolytic and catalytic activities could play an important role in establishing the necrotrophic phase. The expression of a large number of genes encoding enzymes with catalytic and hydrolytic activities during the late infection stages suggests that cell wall degradation could be involved in root necrosis and the establishment of the necrotrophic phase in this pathogen.

Synthesis of copolyesters with bio-based lauric diacid: structure and physico-mechanical studies

Copolyesters developed from bio-based long-chain dicarboxylic acid show promising mechanical properties that are helpful for their application as biodegradable materials.

Epiallelic changes in known stress-responsive genes under extreme drought conditions in Brassica juncea (L.) Czern

Under severe drought conditions, Brassica juncea shows differential methylation and demethylation events, such that certain epialleles are silenced and some are activated. The plant employed avoidance strategy by delaying apoptosis through the activation of several genes. Harsh environmental conditions pose serious threat to normal growth and development of crops, sometimes leading to their death. However, plants have developed an essential mechanism of modulation of gene activities by epigenetic modifications. Brassica juncea is an important oilseed crop contributing effectively to the economy of India. In the present investigation, we studied the changes in the methylation level of various stress-responsive genes of B. juncea variety RH30 by methylation-dependent immune-precipitation-chip in response to severe drought. On the basis of changes in the number of differential methylation regions in response to drought, the promoter regions were designated as hypermethylated and hypomethylated. Gene body methylation increased in all the genes, whereas promoter methylation was dependent on the function of the gene. Overall, the genes responsible for delaying apoptosis were hypomethylated and many genes responsible for normal routine activities were hypermethylated at promoter regions, thereby suggesting that these may be suspending the activities under harsh conditions.

Molecular composition of soil organic matter with land-use change along a bi-continental mean annual temperature gradient

Soil organic matter (SOM) is critical for maintaining soil fertility and long-term agricultural sustainability. The molecular composition of SOM is likely altered due to global climate and land-use change; but rarely are these two aspects studied in tandem. Here we used molecular-level techniques to examine SOM composition along a bi-continental (from North to South America) mean annual temperature (MAT) gradient from seven native grassland/forest and cultivated/pasture sites. Biomarker methods included solvent extraction, base hydrolysis and cupric (II) oxide oxidation for the analysis of free lipids of plant and microbial origin, ester-bound lipids from cutin and suberin, and lignin-derived phenols, respectively. Solid-state ¹³C nuclear magnetic resonance (NMR) was used to examine the overall composition of SOM. Soil cultivation was found to increase the amount of microbial-derived compounds at warmer temperatures (up to 17% increase). The cultivated soils were characterized by much lower contributions of plant-derived SOM components compared to the native soils (up to 64% lower at the coldest site). In addition, cultivation caused an increase in lignin and cutin degradation (up to 68 and 15% increase, respectively), and an increase in the amount of suberin-derived inputs (up to 54% increase). Clear differences in the molecular composition of SOM due to soil cultivation were observed in soils of varying mineral composition and were attributed to disturbance, different vegetation inputs, soil aggregate destruction and MAT. A high organic allophanic tropical soil was characterized by its protection of carbohydrates and nitrogen-containing compounds. The conversion of native to cultivated land shows significant shifts in the degradation stage of SOM. In particular, cutin-derived compounds which are believed to be part of the stable SOM pool may undergo enhanced degradation with long-term cultivation and disruption of soil aggregates. On a per year basis, the total amount of cutin decreased only at the two forest sites that were converted to pasture, likely due to cutin degradation or to changes in vegetation and litter quality associated with land-use change. Overall, our study highlights that the implementation of different agricultural management practices enhances the degradation of recalcitrant SOM compounds that may become a source of atmospheric CO₂ with increasing land-use and climate change.

Fatty acid ω-hydroxylases from Solanum tuberosum

Potato StCYP86A33 complements the Arabidopsis AtCYP86A1 mutant, horst - 1. Suberin is a cell-wall polymer that comprises both phenolic and aliphatic components found in specialized plant cells. Aliphatic suberin is characterized by bi-functional fatty acids, typically ω-hydroxy fatty acids and α,ω-dioic acids, which are linked via glycerol to form a three-dimensional polymer network. In potato (Solanum tuberosum L.), over 65 % of aliphatics are either ω-hydroxy fatty acids or α,ω-dioic acids. Since the biosynthesis of α,ω-dioic acids proceeds sequentially through ω-hydroxy fatty acids, the formation of ω-hydroxy fatty acids represents a significant metabolic commitment during suberin deposition. Four different plant cytochrome P450 subfamilies catalyze ω-hydroxylation, namely, 86A, 86B, 94A, and 704B; though to date, only a few members have been functionally characterized. In potato, CYP86A33 has been identified and implicated in suberin biosynthesis through reverse genetics (RNAi); however, attempts to express the CYP86A33 protein and characterize its catalytic function have been unsuccessful. Herein, we describe eight fatty acid ω-hydroxylase genes (three CYP86As, one CYP86B, three CYP94As, and a CYP704B) from potato and demonstrate their tissue expression. We also complement the Arabidopsis cyp86A1 mutant horst-1 using StCYP86A33 under the control of the Arabidopsis AtCYP86A1 promoter. Furthermore, we provide preliminary analysis of the StCYP86A33 promoter using a hairy root transformation system to monitor pStCYP86A33::GUS expression constructs. These data confirm the functional role of StCYP86A33 as a fatty acid ω-hydroxylase, and demonstrate the utility of hairy roots in the study of root-specific genes.

Complete genome sequence of Pseudomonas citronellolis P3B5, a candidate for microbial phyllo-remediation of hydrocarbon-contaminated sites

Pseudomonas citronellolis is a Gram negative, motile gammaproteobacterium belonging to the order Pseudomonadales and the family Pseudomonadaceae. We isolated strain P3B5 from the phyllosphere of basil plants (Ocimum basilicum L.). Here we describe the physiology of this microorganism, its full genome sequence, and detailed annotation. The 6.95 Mbp genome contains 6071 predicted protein coding sequences and 96 RNA coding sequences. P. citronellolis has been the subject of many studies including the investigation of long-chain aliphatic compounds and terpene degradation. Plant leaves are covered by long-chain aliphates making up a waxy layer that is associated with the leaf cuticle. In addition, basil leaves are known to contain high amounts of terpenoid substances, hinting to a potential nutrient niche that might be exploited by P. citronellolis. Furthermore, the isolated strain exhibited resistance to several antibiotics. To evaluate the potential of this strain as source of transferable antibiotic resistance genes on raw consumed herbs we therefore investigated if those resistances are encoded on mobile genetic elements. The availability of the genome will be helpful for comparative genomics of the phylogenetically broad pseudomonads, in particular with the sequence of the P. citronellolis type strain PRJDB205 not yet publicly available. The genome is discussed with respect to a phyllosphere related lifestyle, aliphate and terpenoid degradation, and antibiotic resistance.

Lignin Valorization through Catalytic Lignocellulose Fractionation: A Fundamental Platform for the Future Biorefinery

Current processes for the fractionation of lignocellulosic biomass focus on the production of high-quality cellulosic fibers for paper, board, and viscose production. The other fractions that constitute a major part of lignocellulose are treated as waste or used for energy production. The transformation of lignocellulose beyond paper pulp to a commodity (e.g., fine chemicals, polymer precursors, and fuels) is the only feasible alternative to current refining of fossil fuels as a carbon feedstock. Inspired by this challenge, scientists and engineers have developed a plethora of methods for the valorization of biomass. However, most studies have focused on using one single purified component from lignocellulose that is not currently generated by the existing biomass fractionation processes. A lot of effort has been made to develop efficient methods for lignin depolymerization. The step to take this fundamental research to industrial applications is still a major challenge. This review covers an alternative approach, in which the lignin valorization is performed in concert with the pulping process. This enables the fractionation of all components of the lignocellulosic biomass into valorizable streams. Lignocellulose fractions obtained this way (e.g., lignin oil and glucose) can be utilized in a number of existing procedures. The review covers historic, current, and future perspectives, with respect to catalytic lignocellulose fractionation processes.

Improvement of soybean transformation via Agrobacterium tumefaciens methods involving α-aminooxyacetic acid and sonication treatments enlightened by gene expression profile analysis

KEY MESSAGE

Antagonists and sonication treatment relieved the structural barriers of Agrobacterium entering into cells; hindered signal perception and transmission; alleviated defense responses and increased cell susceptibility to Agrobacterium infection. Soybean gene expression analysis was performed to elucidate the general response of soybean plant to Agrobacterium at an early stage of infection. Agrobacterium infection stimulated the PAMPs-triggered immunity (BRI1, BAK1, BZR1, FLS2 and EFR) and effector-triggered immunity (RPM1, RPS2, RPS5, RIN4, and PBS1); up-regulated the transcript factors (WRKY25, WRKY29, MEKK1P, MKK4/5P and MYC2) in MAPK pathway; strengthened the biosynthesis of flavonoid and isoflavonoid in the second metabolism; finally led to a fierce defense response of soybean to Agrobacterium infection and thereby lower transformation efficiency. To overcome it, antagonist α-aminooxyacetic acid (AOA) and sonication treatment along with Agrobacterium infection were applied. This novel method dramatically decreased the expression of genes coding for F3'H, HCT, β-glucosidase and IF7GT, etc., which are important for isoflavone biosynthesis or the interconversion of aglycones and glycon; genes coding for peroxidase, FLS2, PBS1 and transcription factor MYC2, etc., which are important components in plant-pathogen interaction; and genes coding for GPAT and α-L-fucosidase, which are important in polyesters formation in cell membrane and the degradation of fucose-containing glycoproteins and glycolipids on the external surface of cell membrane, respectively. This analysis implied that AOA and sonication treatment not only relieved the structural membrane barriers of Agrobacterium entering into cells, but also hindered the perception of 'invasion' signal on cell membrane and intercellular signal transmission, thus effectively alleviated the defense responses and increased the cell susceptibility to Agrobacterium infection. All these factors benefit the transformation process; other measures should also be further explored to improve soybean transformation.

The Plant Polyester Cutin: Biosynthesis, Structure, and Biological Roles

Cutin, a polyester composed mostly of oxygenated fatty acids, serves as the framework of the plant cuticle. The same types of cutin monomers occur across most plant lineages, although some evolutionary trends are evident. Additionally, cutins from some species have monomer profiles that are characteristic of the related polymer suberin. Compositional differences likely have profound structural consequences, but little is known about cutin's molecular organization and architectural heterogeneity. Its biological importance is suggested by the wide variety of associated mutants and gene-silencing lines that show a disruption of cuticular integrity, giving rise to numerous physiological and developmental abnormalities. Mapping and characterization of these mutants, along with suppression of gene paralogs through RNA interference, have revealed much of the biosynthetic pathway and several regulatory factors; however, the mechanisms of cutin polymerization and its interactions with other cuticle and cell wall components are only now beginning to be resolved.

Effect of Coating of Aloe Vera Gelon Shelf Life of Grapes

The present study had been conducted to study the shelf life of grapes with coatings of Aloe Vera suspended in water with concentrations of 0, 10, 20 and 30 per cent Aloe veraand was stored in poly packaging and open plates under different temperatures of 0⁰C and 30⁰C in refrigerator and incubator. The data was compared with the original shelf life of grapes to determine the efficiency of the Aloe Vera coating. Aloe Vera based coatings provided good gloss and 20 per cent coating concentration gave the best visual and physicochemical results. It was found that 20 per cent coating concentration of Aloe Vera is the most effective and appropriate for the extension of shelf life of grapes.It was also found that the use of low temperature storage in combination with edible coating and packaging extends marketability by reducing moisture loss.In short, the shelf life of grapes can be increased by using Aloe Vera gel coating and the spoilage due to fungal infection of grapes can be reduced.

Diverse functions and reactions of class III peroxidases

Higher plants contain plant-specific peroxidases (class III peroxidase; Prxs) that exist as large multigene families. Reverse genetic studies to characterize the function of each Prx have revealed that Prxs are involved in lignification, cell elongation, stress defense and seed germination. However, the underlying mechanisms associated with plant phenotypes following genetic engineering of Prx genes are not fully understood. This is because Prxs can function as catalytic enzymes that oxidize phenolic compounds while consuming hydrogen peroxide and/or as generators of reactive oxygen species. Moreover, biochemical efforts to characterize Prxs responsible for lignin polymerization have revealed specialized activities of Prxs. In conclusion, not only spatiotemporal regulation of gene expression and protein distribution, but also differentiated oxidation properties of each Prx define the function of this class of peroxidases.

The Eucalyptus grandis NBS-LRR Gene Family: Physical Clustering and Expression Hotspots

Eucalyptus grandis is a commercially important hardwood species and is known to be susceptible to a number of pests and pathogens. Determining mechanisms of defense is therefore a research priority. The published genome for E. grandis has aided the identification of one important class of resistance (R) genes that incorporate nucleotide binding sites and leucine-rich repeat domains (NBS-LRR). Using an iterative search process we identified NBS-LRR gene models within the E. grandis genome. We characterized the gene models and identified their genomic arrangement. The gene expression patterns were examined in E. grandis clones, challenged with a fungal pathogen (Chrysoporthe austroafricana) and insect pest (Leptocybe invasa). One thousand two hundred and fifteen putative NBS-LRR coding sequences were located which aligned into two large classes, Toll or interleukin-1 receptor (TIR) and coiled-coil (CC) based on NB-ARC domains. NBS-LRR gene-rich regions were identified with 76% organized in clusters of three or more genes. A further 272 putative incomplete resistance genes were also identified. We determined that E. grandis has a higher ratio of TIR to CC classed genes compared to other woody plant species as well as a smaller percentage of single NBS-LRR genes. Transcriptome profiles indicated expression hotspots, within physical clusters, including expression of many incomplete genes. The clustering of putative NBS-LRR genes correlates with differential expression responses in resistant and susceptible plants indicating functional relevance for the physical arrangement of this gene family. This analysis of the repertoire and expression of E. grandis putative NBS-LRR genes provides an important resource for the identification of novel and functional R-genes; a key objective for strategies to enhance resilience.

Isolation and Compositional Analysis of Plant Cuticle Lipid Polyester Monomers

Terrestrial plants produce extracellular aliphatic biopolyesters that modify cell walls of specific tissues. Epidermal cells synthesize cutin, a polyester of glycerol and modified fatty acids that constitutes the framework of the cuticle that covers aerial plant surfaces. Suberin is a related lipid polyester that is deposited on the cell walls of certain tissues, including the root endodermis and the periderm of tubers, tree bark and roots. These lipid polymers are highly variable in composition among plant species, and often differ among tissues within a single species. Here, we describe a detailed protocol to study the monomer composition of cutin in Arabidopsis thaliana leaves by sodium methoxide (NaOMe)-catalyzed depolymerisation, derivatization, and subsequent gas chromatography-mass spectrometry (GC/MS) analysis. This method can be used to investigate the monomers of insoluble polyesters isolated from whole delipidated plant tissues bearing either cutin or suberin. The method can by applied not only to characterize the composition of lipid polymers in species not previously analyzed, but also as an analytical tool in forward and reverse genetic approaches to assess candidate gene function.

W3 Is a New Wax Locus That Is Essential for Biosynthesis of β-Diketone, Development of Glaucousness, and Reduction of Cuticle Permeability in Common Wheat

The cuticle plays important roles in plant development, growth and defense against biotic and abiotic attacks. Crystallized epicuticular wax, the outermost layer of cuticle, is visible as white-bluish glaucousness. In crops like barley and wheat, glaucousness is trait of adaption to the dry and hot cultivation conditions, and hentriacontane-14,16-dione (β-diketone) and its hydroxy derivatives are the major and unique components of cuticular wax in the upper parts of adult plants. But their biosynthetic pathway and physiological role largely remain unknown. In the present research, we identified a novel wax mutant in wheat cultivar Bobwhite. The mutation is not allelic to the known wax production gene loci W1 and W2, and designated as W3 accordingly. Genetic analysis localized W3 on chromosome arm 2BS. The w3 mutation reduced 99% of β-diketones, which account for 63.3% of the total wax load of the wild-type. W3 is necessary for β-diketone synthesis, but has a different effect on β-diketone hydroxylation because the hydroxy-β-diketones to β-diketone ratio increased 11-fold in the w3 mutant. Loss of β-diketones caused failure to form glaucousness and significant increase of cuticle permeability in terms of water loss and chlorophyll efflux in the w3 mutant. Transcription of 23 cuticle genes from five functional groups was altered in the w3 mutant, 19 down-regulated and four up-regulated, suggesting a possibility that W3 encodes a transcription regulator coordinating expression of cuticle genes. Biosynthesis of β-diketones in wheat and their implications in glaucousness formation and drought and heat tolerance were discussed.

Cellular pathways of source leaf phloem loading and phloem unloading in developing stems of Sorghum bicolor in relation to stem sucrose storage

Cellular pathways of phloem loading in source leaves and phloem unloading in stems of sweet Sorghum bicolor (L.) Moench were deduced from histochemical determinations of cell wall composition and from the relative radial mobilities of fluorescent tracer dyes exiting vascular pipelines. The cell walls of small vascular bundles in source leaves, the predicted site of phloem loading, contained minimal quantities of lignin and suberin. A phloem-loaded symplasmic tracer, carboxyfluorescein, was retained within the collection phloem, indicating symplasmic isolation. Together, these findings suggested that phloem loading in source leaves occurs apoplasmically. Lignin was restricted to the walls of protoxylem elements located in meristematic, elongating and recently elongated regions of the stem. The apoplasmic tracer, 8-hydroxypyrene-1,3,6-trisulfonic acid, moved radially from the transpiration stream, consistent with phloem and storage parenchyma cells being interconnected by an apoplasmic pathway. The major phase of sucrose accumulation in mature stems coincided with heavy lignification and suberisation of sclerenchyma sheath cell walls restricting apoplasmic tracer movement from the phloem to storage parenchyma apoplasms. Phloem unloading at this stage of stem development followed a symplasmic route linking sieve elements and storage parenchyma cells, as confirmed by the phloem-delivered symplasmic tracer, 8-hydroxypyrene-1,3,6-trisulfonic acid, moving radially from the stem phloem.

Selective and cost-effective protocol to separate bioactive triterpene acids from plant matrices using alkalinized ethanol: Application to leaves of Myrtaceae species

Background:

Triterpenes as betulinic (BA), oleanolic (OA) and ursolic acids (UA) have increasingly gained therapeutic relevance due to their wide scope of pharmacological activities. To fit large-scale demands, exploitable sources of these compounds have to be found and simple, cost-effective methods to extract them developed. Leaf material represents the best plant sustainable raw material. To obtain triterpene acid-rich extracts from leaves of Eugenia, Psidium and Syzygium species (Myrtaceae) by directly treating the dry plant material with alkalinized hydrated ethanol. This procedure was adapted from earlier methods to effect depolymerization of the leaf cutin.

Materials and Methods:

Extracts were prepared by shaking the milled dry leaves in freshly prepared 2% NaOH in 95% EtOH solution (1:4 w/v) at room temperature for 6 h. Working up the product in acidic aqueous medium led to clear precipitates in which BA, OA and UA were quantified by gas chromatography.

Results:

Pigment-free and low-polyphenol content extracts (1.2–2.8%) containing 6–50% of total triterpene acids were obtained for the six species assayed. UA (7–20%) predominated in most extracts, but BA preponderated in Eugenia florida (39%). Carried out in parallel, n-hexane defatted leaves led to up to 9% enhancement of total acids in the extracts. The hydroalcoholate treatment of Myrtaceae species dry leaves proved to be a cost-effective and environmentally friendly method to obtain triterpene acids, providing them be resistant to alkaline medium. These combined techniques might be applicable to other plant species and tissues.

Litter Breakdown and Microbial Succession on Two Submerged Leaf Species in a Small Forested Stream

Microbial succession during leaf breakdown was investigated in a small forested stream in west-central Georgia, USA, using multiple culture-independent techniques. Red maple (Acer rubrum) and water oak (Quercus nigra) leaf litter were incubated in situ for 128 days, and litter breakdown was quantified by ash-free dry mass (AFDM) method and microbial assemblage composition using phospholipid fatty acid analysis (PLFA), ribosomal intergenic spacer analysis (RISA), denaturing gradient gel electrophoresis (DGGE), and bar-coded next-generation sequencing of 16S rRNA gene amplicons. Leaf breakdown was faster for red maple than water oak. PLFA revealed a significant time effect on microbial lipid profiles for both leaf species. Microbial assemblages on maple contained a higher relative abundance of bacterial lipids than oak, and oak microbial assemblages contained higher relative abundance of fungal lipids than maple. RISA showed that incubation time was more important in structuring bacterial assemblages than leaf physicochemistry. DGGE profiles revealed high variability in bacterial assemblages over time, and sequencing of DGGE-resolved amplicons indicated several taxa present on degrading litter. Next-generation sequencing revealed temporal shifts in dominant taxa within the phylum Proteobacteria, whereas γ-Proteobacteria dominated pre-immersion and α- and β-Proteobacteria dominated after 1 month of instream incubation; the latter groups contain taxa that are predicted to be capable of using organic material to fuel further breakdown. Our results suggest that incubation time is more important than leaf species physicochemistry in influencing leaf litter microbial assemblage composition, and indicate the need for investigation into seasonal and temporal dynamics of leaf litter microbial assemblage succession.

A focus on the biosynthesis and composition of cuticle in fruits

Cuticles are plant structures, composed mostly by lipidic layers, synthesized by nonwoody aerial plant organs and deposited on the surface of outer epidermal cell walls. Although its significance has been often disregarded, cuticle deposition modifies organ chemistry, influences mechanical properties, and plays a central role in sensing and interacting with the surrounding environment. Even though some research has been undertaken addressing cuticle biosynthesis and composition in vegetative plant tissues, comparatively less information is available regarding cuticle composition in the epidermis of fruits. However, recent work points to a role for cuticles in the modulation of fruit quality and postharvest performance, indicating that current models for the investigation of fruit development, metabolism, and quality need to integrate a comprehensive knowledge of the cuticle layer. This paper provides an overview of recent findings and observations regarding cuticle biosynthesis and composition in fruits from species of agronomic and economic relevance. Important, but often neglected differences in cuticle composition and biosynthesis patterns among diverse fruit species are described herein to generate an atlas of what is currently known about fruit cuticles and to highlight what remains to be explored. Emphasis is placed on the need to investigate each genetic background considering its own specificities, to permit correlations with the particular physiology of each species considered. Both specific composition and changes during maturation and ripening are reviewed.

Suberin: biosynthesis, regulation, and polymer assembly of a protective extracellular barrier

Suberin is a lipid-phenolic biopolyester deposited in the cell walls of certain boundary tissue layers of plants, such as root endodermis, root and tuber peridermis, and seed coats. Suberin serves as a protective barrier in these tissue layers, controlling, for example, water and ion transport. It is also a stress-induced anti-microbial barrier. The suberin polymer contains a variety of C16-C24 chain-length aliphatics, such as ω-hydroxy fatty acids, α,ω-dicarboxylic fatty acids, and primary fatty alcohols. Suberin also contains high amounts of glycerol and phenolics, especially ferulic acid. In addition, non-covalently linked waxes are likely associated with the suberin polymer. This review focusses on the suberin biosynthetic enzymes identified to date, which include β-ketoacyl-CoA synthases, fatty acyl reductases, long-chain acyl-CoA synthetases, cytochrome P450 monooxygenases, glycerol 3-phosphate acyltransferases, and phenolic acyltransferases. We also discuss recent advances in our understanding of the transport of suberin components intracellularly and to the cell wall, polymer assembly, and the regulation of suberin deposition.

Room temperature organocatalyzed reductive depolymerization of waste polyethers, polyesters, and polycarbonates

The reductive depolymerization of a variety of polymeric materials based on polyethers, polyesters, and polycarbonates is described using hydrosilanes as reductants and metal-free catalysts. This strategy enables the selective depolymerization of waste polymers as well as bio-based polyesters to functional chemicals such as alcohols and phenols at room temperature. Commercially available B(C6 F5)3 and [Ph3 C(+),B(C6 F5)4(-)] catalysts are active hydrosilylation catalysts in this procedure and they are compatible with the use of inexpensive and air-stable polymethylhydrosiloxane and tetramethyldisiloxane as reductants. A significant advantage of this recycling method is derived from its tolerance to the additives present in waste plastics and its ability to selectively depolymerize mixtures of polymers.

Cloning and characterization of a novel acidic cutinase from Sirococcus conigenus

A cutinase gene (ScCut1) was amplified by PCR from the genomic DNA of the ascomycetous plant pathogen Sirococcous conigenus VTT D-04989 using degenerate primers designed on the basis of conserved segments of known cutinases and cutinase-like enzymes. No introns or N- or O-glycosylation sites could be detected by analysis of the ScCut1 gene sequence. The alignment of ScCut1 with other fungal cutinases indicated that ScCut1 contained the conserved motif G-Y-S-Q-G surrounding the active site serine as well as the aspartic acid and histidine residues of the cutinase active site. The gene was expressed in Pichia pastoris, and the recombinantly produced ScCut1 enzyme was purified to homogeneity by immobilized metal affinity chromatography exploiting a C-terminal His-tag translationally fused to the protein. The purified ScCut1 exhibited activity at acidic pH. The K(m) and V(max) values determined for pNP-butyrate esterase activity at pH 4.5 were 1.7 mM and 740 nkat mg⁻¹, respectively. Maximal activities were determined at between pH 4.7 and 5.2 and at between pH 4.1 and 4.6 with pNP-butyrate and tritiated cutin as the substrates, respectively. With both substrates, the enzyme was active over a broad pH range (between pH 3.0 and 7.5). Activity could still be detected at pH 3.0 both with tritiated cutin and with p-nitrophenyl butyrate (relative activity of 25 %) as the substrates. ScCut1 showed activity towards shorter (C2 to C3) fatty acid esters of p-nitrophenol than towards longer ones. Circular dichroism analysis suggested that the denaturation of ScCut1 by heating the protein sample to 80 °C was to a great extent reversible.

RNA-Seq reveals leaf cuticular wax-related genes in Welsh onion

The waxy cuticle plays a very important role in plant resistance to various biotic and abiotic stresses and is an important characteristic of Welsh onions. Two different types of biangan Welsh onions (BG) were selected for this study: BG, a wild-type covered by wax, which forms a continuous lipid membrane on its epidermal cells, and GLBG, a glossy mutant of BG whose epidermal cells are not covered by wax. To elucidate the waxy cuticle-related gene expression changes, we used RNA-Seq to compare these two Welsh onion varieties with distinct differences in cuticular wax. The de novo assembly yielded 42,881 putative unigenes, 25.41% of which are longer than 1,000 bp. Among the high-quality unique sequences, 22,289 (52.0%) had at least one significant match to an existing gene model. A total of 798 genes, representing 1.86% of the total putative unigenes, were differentially expressed between these two Welsh onion varieties. The expression patterns of four important unigenes that are related to waxy cuticle biosynthesis were confirmed by RT-qPCR and COG class annotation, which demonstrated that these genes play an important role in defense mechanisms and lipid transport and metabolism. To our knowledge, this study is the first exploration of the Welsh onion waxy cuticle. These results may help to reveal the molecular mechanisms underlying the waxy cuticle and will be useful for waxy gene cloning, genetics and breeding as well as phylogenetic and evolutionary studies of the Welsh onion.

Chemical and structural analysis of Eucalyptus globulus and E. camaldulensis leaf cuticles: a lipidized cell wall region

The plant cuticle has traditionally been conceived as an independent hydrophobic layer that covers the external epidermal cell wall. Due to its complexity, the existing relationship between cuticle chemical composition and ultra-structure remains unclear to date. This study aimed to examine the link between chemical composition and structure of isolated, adaxial leaf cuticles of Eucalyptus camaldulensis and E. globulus by the gradual extraction and identification of lipid constituents (cutin and soluble lipids), coupled to spectroscopic and microscopic analyses. The soluble compounds and cutin monomers identified could not be assigned to a concrete internal cuticle ultra-structure. After cutin depolymerization, a cellulose network resembling the cell wall was observed, with different structural patterns in the regions ascribed to the cuticle proper and cuticular layer, respectively. Our results suggest that the current cuticle model should be revised, stressing the presence and major role of cell wall polysaccharides. It is concluded that the cuticle may be interpreted as a modified cell wall region which contains additional lipids. The major heterogeneity of the plant cuticle makes it difficult to establish a direct link between cuticle chemistry and structure with the existing methodologies.

Elucidating how the saprophytic fungus Aspergillus nidulans uses the plant polyester suberin as carbon source

BACKGROUND

Lipid polymers in plant cell walls, such as cutin and suberin, build recalcitrant hydrophobic protective barriers. Their degradation is of foremost importance for both plant pathogenic and saprophytic fungi. Regardless of numerous reports on fungal degradation of emulsified fatty acids or cutin, and on fungi-plant interactions, the pathways involved in the degradation and utilisation of suberin remain largely overlooked. As a structural component of the plant cell wall, suberin isolation, in general, uses harsh depolymerisation methods that destroy its macromolecular structure. We recently overcame this limitation isolating suberin macromolecules in a near-native state.

RESULTS

Suberin macromolecules were used here to analyse the pathways involved in suberin degradation and utilisation by Aspergillus nidulans. Whole-genome profiling data revealed the complex degrading enzymatic machinery used by this saprophytic fungus. Initial suberin modification involved ester hydrolysis and ω-hydroxy fatty acid oxidation that released long chain fatty acids. These fatty acids were processed through peroxisomal β-oxidation, leading to up-regulation of genes encoding the major enzymes of these pathways (e.g. faaB and aoxA). The obtained transcriptome data was further complemented by secretome, microscopic and spectroscopic analyses.

CONCLUSIONS

Data support that during fungal growth on suberin, cutinase 1 and some lipases (e.g. AN8046) acted as the major suberin degrading enzymes (regulated by FarA and possibly by some unknown regulatory elements). Suberin also induced the onset of sexual development and the boost of secondary metabolism.

Exploring candidate genes for pericarp russet pigmentation of sand pear (Pyrus pyrifolia) via RNA-Seq data in two genotypes contrasting for pericarp color

Sand pear (Pyrus pyrifolia) russet pericarp is an important trait affecting both the quality and stress tolerance of fruits. This trait is controlled by a relative complex genetic process, with some fundamental biological questions such as how many and which genes are involved in the process remaining elusive. In this study, we explored differentially expressed genes between the russet- and green-pericarp offspring from the sand pear (Pyrus pyrifolia) cv. 'Qingxiang' × 'Cuiguan' F1 group by RNA-seq-based bulked segregant analysis (BSA). A total of 29,100 unigenes were identified and 206 of which showed significant differences in expression level (log2fold values>1) between the two types of pericarp pools. Gene Ontology (GO) analyses detected 123 unigenes in GO terms related to 'cellular_component' and 'biological_process', suggesting developmental and growth differentiations between the two types. GO categories associated with various aspects of 'lipid metabolic processes', 'transport', 'response to stress', 'oxidation-reduction process' and more were enriched with genes with divergent expressions between the two libraries. Detailed examination of a selected set of these categories revealed repressed expressions of candidate genes for suberin, cutin and wax biosynthesis in the russet pericarps.Genes encoding putative cinnamoyl-CoA reductase (CCR), cinnamyl alcohol dehydrogenase (CAD) and peroxidase (POD) that are involved in the lignin biosynthesis were suggested to be candidates for pigmentation of sand pear russet pericarps. Nine differentially expressed genes were analyzed for their expressions using qRT-PCR and the results were consistent with those obtained from Illumina RNA-sequencing. This study provides a comprehensive molecular biology insight into the sand pear pericarp pigmentation and appearance quality formation.