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1.
Plasmodesmata-Related Structural and Functional Proteins: The Long Sought-After Secrets of a Cytoplasmic Channel in Plant Cell Walls.
Han, X, Huang, LJ, Feng, D, Jiang, W, Miu, W, Li, N
International journal of molecular sciences. 2019;(12)
Abstract
Plant cells are separated by cellulose cell walls that impede direct cell-to-cell contact. In order to facilitate intercellular communication, plant cells develop unique cell-wall-spanning structures termed plasmodesmata (PD). PD are membranous channels that link the cytoplasm, plasma membranes, and endoplasmic reticulum of adjacent cells to provide cytoplasmic and membrane continuity for molecular trafficking. PD play important roles for the development and physiology of all plants. The structure and function of PD in the plant cell walls are highly dynamic and tightly regulated. Despite their importance, plasmodesmata are among the few plant cell organelles that remain poorly understood. The molecular properties of PD seem largely elusive or speculative. In this review, we firstly describe the general PD structure and its protein composition. We then discuss the recent progress in identification and characterization of PD-associated plant cell-wall proteins that regulate PD function, with particular emphasis on callose metabolizing and binding proteins, and protein kinases targeted to and around PD.
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2.
Cell Wall Proteins Play Critical Roles in Plant Adaptation to Phosphorus Deficiency.
Wu, W, Zhu, S, Chen, Q, Lin, Y, Tian, J, Liang, C
International journal of molecular sciences. 2019;(21)
Abstract
Phosphorus is one of the mineral nutrient elements essential for plant growth and development. Low phosphate (Pi) availability in soils adversely affects crop production. To cope with low P stress, remodeling of root morphology and architecture is generally observed in plants, which must be accompanied by root cell wall modifications. It has been documented that cell wall proteins (CWPs) play critical roles in shaping cell walls, transmitting signals, and protecting cells against environmental stresses. However, understanding of the functions of CWPs involved in plant adaptation to P deficiency remains fragmentary. The aim of this review was to summarize advances in identification and functional characterization of CWPs in responses to P deficiency, and to highlight the critical roles of CWPs in mediating root growth, P reutilization, and mobilization in plants.
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3.
Bacteria from the endosphere and rhizosphere of Quercus spp. use mainly cell wall-associated enzymes to decompose organic matter.
Lasa, AV, Mašínová, T, Baldrian, P, Fernández-López, M
PloS one. 2019;(3):e0214422
Abstract
Due to the ability of soil bacteria to solubilize minerals, fix N2 and mobilize nutrients entrapped in the organic matter, their role in nutrient turnover and plant fitness is of high relevance in forest ecosystems. Although several authors have already studied the organic matter decomposing enzymes produced by soil and plant root-interacting bacteria, most of the works did not account for the activity of cell wall-attached enzymes. Therefore, the enzyme deployment strategy of three bacterial collections (genera Luteibacter, Pseudomonas and Arthrobacter) associated with Quercus spp. roots was investigated by exploring both cell-bound and freely-released hydrolytic enzymes. We also studied the potential of these bacterial collections to produce enzymes involved in the transformation of plant and fungal biomass. Remarkably, the cell-associated enzymes accounted for the vast majority of the total activity detected among Luteibacter strains, suggesting that they could have developed a strategy to maintain the decomposition products in their vicinity, and therefore to reduce the diffusional losses of the products. The spectrum of the enzymes synthesized and the titres of activity were diverse among the three bacterial genera. While cellulolytic and hemicellulolytic enzymes were rather common among Luteibacter and Pseudomonas strains and less detected in Arthrobacter collection, the activity of lipase was widespread among all the tested strains. Our results indicate that a large fraction of the extracellular enzymatic activity is due to cell wall-attached enzymes for some bacteria, and that Quercus spp. root bacteria could contribute at different levels to carbon (C), phosphorus (P) and nitrogen (N) cycles.
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4.
Genomic Characterization of Candidate Division LCP-89 Reveals an Atypical Cell Wall Structure, Microcompartment Production, and Dual Respiratory and Fermentative Capacities.
Youssef, NH, Farag, IF, Hahn, CR, Jarett, J, Becraft, E, Eloe-Fadrosh, E, Lightfoot, J, Bourgeois, A, Cole, T, Ferrante, S, et al
Applied and environmental microbiology. 2019;(10)
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Abstract
Recent experimental and bioinformatic advances enable the recovery of genomes belonging to yet-uncultured microbial lineages directly from environmental samples. Here, we report on the recovery and characterization of single amplified genomes (SAGs) and metagenome-assembled genomes (MAGs) representing candidate phylum LCP-89, previously defined based on 16S rRNA gene sequences. Analysis of LCP-89 genomes recovered from Zodletone Spring, an anoxic spring in Oklahoma, predicts slow-growing, rod-shaped organisms. LCP-89 genomes contain genes for cell wall lipopolysaccharide (LPS) production but lack the entire machinery for peptidoglycan biosynthesis, suggesting an atypical cell wall structure. The genomes, however, encode S-layer homology domain-containing proteins, as well as machinery for the biosynthesis of CMP-legionaminate, inferring the possession of an S-layer glycoprotein. A nearly complete chemotaxis machinery coupled to the absence of flagellar synthesis and assembly genes argues for the utilization of alternative types of motility. A strict anaerobic lifestyle is predicted, with dual respiratory (nitrite ammonification) and fermentative capacities. Predicted substrates include a wide range of sugars and sugar alcohols and a few amino acids. The capability of rhamnose metabolism is confirmed by the identification of bacterial microcompartment genes to sequester the toxic intermediates generated. Comparative genomic analysis identified differences in oxygen sensitivities, respiratory capabilities, substrate utilization preferences, and fermentation end products between LCP-89 genomes and those belonging to its four sister phyla (Calditrichota, SM32-31, AABM5-125-24, and KSB1) within the broader FCB (Fibrobacteres-Chlorobi-Bacteroidetes) superphylum. Our results provide a detailed characterization of members of the candidate division LCP-89 and highlight the importance of reconciling 16S rRNA-based and genome-based phylogenies.IMPORTANCE Our understanding of the metabolic capacities, physiological preferences, and ecological roles of yet-uncultured microbial phyla is expanding rapidly. Two distinct approaches are currently being utilized for characterizing microbial communities in nature: amplicon-based 16S rRNA gene surveys for community characterization and metagenomics/single-cell genomics for detailed metabolic reconstruction. The occurrence of multiple yet-uncultured bacterial phyla has been documented using 16S rRNA surveys, and obtaining genome representatives of these yet-uncultured lineages is critical to our understanding of the role of yet-uncultured organisms in nature. This study provides a genomics-based analysis highlighting the structural features and metabolic capacities of a yet-uncultured bacterial phylum (LCP-89) previously identified in 16S rRNA surveys for which no prior genomes have been described. Our analysis identifies several interesting structural features for members of this phylum, e.g., lack of peptidoglycan biosynthetic machinery and the ability to form bacterial microcompartments. Predicted metabolic capabilities include degradation of a wide range of sugars, anaerobic respiratory capacity, and fermentative capacities. In addition to the detailed structural and metabolic analysis provided for candidate division LCP-89, this effort represents an additional step toward a unified scheme for microbial taxonomy by reconciling 16S rRNA gene-based and genomics-based taxonomic outlines.
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5.
Fruit ripening: the role of hormones, cell wall modifications, and their relationship with pathogens.
Forlani, S, Masiero, S, Mizzotti, C
Journal of experimental botany. 2019;(11):2993-3006
Abstract
Fruits result from complex biological processes that begin soon after fertilization. Among these processes are cell division and expansion, accumulation of secondary metabolites, and an increase in carbohydrate biosynthesis. Later fruit ripening is accomplished by chlorophyll degradation and cell wall lysis. Fruit maturation is an essential step to optimize seed dispersal, and is controlled by a complex network of transcription factors and genetic regulators that are strongly influenced by phytohormones. Abscisic acid (ABA) and ethylene are the major regulators of ripening and senescence in both dry and fleshy fruits, as demonstrated by numerous ripening-defective mutants, effects of exogenous hormone application, and transcriptome analyses. While ethylene is the best characterized player in the final step of a fruit's life, ABA also has a key regulatory role, promoting ethylene production and acting as a stress-related hormone in response to drought and pathogen attack. In this review, we focus on the role of ABA and ethylene in relation to the interconnected biotic and abiotic phenomena that affect ripening and senescence. We integrate and discuss the most recent data available regarding these biological processes, which are crucial for post-harvest fruit conservation and for food safety.
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6.
A Report on Fungal (1→3)-α-d-glucans: Properties, Functions and Application.
Złotko, K, Wiater, A, Waśko, A, Pleszczyńska, M, Paduch, R, Jaroszuk-Ściseł, J, Bieganowski, A
Molecules (Basel, Switzerland). 2019;(21)
Abstract
The cell walls of fungi are composed of glycoproteins, chitin, and α- and β-glucans. Although there are many reports on β-glucans, α-glucan polysaccharides are not yet fully understood. This review characterizes the physicochemical properties and functions of (1→3)-α-d-glucans. Particular attention has been paid to practical application and the effect of glucans in various respects, taking into account unfavourable effects and potential use. The role of α-glucans in plant infection has been proven, and collected facts have confirmed the characteristics of Aspergillus fumigatus infection associated with the presence of glucan in fungal cell wall. Like β-glucans, there are now evidence that α-glucans can also stimulate the immune system. Moreover, α-d-glucans have the ability to induce mutanases and can thus decompose plaque.
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7.
Proteomic and metabolomic approaches unveil relevant biochemical changes in carbohydrate and cell wall metabolisms of two blueberry (Vaccinium corymbosum) varieties with different quality attributes.
Montecchiarini, ML, Margarit, E, Morales, L, Rivadeneira, MF, Bello, F, Gollán, A, Vázquez, D, Podestá, FE, Tripodi, KEJ
Plant physiology and biochemistry : PPB. 2019;:230-244
Abstract
Quality maintenance in rapidly decaying fruit such as blueberries (Vaccinium corymbosum) is of essential importance to guarantee the economic success of the crop. Fruit quality is a multifaceted subject that encompasses flavor, aroma, visual and physical issues as main factors. In this paper we report an ample characterization of different biochemical and physical aspects in two varieties (O'Neal and Emerald) of blueberries that differ in firmness, aspect, flavor and harvesting times, at two different phenological stages (fruit set vs. ripe), with the intention of unveiling how the metabolic signature of each contributes to their contrasting quality. To this effect a metabolomic, ionomic and proteomic approach was selected. The results presented here show marked differences in several variables at the two stages and between varieties. Emerald is an early variety with a large, good taste and firm fruit, while O'Neal is soft, medium sized and very sweet. Proteomic data comparison between both cultivars showed that, at fruit set, processes related with the response to inorganic compounds and small molecule metabolisms are relevant in both varieties. However, solute accumulation (mainly amino acids and organic acids), enzymes related with C: N balance, water transport and cell wall recycling are enhanced in Emerald. In ripe fruit, Emerald showed an enrichment of proteins associated with TCA, nitrogen, small molecules and cell wall in muro recycling processes, while mannitol and fatty acid metabolism were enhanced in the soft variety. The measured variation in metabolite levels gave strong support to the precedent results. This study suggests that at fruit set, a composite scenario of active metabolic recycling of the cell wall, improved C: N balance and solute accumulation give place to a more efficient carbon and water resource management. During the ripe stage, an increased and efficient in muro and metabolic recycling of the cell wall, added to enhanced inositol and secondary metabolism may be responsible for a best turgor conservation in Emerald. These findings may yield clues for improvements in fertilization practices, as well as to assist the guided development of new varieties based on biochemical quality.
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8.
Carbohydrate-binding property of a cell wall integrity and stress response component (WSC) domain of an alcohol oxidase from the rice blast pathogen Pyricularia oryzae.
Oide, S, Tanaka, Y, Watanabe, A, Inui, M
Enzyme and microbial technology. 2019;:13-20
Abstract
The cell wall integrity and stress response component (WSC) domain was first described in the Wsc-family protein of the yeast Saccharomyces cerevisiae, and later found in diverse eukaryotic organisms. Due solely to their presence in the Wsc-family proteins working as a plasma membrane sensor for surface stress and in a fungal β-1,3-exoglucanse, WSC domains have been presumed to possess carbohydrate-binding property without any experimental evidence. Aiming at elucidation of function(s) of WSC domains, we characterized a WSC domain-containing alcohol oxidase from the rice blast pathogen Pyricularia oryzae (PoAlcOX). Recombinant PoAlcOX produced with Pichia pastoris showed alcohol oxidase activity toward a wide range of substrates including two aliphatic alcohols, a branched-chain alcohol, a diol, and a polyol. Deletion of the WSC domain virtually unaffected oxidation of these substrates by PoAlcOX, indicating that the domain makes no contribution to the catalytic activity. In analogy to some carbohydrate-binding modules, we inferred that the WSC domain plays a role in protein anchoring, and evaluated binding capability of PoAlcOX to a set of polysaccharide components of fungal and plant cell walls. This revealed that PoAlcOX binds to xylans and fungal chitin/β-1,3-glucan in the WSC domain-dependent manner, demonstrating for the first time the carbohydrate-binding property of the domain. Additionally, we provide evidence that PoAlcOX immobilized on birch wood xylan retains the catalytic activity. Overall, the data we collected suggest that the role of the WSC domain of PoAlcOX is not recognition of substrates but attaching the enzyme to plant and/or fungal cell wall.
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9.
The Fusarium graminearum cerato-platanins loosen cellulose substrates enhancing fungal cellulase activity as expansin-like proteins.
Quarantin, A, Castiglioni, C, Schäfer, W, Favaron, F, Sella, L
Plant physiology and biochemistry : PPB. 2019;:229-238
Abstract
Cerato-platanin proteins (CPPs) are small non-catalytic, cysteine-rich hydrophobic proteins produced by filamentous fungi. The genome of Fusarium graminearum, the causal agent of Fusarium head blight disease of wheat and other cereal grains, contains two genes putatively encoding for CPPs. To better characterize their features, the two FgCPPs were heterologously expressed in Pichia pastoris. The recombinant FgCPPs reduced the viscosity of a cellulose soluble derivate (carboxymethyl cellulose, CMC). The same effect was not observed on other polysaccharide substrates such as chitin, 1,3-β-glucan, xylan and pectin. Indeed, differently from other fungal CPPs and similarly to expansins, FgCPPs are trapped by cellulose and not by chitin, thus suggesting that these proteins interact with cellulose. A double knock-out mutant deleted of both FgCPPs encoding genes produces much more cellulase activity than the corresponding wild type strain when grown on CMC, likely compensating the absence of FgCPPs. This result prompted us to investigate a possible synergistic effect of these proteins with fungal cellulases. The incubation of FgCPPs in the presence of a fungal cellulase (EC 3.2.1.4) determines an increased enzymatic activity on CMC, filter paper and wheat cell walls. The observation that FgCPPs act with a non-hydrolytic mechanism indicates that these proteins favor fungal cellulase activity in an expansin-like manner. Though the disruption of the FgCPP genes had no demonstrable impact on fungal virulence, our experimental data suggest their probable involvement in virulence, thus we refer to them as accessory virulence genes. Our results suggest also that the FgCPPs could be exploited for future biotechnological application in second-generation biofuels production on lignocellulosic biomasses rich in cellulose. Finally, we demonstrate that FgCPPs act as elicitors of defense responses on Arabidopsis leaves, increasing resistance to Botrytis cinerea infections.
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10.
Secondary cell wall biosynthesis.
Zhong, R, Cui, D, Ye, ZH
The New phytologist. 2019;(4):1703-1723
Abstract
Contents Summary 1703 I. Introduction 1703 II. Cellulose biosynthesis 1705 III. Xylan biosynthesis 1709 IV. Glucomannan biosynthesis 1713 V. Lignin biosynthesis 1714 VI. Concluding remarks 1717 Acknowledgements 1717 References 1717 SUMMARY Secondary walls are synthesized in specialized cells, such as tracheary elements and fibers, and their remarkable strength and rigidity provide strong mechanical support to the cells and the plant body. The main components of secondary walls are cellulose, xylan, glucomannan and lignin. Biochemical, molecular and genetic studies have led to the discovery of most of the genes involved in the biosynthesis of secondary wall components. Cellulose is synthesized by cellulose synthase complexes in the plasma membrane and the recent success of in vitro synthesis of cellulose microfibrils by a single recombinant cellulose synthase isoform reconstituted into proteoliposomes opens new doors to further investigate the structure and functions of cellulose synthase complexes. Most genes involved in the glycosyl backbone synthesis, glycosyl substitutions and acetylation of xylan and glucomannan have been genetically characterized and the biochemical properties of some of their encoded enzymes have been investigated. The genes and their encoded enzymes participating in monolignol biosynthesis and modification have been extensively studied both genetically and biochemically. A full understanding of how secondary wall components are synthesized will ultimately enable us to produce plants with custom-designed secondary wall composition tailored to diverse applications.