Summary
Plants have evolved a repertoire of monitoring systems to sense plant morphogenesis and to face environmental changes and threats caused by different attackers. These systems integrate ...different signals into overreaching triggering pathways which coordinate developmental and defence‐associated responses. The plant cell wall, a dynamic and complex structure surrounding every plant cell, has emerged recently as an essential component of plant monitoring systems, thus expanding its function as a passive defensive barrier. Plants have a dedicated mechanism for maintaining cell wall integrity (CWI) which comprises a diverse set of plasma membrane‐resident sensors and pattern recognition receptors (PRRs). The PRRs perceive plant‐derived ligands, such as peptides or wall glycans, known as damage‐associated molecular patterns (DAMPs). These DAMPs function as ‘danger’ alert signals activating DAMP‐triggered immunity (DTI), which shares signalling components and responses with the immune pathways triggered by non‐self microbe‐associated molecular patterns that mediate disease resistance. Alteration of CWI by impairment of the expression or activity of proteins involved in cell wall biosynthesis and/or remodelling, as occurs in some plant cell wall mutants, or by wall damage due to colonization by pathogens/pests, activates specific defensive and growth responses. Our current understanding of how these alterations of CWI are perceived by the wall monitoring systems is scarce and few plant sensors/PRRs and DAMPs have been characterized. The identification of these CWI sensors and PRR–DAMP pairs will help us to understand the immune functions of the wall monitoring system, and might allow the breeding of crop varieties and the design of agricultural strategies that would enhance crop disease resistance.
Significance Statement
The plant cell wall has emerged as an essential component of plant stress‐monitoring systems, thus expanding its function as a passive defensive barrier. Here we review current knowledge about the systems that monitor plant cell wall integrity and their functions in triggering specific disease resistance and growth responses.
Plant cell walls are dynamic structures that are synthesized by plants to provide durable coverings for the delicate cells they encase. They are made of polysaccharides, proteins, and other ...biomolecules and have evolved to withstand large amounts of physical force and to resist external attack by herbivores and pathogens but can in many cases expand, contract, and undergo controlled degradation and reconstruction to facilitate developmental transitions and regulate plant physiology and reproduction. Recent advances in genetics, microscopy, biochemistry, structural biology, and physical characterization methods have revealed a diverse set of mechanisms by which plant cells dynamically monitor and regulate the composition and architecture of their cell walls, but much remains to be discovered about how the nanoscale assembly of these remarkable structures underpins the majestic forms and vital ecological functions achieved by plants.
Throughout their life, plants typically remain in one location utilizing sunlight for the synthesis of carbohydrates, which serve as their sole source of energy as well as building blocks of a ...protective extracellular matrix, called the cell wall. During the course of evolution, plants have repeatedly adapted to their respective niche, which is reflected in the changes of their body plan and the specific design of cell walls. Cell walls not only changed throughout evolution but also are constantly remodelled and reconstructed during the development of an individual plant, and in response to environmental stress or pathogen attacks. Carbohydrate-rich cell walls display complex designs, which together with the presence of phenolic polymers constitutes a barrier for microbes, fungi, and animals. Throughout evolution microbes have co-evolved strategies for efficient breakdown of cell walls. Our current understanding of cell walls and their evolutionary changes are limited as our knowledge is mainly derived from biochemical and genetic studies, complemented by a few targeted yet very informative imaging studies. Comprehensive plant cell wall models will aid in the re-design of plant cell walls for the purpose of commercially viable lignocellulosic biofuel production as well as for the timber, textile, and paper industries. Such knowledge will also be of great interest in the context of agriculture and to plant biologists in general. It is expected that detailed plant cell wall models will require integrated correlative multimodal, multiscale imaging and modelling approaches, which are currently underway.
The walls surrounding the cells of all land-based plants provide mechanical support essential for growth and development as well as protection from adverse environmental conditions like biotic and ...abiotic stress. Composition and structure of plant cell walls can differ markedly between cell types, developmental stages and species. This implies that wall composition and structure are actively modified during biological processes and in response to specific functional requirements. Despite extensive research in the area, our understanding of the regulatory processes controlling active and adaptive modifications of cell wall composition and structure is still limited. One of these regulatory processes is the cell wall integrity maintenance mechanism, which monitors and maintains the functional integrity of the plant cell wall during development and interaction with environment. It is an important element in plant pathogen interaction and cell wall plasticity, which seems at least partially responsible for the limited success that targeted manipulation of cell wall metabolism has achieved so far. Here, we provide an overview of the cell wall polysaccharides forming the bulk of plant cell walls in both monocotyledonous and dicotyledonous plants and the effects their impairment can have. We summarize our current knowledge regarding the cell wall integrity maintenance mechanism and discuss that it could be responsible for several of the mutant phenotypes observed.
Wall‐slab‐wall buildings, in precast configuration or not, are relatively widespread in many European and non‐European countries, independently of the level and nature of seismic hazard to which the ...country is prone. Thus, this building archetype, featuring no columns or beams, but only slabs and walls, can be equally found both in areas characterized by potentially high‐damaging tectonic earthquakes and regions where small‐to‐medium‐size natural/anthropogenic seismic events would instead be expected.
Notwithstanding the above, relatively little information has been offered so far on the seismic response/performance of these structures and their key components, which in case of a precast system/layout will inevitably be the connections between the structural elements. To partly fill such knowledge gap, this paper concerns the latter configuration and deals with experimental testing of panel‐to‐panel joints, which are not only two‐way links but also three‐way connections because it is very common for such structures that contiguous panels are connected to a transverse shear wall.
Not surprisingly, very recent pseudostatic and shake‐table tests on full‐scale specimens, undertaken by the authors to characterize the performance of this structural system up to incipient/near collapse, have indicated how the latter panel joints are the weakest link of the system tested, thus prompting further component testing, in cyclic/asymmetric fashion, to single out the response of the joint. Monotonic and cyclic response curves of the five specimens and the counterpart damage patterns revealed that the observed flexural failure mechanism is very stable and aligns very well with that mobilized by the full‐scale building tests.
•Paper containing 1-MCP slowed down softening development in harvested Younai plums.•Paper containing 1-MCP reduced cell wall-degrading enzyme activities in Younai plums.•Paper containing 1-MCP ...helped preserve cell wall polysaccharides in Younai plums.•Paper containing 1-MCP suppressed cell wall disassembly in harvested Younai plums.•Paper containing 1-MCP is a convenient approach of keeping quality of Younai plums.
Disassembly of cell wall polysaccharides accompanied with softening is very common in harvested fruits. To develop a facile postharvest approach, which can be used at ambient temperature, for suppressing softening and maintaining higher nutritive cell wall polysaccharides of Younai plums, influences of paper containing 1-methylcyclopropene (1-MCP) on firmness, activities of cell wall-degrading enzymes, and contents of cell wall polysaccharide in Younai plums during storage at 25 ± 1 °C were investigated. As compared to the control plums, 1.2 μL·L−1 1-MCP-treated plums exhibited higher firmness, lower activities of cell wall-degrading enzymes (pectinesterase, polygalacturonase, cellulase and β-galactosidase), higher contents of cell wall polysaccharides (sodium carbonate-soluble pectin, chelate-soluble pectin, cellulose, and hemicelluloses), and lower content of water-soluble pectin. The results suggested that paper containing 1-MCP, which was convenient to apply under ambient temperature, could significantly inhibit activities of cell wall degrading-enzymes and decrease disassembly of cell wall polysaccharides, and subsequently retard softening in Younai plums.
Background and AimsBrown algae are photosynthetic multicellular marine organisms evolutionarily distant from land plants, with a distinctive cell wall. They feature carbohydrates shared with plants ...(cellulose), animals (fucose-containing sulfated polysaccharides, FCSPs) or bacteria (alginates). How these components are organized into a three-dimensional extracellular matrix (ECM) still remains unclear. Recent molecular analysis of the corresponding biosynthetic routes points toward a complex evolutionary history that shaped the ECM structure in brown algae.MethodsExhaustive sequential extractions and composition analyses of cell wall material from various brown algae of the order Fucales were performed. Dedicated enzymatic degradations were used to release and identify cell wall partners. This approach was complemented by systematic chromatographic analysis to study polymer interlinks further. An additional structural assessment of the sulfated fucan extracted from Himanthalia elongata was made.Key ResultsThe data indicate that FCSPs are tightly associated with proteins and cellulose within the walls. Alginates are associated with most phenolic compounds. The sulfated fucans from H. elongata were shown to have a regular α-(1→3) backbone structure, while an alternating α-(1→3), (1→4) structure has been described in some brown algae from the order Fucales.ConclusionsThe data provide a global snapshot of the cell wall architecture in brown algae, and contribute to the understanding of the structure–function relationships of the main cell wall components. Enzymatic cross-linking of alginates by phenols may regulate the strengthening of the wall, and sulfated polysaccharides may play a key role in the adaptation to osmotic stress. The emergence and evolution of ECM components is further discussed in relation to the evolution of multicellularity in brown algae.
Summary
The transcription factor KNOTTED ARABIDOPSIS THALIANA7 (KNAT7) is a Class II KNOTTED1‐like homeobox (KNOX2) gene that, in interfascicular fibres, acts as a negative regulator of secondary ...cell wall biosynthesis. In addition, knat7 loss‐of‐function mutants display an irregular xylem (irx) phenotype, suggesting a potential positive regulatory role in xylem vessel secondary cell wall deposition. Although our understanding of the role of KNAT7 is evolving, the function(s) of the closely related KNOX2 genes, KNAT3, KNAT4, and KNAT5, in secondary wall formation still remain unclear. We found that all four Arabidopsis KNOX2 genes were expressed in the inflorescence stems. However, only the knat3 knat7 double mutants showed a phenotype, displaying an enhanced irx phenotypes relative to the single mutants, as well as decreased interfascicular fibre cell wall thickness. Moreover, knat3 knat7 double mutants had reduced stem tensile and flexural strength compared with wild‐type and single mutants. In contrast, KNAT3 overexpression resulted in thicker interfascicular fibre secondary cell walls in inflorescence stems, suggesting a potential positive regulation in interfascicular fibre secondary wall development. This work identifies KNAT3 as a potential transcriptional activator working together with KNAT7 to promote secondary cell wall biosynthesis in xylem vessels, while concurrently acting antagonistically with KNAT7 to influence secondary wall formation in interfascicular fibres.
Significance Statement
This work identifies KNAT3 as a potential transcriptional activator working together with KNAT7 to promote secondary cell wall biosynthesis in xylem vessels, while concurrently acting antagonistically with KNAT7 to influence secondary wall formation in interfascicular fibres.
Silicon (Si) plays a large number of diverse roles in plants, but the structural and chemical mechanisms operating at the single‐cell level remain unclear. We isolate the cell walls from ...suspension‐cultured individual cells of rice (Oryza sativa) and fractionate them into three main fractions including cellulose (C), hemicellulose (HC) and pectin (P). We find that most of the Si is in HC as determined by inductively coupled plasma‐mass spectrometry (ICP‐MS), where Si may covalently crosslink the HC polysacchrides confirmed by X‐ray photoelectron spectroscopy (XPS). The HC‐bound form of Si could improve both the mechanical property and regeneration of the cell walls investigated by a combination of atomic force microscopy (AFM) and confocal laser scanning microscopy (CLSM). This study provides further evidence that HC could be the major ligand bound to Si, which broadens our understanding of the chemical nature of ‘anomalous’ Si in plant cell walls.
The peptidoglycan layers of many gram-positive bacteria are densely functionalized with anionic glycopolymers known as wall teichoic acids (WTAs). These polymers play crucial roles in cell shape ...determination, regulation of cell division, and other fundamental aspects of gram-positive bacterial physiology. Additionally, WTAs are important in pathogenesis and play key roles in antibiotic resistance. We provide an overview of WTA structure and biosynthesis, review recent studies on the biological roles of these polymers, and highlight remaining questions. We also discuss prospects for exploiting WTA biosynthesis as a target for new therapies to overcome resistant infections.
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