Dynamic imaging of cell wall polysaccharides by metabolic click-mediated labeling of pectins in living elongating cells

Probing homogalacturonan in situ: A comprehensive review of available molecular recognition tools

Among the major plant cell wall components, pectic-type homogalacturonan emerges as a chemically and spatiotemporally dynamic matrix-forming agent embedded within the cell wall through various inter- and intramolecular interactions. Its abundance, localization, and chemistry profoundly influence cell wall biomechanics and all facets of plant physiology. Precise tracking of homogalacturonan in a native context is crucial for understanding cell wall organization, particularly the relation between molecular structure and function. It also enables the detailed characterization of plant-based resources for industrial, food, and biomedical applications. This review offers a comprehensive and focused survey of the state-of-the-art molecular recognition tools being employed to visualize homogalacturonan in diverse plant samples. We particularly highlight homogalacturonan-specific monoclonal antibodies, which represent the most used and well-established probes. However, we also discuss less common reagents, such as fluorophores, oligosaccharide-based probes, carbohydratebinding modules, and whole enzymes, as well as emerging chemical biology approaches exemplified by click chemistry. We critically evaluate their strengths, limitations, and suitability for given research objectives and provide the most notable examples of their usage. Lastly, we outline the anticipated future expansion of an advanced, improved range of new molecular tools, which holds the potential to overcome some of the current experimental hurdles.

Design and Synthesis of Thioglycosylated Monolignol Dual Probes for Bioimaging of Lignin Biosynthesis

Lignin biosynthesis is a critical process that underpins plant structural integrity and defenses. Central to this pathway are monolignol glucosides (MLGs), whose role as intermediates remains debated. To elucidate MLGs' involvement, we developed thioglycosylated monolignol probes compatible with click chemistry for in situ visualization of lignin biosynthesis. Using a highly selective Buchwald-Hartwig-Migita cross-coupling approach, these probes incorporate glycosyl thiols into MLGs, creating stable thioacetal bonds to enhance both metabolic stability and tracking precision. The unique chemistry of these probes allows for incorporation within the lignification pathway, enabling specific visualization of MLG involvement in lignin formation. The probes are compatible with bioorthogonal chemistry labeling and confocal microscopy, allowing detailed tracking of MLG transport, storage, and incorporation into cell walls. Our findings provide new insights into lignification dynamics, underscoring the metabolic roles of MLGs and demonstrating their potential as metabolic intermediates in lignin polymerization. This approach offers a novel chemical biology toolset to dissect plant cell wall biosynthesis and will help elucidatethe molecular roles of MLGs in the context of plant biochemistry and resilience.

An in-depth review: Unraveling the extraction, structure, bio-functionalities, target molecules, and applications of pectic polysaccharides

Pectic polysaccharides have long been a challenging subject of research in the field of macromolecular science, given their complex structures and wide range of biological effects. However, the extensive exploration of pectic polysaccharides has been limited due to the intricacy of their structures. In this comprehensive review, we aim to provide a thorough summary of the existing knowledge on pectic polysaccharides, with a particular focus on aspects such as classification, extraction methodologies, structural analysis, elucidation of biological activities, and exploration of target molecules and signaling pathways. By conducting a comprehensive analysis of existing literature and research achievements, we strive to establish a comprehensive and systematic framework that can serve as a reference and guide for further investigations into pectic polysaccharides. Furthermore, this review delves into the applications of pectic polysaccharides beyond their fundamental attributes and characteristics, exploring their potential in fields such as materials, food, and pharmaceuticals. We pay special attention to the promising opportunities for pectic polysaccharides in the pharmaceutical domain and provide an overview of related drug development research. The aim of this review is to facilitate a holistic understanding of pectic polysaccharides by incorporating multifaceted research, providing valuable insights for further in-depth investigations into this significant polymer.

Top five unanswered questions in plant cell surface research

Plant cell wall researchers were asked their view on what the major unanswered questions are in their field. This article summarises the feedback that was received from them in five questions. In this issue you can find equivalent syntheses for researchers working on bacterial, unicellular parasite and fungal systems.

Plant cell wall-mediated disease resistance: Current understanding and future perspectives

Beyond their function as structural barriers, plant cell walls are essential elements for the adaptation of plants to environmental conditions. Cell walls are dynamic structures whose composition and integrity can be altered in response to environmental challenges and developmental cues. These wall changes are perceived by plant sensors/receptors to trigger adaptative responses during development and upon stress perception. Plant cell wall damage caused by pathogen infection, wounding, or other stresses leads to the release of wall molecules, such as carbohydrates (glycans), that function as damage-associated molecular patterns (DAMPs). DAMPs are perceived by the extracellular ectodomains (ECDs) of pattern recognition receptors (PRRs) to activate pattern-triggered immunity (PTI) and disease resistance. Similarly, glycans released from the walls and extracellular layers of microorganisms interacting with plants are recognized as microbe-associated molecular patterns (MAMPs) by specific ECD-PRRs triggering PTI responses. The number of oligosaccharides DAMPs/MAMPs identified that are perceived by plants has increased in recent years. However, the structural mechanisms underlying glycan recognition by plant PRRs remain limited. Currently, this knowledge is mainly focused on receptors of the LysM-PRR family, which are involved in the perception of various molecules, such as chitooligosaccharides from fungi and lipo-chitooligosaccharides (i.e., Nod/MYC factors from bacteria and mycorrhiza, respectively) that trigger differential physiological responses. Nevertheless, additional families of plant PRRs have recently been implicated in oligosaccharide/polysaccharide recognition. These include receptor kinases (RKs) with leucine-rich repeat and Malectin domains in their ECDs (LRR-MAL RKs), Catharanthus roseus RECEPTOR-LIKE KINASE 1-LIKE group (CrRLK1L) with Malectin-like domains in their ECDs, as well as wall-associated kinases, lectin-RKs, and LRR-extensins. The characterization of structural basis of glycans recognition by these new plant receptors will shed light on their similarities with those of mammalians involved in glycan perception. The gained knowledge holds the potential to facilitate the development of sustainable, glycan-based crop protection solutions.

Cell wall dynamics: novel tools and research questions

Years ago, a classic textbook would define plant cell walls based on passive features. For instance, a sort of plant exoskeleton of invariable polysaccharide composition, and probably painted in green. However, currently, this view has been expanded to consider plant cell walls as active, heterogeneous, and dynamic structures with a high degree of complexity. However, what do we mean when we refer to a cell wall as a dynamic structure? How can we investigate the different implications of this dynamism? While the first question has been the subject of several recent publications, defining the ideal strategies and tools needed to address the second question has proven to be challenging due to the myriad of techniques available. In this review, we will describe the capacities of several methodologies to study cell wall composition, structure, and other aspects developed or optimized in recent years. Keeping in mind cell wall dynamism and plasticity, the advantages of performing long-term non-invasive live-imaging methods will be emphasized. We specifically focus on techniques developed for Arabidopsis thaliana primary cell walls, but the techniques could be applied to both secondary cell walls and other plant species. We believe this toolset will help researchers in expanding knowledge of these dynamic/evolving structures.

The Light-Controlled Release of 2-fluoro-l-fucose, an Inhibitor of the Root Cell Elongation, from a nitrobenzyl-caged Derivative

Glycan metabolic engineering is a powerful tool for studying the glycosylation in living plant cells. The use of modified monosaccharides such as deoxy or fluorine-containing glycosides has been reported as a powerful pharmacological approach for studying the carbohydrate metabolism. 1,3,4-tri-O-acetyl-2-fluoro-l-fucose (2F-Fuc) is a potent inhibitor of the plant cell elongation. After feeding plant seedlings with 2F-Fuc, this monosaccharide derivative is deacetylated and converted by the endogenous metabolic machinery into the corresponding nucleotide-sugar, which then efficiently inhibits Golgi-localized fucosyltransferases. Among plant cell wall polymers, defects in the fucosylation of the pectic rhamnogalacturonan-II cause a decrease in RG-II dimerization, which in turn induce the arrest of the cell elongation. In order to perform the inhibition of the cell elongation process in a spatio-temporal manner, we synthesized a caged 3,4-di-O-acetyl-1-hydroxy-2-fluoro-l-fucose (1-OH-2F-Fuc) derivative carrying a photolabile ortho-nitrobenzyl alcohol function at the anomeric position: 3,4-di-O-acetyl-1-ortho-nitrobenzyl-2-fluoro-l-fucose (2F-Fuc-NB). The photorelease of the trapped 1-OH-2F-Fuc was performed under a 365 nm LED illumination. We demonstrated that the in planta elimination by photoexcitation of the photolabile group releases free 2F-Fuc in plant cells, which in turn inhibits in a dose-dependent manner and, reversibly, the root cell elongation.

Metabolic glycoengineering - exploring glycosylation with bioorthogonal chemistry

Glycans are involved in numerous biological recognition events. Being secondary gene products, their labeling by genetic methods - comparable to GFP labeling of proteins - is not possible. To overcome this limitation, metabolic glycoengineering (MGE, also known as metabolic oligosaccharide engineering, MOE) has been developed. In this approach, cells or organisms are treated with synthetic carbohydrate derivatives that are modified with a chemical reporter group. In the cytosol, the compounds are metabolized and incorporated into newly synthesized glycoconjugates. Subsequently, the reporter groups can be further derivatized in a bioorthogonal ligation reaction. In this way, glycans can be visualized or isolated. Furthermore, diverse targeting strategies have been developed to direct drugs, nanoparticles, or whole cells to a desired location. This review summarizes research in the field of MGE carried out in recent years. After an introduction to the bioorthogonal ligation reactions that have been used in in connection with MGE, an overview on carbohydrate derivatives for MGE is given. The last part of the review focuses on the many applications of MGE starting from mammalian cells to experiments with animals and other organisms.

Regulation of pollen tube growth by cellular pH and ions

Tip growth of the pollen tube is a model system for the study of cell polarity establishment in flowering plants. The tip growth of the pollen tube displays an oscillating pattern corresponding to cellular ion and pH dynamics. Therefore, cellular pH and ions play an important role in pollen growth and development. In this review, we summarized the current advances in understanding the function of cellular pH and ions in regulating pollen tube growth. We analyzed the physiological roles and underlying mechanisms of cellular pH and ions, including Ca²⁺, K⁺, and Cl^-, in regulating pollen tube growth. We further examined the function of Ca²⁺ in regulating cytoskeletons, small G proteins, and cell wall development in relation to pollen tube growth. We also examined the regulatory roles of cellular pH in pollen tube growth as well as pH regulation of ion flow, cell wall development, auxin signaling, and cytoskeleton function in pollen. In addition, we assessed the regulation of pollen tube growth by proton pumps and the maintenance of pH homeostasis in the trans-Golgi network by ion transporters. The interplay of ion homeostasis and pH dynamics was also assessed. We discussed the unanswered questions regarding pollen tube growth that need to be addressed in the future.

Plant cytokinesis and the construction of new cell wall

Cytokinesis in plants is fundamentally different from that in animals and fungi. In plant cells, a cell plate forms through the fusion of cytokinetic vesicles and then develops into the new cell wall, partitioning the cytoplasm of the dividing cell. The formation of the cell plate entails multiple stages that involve highly orchestrated vesicle accumulation, fusion, and membrane maturation, which occur concurrently with the timely deposition of polysaccharides such as callose, cellulose, and cross-linking glycans. This review summarizes the major stages in cytokinesis, endomembrane components involved in cell plate assembly and its transition to a new cell wall. An animation that can be widely used for educational purposes further summarizes the process.