Cell Wall Fragments Research Articles

Postbiotics for gut health: an overview

There is growing interest in postbiotics thanks to their potentially better safety profile compared with probiotics. Postbiotics are byproducts of the healthy bacteria in the gut (probiotic bacteria) breaking down prebiotic fibre. Several fermented foods contain bacterial strains that produce postbiotics. Although research into postbiotics is an emerging field, they are known to have antibacterial, anti-inflammatory, immunomodulatory, anti-proliferative and antioxidant activities. Postbiotic supplementation might be particularly beneficial for people with irritable bowel syndrome, inflammatory bowel disease or similar symptoms; they may also help prevent respiratory tract infections. Currently available postbiotics include nutrients and amino acids, as well as exopolysaccharides, enzymes, short-chain fatty acids, bacterial lysates, cell wall fragments and cell-free supernatants. This article will explore existing research around the safety considerations of probiotics compared with postbiotics, the production processes of postbiotics, the different types of postbiotics, their clinical use and effectiveness for gut health, and identify areas for future research.

Fidelibacter multiformis gen. nov., sp. nov., isolated from a deep subsurface aquifer and proposal of Fidelibacterota phyl. nov., formerly called Marine Group A, SAR406 or Candidatus Marinimicrobia.

A Gram-negative, obligatory anaerobic, chemoheterotrophic bacterium, designated strain IA91T, was isolated from sediments and formation water from deep aquifers in Japan. IA91T derives its peptidoglycan, energy and carbon from exogenous cell wall fragments, namely muropeptides, released from actively reproducing bacteria, and is dependent on other bacteria for cell wall formation, growth and even cell shape: IA91T is irregular rod-shaped but coccoids when muropeptide is absent. IA91T grew in a temperature range of 25-45 °C with optimum growth at 40 °C. IA91T utilized limited substrates, yeast extract, muropeptides and d-lactate. The major end products from yeast extract degradation were acetate, hydrogen and carbon dioxide. Co-cultivation with a hydrogen-scavenging methanogenic archaeon promoted IA91T growth. No anaerobic respiration with nitrate, nitrite, sulphate or Fe(III) was observed. The major cellular fatty acids are C16 : 0, C18 : 1 trans9, C18 : 0 and C17 : 0. The G+C content of the genomic DNA was 45.6 mol%. Phylogenetic analysis based on 16S rRNA gene and conserved protein sequences involved in replication, transcription and translation indicated that IA91T belonged to the candidate phylum Marine Group A (MG-A, SAR406 or Ca. Marinimicrobia) with no cultivated representatives. Based on the phenotypic and phylogenomic characteristics, a new genus and species, Fidelibacter multiformis gen. nov., sp. nov., is proposed for IA91T (= JCM 39387T = KCTC 25736T). In addition, a new bacterial phylum named Fidelibacterota phyl. nov. is proposed for the candidate phylum MG-A represented by F. multiformis and Fidelibacteraceae fam. nov., Fidelibacterales ord. nov. and Fidelibacteria classis nov.

The Vacuolar H+-ATPase subunit C is involved in oligogalacturonide (OG) internalization and OG-triggered immunity

In plants, the perception of cell wall fragments initiates signal transduction cascades that activate the immune response. Previous research on early protein dynamics induced by oligogalacturonides (OGs), pectin fragments acting as damage-associated molecular patterns (DAMPs), revealed significant phosphorylation changes in several proteins. Among them, the subunit C of the vacuolar H+-ATPase, known as DE-ETIOLATED 3 (DET3), was selected to elucidate its role in the OG-triggered immune response. The Arabidopsis det3 knockdown mutant exhibited defects in H2O2 accumulation, mitogen-activated protein kinases (MAPKs) activation, and induction of defense marker genes in response to OG treatment. Interestingly, the det3 mutant showed a higher basal resistance to the fungal pathogen Botrytis cinerea that, in turn, was completely reversed by the pre-treatment with OGs. Our results suggest a compromised ability of the det3 mutant to maintain a primed state over time, leading to a weaker defense response when the plant is later exposed to the fungal pathogen. Using fluorescently labelled OGs, we demonstrated that endocytosis of OGs was less efficient in the det3 mutant, implicating DET3 in the internalization process of OGs. This impairment aligns with the observed defect in the priming response in the det3 mutant, underscoring that proper internalization and signaling of OGs are crucial for initiating and maintaining a primed state in plant defense responses.

Postbiotics: Enhancing human health with a novel concept

AbstractPostbiotics is a novel category of biotics that encompasses dead cells, metabolites, and derivatives from gut microbiota. These substances can exhibit their effects without containing cells, such as in cell‐free supernatants and spent media. Examples of widely studied postbiotics include short‐chain fatty acids, exopolysaccharides, cell wall fragments, and bacterial lysates. Evidence suggests that postbiotics have numerous benefits for human health, including antiaging, and anti‐inflammatory properties, and participation in immune and lipid metabolism regulation. Specifically, postbiotics can improve intestinal health by strengthening the intestinal barrier, reducing inflammation, and promoting antibacterial activity. These findings may pave the way for the development of postbiotic functional foods in the future. This review provides an overview of the components, health effects, and industrial applications of postbiotics, aiming to consolidate existing research conclusions and serve as a reference for future studies.

Bioorthogonal labeling of chitin in pathogenic Candida species reveals biochemical mechanisms of hyphal growth and homeostasis.

Pathogenic fungi rely on the cell wall component, chitin, for critical structural and immunological functions. Here a chitin labeling method to visualize the hyphal pathogenic response was developed. The data show that filamentous fungi, Candida albicans , transport N -acetylglucosamine (NAG) bio-orthogonal probes and incorporate them into the cell wall, indicating the probes utility for in vivo study of the morphological, pathogenic switch. As yeast reside in complex microenvironments, The data show that the opportunistic microbe C. albicans , has developed processes to utilize surrounding bacterial cell wall fragments to initiate the morphogenic switch. The probes are utilized for visualization of growth patterns of pathogenic fungi, providing insights into novel mechanisms for the development of antifungals. Remodeling chitin in fungi using NAG derivatives will advance yeast pathogenic studies.

Postbiotics as Adjuvant Therapy in Cancer Care.

Postbiotics are defined as a preparation of inanimate microorganisms and/or their components that confers a health benefit to the host. They range from cell wall fragments to metabolites, bacterial lysates, extracellular vesicles, and short-chain fatty acids (SCFAs). Postbiotics may influence carcinogenesis via a variety of mechanisms. They can promote homeostatic immune responses, reduce inflammation, induce selective cytotoxicity against tumor cells, as well as the enabling the control of tumor cell proliferation and enhancing intestinal epithelial barrier function. Therefore, probiotics can serve as an adjunct strategy in anticancer treatment together with chemotherapy and immunotherapy. Up to now, the only relevant postbiotics used as interventions in oncological patients remain vitamin K molecules, with few phase-II and III trials available. In fact, postbiotics' levels are strictly dependent on the gut microbiota's composition, which may vary between individuals and can be altered under different physiological and pathological conditions. Therefore, the lack of consistent clinical evidence supporting postbiotics' efficacy is due to their poor bioavailability, short half-life, and fluctuating levels. Synbiotics, a mixture of prebiotics and probiotics, are expected to have a more homogeneous bioavailability with respect to postbiotics and may have greater potential for future development. In this review, we focus on the role of postbiotics as an adjuvant therapy in cancer treatment.

Recent Advances in the Understanding of Stress Resistance Mechanisms in Probiotics: Relevance for the Design of Functional Food Systems.

In recent years, more and more scientific community, food producers, and food industry show increased interest in functional foods containing probiotics, which is a big challenge. The consumption of probiotics in the context of a balanced diet through the consumption of functional foods or through the intake of pharmaceutical preparations has proven to contribute to the improvement of human health, even contributing to the prevention of diseases. In order for probiotics to be considered suitable for consumption, they must contain a minimum concentration of viable cells, namely, at least 107 colony forming units of beneficial microbes per gram. Ensuring the viability of bacterial cells until the moment of consumption is the overriding priority of functional probiotic food manufacturers. Probiotic bacteria are subject to stress conditions not only during food manufacturing but also during gastrointestinal passage, which limit or even compromise their functionality. This paper first examines all the stressful conditions faced by probiotic cells in their production stages and related to the conditions present in the bioreactor fermentation and drying processes as well as factors related to the food matrix and storage. The stress situations faced by probiotic microorganisms during the gastrointestinal transit especially during stomach and intestinal residence are also analyzed. In order to understand the adaptation mechanisms of probiotic bacteria to gastrointestinal stress, intrinsic and adaptive mechanisms identified in probiotic strains in response to acid stress and to bile and bile acid stress are analyzed. In addition, improvement strategies for multiple stress tolerance of lactic acid bacteria through directions dealing with stress, accumulation of metabolites, use of protectants, and regulation of technological parameters are examined. Finally, the definition of postbiotics, inanimate microorganisms and/or their components conferring health benefits, is also introduced. Postbiotics include cell lysates, enzymes, and cell wall fragments derived from probiotic bacteria and may represent an alternative to the use of probiotics, when they do not tolerate stressful conditions.

A Marine Group A isolate relies on other growing bacteria for cell wall formation.

Most of Earth's prokaryotes live under energy limitation, yet the full breadth of strategies that enable survival under such conditions remain poorly understood. Here we report the isolation of a bacterial strain, IA91, belonging to the candidate phylum Marine Group A (SAR406 or 'Candidatus Marinimicrobia') that is unable to synthesize the central cell wall compound peptidoglycan itself. Using cultivation experiments and microscopy, we show that IA91 growth and cell shape depend on other bacteria, deriving peptidoglycan, energy and carbon from exogenous muropeptide cell wall fragments released from growing bacteria. Reliance on exogenous muropeptides is traceable to the phylum's ancestor, with evidence of vertical inheritance across several classes. This dependency may be widespread across bacteria (16 phyla) based on the absence of key peptidoglycan synthesis genes. These results suggest that uptake of exogenous cell wall components could be a relevant and potentially common survival strategy in energy-limited habitats like the deep biosphere.

Microstructure and viscosity of in vitro-digested rye and wheat food products

Understanding rye and wheat digestion is vital for evaluating impacts on nutrient availability and glycaemic responses. This study investigated the disintegration of processed high-fibre rye foods and refined wheat products during simulated intestinal digestion, aiming to link product characteristics with nutrient liberation. The overarching aim was to elucidate how these rye products contribute to the observed benefits in human intervention studies, particularly regarding satiety, weight loss, and metabolism.Analysis included four wholegrain rye products and three refined wheat products, spanning yeast-fermented breads and un-leavened cereal products. Microstructure examination revealed larger, partially intact digesta particles in wholegrain rye products after 120 min of digestion, alongside more aggregated and less degraded starch granules compared to refined wheat bread. Fermented rye bread exhibited greater degradation of subaleurone cell wall fragments than un-fermented rye bread. Viscosity assessments indicated lower viscosity for wheat products than for rye products, with yeast-fermented soft rye bread and rye crispbread showing notably lower viscosity than unfermented rye products. Post-digestion carbohydrate analysis uncovered higher glucose and maltose release during digestion for wheat products. PCA analysis confirmed negative correlations between glucose and maltose release and rye products, characterized by larger post-digestion bolus particles and higher dietary fibre. The elevated cell wall content in rye products acted as a protective barrier for starch granules, mitigating swelling and amylose release, explaining the observed viscosity differences between wheat and rye products and potentially influencing starch digestibility. Consequently, rye products undergo slower and less complete digestion than wheat, aligning with findings from human intervention studies.

Physical Stability of Lotus Seed and Lily Bulb Beverage: The Effects of Homogenisation on Particle Size Distribution, Microstructure, Rheological Behaviour, and Sensory Properties.

The lotus seed and lily bulb beverage (LLB) has a problem with solid particle sedimentation. To address this issue, LLB was homogenised twice at different pressures (0~100 MPa) using a homogeniser. This study aims to investigate the changes in the particle size distribution (PSD), microstructure, rheological behaviour, sedimentation index (IS), turbidity, physicochemical properties, and sensory quality of LLBs after homogenisation treatments. The results regarding PSD and microstructure showed that the suspended particles were decomposed at high pressure with increasing homogenisation pressure, forming small particles of cellular material, cell wall fragments, fibre fractions, and polymers. The LLB showed shear-thinning behaviour and weak gelation characteristics (G' > G″) and rheological properties. Among all homogenisation pressures, the 60 MPa sample showed the lowest sedimentation rate and the highest turbidity. When the pressure was increased from 0 to 100 MPa, the total soluble solid (TSS) content showed an upward trend, while the ascorbic acid content (AAC) gradually decreased. The highest sensory evaluation was observed in the 60 MPa sample in terms of overall acceptability.

Mechanisms of Regulation Allergic and Autoimmune Reactions by Bacterial Origin Bioregulators

Relevance. The increase in allergic and autoimmune diseases observed in recent decades highlights the need for therapy and prevention, which requires detailed research into the mechanisms of their occurrence. The onset and progression of allergic and autoimmune diseases are influenced by genetic predisposition, lifestyle, environmental factors, and disruptions in the coordinated operation of the immune system, and as a consequence of immune homeostasis. Treatment of these diseases is primarily symptomatic and often accompanied by undesirable side effects. Immune system disorders in various pathologies have their own characteristics for each type of disease, and at the same time have common mechanisms. Considering the presence of a large number of various microorganisms in the human body, taking their influence into account is of paramount importance. Microorganisms are a source of biologically active molecules, the action of which can either prevent and reduce the severity of the disease or exacerbate it. The aim of this study was to analyze the cytokine profile of the effects of fragments of cell walls of Gram-negative and Gram-positive bacteria - lipopolysaccharide (LPS) and muramyl peptide (MP), as well as nisin - an antimicrobial peptide of bacterial origin on human mononuclear cells. Materials and Methods. Mononuclear cells were obtained from peripheral blood of healthy volunteers using Cell separation media Lympholyte CL 5015, and were cultured in the presence of LPS, GMDP and bacteriocin nisin. The cytokine activity of LPS, GMDP and bacteriocin nisin was examined using the multiplex cytokine analysis; the analysis of surface markers was determined flow cytometry. Results and Discussion. It was shown that bacterial cell wall fragments to a much greater extent than nisin induce the production of cytokines, chemokines, and growth factors. It was established that LPS and MP increase the expression of CD11c on dendritic cells, while bacteriocin nisin does not affect the increase of CD11c+ DCs. LPS and MP in the conducted ex vivo studies did not affect the emergence of CCR7. Conclusion. Bacterial origin bioregulators trigger a negative feedback mechanism by inducing the synthesis of anti-inflammatory factors, that can prevent the inflammatory process. Understanding the molecular mechanisms of the influence of bacterial origin bioregulators on the human body opens new approaches in the prevention and development of personalized therapy strategies.

Mutation of mltG increases peptidoglycan fragment release, cell size, and antibiotic susceptibility in Neisseria gonorrhoeae.

Neisseria gonorrhoeae is unusual in that the bacteria release larger amounts of cell wall material as they grow as compared to related bacteria, and the released cell wall fragments induce inflammation that leads to tissue damage in infected people. The study of MltG revealed the importance of this enzyme for controlling cell wall growth, cell wall fragment production, and bacterial cell size and suggests a role for MltG in a cell wall synthesis and degradation complex. The increased antibiotic sensitivities of mltG mutants suggest that an antimicrobial drug inhibiting MltG would be useful in combination therapy to restore the sensitivity of the bacteria to cell wall targeting antibiotics to which the bacteria are currently resistant.

Efficacy of RUTI® immunotherapy against active tuberculosis in a mouse model challenges the Koch phenomenon

ObjectivesThe objective of this study was to evaluate the safety and efficacy of the therapeutic vaccine RUTI® with or without the standard of care (SOC) chemotherapy for TB in an experimental murine model.MethodsWe assessed the efficacy of RUTI®, a vaccine based on pasteurized and freeze-dried cell-wall fragments from Mycobacterium tuberculosis (Mtb), the SOC for sensitive TB (isoniazid, rifampicin, ethambutol, and pyrazinamide) in the murine active TB model in C3HeB/FeJ strain (Kramnik model). We evaluated the bacillary load in the lungs and spleen, the immune response against specific Mtb antigens (PPD, HSP16.3, ESAT-6, and PsTS1), and lung damage in paraffined tissues for qualitative and quantitative analysis.ResultsRUTI® significantly reduces the pulmonary damage (x3) and the bacterial burden in the lungs (1.5 log10) and spleen (1 log10), and maintains the cellular immune response against ESAT-6, compared to SOC. There was also an additive effect when administered in combination with SOC, increasing the reduction of the lung damage (x2), the bacillary load in lungs (1 log10) and increasing the immune response against PPD, HSP16.3 and PsTS1.DiscussionTherapeutic vaccination against TB has been avoided for decades due to fear of toxicity through the Koch phenomenon. These data show for the first time the safety of immunotherapy with Mtb antigens in an active TB model, adding efficacy to SOC. This encourages the beginning of clinical studies to evaluate the safety and efficacy of RUTI® in TB patients to improve their health, reduce its potential infectiousness, and reduce the length of treatment.

Outdoor airborne allergens: Characterization, behavior and monitoring in Europe

Aeroallergens or inhalant allergens, are proteins dispersed through the air and have the potential to induce allergic conditions such as rhinitis, conjunctivitis, and asthma. Outdoor aeroallergens are found predominantly in pollen grains and fungal spores, which are allergen carriers. Aeroallergens from pollen and fungi have seasonal emission patterns that correlate with plant pollination and fungal sporulation and are strongly associated with atmospheric weather conditions. They are released when allergen carriers come in contact with the respiratory system, e.g. the nasal mucosa. In addition, due to the rupture of allergen carriers, airborne allergen molecules may be released directly into the air in the form of micronic and submicronic particles (cytoplasmic debris, cell wall fragments, droplets etc.) or adhered onto other airborne particulate matter. Therefore, aeroallergen detection strategies must consider, in addition to the allergen carriers, the allergen molecules themselves. This review article aims to present the current knowledge on inhalant allergens in the outdoor environment, their structure, localization, and factors affecting their production, transformation, release or degradation. In addition, methods for collecting and quantifying aeroallergens are listed and thoroughly discussed. Finally, the knowledge gaps, challenges and implications associated with aeroallergen analysis are described.

Antimicrobial activity of dietary supplements based on bacterial lysate of Lactobacillus rhamnosus DV.

According to WHO, antibiotic resistance is increasing to hazardous levels worldwide. Candidiasis often occurs after taking antibiotics. Therefore, antibiotic resistance is a global problem and searching for antibacterial agents is necessary. To determine the antimicrobial activity of bacterial lysate of Lactobacillus (L.) rhamnosus DV separately and with plant extracts against bacterial and yeast test cultures. Antimicrobial activity of Del-Immune V® (cell wall and DNA fragments from a L. rhamnosus DV) separately and with cinnamon, beetroot, and blackcurrant extracts was determined by the minimum inhibitory concentration (MIC). Twofold serial dilutions determined the MIC in previously prepared meat-peptone broth (MPB) for bacteria and liquid wort for yeast. In the study, gram-negative (Escherichia coli IEM-1, Proteus vulgaris PА-12, Pseudomonas sp. MI-2, L. rhamnosus 13/2) and gram-positive (Bacillus (B.) subtilis BТ-2, Staphylococcus aureus BМС-1) bacteria, as well as yeast (Candida (C.) albicans D-6, C. tropicalis PE-2, C. utilis BVS-65) were used as test cultures. The MIC for the studied bacterial test cultures after application of L. rhamnosus DV bacterial lysates was from 1.0 ± 0.05 mg/mL to 12.5 ± 0.63 mg/mL, which was significantly less than that of the thermally inactivated control (MIC from 125.0 ± 6.25 mg/mL to 250.0 ± 12.5 mg/mL). B. subtilis BT-2 culture was the least sensitive to the action of the bacterial lysate (MIC-12.5 ± 0.63 mg/mL). It showed the best antibacterial and antifungal effect bacterial lysate with the phytonutrient blackcurrant. It was demonstrated that bacterial lysate of lactic acid bacteria L. rhamnosus DV exhibits antibacterial and antifungal properties during direct contact with pathogenic agents.

Postbiotics in oncology: science or science fiction?

The gut microbiome has been increasingly understood to play a critical role in carcinogenesis and cancer disease progression. The most recent research advancements have shown that different tools of microbiota manipulation contribute to gut microbiome-immune-oncology axis modulation, offering exciting opportunities for targeted interventions aimed at improving the efficacy of established anti-cancer therapy. Postbiotics are a new entry among the biotics showing beneficial effects on human health while not requiring living cells to obtain the health effect and therefore not subjected to food safety rules for live microorganisms. Postbiotics are recently defined as the "preparation of inanimate microorganisms and/or their components that confers a health benefit on the host" and have gradually become the focus of the scientific community. Since the beginning of research on this topic, numerous studies about postbiotics have been proven to strengthen the gut barrier, reduce inflammation, and promote antimicrobial activity. However, research on the potential application of cancer therapy is still at the early stages of its efforts to uncover all the secrets surrounding postbiotics. This review aims to increase our understanding of the anti-cancer effect of postbiotics throughout a "bibliographic journey" on the biological activity of their components, including exopolysaccharides, cell wall fragments, tryptophan metabolites, enzymes, bacterial lysates, extracellular vesicles, and short-chain fatty acids, highlighting their perspective as a new supportive therapeutic method of treatment and identifying the literature gaps where further research is needed.

Innate Immunity and Sex: Distinct Inflammatory Profiles Associated with Murine Pain in Acute Synovitis.

Joint pain severity in arthritic diseases differs between sexes and is often more pronounced in women. This disparity is thought to stem from biological mechanisms, particularly innate immunity, yet the understanding of sex-specific differences in arthritic pain remains incomplete. This study aims to investigate these disparities using an innate immunity-driven inflammation model induced by intra-articular injections of Streptococcus Cell Wall fragments to mimic both acute and pre-sensitized joint conditions. Nociceptive behavior was evaluated via gait analysis and static weight-bearing, and inflammation was evaluated via joint histology and the synovial gene expression involved in immune response. Although acute inflammation and pain severity were comparable between sexes, distinct associations between synovial inflammatory gene expression and static nociceptive behavior emerged. These associations delineated sex-specific relationships with pain, highlighting differential gene interactions (Il6 versus Cybb on day 1 and Cyba/Gas6 versus Nos2 on day 8) between sexes. In conclusion, our study found that, despite similar pain severity between sexes, the association of inflammatory synovial genes revealed sex-specific differences in the molecular inflammatory mechanisms underlying pain. These findings suggest a path towards more personalized treatment strategies for pain management in arthritis and other inflammatory joint diseases.

A universal reagent for detection of emerging diseases using bioengineered multifunctional yeast nanofragments.

Accurate and early detection of biomarkers provides the molecular evidence for disease management, allowing prompt actions and timely treatments to save lives. Multivalent biomolecular interactions between the probe and biomarker as well as controlled probe orientation on material surfaces are keys for highly sensitive detection. Here we report the bioengineering of programmable and multifunctional nanoprobes, which can provide rapid, specific and highly sensitive detection of emerging diseases in a range of widely used diagnostic systems. These nanoprobes composed of nanosized cell wall fragments, termed as synthetic bionanofragments (SynBioNFs), are generated by the fragmentation of genetically programmed yeast cells. SynBioNFs display multiple copies of biomolecules for high-affinity target binding and molecular handles for the precisely orientated attachment on surfaces used in diagnostic platforms. SynBioNFs are demonstrated for the capture and detection of SARS-CoV-2 virions using multiple diagnostic platforms, including surface-enhanced Raman scattering, fluorescence, electrochemical and colorimetric-based lateral flow systems with sensitivity comparable with the gold-standard reverse-transcription quantitative polymerase chain reaction.

Radical cation scavenging activity of berberine bridge enzyme-like oligosaccharide oxidases acting on short cell wall fragments

Oligogalacturonide-oxidases (OGOXs) and cellodextrin-oxidase (CELLOX) are plant berberine bridge enzyme-like oligosaccharide-oxidases (OSOXs) that oxidize, respectively, oligogalacturonides (OGs) and cellodextrins (CDs), thereby inactivating their elicitor nature and concomitantly releasing H2O2. Little is known about the physiological role of OSOX activity. By using an ABTS·+-reduction assay, we identified a novel reaction mechanism through which the activity of OSOXs on cell wall oligosaccharides scavenged the radical cation ABTS·+ with an efficiency dependent on the type and length of the oxidized oligosaccharide. In contrast to the oxidation of longer oligomers such as OGs (degree of polymerization from 10 to 15), the activity of OSOXs on short galacturonan- and cellulose-oligomers (degree of polymerization ≤ 4) successfully counteracted the radical cation-generating activity of a fungal laccase, suggesting that OSOXs can generate radical cation scavenging activity in the apoplast with a power proportional to the extent of degradation of the plant cell wall, with possible implications for redox homeostasis and defense against oxidative stress.

Cell Wall Integrity Signaling in Fruit Ripening

Plant cell walls are essential structures for plant growth and development as well as plant adaptation to environmental stresses. Thus, plants have evolved signaling mechanisms to monitor the changes in the cell wall structure, triggering compensatory changes to sustain cell wall integrity (CWI). CWI signaling can be initiated in response to environmental and developmental signals. However, while environmental stress-associated CWI signaling has been extensively studied and reviewed, less attention has been paid to CWI signaling in relation to plant growth and development under normal conditions. Fleshy fruit development and ripening is a unique process in which dramatic alternations occur in cell wall architecture. Emerging evidence suggests that CWI signaling plays a pivotal role in fruit ripening. In this review, we summarize and discuss the CWI signaling in relation to fruit ripening, which will include cell wall fragment signaling, calcium signaling, and NO signaling, as well as Receptor-Like Protein Kinase (RLKs) signaling with an emphasis on the signaling of FERONIA and THESEUS, two members of RLKs that may act as potential CWI sensors in the modulation of hormonal signal origination and transduction in fruit development and ripening.