Cell Wall Rigidity Research Articles

Deciphering the Genetic and Biochemical Drivers of Fruit Cracking in Akebia trifoliata.

This study investigates the molecular mechanisms underlying fruit cracking in Akebia trifoliata, a phenomenon that significantly impacts fruit quality and marketability. Through comprehensive physiological, biochemical, and transcriptomic analyses, we identified key changes in cell wall components and enzymatic activities during fruit ripening. Our results revealed that ventral suture tissues exhibit significantly elevated activities of polygalacturonase (PG) and β-galactosidase compared to dorsoventral line tissues, indicating their crucial roles in cell wall degradation and structural weakening. The cellulose content in VS tissues peaked early and declined during ripening, while DL tissues maintained relatively stable cellulose levels, highlighting the importance of cellulose dynamics in fruit cracking susceptibility. Transcriptomic analysis revealed differentially expressed genes (DEGs) associated with pectin biosynthesis and catabolism, cell wall organization, and oxidoreductase activities, indicating significant transcriptional regulation. Key genes like AKT032945 (pectinesterase) and AKT045678 (polygalacturonase) were identified as crucial for cell wall loosening and pericarp dehiscence. Additionally, expansin-related genes AKT017642, AKT017643, and AKT021517 were expressed during critical stages, promoting cell wall loosening. Genes involved in auxin-activated signaling and oxidoreductase activities, such as AKT022903 (auxin response factor) and AKT054321 (peroxidase), were also differentially expressed, suggesting roles in regulating cell wall rigidity. Moreover, weighted gene co-expression network analysis (WGCNA) identified key gene modules correlated with traits like pectin lyase activity and soluble pectin content, pinpointing potential targets for genetic manipulation. Our findings offer valuable insights into the molecular basis of fruit cracking in A. trifoliata, laying a foundation for breeding programs aimed at developing crack-resistant varieties to enhance fruit quality and commercial viability.

Novel Populations of Mycobacterium smegmatis Under Hypoxia and Starvation: Some Insights on Cell Viability and Morphological Changes.

The general features of the shift to a dormant state in mycobacterial species include several phenotypic changes, reduced metabolic activities, and increased resistance to host and environmental stress conditions. In this study, we aimed to provide novel insights into the viability state and morphological changes in dormant M. smegmatis that contribute to its long-term survival under starvation or hypoxia. To this end, we conducted assays to evaluate cell viability, morphological changes and gene expression. During starvation, M. smegmatis exhibited a reduction in cell length, the presence of viable but non-culturable (VBNC) cells and the formation of anucleated small cells, potentially due to a phenomenon known as reductive cell division. Under hypoxia, a novel population of pleomorphic mycobacteria with a rough surface before the cells reached nonreplicating persistence 1 (NRP1) was identified. This population exhibited VBNC-like behaviour, with a loss of cell wall rigidity and the presence of lipid-body-like structures. Based on dosR and hspX expression, we suggest that M. smegmatis encounters reductive stress conditions during starvation, while lipid storage may induce oxidative stress during hypoxia. These insights into the heterogeneous populations presented here could offer valuable opportunities for developing new therapeutic strategies to control dormant mycobacterial populations.

Protein Involved in Tip Elongation (PITE) regulates root hair growth in rice.

Polar tip growth in plants occurs only in root hairs and pollen tubes. In particular, root hair growth is considered very important in the growth of plants, as it is critical for water and nutrient absorption. Polar tip growth is regulated by various factors, including plant hormones such as abscisic acid (ABA) and gibberellin (GA) and cell wall modifications. We aimed to elucidate the effects and mechanisms on tip growth of a novel gene containing the domain of unknown function (DUF) 3511. We found that Protein Involved in Tip Elongation (PITE) is involved in root hair development in rice (Oryza sativa L.). PITE protein was observed in the plasma membrane and cytoplasm of root hairs. Pite mutants generated by the CRISPR/Cas9 system showed a shorter root hair phenotype compared to the wild type. Through RNA sequencing and quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analysis, we found that the expression of genes that affect cell wall rigidity and GA metabolism-related genes were differently regulated in pite mutants. PITE could interact with acyl transferase and haloacid dehalogenase-like hydrolase (HAD9) in the nucleus and cytoplasm. Our study suggests that PITEs containing the DUF3511 domain regulate root hair growth in rice by mediating the expression of genes that can regulate cell wall rigidity or cause changes in GA metabolism through interactors such as HAD9.

Cellulose nanofiber aerogels: effect of the composition and the drying method

Highly porous and lightweight aerogels of cellulose nanofibers (CNFs) have emerged as a promising class of material. This study delves into the impact of the composition (lignocellulose nanofibers–LCNFs and CNFs) and the drying methods (supercritical drying and freeze-drying) on the morphology and the properties of nanocellulose-based aerogels. The investigation evaluates the concentrations of nanofibers and the influence of lignin, a constituent of LCNFs recognized for enhancing the rigidity of plant cell walls, on the aerogel’s properties. The shrinkage rates, density, pore structure, and mechanical properties of the obtained aerogels are comprehensively compared. Supercritical drying proves advantageous for aerogel formation, resulting in materials with lower density and higher surface area than their freeze-dried counterparts at each concentration level. The use of acetone for supercritical drying contributes to reduce the shrinkage rates compared to ethanol. This decrease is attributed to the formation of a more rigid hydrogel during solvent exchange. Freeze-drying exhibits the lowest shrinkage rates and relatively higher porosity. The presence of lignin in the nanofibers influences the microstructure, yielding smoother and thicker pore walls. This study contributes to the comprehensive understanding of the intricate factors shaping nanocellulose aerogel properties, paving the way for the development of innovative and environmentally-friendly materials.

Antifungal characterizations of a novel endo-β-1,6-glucanase from Flavobacterium sp. NAU1659

β-1,6-Glucan plays a crucial role in fungal cell walls by linking the outer layer of mannoproteins and the inner layer of β-1,3-glucan, contributing significantly to the maintenance of cell wall rigidity. Therefore, the hydrolysis of β-1,6-glucan by β-1,6-glucanase directly leads to the disintegration of the fungal cell wall. Here, a novel β-1,6-glucanase FlGlu30 was identified from the endophytic Flavobacterium sp. NAU1659 and heterologously expressed in Escherichia coli BL21 (DE3). The optimal reaction conditions of purified FlGlu30 were 50℃ and pH 6.0, resulting in a specific activity of 173.1 U/mg using pustulan as the substrate. The hydrolyzed products of FlGlu30 to pustulan were mainly gentianose within 1 h of reaction. With the extension of reaction time, gentianose was gradually hydrolyzed to glucose, indicating that FlGlu30 is an endo-β-1,6-glucanase. The germination of Magnaporthe oryzae Guy11 spores could not be inhibited by FlGlu30, but the appressorium formation of spores was completely inhibited under the concentration of 250.0 U/mL FlGlu30. The disruptions of cell wall and accumulation of intracellular reactive oxide species (ROS) were observed in FlGlu30-treated M. oryzae Guy11 cells, suggesting the significant importance of β-1,6-glucan as a potential antifungal target and the potential application of FlGlu30.Key points• β-1,6-Glucan is a key component maintaining the rigid structure of fungal cell wall.• β-1,6-Glucanase is an antifungal protein with significant potential applications.• FlGlu30 is the first reported β-1, 6-glucanase derived from Flavobacterium.

Xyloglucan endotransglucosylase-hydrolase 22 positively regulates response to cold stress in upland cotton (Gossypium hirsutum L.)

Xyloglucan endotransglucosylase/hydrolases (XTHs) are cell wall modifying enzymes that function in response to multiple abiotic stresses by promoting cell wall reinforcement in plants. However, it is elusive whether GhXTH22 plays a role in cold stress tolerance in upland cotton (Gossypium hirsutum L.). In this study, we found that Arabidopsis (Arabidopsis thaliana (L.) Heynh) transgenic lines overexpressing GhXTH22 exhibit clearly increased cold tolerance compared with wild type (WT). Moreover, cold stress results in markable enhancements in the activities of catalase (CAT) and peroxidase (POD), cell wall rigidity, and the expression of cold responsive genes, as well as a notable reduction in malondialdehyde (MDA) levels in the overexpression (OE) lines compared with those in WT plants. Consistently, silencing GhXTH22 by virus-induced gene silencing (VIGS) method causes markedly decreases in cold stress tolerance in upland cotton. Additionally, by electrophoretic mobility shift assay (EMSA) and dual-luciferase assay, it was confirmed that GhMYB44 activate the expression of GhXTH22 by binding to AACNG motif on the promoter, and silencing the expression of GhMYB44 can decrease the cold resistance of cotton. In summary, this study systematically confirmed the cold resistance function of GhXTH22 and discovered the upstream regulating gene of GhXTH22, providing gene resources for cold resistance and enriching the knowledge on the mechanism of cold resistance.

Formation mechanism and regulation analysis of trumpet leaf in Ginkgo biloba L.

The research on plant leaf morphology is of great significance for understanding the development and evolution of plant organ morphology. As a relict plant, the G. biloba leaf morphology typically exhibits bifoliate and peltate forms. However, throughout its long evolutionary history, Ginkgo leaves have undergone diverse changes. This study focuses on the distinct "trumpet" leaves and normal fan-shaped leaves of G. biloba for analysis of their phenotypes, photosynthetic activity, anatomical observations, as well as transcriptomic and metabolomic analyses. The results showed that trumpet-shaped G. biloba leaves have fewer cells, significant morphological differences between dorsal and abaxial epidermal cells, leading to a significantly lower net photosynthetic rate. Additionally, this study found that endogenous plant hormones such as GA, auxin, and JA as well as metabolites such as flavonoids and phenolic acids play roles in the formation of trumpet-shaped G. biloba leaves. Moreover, the experiments revealed the regulatory mechanisms of various key biological processes and gene expressions in the trumpet-shaped leaves of G. biloba. Differences in the dorsal and abdominal cells of G. biloba leaves can cause the leaf to curl, thus reducing the overall photosynthetic efficiency of the leaves. However, the morphology of plant leaves is determined during the primordia leaf stage. In the early stages of leaf development, the shoot apical meristem (SAM) determines the developmental morphology of dicotyledonous plant leaves. This process involves the activity of multiple gene families and small RNAs. The establishment of leaf morphology is complexly regulated by various endogenous hormones, including the effect of auxin on cell walls. Additionally, changes in intracellular ion concentrations, such as fluctuations in Ca2+ concentration, also affect cell wall rigidity, thereby influencing leaf growth morphology.

Phosphate bio-solubilization and cadmium tolerance interplay in the root-microbe interface and consequences on root P absorption in wheat

Functional soil microbial communities, including phosphate solubilizing bacteria (PSB), are known for their ability to enhance P availability along with additional properties such as the immobilization of trace elements like cadmium (Cd). Bacterial P solubilization and tolerance to Cd are important biological processes that might occur simultaneously with positive influence on plant growth, thus physiological mechanisms controlling both processes need to be deciphered. This interplay was investigated in three PSB isolates (Bacillus siamensis "B. Siam", Rahnella aceris "R. Acer" and Bacillus cereus "B. Cer") and their consortium (PSBCs) with contrasting P solubilizing capacities (high-medium-low), through bacterial culture-based and plant inoculation experiments under increasing Cd concentrations and low P availability conditions (Tri-calcium P "TCP" and Rock P "RP"). Results show that PSB, particularly R. Acer and PSBCs, significantly increased P bioavailability (from TCP) under increasing Cd2+ concentrations (33 ppm “Cd33”, 67 ppm “Cd67”, 134 ppm “Cd134” and 201 ppm “Cd201”). The enhanced bioavailable P strongly correlated (B. Siam and PSBCs) with Cd bioaccumulation capacity, phosphatase enzyme activity, and organic acids (OA) production. Co-application of RP and PSB inoculation under Cd2+ stress (Cd8 and Cd16) improved wheat seedling root growth, P acquisition, and root hairs density in the piliferous zone and root cap. Moreover, inoculation with B. Cer significantly improved root inorganic P (Pi) (384 and 752%) and root acid phosphatases (176 and 131%) under Cd8 and Cd16 compared to uninoculated Cd-stressed seedlings. Such a beneficial root adaptation mechanism could be explained by the significant correlations (mainly under Cd16) between Pi content and morphological traits of wheat roots. Findings from this study demonstrate that P solubilization and Cd tolerance are likely interconnected rhizosphere processes triggered by inoculation that presumably induced the elongation of root hairs and likely the rigidity of the root cell wall to reduce Cd entrance while increasing P acquisition.

DENSIDADE DE SEMENTES E APLICAÇÃO FOLIAR DE FERTILIZANTE ORGANOMINERAL À BASE DE CÁLCIO E POTÁSSIO NA CULTURA DA AVEIA

Purpose: To present the benefits of increasing oat sowing density on productivity, uniformity, soil quality and reduction of pesticides and the use of an organomineral product based on calcium and potassium as an alternative to lodging control, promoting more sustainable cultivation systems. Theoretical framework: Increasing plant density can promote productivity, rapid soil coverage, reduction of weeds and greater harvest uniformity, reducing the use of pesticides. However, increasing seeding density can promote lodging. Lodging is the phenomenon in which plants leave the vertical position and fall to the ground, affecting the quality of the grains. The commercial product registered to control lodging is highly toxic to the environment. Organomineral sources with potassium and calcium represent an alternative for controlling lodging with reduced environmental impacts. Results: Benefits of increased seeding density to promote grain yield have been found for several crop species, reinforcing the need for adapting seeding density for oat crops. The use trinexapac-ethyl as a growth regulator, it poses risks of phytotoxicity and environmental contamination. In this context, several studies have indicated that potassium and calcium favor cell wall rigidity, potentially contributing to oat stem strength. Originality/value: This study provides significant contribution to the advancement of research on oat in Brazil, bringing new information benefiting farmers, technical assistance agents, and the food industry and improving the production system to ensure food security and care for the environment.

A critical concentration of magainin 2 is required to decrease cell stiffness but not to decrease cell wall rigidity in Staphylococcus epidermidis

A critical concentration of magainin 2 is required to decrease cell stiffness but not to decrease cell wall rigidity in Staphylococcus epidermidis

Mechanical advantage of subsidiary cells depends on the stomatal complex structure

Structural features of stomatal complexes influencing the mechanical advantage of subsidiary cells were studied. Light, scanning and transmission electron microscopy were used to research the morphology of Fagraea ceilanica stomatal complexes. Their guard cells are located on subsidiary cells. The walls of the subsidiary cells are thickened unevenly. The inner tangential walls are thin and most extensive as compared to other walls of these cells. The data obtained allowed a 3D model of F. ceilanica stomatal complex to be constructed. To elucidate the interaction between the guard and subsidiary cells during stomatal movements, we have applied modelling using the finite-element method. According to the modelling results, the mechanical advantage of the subsidiary cells depends on mutual location of the guard and subsidiary cells, uneven thickening, area and rigidity of the subsidiary cell walls and presence of substomatal chambers, into which the inner tangential walls of the subsidiary cells can bulge when turgor pressure in these cells increases. The modelling results were confirmed by the observed deformations in actual stomatal complex cells of F. ceilanica. The decrease in mechanical advantage of the subsidiary cells ensures stoma opening in the conditions of excessive saturation of the epidermis with water, for example, in the conditions of tropical rainforests.

Svx Peptidases of Phytopathogenic Pectolytic Bacteria: Structural, Catalytic and Phytoimmune Properties.

Svx proteins are virulence factors secreted by phytopathogenic bacteria of the Pectobacterium genus into the host plant cell wall. Svx-encoding genes are present in almost all species of the soft rot Pectobacteriaceae (Pectobacterium and Dickeya genera). The Svx of P. atrosepticum (Pba) has been shown to be a gluzincin metallopeptidase that presumably targets plant extensins, proteins that contribute to plant cell wall rigidity and participate in cell signaling. However, the particular "output" of the Pba Svx action in terms of plant-pathogen interactions and plant immune responses remained unknown. The Svx proteins are largely unexplored in Dickeya species, even though some of them have genes encoding two Svx homologs. Therefore, our study aims to compare the structural and catalytic properties of the Svx proteins of Pba and D. solani (Dso) and to test the phytoimmune properties of these proteins. Two assayed Dso Svx proteins, similar to Pba Svx, were gluzincin metallopeptidases with conservative tertiary structures. The two domains of the Svx proteins form electronegative clefts where the active centers of the peptidase domains are located. All three assayed Svx proteins possessed phytoimmunosuppressory properties and induced ethylene-mediated plant susceptible responses that play a decisive role in Pba-caused disease.

Leaf hydraulic properties of Antarctic plants: effects of growth temperature and its coordination with photosynthesis.

One of the well-documented effects of regional warming in Antarctica is the impact on flora. Warmer conditions modify several leaf anatomical traits of Antarctic vascular plants, increasing photosynthesis and growth. Given that CO2 and water vapor partially share their diffusion pathways through the leaf, changes in leaf anatomy could also affect the hydraulic traits of Antarctic plants. We evaluated the effects of growth temperature on several anatomical and hydraulic parameters of Antarctic plants and assessed the trait co-variation between these parameters and photosynthetic performance. Warmer conditions promoted an increase in leaf and whole plant hydraulic conductivity, correlating with adjustments in carbon assimilation. These adjustments were consistent with changes in leaf vasculature, where Antarctic species displayed different strategies. At higher temperature, Colobanthus quitensis decreased the number of leaf xylem vessels, but increased their diameter. In contrast, in Deschampsia antarctica the diameter did not change, but the number of vessels increased. Despite this contrasting behavior, some traits such as a small leaf diameter of vessels and a high cell wall rigidity were maintained in both species, suggesting a water-conservation response associated with the ability of Antarctic plants to cope with harsh environments.

The maize preligule band is subdivided into distinct domains with contrasting cellular properties prior to ligule outgrowth.

The maize ligule is an epidermis-derived structure that arises from the preligule band (PLB) at a boundary between the blade and sheath. A hinge-like auricle also develops immediately distal to the ligule and contributes to blade angle. Here, we characterize the stages of PLB and early ligule development in terms of topography, cell area, division orientation, cell wall rigidity, and auxin response dynamics. Differential thickening of epidermal cells and localized periclinal divisions contributed to the formation of a ridge within the PLB, which ultimately produces the ligule fringe. Patterns in cell wall rigidity were consistent with the subdivision of the PLB into two regions along a distinct line positioned at the nascent ridge. The proximal region produces the ligule, while the distal region contributes to one epidermal face of the auricles. Whereas the auxin transporter PIN1 accumulated in the PLB, observed differential auxin transcriptional response did not underlie the partitioning of the PLB. Our data demonstrate that two zones with contrasting cellular properties, the preligule and preauricle, are specified within the ligular region prior to ligule outgrowth.

Drought responsiveness in six wheat genotypes: identification of stress resistance indicators.

Wheat (Triticum aestivum L.) is among the world's most important staple food crops. In the current climate change scenario, a better understanding of wheat response mechanisms to water stress could help to enhance its productivity in arid ecosystems. In this study, water relations, gas exchange, membrane integrity, agronomic traits and molecular analysis were evaluated in six wheat genotypes (D117, Syndiouk, Tunisian durum7 (Td7), Utique, Mahmoudi AG3 and BT) subjected to drought-stress. For all the studied genotypes, drought stress altered leaf area, chlorophyll content, stomatal density, photosynthetic rate and water-use efficiency, while the relative water content at turgor loss point (RWC0) remained stable. Changes in osmotic potential at turgor loss point (Ψπ0), bulk modulus of elasticity (Ɛmax) and stomatal regulation, differed greatly among the studied genotypes. For the drought-sensitive genotypes AG3 and BT, no significant changes were observed in Ψπ0, whereas the stomatal conductance (gs) and transpiration rate (E) decreased under stress conditions. These two varieties avoided turgor loss during drought treatment through an accurate stomatal control, resulting in a significant reduction in yield components. On the contrary, for Syndiouk, D117, Td7 and Utique genotypes, a solute accumulation and an increase in cell wall rigidity were the main mechanisms developed during drought stress. These mechanisms were efficient in enhancing soil water uptake, limiting leaf water loss and protecting cells membranes against leakage induced by oxidative damages. Furthermore, leaf soluble sugars accumulation was the major component of osmotic adjustment in drought-stressed wheat plants. The transcriptional analysis of genes involved in the final step of the ABA biosynthesis (AAO) and in the synthesis of an aquaporin (PIP2:1) revealed distinct responses to drought stress among the selected genotypes. In the resistant genotypes, PIP2:1 was significantly upregulated whereas in the sensitive ones, its expression showed only a slight induction. Conversely, the sensitive genotypes exhibited higher levels of AAO gene expression compared to the resistant genotypes. Our results suggest that drought tolerance in wheat is regulated by the interaction between the dynamics of leaf water status and stomatal behavior. Based on our findings, Syndiouk, D117, Utique and Td7, could be used in breeding programs for developing high-yielding and drought-tolerant wheat varieties.

Ghosts of dry seasons past: Legacy of severe drought enhances mangrove salinity tolerance through coordinated cellular osmotic and elastic adjustments.

The incidence and severity of global mangrove mortality due to drought is increasing. Yet, little is understood of the capacity of mangroves to show long-term acclimation of leaf water relations to severe drought. We tested for differences between mid-dry season leaf water relations in two cooccurring mangroves, Aegiceras corniculatum and Rhizophora stylosa before a severe drought (a heatwave combined with low rainfall) and after its relief by the wet season. Consistent with ecological stress memory, the legacy of severe drought enhanced salinity tolerance in the subsequent dry season through coordinated adjustments that reduced the leaf water potential at the turgor loss point and increased cell wall rigidity. These adjustments enabled maintenance of turgor and relative water content with increasing salinity. As most canopy growth occurs during the wet season, acclimation to the 'memory'of higher salinity in the previous dry season enables greater leaf function with minimal adjustments, as long-lived leaves progress from wet through dry seasons. However, declining turgor safety margins - the difference between soil water potential and leaf water potential at turgor loss - implied increasing limitation to water use with increasing salinity. Thus, plasticity in leaf water relations contributes fundamentally to mangrove function under varying salinity regimes.

Cotton 4-coumarate-CoA ligase 3 enhanced plant resistance to Verticillium dahliae by promoting jasmonic acid signaling-mediated vascular lignification and metabolic flux.

Lignins and their antimicrobial-related polymers cooperatively enhance plant resistance to pathogens. Several isoforms of 4-coumarate-coenzyme A ligases (4CLs) have been identified as indispensable enzymes involved in lignin and flavonoid biosynthetic pathways. However, their roles in plant-pathogen interaction are still poorly understood. This study uncovers the role of Gh4CL3 in cotton resistance to the vascular pathogen Verticillium dahliae. The cotton 4CL3-CRISPR/Cas9 mutant (CR4cl) exhibited high susceptibility to V. dahliae. This susceptibility was most probably due to the reduction in the total lignin content and the biosynthesis of several phenolic metabolites, e.g., rutin, catechin, scopoletin glucoside, and chlorogenic acid, along with jasmonic acid (JA) attenuation. These changes were coupled with a significant reduction in 4CL activity toward p-coumaric acid substrate, and it is likely that recombinant Gh4CL3 could specifically catalyze p-coumaric acid to form p-coumaroyl-coenzyme A. Thus, overexpression of Gh4CL3 (OE4CL) showed increasing 4CL activity that augmented phenolic precursors, cinnamic, p-coumaric, and sinapic acids, channeling into lignin and flavonoid biosyntheses and enhanced resistance to V. dahliae. Besides, Gh4CL3 overexpression activated JA signaling that instantly stimulated lignin deposition and metabolic flux in response to pathogen, which all established an efficient plant defense response system, and inhibited V. dahliae mycelium growth. Our results propose that Gh4CL3 acts as a positive regulator for cotton resistance against V. dahliae by promoting JA signaling-mediated enhanced cell wall rigidity and metabolic flux.

Texture and Key Components of Frozen Cabbage Leaves as Affected by Maturity Type

The objectives of this study were to (i) evaluate the impact of maturity types on the texture and microstructure of frozen cabbage leaves and (ii) elucidate the relationships between variables (alcohol-insoluble solid (AIS), pectin, insoluble dietary fiber (IDF), total soluble solid (TSS), and pH) and the firmness of frozen cabbage leaves. Fourteen cabbage cultivars of four maturity types grown in three regions of Japan for 3 years were used as samples. Higher firmness and less drip loss in frozen cabbage leaves were obtained in the late maturing cultivars, followed by the medium-late, medium, and early maturing cultivars. Scanning electron microscopy showed severe cell wall damage in frozen leaves of the early maturing cabbage, while well-defined individual cells could be observed in the late maturing cabbage. Positive linear correlations between the firmness of frozen cabbage leaves and the amount of cell wall components (AIS (R2 = 0.818), pectin (R2 = 0.670), IDF (R2 = 0.841)) and the concentration of solutes (TSS (R2 = 0.799)) were detected. On the other hand, there was no relationship between pH values and the firmness of frozen cabbage leaves (R2 < 0.1). Thus, we proposed the combination of two phenomena (i.e., greater cell wall rigidity and smaller ice crystals due to the higher solute concentration) regulating the firmness of frozen cabbage leaves. These results highlight the importance of cultivar selection, especially with respect to maturity type, for the manufacture of frozen cut cabbage.

Solid-state NMR molecular snapshots of Aspergillus fumigatus cell wall architecture during a conidial morphotype transition

While establishing an invasive infection, the dormant conidia of Aspergillus fumigatus transit through swollen and germinating stages, to form hyphae. During this morphotype transition, the conidial cell wall undergoes dynamic remodeling, which poses challenges to the host immune system and antifungal drugs. However, such cell wall reorganization during conidial germination has not been studied so far. Here, we explored the molecular rearrangement of Aspergillus fumigatus cell wall polysaccharides during different stages of germination. We took advantage of magic-angle spinning NMR to investigate the cell wall polysaccharides, without employing any destructive method for sample preparation. The breaking of dormancy was associated with a significant change in the molar ratio between the major polysaccharides β-1,3-glucan and α-1,3-glucan, while chitin remained equally abundant. The use of various polarization transfers allowed the detection of rigid and mobile polysaccharides; the appearance of mobile galactosaminogalactan was a molecular hallmark of germinating conidia. We also report for the first time highly abundant triglyceride lipids in the mobile matrix of conidial cell walls. Water to polysaccharides polarization transfers revealed an increased surface exposure of glucans during germination, while chitin remained embedded deeper in the cell wall, suggesting a molecular compensation mechanism to keep the cell wall rigidity. We complement the NMR analysis with confocal and atomic force microscopies to explore the role of melanin and RodA hydrophobin on the dormant conidial surface. Exemplified here using Aspergillus fumigatus as a model, our approach provides a powerful tool to decipher the molecular remodeling of fungal cell walls during their morphotype switching.

Emerging trends in the pretreatment of microalgal biomass and recovery of value-added products: A review

Microalgae are a promising source of raw material (i.e., proteins, carbohydrates, lipids, pigments, and micronutrients) for various value-added products and act as a carbon sink for atmospheric CO2. The rigidity of the microalgal cell wall makes it difficult to extract different cellular components for its applications, including biofuel production, food and feed supplements, and pharmaceuticals. To improve the recovery of products from microalgae, pretreatment strategies such as biological, physical, chemical, and combined methods have been explored to improve whole-cell disruption and product recovery efficiency. However, the diversity and uniqueness of the microalgal cell wall make the pretreatment process more species-specific and limit its large-scale application. Therefore, advancing the currently available technologies is required from an economic, technological, and environmental perspective. Thus, this paper provides a state-of-art review of the current trends, challenges, and prospects of sustainable microalgal pretreatment technologies from a microalgae-based biorefinery concept.