Fungal cell wall organization and biosynthesis

Whole-Genome Sequencing and Genome Annotation of Pathogenic Elsinoë batatas Causing Stem and Foliage Scab Disease in Sweet Potato

A pathogen strain responsible for sweet potato stem and foliage scab disease was isolated from sweet potato stems. Through a phylogenetic analysis based on the rDNA internal transcribed spacer (ITS) region, combined with morphological methods, the isolated strain was identified as Elsinoë batatas. To comprehensively analyze the pathogenicity of the isolated strain from a genetic perspective, the whole-genome sequencing of E. batatas HD-1 was performed using both the PacBio and Illumina platforms. The genome of E. batatas HD-1 is about 26.31 Mb long in 167 scaffolds, with a GC content of 50.81%, and 7898 protein-coding genes, 131 non-coding RNAs, and 1954 interspersed repetitive sequences were predicted. Functional annotation revealed that 408 genes encode virulence factors involved in plant disease (DFVF-Plant). Notably, twenty-eight of these virulence genes encode secretory carbohydrate-active enzymes (CAZymes), including two endo-1,4-β-xylanase genes and seven cutinase genes, which suggested that endo-1,4-β-xylanase and cutinase play a vital role in the pathogenicity of E. batatas HD-1 within sweet potato. In total, twelve effectors were identified, including five LysM effectors and two CDIP effectors, suggesting that LysM and CDIP effectors play significant roles in the interaction between E. batatas HD-1 and sweet potato. Additionally, our analysis of biosynthetic gene clusters (BGCs) showed that two gene clusters are involved in melanin and choline metabolism. This study enriches the genomic resources of E. batatas and provides a theoretical foundation for future investigations into the pathogenic mechanisms of its infection in sweet potatoes, as well as potential targets for disease control.

Threats from the Candida parapsilosis complex: the surge of multidrug resistance and a hotbed for new emerging pathogens

SUMMARYCandida parapsilosis is a common agent of candidiasis that has gained increased attention in recent years, culminating with its recent consideration as a high-priority fungal pathogen by the World Health Organization. Reasons for this classification are the recent surge in incidence and the alarmingly growing rates of drug and multidrug resistance. In addition, several closely related species such as Candida metapsilosis and Candida orthopsilosis may represent recently emerged opportunistic pathogens originated from environmental niches through interspecies hybridization. Here, I review recent research focused on the potential origin and spread of drug resistance and of emerging species in this complex. I will also discuss open questions regarding the possible implications of human activities in these two epidemiological phenomena.

β-1,6-Glucan plays a central role in the structure and remodeling of the bilaminate fungal cell wall

The cell wall of human fungal pathogens plays critical roles as an architectural scaffold and as a target and modulator of the host immune response. Although the cell wall of the pathogenic yeast Candida albicans is intensively studied, one of the major fibrillar components in its cell wall, β-1,6-glucan, has been largely neglected. Here, we show that β-1,6-glucan is essential for bilayered cell wall organization, cell wall integrity, and filamentous growth. For the first time, we show that β-1,6-glucan production compensates the defect in mannan elongation in the outer layer of the cell wall. In addition, β-1,6-glucan dynamics are also coordinated by host environmental stimuli and stresses with wall remodeling, where the regulation of β-1,6-glucan structure and chain length is a crucial process. As we point out that β-1,6-glucan is exposed at the yeast surface and modulate immune response, β-1,6-glucan must be considered a key factor in host-pathogen interactions.

Receptor polarization through localized activity and global sensitization

Eukaryotic cells chemosense concentration gradients of extracellular ligands using membrane-bound receptors that polarize their activity. Receptors from several chemosensing families are preferentially degraded after activation and undergo significant lateral diffusion, both of which may blunt their polarization. To explore the combined role of these two seemingly detrimental phenomena on active receptor polarization, we use a reaction/diffusion model. The model elucidates a counterintuitive principle that governs receptor polarization under external gradients: Localized Activity and Global Sensitization (LAGS). In LAGS, receptor activity is localized through receptor degradation or ligand unbinding. In contrast, uniform sensitivity to ligands is maintained over the plasma membrane through lateral receptor diffusion. Surprisingly, increasing preferential degradation of active receptors and increasing lateral diffusion of all receptors both sharpen active receptor polarization. Additionally, when combined with receptor oligomerization, an increase in preferential degradation allows cells to sense relative ligand gradients over a larger range of background ligand concentrations. An analytical model identifies parameter regimes that dictate which processes dominate receptor polarization. A survey of kinetic parameters suggests that receptor polarization in many mammalian pathways can be modeled using LAGS.

Human birth tissue products as a non-opioid medicine to inhibit post-surgical pain

Pain after surgery causes significant suffering. Opioid analgesics cause severe side effects and accidental death. Therefore, there is an urgent need to develop non-opioid therapies for managing post-surgical pain. Local application of Clarix Flo (FLO), a human amniotic membrane (AM) product, attenuated established post-surgical pain hypersensitivity without exhibiting known side effects of opioid use in mice. This effect was achieved through direct inhibition of nociceptive dorsal root ganglion (DRG) neurons via CD44-dependent pathways. We further purified the major matrix component, the heavy chain-hyaluronic acid/pentraxin 3 (HC-HA/PTX3) from human AM that has greater purity and water solubility than FLO. HC-HA/PTX3 replicated FLO-induced neuronal and pain inhibition. Mechanistically, HC-HA/PTX3 induced cytoskeleton rearrangements to inhibit sodium current and high-voltage activated calcium current on nociceptive neurons, suggesting it is a key bioactive component mediating pain relief. Collectively, our findings highlight the potential of naturally derived biologics from human birth tissues as an effective non-opioid treatment for post-surgical pain. Moreover, we unravel the underlying mechanisms of pain inhibition induced by FLO and HC-HA/PTX3.

Two structurally different oomycete lipophilic microbe-associated molecular patterns induce distinctive plant immune responses

Plants recognize a variety of external signals and induce appropriate mechanisms to increase their tolerance to biotic and abiotic stresses. Precise recognition of attacking pathogens and induction of effective resistance mechanisms are critical functions for plant survival. Some molecular patterns unique to a certain group of microbes, microbe-associated molecular patterns (MAMPs), are sensed by plant cells as nonself molecules via pattern recognition receptors. While MAMPs of bacterial and fungal origin have been identified, reports on oomycete MAMPs are relatively limited. This study aimed to identify MAMPs from an oomycete pathogen Phytophthora infestans, the causal agent of potato late blight. Using reactive oxygen species (ROS) production and phytoalexin production in potato (Solanum tuberosum) as markers, two structurally different groups of elicitors, namely ceramides and diacylglycerols, were identified. P. infestans ceramides (Pi-Cer A, B, and D) induced ROS production, while diacylglycerol (Pi-DAG A and B), containing eicosapentaenoic acid (EPA) as a substructure, induced phytoalexins production in potato. The molecular patterns in Pi-Cers and Pi-DAGs essential for defense induction were identified as 9-methyl-4,8-sphingadienine (9Me-Spd) and 5,8,11,14-tetraene-type fatty acid (5,8,11,14-TEFA), respectively. These structures are not found in plants, but in oomycetes and fungi, indicating that they are microbe molecular patterns recognized by plants. When Arabidopsis (Arabidopsis thaliana) was treated with Pi-Cer D and EPA, partially overlapping but different sets of genes were induced. Furthermore, expression of some genes is upregulated only after the simultaneous treatment with Pi-Cer D and EPA, indicating that plants combine the signals from simultaneously recognized MAMPs to adapt their defense response to pathogens.

Mechanical strategies supporting growth and size diversity in Filamentous Fungi

The stereotypical tip growth of filamentous fungi supports their lifestyles and functions. It relies on the polarized remodeling and expansion of a protective elastic cell wall (CW) driven by large cytoplasmic turgor pressure. Remarkably, hyphal filament diameters and cell elongation rates can vary extensively among different fungi. To date, however, how fungal cell mechanics may be adapted to support these morphological diversities while ensuring surface integrity remains unknown. Here, we combined super-resolution imaging and deflation assays to measure local CW thickness, elasticity and turgor in a set of fungal species spread on the evolutionary tree that spans a large range in cell size and growth speeds. While CW elasticity exhibited dispersed values, presumably reflecting differences in CW composition, both thickness and turgor scaled in dose-dependence with cell diameter and growth speeds. Notably, larger cells exhibited thinner lateral CWs, and faster cells thinner apical CWs. Counterintuitively, turgor pressure was also inversely scaled with cell diameter and tip growth speed, challenging the idea that turgor is the primary factor dictating tip elongation rates. We propose that fast-growing cells with rapid CW turnover have evolved strategies based on a less turgid cytoplasm and thin walls to safeguard surface integrity and survival.

Self-organizing ovarian somatic organoids preserve cellular heterogeneity and reveal cellular contributions to ovarian aging

Ovarian somatic cells are essential for reproductive function, but no existing ex vivo models recapitulate the cellular heterogeneity or interactions within this compartment. We engineered a novel ovarian somatic organoid model by culturing a stroma-enriched fraction of mouse ovaries in scaffold-free agarose micromolds. Ovarian somatic organoids self-organized, maintained diverse cell populations, produced extracellular matrix, and secreted hormones. Organoids generated from reproductively old mice exhibited reduced aggregation and growth compared to young counterparts, as well as differences in cellular composition. Interestingly, matrix fibroblasts from old mice demonstrated upregulation of pathways associated with the actin cytoskeleton and downregulation of cell adhesion pathways, indicative of increased cellular stiffness which may impair organoid aggregation. Cellular morphology, which is regulated by the cytoskeleton, significantly changed with age and in response to actin depolymerization. Moreover, actin depolymerization rescued age-associated organoid aggregation deficiency. Overall, ovarian somatic organoids have advanced fundamental knowledge of cellular contributions to ovarian aging.

Chemical Profile and In Vitro Gut Microbiota Modulation of Wild Edible Mushroom Phallus atrovolvatus Fruiting Body at Different Maturity Stages

Phallus atrovolvatus, a wild edible mushroom, has attracted increasing interest for consumption due to its unique taste and beneficial health benefits. This study determined the chemical components in the so-called fruiting body during the egg and mature stages and investigated its gut microbiota-modulating activities. The egg stage contained higher total carbohydrates, dietary fiber, glucans, ash, and fat, while the total protein content was lower than in the mature stage. Two consumption forms, including cooked mushrooms and a mushroom aqueous extract from both stages, were used in this study. An in vitro gut fermentation was performed for 24 h to assess gut microbiota regulation. All mushroom-supplemented fermentations increased short-chain fatty acid (SCFA) production compared to the blank control. Furthermore, all mushroom supplementations promoted the growth of Bifidobacterium and Streptococcus. Samples from the mature stage increased the relative abundance of Clostridium sensu stricto 1, while those from the egg stage increased the Bacteroides group. The inhibition of harmful bacteria, including Escherichia-Shigella, Klebsiella, and Veillonella, was only observed for the mature body. Our findings demonstrate that P. atrovolvatus exhibits potential benefits on gut health by promoting SCFA production and the growth of beneficial bacteria, with the mature stage demonstrating superior effects compared to the egg stage.

The Forkhead Box Gene, MaSep1, Negatively Regulates UV- and Thermo-Tolerances and Is Required for Microcycle Conidiation in Metarhizium acridum

Insect pathogenic fungi have shown great potential in agricultural pest control. Conidiation is crucial for the survival of filamentous fungi, and dispersal occurs through two methods: normal conidiation, where conidia differentiate from mycelium, and microcycle conidiation, which involves conidial budding. The conidiation process is related to cell separation. The forkhead box gene Sep1 in Schizosaccharomyces pombe plays a crucial role in cell separation. Nevertheless, the function of Sep1 has not been clarified in filamentous fungi. Here, MaSep1, the homolog of Sep1 in Metarhizium acridum, was identified and subjected to functional analysis. The findings revealed that conidial germination of the MaSep1-deletion strain (ΔMaSep1) was accelerated and the time for 50% germination rate of conidial was shortened by 1 h, while the conidial production of ΔMaSep1 was considerably reduced. The resistances to heat shock and UV-B irradiation of ΔMaSep1 were enhanced, and the expression of some genes involved in DNA damage repair and heat shock response was significantly increased in ΔMaSep1. The disruption of MaSep1 had no effect on the virulence of M. acridum. Interestingly, ΔMaSep1 conducted the normal conidiation on the microcycle conidiation medium, SYA. Furthermore, 127 DEGs were identified by RNA-Seq between the wild-type and ΔMaSep1 strains during microcycle conidiation, proving that MaSep1 mediated the conidiation pattern shift by governing some genes associated with conidiation, cell division, and cell wall formation.

Transcription factor FoAce2 regulates virulence, vegetative growth, conidiation, and cell wall homeostasis in Fusarium oxysporum f. sp. cubense

Fusarium wilt of banana, caused by the fungus Fusarium oxysporum f. sp. cubense (Foc), is a serious fungal disease that affects banana plants globally. To explore the virulence mechanisms of this pathogen, we created a null mutation of the transcription factor gene FoAce2 (encoding F. oxysporum angiotensin converting enzyme 2). Deletion of FoAce2 resulted in slower growth, decreased aerial mycelia and conidiation, and a significant decrease in fungal virulence against banana hosts relative to those of the wild-type (WT) fungus. Additionally, transmission electron microscopy showed that the cell wall was thicker in the FoAce2 deletion mutants. Consistent with this finding, the cell wall glucose level was decreased in the ΔFoAce2 mutants compared with that in the WT and complemented strain, ΔFoAce2-C1. Complementation with the WT FoAce2 gene fully reversed the mutant phenotypes. Analysis of the transcriptome of ΔFoAce2 and the WT strain showed alterations in the expression levels of many genes associated with virulence and growth. Thus, FoAce2 appears to be essential for Foc virulence, cell wall homeostasis, conidiation, and vegetative growth.

Glyoxal oxidase-mediated detoxification of reactive carbonyl species contributes to virulence, stress tolerance, and development in a pathogenic fungus

Reactive carbonyl and oxygen species (RCS/ROS), often generated as metabolic byproducts, particularly under conditions of pathology, can cause direct damage to proteins, lipids, and nucleic acids. Glyoxal oxidases (Gloxs) oxidize aldehydes to carboxylic acids, generating hydrogen peroxide (H2O2). Although best characterized for their roles in lignin degradation, Glox in plant fungal pathogens are known to contribute to virulence, however, the mechanism underlying such effects are unclear. Here, we show that Glox in the insect pathogenic fungus, Metarhizium acridum, is highly expressed in mycelia and during formation of infection structures (appressoria), with the enzyme localizing to the cell membrane. MaGlox targeted gene disruption mutants showed RCS and ROS accumulation, resulting in cell toxicity, induction of apoptosis and increased autophagy, inhibiting normal fungal growth and development. The ability of the MaGlox mutant to scavenge RCS was significantly reduced, and the mutant exhibited increased susceptibility to aldehydes, oxidative and cell wall perturbing agents but not toward osmotic stress, with altered cell wall contents. The ΔMaGlox mutant was impaired in its ability to penetrate the host cuticle and evade host immune defense resulting in attenuated pathogenicity. Overexpression of MaGlox promoted fungal growth and conidial germination, increased tolerance to H2O2, but had little to other phenotypic effects. Transcriptomic analyses revealed downregulation of genes related to cell wall synthesis, conidiation, stress tolerance, and host cuticle penetration in the ΔMaGlox mutant. These findings demonstrate that MaGlox-mediated scavenging of RCS is required for virulence, and contributes to normal fungal growth and development, stress resistance.

Innate immune signal transduction pathways to fungal infection: Components and regulation

Candida species are significant causes of mucosal and systemic infections in immune compromised populations, including HIV-infected individuals and cancer patients. Drug resistance and toxicity have limited the use of anti-fungal drugs. A good comprehension of the nature of the immune responses to the pathogenic fungi will aid in the developing of new approaches to the treatment of fungal diseases. In recent years, extensive research has been done to understand the host defending systems to fungal infections. In this review, we described how pattern recognition receptors senses the cognate fungal ligands and the cellular and molecular mechanisms of anti-fungal innate immune responses. Furthermore, particular focus is placed on how anti-fungal signal transduction cascades are being activated for host defense and being modulated to better treat the infections in terms of immunotherapy. Understanding the role that these pathways have in mediating host anti-fungal immunity will be crucial for future therapeutic development.

Diffusion barriers imposed by tissue topology shape morphogen gradients

Animals use a small number of morphogens to pattern tissues, but it is unclear how evolution modulates morphogen signaling range to match tissues of varying sizes. Here, we used single molecule imaging in reconstituted morphogen gradients and in tissue explants to determine that Hedgehog diffused extra-cellularly as a monomer, and rapidly transitioned between membrane-confined and -unconfined states. Unexpectedly, the vertebrate-specific protein SCUBE1 expanded Hedgehog gradients by accelerating the transition rates between states without affecting the relative abundance of molecules in each state. This observation could not be explained under existing models of morphogen diffusion. Instead, we developed a topology-limited diffusion model in which cell-cell gaps create diffusion barriers, and morphogens can only overcome the barrier by passing through a membrane-unconfined state. Under this model, SCUBE1 promotes Hedgehog secretion and diffusion by allowing it to transiently overcome diffusion barriers. This multiscale understanding of morphogen gradient formation unified prior models and discovered novel knobs that nature can use to tune morphogen gradient sizes across tissues and organisms.

Chitin-induced disease resistance in plants: A review

Chitin is composed of N-acetylglucosamine units. Chitin a polysaccharide found in the cell walls of fungi and exoskeletons of insects and crustaceans, can elicit a potent defense response in plants. Through the activation of defense genes, stimulation of defensive compound production, and reinforcement of physical barriers, chitin enhances the plant's ability to defend against pathogens. Chitin-based treatments have shown efficacy against various plant diseases caused by fungal, bacterial, viral, and nematode pathogens, and have been integrated into sustainable agricultural practices. Furthermore, chitin treatments have demonstrated additional benefits, such as promoting plant growth and improving tolerance to abiotic stresses. Further research is necessary to optimize treatment parameters, explore chitin derivatives, and conduct long-term field studies. Continued efforts in these areas will contribute to the development of innovative and sustainable strategies for disease management in agriculture, ultimately leading to improved crop productivity and reduced reliance on chemical pesticides.

Structural diversification of fungal cell wall in response to the stress signaling and remodeling during fungal pathogenesis

Fungi are one of the most diverse organisms found in our surroundings. The heterotrophic lifestyle of fungi and the ever-changing external environmental factors pose numerous challenges for their survival. Despite all adversities, fungi continuously develop new survival strategies to secure nutrition and space from their host. During host-pathogen interaction, filamentous phytopathogens in particular, effectively infect their hosts by maintaining polarised growth at the tips of hyphae. The fungal cell wall, being the prime component of host contact, plays a crucial role in fortifying the intracellular environment against the harsh external environment. Structurally, the fungal cell wall is a highly dynamic yet rigid component, responsible for maintaining cellular morphology. Filamentous pathogens actively maintain their dynamic cell wall to compensate rapid growth on the host. Additionally, they secrete effectors to dampen the sophisticated mechanisms of plant defense and initiate various downstream signaling cascades to repair the damage inflicted by the host. Thus, the fungal cell wall serves as a key modulator of fungal pathogenicity. The fungal cell wall with their associated signaling mechanisms emerge as intriguing targets for host immunity. This review comprehensively examines and summarizes the multifaceted findings of various research groups regarding the dynamics of the cell wall in filamentous fungal pathogens during host invasion.

Marine-Derived Metabolites Act as Promising Antifungal Agents

The incidence of invasive fungal diseases (IFDs) is on the rise globally, particularly among immunocompromised patients, leading to significant morbidity and mortality. Current clinical antifungal agents, such as polyenes, azoles, and echinocandins, face increasing resistance from pathogenic fungi. Therefore, there is a pressing need for the development of novel antifungal drugs. Marine-derived secondary metabolites represent valuable resources that are characterized by varied chemical structures and pharmacological activities. While numerous compounds exhibiting promising antifungal activity have been identified, a comprehensive review elucidating their specific underlying mechanisms remains lacking. In this review, we have compiled a summary of antifungal compounds derived from marine organisms, highlighting their diverse mechanisms of action targeting various fungal cellular components, including the cell wall, cell membrane, mitochondria, chromosomes, drug efflux pumps, and several biological processes, including vesicular trafficking and the growth of hyphae and biofilms. This review is helpful for the subsequent development of antifungal drugs due to its summary of the antifungal mechanisms of secondary metabolites from marine organisms.

Biotransformation of the azo dye reactive orange 16 by Aspergillus flavus A5P1: Performance, genetic background, pathway, and mechanism

This study reports the strain Aspergillus flavus A5P1 (A5P1), which is with the capable of degrading the azo dye reactive orange 16 (RO16). The mechanism of RO16 degradation by A5P1 was elucidated through genomic analysis, enzymatic analysis, degradation pathway analysis and oxidative stress analysis. Strain A5P1 exhibited aerobic degradation of RO16, with optimal degradation at an initial pH of 3.0. Genomic analysis indicates that strain A5P1 possesses the potential for acid tolerance and degradation of azo dye. Enzymatic analysis, combined with degradation product analysis, demonstrated that extracellular laccase, intracellular lignin peroxidase, and intracellular quinone reductase were likely key enzymes in the RO16 degradation process. Oxidative stress analysis revealed that cell stress responses may participate in the RO16 biotransformation process. The results indicated that the biotransformation of RO16 may involves biological processes such as transmembrane transport of RO16, cometabolism of the strain with RO16, and cell stress responses. These findings shed light on the biodegradation of RO16 by A5P1, indicating A5P1's potential for environmental remediation.

Endogenous cell wall degrading enzyme LytD is important for the biocontrol activity of Bacillus subtilis

Autolysins are endogenous cell wall degrading enzymes (CWDEs) in bacteria that remodel the peptidoglycan layer of its own cell wall. In the Bacillus subtilis genome, at least 35 autolysin genes have been identified. However, the study of their roles in bacterial physiology has been hampered by their complexity and functional redundancy. B. subtilis GLB191 is an effective biocontrol strain against grape downy mildew disease, the biocontrol effect of which results from both direct effect against the pathogen and stimulation of the plant defense. In this study, we show that the autolysin N-acetylglucosaminidase LytD, a major autolysin of vegetative growth in B. subtilis, plays an important role in its biocontrol activity against grape downy mildew. Disruption of lytD resulted in reduced suppression of the pathogen Plasmopara viticola and stimulation of the plant defense. LytD is also shown to affect the biofilm formation and colonization of B. subtilis on grape leaves. This is the first report that demonstrates the role of an endogenous CWDE in suppressing plant disease infection of a biological control microorganism. These findings not only expand our knowledge on the biological function of autolysins but also provide a new target to promote the biocontrol activity of B. subtilis.

Melanin depletion affects Aspergillus flavus conidial surface proteins, architecture, and virulence

Melanin is an Aspergillus flavus cell wall component that provides chemical and physical protection to the organism. However, the molecular and biological mechanisms modulating melanin-mediated host-pathogen interaction in A. flavus keratitis are not well understood. This work aimed to compare the morphology, surface proteome profile, and virulence of melanized conidia (MC) and non-melanized conidia (NMC) of A. flavus. Kojic acid treatment inhibited melanin synthesis in A. flavus, and the conidial surface protein profile was significantly different in kojic acid-treated non-melanized conidia. Several cell wall-associated proteins and proteins responsible for oxidative stress, carbohydrate, and chitin metabolic pathways were found only in the formic acid extracts of NMC. Scanning electron microscopy (SEM) analysis showed the conidial surface morphology difference between the NMC and MC, indicating the role of melanin in the structural integrity of the conidial cell wall. The levels of calcofluor white staining efficiency were different, but there was no microscopic morphology difference in lactophenol cotton blue staining between MC and NMC. Evaluation of the virulence of MC and NMC in the Galleria mellonella model showed NMC was less virulent compared to MC. Our findings showed that the integrity of the conidial surface is controlled by the melanin layer. The alteration in the surface protein profile indicated that many surface proteins are masked by the melanin layer, and hence, melanin can modulate the host response by preventing the exposure of fungal proteins to the host immune defense system. The G. mellonella virulence assay also confirmed that the NMC were susceptible to host defense as in other Aspergillus pathogens. KEY POINTS: • l-DOPA melanin production was inhibited in A. flavus isolates by kojic acid, and for the first time, scanning electron microscopy (SEM) analysis revealed morphological differences between MC and NMC of A. flavus strains • Proteome profile of non-melanized conidia showed more conidial surface proteins and these proteins were mainly involved in the virulence, oxidative stress, and metabolism pathways • Non-melanized conidia of A. flavus strains were shown to be less virulent than melanised conidia in an in vivo virulence experiment with the G. melonella model.

Yeast cell wall mannan structural features, biological activities, and production strategies

Mannan and outer structural yeast cell wall polysaccharides have recently garnered attention for their health defense and cosmetic applications. In addition, many studies have confirmed that yeast cell wall mannans exhibit various biological activities, such as antioxidant, immune regulation, reducing hyperlipidemia, and gut health promotion. This paper elucidates yeast cell wall mannan structural features, biological activities, underlying molecular mechanisms, and biosynthesis. Moreover, mannan-overproducing strategies through yeast strain engineering are emphasized and discussed. This review will provide a scientific basis for yeast cell wall mannan research and industrial applications.

Generation and characterization of temperature-sensitive alleles of the glucanosyltransferase Gas1 in Schizosaccharomyces pombe

The Schizosaccharomyces pombe Gas family of β-1,3-glucanosyltransferases modify the cell wall by elongating β-1,3-glucan chains. While gas1Δ cells are inviable under standard laboratory growth conditions, they are viable in the presence of an osmotic stabilizer. Even under these conditions however, gas1Δ cells are slow-growing and display cell separation and morphology defects. Here, we isolated and characterized two gas1 temperature-sensitive alleles. Our data support that Gas1 is the primary S. pombe β-1,3-glucanosyltransferase important for cell separation and cell viability and provide useful tools for further analysis of S. pombe cell wall formation.

Fungal Cell Wall-Associated Effectors: Sensing, Integration, Suppression, and Protection

The cell wall (CW) of plant-interacting fungi, as the direct interface with host plants, plays a crucial role in fungal development. A number of secreted proteins are directly associated with the fungal CW, either through covalent or non-covalent interactions, and serve a range of important functions. In the context of plant-fungal interactions many are important for fungal development in the host environment and may therefore be considered fungal CW-associated effectors (CWAEs). Key CWAE functions include integrating chemical/physical signals to direct hyphal growth, interfering with plant immunity, and providing protection against plant defenses. In recent years, a diverse range of mechanisms have been reported that underpin their roles, with some CWAEs harboring conserved motifs or functional domains, while others are reported to have novel features. As such, the current understanding regarding fungal CWAEs is systematically presented here from the perspective of their biological functions in plant-fungal interactions. An overview of the fungal CW architecture and the mechanisms by which proteins are secreted, modified, and incorporated into the CW is first presented to provide context for their biological roles. Some CWAE functions are reported across a broad range of pathosystems or symbiotic/mutualistic associations. Prominent are the chitin interacting-effectors that facilitate fungal CW modification, protection, or suppression of host immune responses. However, several alternative functions are now reported and are presented and discussed. CWAEs can play diverse roles, some possibly unique to fungal lineages and others conserved across a broad range of plant-interacting fungi. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Macrophage pyroptosis induced by Candida albicans

Candida albicans (C. albicans) is a prevalent opportunistic pathogen that causes mucocutaneous and systemic infections, particularly in immunocompromised individuals. Macrophages play a crucial role in eliminating C. albicans in local and bloodstream contexts, while also regulating antifungal immune responses. However, C. albicans can induce macrophage lysis through pyroptosis, a type of regulated cell death. This process can enable C. albicans to escape from immune cells and trigger the release of IL-1β and IL-18, which can impact both the host and the pathogen. Nevertheless, the mechanisms by which C. albicans triggers pyroptosis in macrophages and the key factors involved in this process remain unclear. In this review, we will explore various factors that may influence or trigger pyroptosis in macrophages induced by C. albicans, such as hypha, ergosterol, cell wall remodeling, and other virulence factors. We will also examine the possible immune response following macrophage pyroptosis.

Regulatory role of cholesterol in modulating actin dynamics and cell adhesive interactions in the trabecular meshwork

The trabecular meshwork (TM) tissue plays a crucial role in maintaining intraocular pressure (IOP) homeostasis. Increased TM contractility and stiffness are directly correlated with elevated IOP. Although cholesterol is known to be a determinant of glaucoma occurrence and elevated IOP, the underlying mechanisms remain elusive. In this study, we used human TM (HTM) cells to unravel the effects of cholesterol on TM stiffness. We achieved this by performing acute cholesterol depletion with Methyl-β-cyclodextrin (MβCD) and cholesterol enrichment/replenishment with MβCD cholesterol complex (CHOL). Interestingly, cholesterol depletion triggered notable actin depolymerization and decreased focal adhesion formation, while enrichment/replenishment promoted actin polymerization, requiring the presence of actin monomers. Using a specific reporter of phosphatidylinositol 4,5-bisphosphate (PIP2), we demonstrated that cholesterol depletion decreases PIP2 levels on the cell membrane, whereas enrichment increases them. Given the critical role of PIP2 in actin remodeling and focal adhesion formation, we postulate that cholesterol regulates actin dynamics by modulating PIP2 levels on the membrane. Furthermore, we showed that cholesterol levels regulate integrin α5β1 and αVβ3 distribution and activation, subsequently altering cell-extracellular matrix (ECM) interactions. Notably, the depletion of cholesterol, as a major lipid constituent of the cell membrane, led to a decrease in HTM cell membrane tension, which was reversed upon cholesterol replenishment. Overall, our systematic exploration of cholesterol modulation on TM stiffness highlights the critical importance of maintaining appropriate membrane and cellular cholesterol levels for achieving IOP homeostasis.

A Review about the Mycoremediation of Soil Impacted by War-like Activities: Challenges and Gaps

(1) Background: The frequency and intensity of war-like activities (war, military training, and shooting ranges) worldwide cause soil pollution by metals, metalloids, explosives, radionuclides, and herbicides. Despite this environmentally worrying scenario, soil decontamination in former war zones almost always involves incineration. Nevertheless, this practice is expensive, and its efficiency is suitable only for organic pollutants. Therefore, treating soils polluted by wars requires efficient and economically viable alternatives. In this sense, this manuscript reviews the status and knowledge gaps of mycoremediation. (2) Methods: The literature review consisted of searches on ScienceDirect and Web of Science for articles (1980 to 2023) on the mycoremediation of soils containing pollutants derived from war-like activities. (3) Results: This review highlighted that mycoremediation has many successful applications for removing all pollutants of war-like activities. However, the mycoremediation of soils in former war zones and those impacted by military training and shooting ranges is still very incipient, with most applications emphasizing explosives. (4) Conclusion: The mycoremediation of soils from conflict zones is an entirely open field of research, and the main challenge is to optimize experimental conditions on a field scale.

Functional, transcriptomic, and lipidomic studies of the choC gene encoding a phospholipid methyltransferase in Aspergillus fumigatus

IMPORTANCE

This study explored the phospholipid metabolic pathway in A. fumigatus and its relationship with fungal growth, metabolism, and pathogenicity. ChoC, based on its critical roles in many aspects of the fungus and relatively conserved characteristics in filamentous fungi with low similarity with mammalian ones, can be a novel target of new antifungal drugs.

Fluorescence and Biochemical Assessment of the Chitin and Chitosan Content of Cryptococcus

The cell wall of the fungal pathogens Cryptococcus neoformans and C. gattii is critical for cell wall integrity and signaling external threats to the cell, allowing it to adapt and grow in a variety of changing environments. Chitin is a polysaccharide found in the cell walls of fungi that is considered to be essential for fungal survival. Chitosan is a polysaccharide derived from chitin via deacetylation that is also essential for cryptococcal cell wall integrity, fungal pathogenicity, and virulence. Cryptococcus has evolved mechanisms to regulate the amount of chitin and chitosan during growth under laboratory conditions or during mammalian infection. Therefore, levels of chitin and chitosan have been useful phenotypes to define mutant Cryptococcus strains. As a result, we have developed and/or refined various qualitative and quantitative methods for measuring chitin and chitosan. These techniques include those that use fluorescent probes that are known to bind to chitin (e.g., calcofluor white and wheat germ agglutinin), as well as those that preferentially bind to chitosan (e.g., eosin Y and cibacron brilliant red 3B-A). Techniques that enhance the localization and quantification of chitin and chitosan in the cell wall include (i) fluorescence microscopy, (ii) flow cytometry, (iii) and spectrofluorometry. We have also modified two highly selective biochemical methods to measure cellular chitin and chitosan content: the Morgan-Elson and the 3-methyl-2-benzothiazolone hydrazine hydrochloride (MBTH) assays, respectively.

Structural Color from Cellulose Nanocrystals or Chitin Nanocrystals: Self-Assembly, Optics, and Applications

Widespread concerns over the impact of human activity on the environment have resulted in a desire to replace artificial functional materials with naturally derived alternatives. As such, polysaccharides are drawing increasing attention due to offering a renewable, biodegradable, and biocompatible feedstock for functional nanomaterials. In particular, nanocrystals of cellulose and chitin have emerged as versatile and sustainable building blocks for diverse applications, ranging from mechanical reinforcement to structural coloration. Much of this interest arises from the tendency of these colloidally stable nanoparticles to self-organize in water into a lyotropic cholesteric liquid crystal, which can be readily manipulated in terms of its periodicity, structure, and geometry. Importantly, this helicoidal ordering can be retained into the solid-state, offering an accessible route to complex nanostructured films, coatings, and particles. In this review, the process of forming iridescent, structurally colored films from suspensions of cellulose nanocrystals (CNCs) is summarized and the mechanisms underlying the chemical and physical phenomena at each stage in the process explored. Analogy is then drawn with chitin nanocrystals (ChNCs), allowing for key differences to be critically assessed and strategies toward structural coloration to be presented. Importantly, the progress toward translating this technology from academia to industry is summarized, with unresolved scientific and technical questions put forward as challenges to the community.

Bioconversion of rice straw by Lentinula edodes under different spawn formulations

To attend to the growing world demand for mushrooms, it is interesting to increase the system's productivity, improve quality and reduce production costs. This study aimed to optimize the production and quality of fruiting bodies of the edible and medicinal mushroom Lentinula edodes (shiitake), in agroresidues substrate using appropriate strain and spawn formulation. The evaluation was conducted using two strains under seven different spawn formulations (Control [C]: Sorghum grain + 2.5% CaCO3; (2) C + 2.5% sawdust; (T3) C + 5% sawdust; (T4) C + 2.5% peat; (T5) C + 5% peat; (T6) C + 1.25% sawdust + 1.25% peat; (T7) C + 2.5% sawdust + 2.5% peat) that were inoculated into the blocks at a proportion of 2% (w/w). The substrate was formulated with 63% rice straw, 20% sawdust, 15% wheat bran, and 2% CaCO3 and sterilized. The incubation period was 87 days. Two flushes were obtained. Adding small aliquots of peat and sawdust to the inoculum gave significantly higher morphological results than the control in all variables analyzed. The days required for the first harvest ranged from 87 to 94 days. The average weight of basidiomes ranged from 6.38 to 28.75 g. The productivity data show superior results for the treatments in which the spawn was supplemented with sawdust and peat. Enhanced bioconversion with supplemented spawn shows promises for yield and composition improvement, crucial for commercial viability. It can be concluded that shiitake production using agroresidues such as straw can be increased using a suitable strain/spawn for optimal production.

The Prospect of Hydrolytic Enzymes from Bacillus Species in the Biological Control of Pests and Diseases in Forest and Fruit Tree Production

Plant diseases and insect pest damage cause tremendous losses in forestry and fruit tree production. Even though chemical pesticides have been effective in the control of plant diseases and insect pests for several decades, they are increasingly becoming undesirable due to their toxic residues that affect human life, animals, and the environment, as well as the growing challenge of pesticide resistance. In this study, we review the potential of hydrolytic enzymes from Bacillus species such as chitinases, β-1,3-glucanases, proteases, lipases, amylases, and cellulases in the biological control of phytopathogens and insect pests, which could be a more sustainable alternative to chemical pesticides. This study highlights the application potential of the hydrolytic enzymes from different Bacillus sp. as effective biocontrol alternatives against phytopathogens/insect pests through the degradation of cell wall/insect cuticles, which are mainly composed of structural polysaccharides like chitins, β-glucans, glycoproteins, and lipids. This study demonstrates the prospects for applying hydrolytic enzymes from Bacillus sp. as effective biopesticides in forest and fruit tree production, their mode of biocidal activity and dual antimicrobial/insecticidal potential, which indicates a great prospect for the simultaneous biocontrol of pests/diseases. Further research should focus on optimizing the production of hydrolytic enzymes, and the antimicrobial/insecticidal synergism of different Bacillus sp. which could facilitate the simultaneous biocontrol of pests and diseases in forest and fruit tree production.

Euglena gracilis β-Glucans (1,3): Enriching Colostrum of Sow for Enhanced Piglet Immunity

The effects of supplementing the diet of sows with βG-(1,3) derived from Euglena gracilis algae were assessed regarding quality and amount of colostrum as well as performance of piglets. A total of 120 sows (first (nulliparous) to sixth parity (multiparous)) from D85 of gestation until weaning were divided into two groups: the control diet group (n = 60) and the βG-(1,3) diet group (n = 60). Sows receiving βG-(1,3) exhibited an average increase of 870 g (24.9%) in colostrum production, leading to a 25.17% higher intake of colostrum by piglets. Furthermore, piglets in the βG-(1,3) group showed significantly superior weight gain of 34 g (50%) compared to the control group 18 h after birth (p < 0.05). Sows fed with βG-(1,3) produced colostrum with significantly higher concentrations of IgG (5.914 mg/mL, 16.16%) and IgM (0.378 mg/mL, 16.29%) than the control group (p < 0.05). Similarly, serum concentrations of IgG (13.86 mg/mL, 51.25%), IgA (17.16 mg/mL, 120.19%), and IgM (13.23 mg/mL, 144.78%) were significantly higher in sows fed with βG-(1,3) than in the control group (p < 0.05). Supplementing sows with βG-(1,3) derived from the Euglena gracilis algae resulted in increased colostrum production and consumption, along with greater weight gain in piglets during the first 18 h after birth. Additionally, both the colostrum produced by the sows and the blood serum of the piglets exhibited higher concentrations of immunoglobulins.

The Arp2/3 complex promotes periodic removal of Pak1-mediated negative feedback to facilitate anticorrelated Cdc42 oscillations

The conserved GTPase Cdc42 is a major regulator of polarized growth in most eukaryotes. Cdc42 periodically cycles between active and inactive states at sites of polarized growth. These periodic cycles are caused by positive feedback and time-delayed negative feedback loops. In the bipolar yeast S. pombe, both growing ends must regulate Cdc42 activity. At each cell end, Cdc42 activity recruits the Pak1 kinase which prevents further Cdc42 activation thus establishing negative feedback. It is unclear how Cdc42 activation returns to the end after Pak1-dependent negative feedback. Using genetic and chemical perturbations, we find that disrupting branched actin-mediated endocytosis disables Cdc42 reactivation at the cell ends. With our experimental data and mathematical models, we show that endocytosis-dependent Pak1 removal from the cell ends allows the Cdc42 activator Scd1 to return to that end to enable reactivation of Cdc42. Moreover, we show that Pak1 elicits its own removal via activation of endocytosis. In agreement with these observations, our model and experimental data show that in each oscillatory cycle, Cdc42 activation increases followed by an increase in Pak1 recruitment at that end. These findings provide a deeper insight into the self-organization of Cdc42 regulation and reveal previously unknown feedback with endocytosis in the establishment of cell polarity.

Turn-On Protein Switches for Controlling Actin Binding in Cells

Within a shared cytoplasm, filamentous actin (F-actin) plays numerous and critical roles across the cell body. Cells rely on actin-binding proteins (ABPs) to organize F-actin and to integrate its polymeric characteristics into diverse cellular processes. Yet, the multitude of ABPs that engage with and shape F-actin make studying a single ABP's influence on cellular activities a significant challenge. Moreover, without a means of manipulating actin-binding subcellularly, harnessing the F-actin cytoskeleton for synthetic biology purposes remains elusive. Here, we describe a suite of designed proteins, Controllable Actin-binding Switch Tools (CASTs), whose actin-binding behavior can be controlled with external stimuli. CASTs were developed that respond to different external inputs, providing options for turn-on kinetics and enabling orthogonality. Being genetically encoded, we show that CASTs can be inserted into native protein sequences to control F-actin association locally and engineered into new structures to control cell and tissue shape and behavior.

Unraveling the Polysaccharide Biosynthesis Potential of Ganoderma lucidum: A Chromosome-Level Assembly Using Hi-C Sequencing

Ganoderma lucidum exhibits the ability to synthesize a diverse range of biologically active molecules with significant pharmaceutical potential, including xylomannan and fucogalactan, which have demonstrated antitumor activity. However, there exists considerable intra-species variability in the capacity to produce these metabolites at high concentrations, likely reflecting the high genomic diversity observed from a limited number of strains sequenced to date. We employed high-throughput shotgun sequencing to obtain the complete genome sequence of G. lucidum strain 5.1, which is distinguished by its remarkable xylomannan synthesis capabilities. Through the utilization of semi-automatic reordering based on conformation capture (Hi-C) data, we substantially enhanced the assembly process, resulting in the generation of 12 chromosome-level scaffolds with a cumulative length of 39 Mbp. By employing both de novo and homology-based approaches, we performed comprehensive annotation of the genome, thereby identifying a diverse repertoire of genes likely involved in polysaccharide biosynthesis. The genome sequence generated in this study serves as a valuable resource for elucidating the molecular mechanisms underlying the medicinal potential of Ganoderma species, discovering novel pharmaceutically valuable compounds, and elucidating the ecological mechanisms of the species. Furthermore, the chromosome contact map obtained for the first time for this species extends our understanding of 3D fungal genomics and provides insights into the functional and structural organization within the fungal kingdom.

Elevated levels of sphingolipid MIPC in the plasma membrane disrupt the coordination of cell growth with cell wall formation in fission yeast

Coupling cell wall expansion with cell growth is a universal challenge faced by walled organisms. Mutations in Schizosaccharomyces pombe css1, which encodes a PM inositol phosphosphingolipid phospholipase C, prevent cell wall expansion but not synthesis of cell wall material. To probe how Css1 modulates cell wall formation we used classical and chemical genetics coupled with quantitative mass spectrometry. We found that elevated levels of the sphingolipid biosynthetic pathway's final product, mannosylinositol phosphorylceramide (MIPC), specifically correlated with the css1-3 phenotype. We also found that an apparent indicator of sphingolipids and a sterol biosensor accumulated at the cytosolic face of the PM at cell tips and the division site of css1-3 cells and, in accord, the PM in css1-3 was less dynamic than in wildtype cells. Interestingly, disrupting the protein glycosylation machinery recapitulated the css1-3 phenotype and led us to investigate Ghs2, a glycosylated PM protein predicted to modify cell wall material. Disrupting Ghs2 function led to aberrant cell wall material accumulation suggesting Ghs2 is dysfunctional in css1-3. We conclude that preventing an excess of MIPC in the S. pombe PM is critical to the function of key PM-localized proteins necessary for coupling growth with cell wall formation.

Synthetic control of actin polymerization and symmetry breaking in active protocells

Non-linear biomolecular interactions on the membranes drive membrane remodeling that underlies fundamental biological processes including chemotaxis, cytokinesis, and endocytosis. The multitude of biomolecules, the redundancy in their interactions, and the importance of spatiotemporal context in membrane organization hampers understanding the physical principles governing membrane mechanics. A minimal, in vitro system that models the functional interactions between molecular signaling and membrane remodeling, while remaining faithful to cellular physiology and geometry is powerful yet remains unachieved. Here, inspired by the biophysical processes underpinning chemotaxis, we reconstituted externally-controlled actin polymerization inside giant unilamellar vesicles, guiding self-organization on the membrane. We show that applying undirected external chemical inputs to this system results in directed actin polymerization and membrane deformation that are uncorrelated with upstream biochemical cues, indicating symmetry breaking. A biophysical model of the dynamics and mechanics of both actin polymerization and membrane shape suggests that inhomogeneous distributions of actin generate membrane shape deformations in a non-linear fashion, a prediction consistent with experimental measurements and subsequent local perturbations. The active protocellular system demonstrates the interplay between actin dynamics and membrane shape in a symmetry breaking context that is relevant to chemotaxis and a suite of other biological processes.

Recent developments in membrane targeting antifungal agents to mitigate antifungal resistance

Fungal infections cause severe and life-threatening complications especially in immunocompromised individuals. Antifungals targeting cellular machinery and cell membranes including azoles are used in clinical practice to manage topical to systemic fungal infections. However, continuous exposure to clinically used antifungal agents in managing the fungal infections results in the development of multi-drug resistance via adapting different kinds of intrinsic and extrinsic mechanisms. The unique chemical composition of fungal membranes presents attractive targets for antifungal drug discovery as it is difficult for fungal cells to modify the membrane targets for emergence of drug resistance. Here, we discussed available antifungal drugs with their detailed mechanism of action and described different antifungal resistance mechanisms. We further emphasized structure-activity relationship studies of membrane-targeting antifungal agents, and classified membrane-targeting antifungal agents on the basis of their core scaffold with detailed pharmacological properties. This review aims to pique the interest of potential researchers who could explore this interesting and intricate fungal realm.

A dynamic actin cytoskeleton is required to prevent constitutive VDAC-dependent MAPK signalling and aberrant lipid homeostasis

The dynamic nature of the actin cytoskeleton is required to coordinate many cellular processes, and a loss of its plasticity has been linked to accelerated cell aging and attenuation of adaptive response mechanisms. Cofilin is an actin-binding protein that controls actin dynamics and has been linked to mitochondrial signaling pathways that control drug resistance and cell death. Here we show that cofilin-driven chronic depolarization of the actin cytoskeleton activates cell wall integrity mitogen-activated protein kinase (MAPK) signalling and disrupts lipid homeostasis in a voltage-dependent anion channel (VDAC)-dependent manner. Expression of the cof1-5 mutation, which reduces the dynamic nature of actin, triggers loss of cell wall integrity, vacuole fragmentation, disruption of lipid homeostasis, lipid droplet (LD) accumulation, and the promotion of cell death. The integrity of the actin cytoskeleton is therefore essential to maintain the fidelity of MAPK signaling, lipid homeostasis, and cell health in S. cerevisiae.

Antifungal Efficacy of Antimicrobial Peptide Octominin II against Candida albicans

Most clinically isolated Candida albicans strains are drug-resistant, emphasizing the urgent need to discover alternative therapies. In this study, the previously characterized Octominin was modified into a shorter peptide with an 18 amino acid sequence (1GWLIRGAIHAGKAIHGLI18) and named Octominin II. The secondary structure of Octominin II is a random coil with a helical turn and a positive charge (+2.46) with a hydrophobic ratio of 0.46. Octominin II inhibited C. albicans, C. auris, and C. glabrata with minimum inhibitory and fungicidal concentrations against C. albicans of 80 and 120 µg/mL, respectively. Field emission scanning electron microscopy confirmed that Octominin II treatment caused ultra-structural changes in C. albicans cells. Furthermore, membrane permeability results for the fluorescent indicator propidium iodide revealed modifications in cell wall integrity in Octominin II-treated C. albicans. Octominin II treatment increases the production of reactive oxygen species (ROS) in C. albicans. Gene expression studies revealed that Octominin II suppresses virulence genes of C. albicans such as CDR1, TUP1, AGE3, GSC1, SAP2, and SAP9. In addition, a nucleic acid binding assay revealed that Octominin II degraded genomic DNA and total RNA in a concentration-dependent manner. Additionally, Octominin II inhibited and eradicated C. albicans biofilm formation. Octominin II showed relatively less cytotoxicity on raw 264.7 cells (0-200 µg/mL) and hemolysis activity on murine erythrocytes (6.25-100 µg/mL). In vivo studies confirmed that Octominin II reduced the pathogenicity of C. albicans. Overall, the data suggests that Octominin II inhibits C. albicans by employing different modes of action and can be a promising candidate for controlling multidrug-resistant Candida infections.

Confronting antifungal resistance, tolerance, and persistence: Advances in drug target discovery and delivery systems

Human pathogenic fungi pose a serious threat to human health and safety. Unfortunately, the limited number of antifungal options is exacerbated by the continuous emergence of drug-resistant variants, leading to frequent drug treatment failures. Recent studies have also highlighted the clinical importance of other modes of fungal survival of antifungal treatment, including drug tolerance and persistence, pointing to the complexity of the fungal response to antifungal drugs. A lack of understanding of the fungal drug response has hampered the identification of new targets, the development of alternative antifungal strategies and the design of appropriate delivery systems. In this review we summarize recent advances in the study of antifungal resistance, tolerance and persistence, with an emphasis on promising drug targets and drug delivery systems that may yield important insights into the development of new or improved antifungal therapies against fungal infections.

Toxoplasma gondii actin filaments are tuned for rapid disassembly and turnover

The cytoskeletal protein actin plays a critical role in the pathogenicity of Toxoplasma gondii, mediating invasion and egress, cargo transport, and organelle inheritance. Advances in live cell imaging have revealed extensive filamentous actin networks in the Apicomplexan parasite, but there is conflicting data regarding the biochemical and biophysical properties of Toxoplasma actin. Here, we imaged the in vitro assembly of individual Toxoplasma actin filaments in real time, showing that native, unstabilized filaments grow tens of microns in length. Unlike skeletal muscle actin, Toxoplasma filaments intrinsically undergo rapid treadmilling due to a high critical concentration, fast monomer dissociation, and rapid nucleotide exchange. Cryo-EM structures of stabilized and unstabilized filaments show an architecture like skeletal actin, with differences in assembly contacts in the D-loop that explain the dynamic nature of the filament, likely a conserved feature of Apicomplexan actin. This work demonstrates that evolutionary changes at assembly interfaces can tune dynamic properties of actin filaments without disrupting their conserved structure.

Suppression of Chitin-Triggered Immunity by Plant Fungal Pathogens: A Case Study of the Cucurbit Powdery Mildew Fungus Podosphaera xanthii

Fungal pathogens are significant plant-destroying microorganisms that present an increasing threat to the world's crop production. Chitin is a crucial component of fungal cell walls and a conserved MAMP (microbe-associated molecular pattern) that can be recognized by specific plant receptors, activating chitin-triggered immunity. The molecular mechanisms underlying the perception of chitin by specific receptors are well known in plants such as rice and Arabidopsis thaliana and are believed to function similarly in many other plants. To become a plant pathogen, fungi have to suppress the activation of chitin-triggered immunity. Therefore, fungal pathogens have evolved various strategies, such as prevention of chitin digestion or interference with plant chitin receptors or chitin signaling, which involve the secretion of fungal proteins in most cases. Since chitin immunity is a very effective defensive response, these fungal mechanisms are believed to work in close coordination. In this review, we first provide an overview of the current understanding of chitin-triggered immune signaling and the fungal proteins developed for its suppression. Second, as an example, we discuss the mechanisms operating in fungal biotrophs such as powdery mildew fungi, particularly in the model species Podosphaera xanthii, the main causal agent of powdery mildew in cucurbits. The key role of fungal effector proteins involved in the modification, degradation, or sequestration of immunogenic chitin oligomers is discussed in the context of fungal pathogenesis and the promotion of powdery mildew disease. Finally, the use of this fundamental knowledge for the development of intervention strategies against powdery mildew fungi is also discussed.

Optical Control of G-Actin with a Photoswitchable Latrunculin

Actin is one of the most abundant proteins in eukaryotic cells and a key component of the cytoskeleton. A range of small molecules have emerged that interfere with actin dynamics by either binding to polymeric F-actin or monomeric G-actin to stabilize or destabilize filaments or prevent their formation and growth, respectively. Amongst these, the latrunculins, which bind to G-actin and affect polymerization, are widely used as tools to investigate actin-dependent cellular processes. Here, we report a photoswitchable version of latrunculin, termed opto-latrunculin (OptoLat), which binds to G-actin in a light-dependent fashion and affords optical control over actin polymerization. OptoLat can be activated with 390 - 490 nm pulsed light and rapidly relaxes to the inactive form in the dark. Light activated OptoLat induced depolymerization of F-actin networks in oligodendrocytes and budding yeast, as shown by fluorescence microscopy. Subcellular control of actin dynamics in human cancer cell lines was demonstrated by live cell imaging. Light-activated OptoLat also reduced microglia surveillance in organotypic mouse brain slices while ramification was not affected. Incubation in the dark did not alter the structural and functional integrity of microglia. Together, our data demonstrate that OptoLat is a useful tool for the elucidation of G-actin dependent dynamic processes in cells and tissues.

Interaction of oxalate with β-glucan: Implications for the fungal extracellular matrix, and metabolite transport

β-glucan is the major component of the extracellular matrix (ECM) of many fungi, including wood degrading fungi. Many of these species also secrete oxalate into the ECM. Our research demonstrates that β-glucan forms a novel, previously unreported, hydrogel at room temperature with oxalate. Oxalate was found to alter the rheometric properties of the β-glucan hydrogels, and modeling showed that β-glucan hydrogen bonds with oxalate in a non-covalent matrix. Change of oxalate concentration also impacted the diffusion of a high-molecular-weight protein through the gels. This finding has relevance to the diffusion of extracellular enzymes into substrates and helps to explain why some types of wood-decay fungi rely on non-enzymatic degradation schemes for carbon cycling. Further, this research has potential impact on the diffusion of metabolites in association with pathogenic/biomedical fungi.

Cell Wall Carbohydrate Dynamics during the Differentiation of Infection Structures by the Apple Scab Fungus, Venturia inaequalis

Scab, caused by the biotrophic fungal pathogen Venturia inaequalis, is the most economically important disease of apples. During infection, V. inaequalis colonizes the subcuticular host environment, where it develops specialized infection structures called runner hyphae and stromata. These structures are thought to be involved in nutrient acquisition and effector (virulence factor) delivery, but also give rise to conidia that further the infection cycle. Despite their importance, very little is known about how these structures are differentiated. Likewise, nothing is known about how these structures are protected from host defenses or recognition by the host immune system. To better understand these processes, we first performed a glycosidic linkage analysis of sporulating tubular hyphae from V. inaequalis developed in culture. This analysis revealed that the V. inaequalis cell wall is mostly composed of glucans (44%) and mannans (37%), whereas chitin represents a much smaller proportion (4%). Next, we used transcriptomics and confocal laser scanning microscopy to provide insights into the cell wall carbohydrate composition of runner hyphae and stromata. These analyses revealed that, during subcuticular host colonization, genes of V. inaequalis putatively associated with the biosynthesis of immunogenic carbohydrates, such as chitin and β-1,6-glucan, are downregulated relative to growth in culture, while on the surface of runner hyphae and stromata, chitin is deacetylated to the less-immunogenic carbohydrate chitosan. These changes are anticipated to enable the subcuticular differentiation of runner hyphae and stromata by V. inaequalis, as well as to protect these structures from host defenses and recognition by the host immune system. IMPORTANCE Plant-pathogenic fungi are a major threat to food security. Among these are subcuticular pathogens, which often cause latent asymptomatic infections, making them difficult to control. A key feature of these pathogens is their ability to differentiate specialized subcuticular infection structures that, to date, remain largely understudied. This is typified by Venturia inaequalis, which causes scab, the most economically important disease of apples. In this study, we show that, during subcuticular host colonization, V. inaequalis downregulates genes associated with the biosynthesis of two immunogenic cell wall carbohydrates, chitin and β-1,6-glucan, and coats its subcuticular infection structures with a less-immunogenic carbohydrate, chitosan. These changes are anticipated to enable host colonization by V. inaequalis and provide a foundation for understanding subcuticular host colonization by other plant-pathogenic fungi. Such an understanding is important, as it may inform the development of novel control strategies against subcuticular plant-pathogenic fungi.

Comparative proteomic analysis of two divergent strains provides insights into thermotolerance mechanisms of Ganoderma lingzhi

Heat stress (HS) is a major abiotic factor influencing fungal growth and metabolism. However, the genetic basis of thermotolerance in Ganoderma lingzhi (G. lingzhi) remains largely unknown. In this study, we investigated the thermotolerance capacities of 21 G. lingzhi strains and screened the thermo-tolerant (S566) and heat-sensitive (Z381) strains. The mycelia of S566 and Z381 were collected and subjected to a tandem mass tag (TMT)-based proteome assay. We identified 1493 differentially expressed proteins (DEPs), with 376 and 395 DEPs specific to the heat-tolerant and heat-susceptible genotypes, respectively. In the heat-tolerant genotype, upregulated proteins were linked to stimulus regulation and response. Proteins related to oxidative phosphorylation, glycosylphosphatidylinositol-anchor biosynthesis, and cell wall macromolecule metabolism were downregulated in susceptible genotypes. After HS, the mycelial growth of the heat-sensitive Z381 strain was inhibited, and mitochondrial cristae and cell wall integrity of this strain were severely impaired, suggesting that HS may inhibit mycelial growth of Z381 by damaging the cell wall and mitochondrial structure. Furthermore, thermotolerance-related regulatory pathways were explored by analyzing the protein-protein interaction network of DEPs considered to participate in the controlling the thermotolerance capacity. This study provides insights into G. lingzhi thermotolerance mechanisms and a basis for breeding a thermotolerant germplasm bank for G. lingzhi and other fungi.

Overexpression of a beta-1,6-glucanase gene GluM in transgenic rice confers high resistance to rice blast, sheath blight and false smut

BACKGROUND

Frequent fungal diseases tend to lead to severe losses in rice production. As a main component of the fungal cell wall, glucan plays an important role in the growth and development of fungi. Glucanase can inhibit the growth of fungi by breaking glycosidic bonds, and may be a promising target for developing rice varieties with broad-spectrum disease resistance.

RESULTS

We transferred a codon-optimized β-1,6-glucanase gene (GluM) from myxobacteria into the japonica rice variety Zhonghua11 (ZH11), and obtained a large number of individual transgenic plants with GluM overexpression. Based on molecular analysis, three single-copy homozygous lines with GluM overexpression were selected for assessment of fungal disease resistance at the T₃ generation. Compared with that of the recipient cultivar ZH11, the area of rice blast lesion in transgenic rice was reduced by 82.71%; that of sheath blight lesion was decreased by 35.76%-43.67%; the sheath blight resistance in the field was enhanced by an average of 0.75 grade over 3 years; and the incidence of diseased panicles due to rice false smut was decreased by 65.79%. More importantly, there was no obvious loss of yield (without a significant effect on agronomic traits). Furthermore, plants overexpressing a β-1,6-glucanase gene showed higher disease resistance than rice plants overexpressing a β-1,3-glucanase gene derived from tobacco.

CONCLUSION

The β-1,6-glucanase gene GluM can confer broad-spectrum disease resistance to rice, providing an environmentally friendly alternative way to effectively manage fungal pathogens in rice production. © 2023 Society of Chemical Industry.

Mitogen-Activated Protein Kinases SvPmk1 and SvMps1 Are Critical for Abiotic Stress Resistance, Development and Pathogenesis of Sclerotiophoma versabilis

Mitogen-activated protein kinase (MAPK) signaling pathways are evolutionarily conserved in eukaryotes and modulate responses to both internal and external stimuli. Pmk1 and Mps MAPK pathways regulate stress tolerance, vegetative growth and cell wall integrity in Saccharomyces cerevisiae and Pyricularia oryzae. Here, we deployed genetic and cell biology strategies to investigate the roles of the orthologs of Pmk1 and Mps1 in Sclerotiophoma versabilis (herein referred to as SvPmk1 and SvMps1, respectively). Our results showed that SvPmk1 and SvMps1 are involved in hyphal development, asexual reproduction and pathogenesis in S. versabilis. We found that ∆Svpmk1 and ∆Svmps1 mutants have significantly reduced vegetative growths on PDA supplemented with osmotic stress-inducing agents, compared to the wild type, with ∆Svpmps1 being hypersensitive to hydrogen peroxide. The two mutants failed to produce pycnidia and have reduced pathogenicity on Pseudostellaria heterophylla. Unlike SvPmk1, SvMps1 was found to be indispensable for the fungal cell wall integrity. Confocal microscopic analyses revealed that SvPmk1 and SvMps1 are ubiquitously expressed in the cytosol and nucleus. Taken together, we demonstrate here that SvPmk1 and SvMps1 play critical roles in the stress resistance, development and pathogenesis of S. versabilis.

Light-induced antifungal activity of nanoparticles with an encapsulated porphyrin photosensitizer

The strong antifungal effect of sulfonated polystyrene nanoparticles (NPs) with an encapsulated tetraphenylporphyrin (TPP) photosensitizer is reported here. TPP is activated by visible light, resulting in the generation of singlet oxygen. Its antifungal action is potentiated in the presence of potassium iodide, yielding I₂/I₃⁻, another antifungal species. The NPs exhibit no dark toxicity, but a broad spectrum of antifungal photodynamic effects. The efficiency of this rapid killing (on the order of minutes) depends on the concentration of TPP NPs, potassium iodide, yeast species and temperature. A strong antifungal activity of TPP NPs is demonstrated on eleven pathogenic and opportunistic pathogenic yeast species (six Candida species and other yeast species, including melanized Hortaea werneckii). The composition and architecture of yeast cell envelope structures clearly influence the efficacy of photodynamic therapy. Candida krusei is the most sensitive to photodynamic therapy. Despite expectations, melanin does not provide Hortaea cells with marked resistance compared to white yeast species. The kinetics of the interaction of NPs with yeast cells is also described. This study may inspire and promote the fabrication of a new type of antiseptic for various skin injuries in clinical medicine.