Apoptosis pathways in fungal growth, development and ageing

Construction and activity evaluation of novel CHS inhibitors against fungal infections

Chitin synthase (CHS), as crucial antifungal target, plays a pivotal role in the fungal proliferation and invasion processes. This study constructed pharmacophore models based on ligand and receptor features. These models were used to guide the construction of novel CHS inhibitors via the scaffold-growth pathway. The corresponding molecular structures were synthesized, and their biological activities were evaluated. Among them, compounds 9c, 9e, and 9f exhibited significant inhibitory activity against chitin synthesis, achieving high potent antifungal effect. Furthermore, the potential compound 9f, in combination with immune activators, could accelerate the recovery rate of drug-resistant fungal infections in vivo. This study not only successfully established scientific pharmacophore models but also discovered novel CHS inhibitors, opening up a potential new pathway for effectively treating fungal infections by regulating chitin synthesis pathways.

The antifungal peptide AnAFP from Aspergillus niger promotes nutrient mobilization through autophagic recycling during asexual development

Antifungal peptides are promising drug candidates to fight fungal infections in the clinics and agriculture. However, recent data suggest that antifungal peptides might also play a role within their own producing organism to survive nutrient limiting conditions. We have therefore studied the function of the antifungal AnAFP in Aspergillus niger in more detail. To achieve this, we established a Tet-on controlled anafp expression system, which allowed us to study a null and an overexpression phenotype in the same isolate. We observed that increased intracellular AnAFP expression reduces growth of A. niger and prematurely activates autophagy. Comparative transcriptome analyses of glucose-starving mycelium demonstrated that increased anafp expression strongly impacts expression of genes important for cell wall integrity and remodeling, as well as genes with a predicted function in metabolism and transport of carbohydrates, proteins, and lipids. Notably, genes encoding regulators of conidiophore development such as flbC and flbD became induced upon anafp overexpression. Fluorescent analyses of a Tet-on driven AnAFP::eGFP fusion protein congruently unraveled that AnAFP localizes to cell walls and septa of A. niger. Moreover, AnAFP::eGFP expression is spatially restricted to selected compartments only and affected cells displayed a sudden reduction in hyphal diameter. From these data we conclude that AnAFP is important to drive vegetative growth and sporulation in A. niger during nutrient limitation through autophagic recycling. We predict that AnAFP drives nutrient mobilization through selective cell lysis to ensure the survival of the whole colony during phases of starvation.

The Killer Saccharomyces cerevisiae Toxin: From Origin to Biomedical Research

The killer systems of S. cerevisiae are defined by the co-infection of two viral agents, an M virus and a helper virus. Each killer toxin is determined by the type of M virus (ScV-M1, ScV-M2, ScV-M28, and ScV-Mlus), which encodes a specific toxin (K1, K2, K28, and Klus). Since their discovery, interest in their potential use as antimicrobial agents has driven research into the mechanisms of action of these toxins on susceptible cells. This review provides an overview of the key aspects of killer toxins, including their origin and the evolutionary implications surrounding the viruses involved in the killer system, as well as their potential applications in the biomedical field and as a biological control strategy. Special attention is given to the mechanisms of action described to date for the various S. cerevisiae killer toxins.

An apoptosis-inducing factor controls programmed cell death and laccase expression during fungal interactions

Apoptotic-like programmed cell death (PCD) is one of the main strategies for fungi to resist environmental stresses and maintain homeostasis. The apoptosis-inducing factor (AIF) has been shown in different fungi to trigger PCD through upregulating reactive oxygen species (ROS). This study identified a mitochondrial localized AIF homolog, CcAIF1, from Coprinopsis cinerea monokaryon Okayama 7. Heterologous overexpression of CcAIF1 in Saccharomyces cerevisiae caused apoptotic-like PCD of the yeast cells. Ccaif1 was increased in transcription when C. cinerea interacted with Gongronella sp. w5, accompanied by typical apoptotic-like PCD in C. cinerea, including phosphatidylserine externalization and DNA fragmentation. Decreased mycelial ROS levels were observed in Ccaif1 silenced C. cinerea transformants during cocultivation, as well as reduction of the apoptotic levels, mycelial growth, and asexual sporulation. By comparison, Ccaif1 overexpression led to the opposite phenotypes. Moreover, the transcription and expression levels of laccase Lcc9 decreased by Ccaif1 silencing but increased firmly in Ccaif1 overexpression C. cinerea transformants in coculture. Thus, in conjunction with our previous report that intracellular ROS act as signal molecules to stimulate defense responses, we conclude that CcAIF1 is a regulator of ROS to promote apoptotic-like PCD and laccase expression in fungal-fungal interactions. In an axenic culture of C. cinerea, CcAIF1 overexpression and H2O2 stimulation together increased laccase secretion with multiplied production yield. The expression of two other normally silent isozymes, Lcc8 and Lcc13, was unexpectedly triggered along with Lcc9. KEY POINTS: • Mitochondrial CcAIF1 induces PCD during fungal-fungal interactions • CcAIF1 is a regulator of ROS to trigger the expression of Lcc9 for defense • CcAIF1 overexpression and H2O2 stimulation dramatically increase laccase production.

Fungal Apoptosis-Related Proteins

Programmed cell death (PCD) plays a crucial role in the development and homeostasis maintenance of multicellular organisms. Apoptosis is a form of PCD that prevents pathological development by eliminating damaged or useless cells. Despite the complexity of fungal apoptosis mechanisms being similar to those of plants and metazoans, fungal apoptosis lacks the core regulatory elements of animal apoptosis. Apoptosis-like PCD in fungi can be triggered by a variety of internal and external factors, participating in biological processes such as growth, development, and stress response. Although the core regulatory elements are not fully understood, apoptosis-inducing factor and metacaspase have been found to be involved. This article summarizes various proteins closely related to fungal apoptosis, such as apoptosis-inducing factor, metacaspase, and inhibitors of apoptosis proteins, as well as their structures and functions. This research provides new strategies and ideas for the development of natural drugs targeting fungal apoptosis and the control of fungal diseases.

Induction of apoptosis by double-stranded RNA was present in the last common ancestor of cnidarian and bilaterian animals

Apoptosis, a major form of programmed cell death, is an essential component of host defense against invading intracellular pathogens. Viruses encode inhibitors of apoptosis to evade host responses during infection, and to support their own replication and survival. Therefore, hosts and their viruses are entangled in a constant evolutionary arms race to control apoptosis. Until now, apoptosis in the context of the antiviral immune system has been almost exclusively studied in vertebrates. This limited phyletic sampling makes it impossible to determine whether a similar mechanism existed in the last common ancestor of animals. Here, we established assays to probe apoptosis in the sea anemone Nematostella vectensis, a model species of Cnidaria, a phylum that diverged approximately 600 million years ago from the rest of animals. We show that polyinosinic:polycytidylic acid (poly I:C), a synthetic long double-stranded RNA mimicking viral RNA and a primary ligand for the vertebrate RLR melanoma differentiation-associated protein 5 (MDA5), is sufficient to induce apoptosis in N. vectensis. Furthermore, at the transcriptomic level, apoptosis related genes are significantly enriched upon poly(I:C) exposure in N. vectensis as well as bilaterian invertebrates. Our phylogenetic analysis of caspase family genes in N. vectensis reveals conservation of all four caspase genes involved in apoptosis in mammals and revealed a cnidarian-specific caspase gene which was strongly upregulated. Altogether, our findings suggest that apoptosis in response to a viral challenge is a functionally conserved mechanism that can be traced back to the last common ancestor of Bilateria and Cnidaria.

Impact of Mitochondrial Architecture, Function, Redox Homeostasis, and Quality Control on Organismic Aging: Lessons from a Fungal Model System

Significance: Mitochondria are eukaryotic organelles with various essential functions. They are both the source and the targets of reactive oxygen species (ROS). Different branches of a mitochondrial quality control system (mQCS), such as ROS balancing, degradation of damaged proteins, or whole mitochondria, can mitigate the adverse effects of ROS stress. However, the capacity of mQCS is limited. Overwhelming this capacity leads to dysfunctions and aging. Strategies to interfere into mitochondria-dependent human aging with the aim to increase the healthy period of life, the health span, rely on the precise knowledge of mitochondrial functions. Experimental models such as Podospora anserina, a filamentous fungus with a clear mitochondrial aging etiology, proved to be instrumental to reach this goal. Recent Advances: Investigations of the P. anserina mQCS revealed that it is constituted by a complex network of different branches. Moreover, mitochondrial architecture and lipid homeostasis emerged to affect aging. Critical Issues: The regulation of the mQCS is only incompletely understood. Details about the involved signaling molecules and interacting pathways remain to be elucidated. Moreover, most of the currently generated experimental data were generated in well-controlled experiments that do not reflect the constantly changing natural life conditions and bear the danger to miss relevant aspects leading to incorrect conclusions. Future Directions: In P. anserina, the precise impact of redox signaling as well as of molecular damaging for aging remains to be defined. Moreover, natural fluctuation of environmental conditions needs to be considered to generate a realistic picture of aging mechanisms as they developed during evolution.

The CfKOB1 gene related to cell apoptosis is required for pathogenicity and involved in mycovirus-induced hypovirulence in Colletotrichum fructicola

Colletotrichum fructicola is a globally significant phytopathogenic fungus. Mycovirus-induced hypovirulence has great potential for biological control and study of fungal pathogenic mechanisms. We previously reported that the mycovirus Colletotrichum alienum partitivirus 1 (CaPV1) is associated with the hypovirulence of C. fructicola, and the present study aimed to further investigate a host factor and its roles in mycovirus-induced hypovirulence. A gene named CfKOB1, which encodes putative protein homologous to the β-subunit of voltage-gated potassium channels and aldo-keto reductase, is downregulated upon CaPV1 infection and significantly upregulated during the early infection phase of Nicotiana benthamiana by C. fructicola. Deleting the CfKOB1 gene resulted in diminished vegetative growth, decreased production of asexual spores, hindered appressorium formation, reduced virulence, and altered tolerance to abiotic stresses. Transcriptome analysis revealed that CfKOB1 regulates many metabolic pathways as well as the cell cycle and apoptosis. Furthermore, enhanced apoptosis was observed in the ΔCfKOB1 mutants. Viral RNA accumulation was significantly increased in the CfKOB1 deletion mutant. Additionally, our findings demonstrated that CaPV1 infection in the WT strain also induced cell apoptosis. Collectively, these results highlight the diverse biological roles of the CfKOB1 gene in the fungus C. fructicola, while it also participates in mycovirus-induced hypovirulence by regulating apoptosis.

Fungal biomineralization of toxic metals accelerates organic pollutant removal

Fungal biomineralization plays an important role in the biogeochemical cycling of metals in the environment and has been extensively explored for bioremediation and element biorecovery. However, the cellular and metabolic responses of fungi in the presence of toxic metals during biomineralization and their impact on organic matter transformations are unclear. This is an important question because co-contamination by toxic metals and organic pollutants is a common phenomenon in the natural environment. In this research, the biomineralization process and oxidative stress response of the geoactive soil fungus Aspergillus niger were investigated in the presence of toxic metals (Co, Cu, Mn, and Fe) and the azo dye orange II (AO II). We have found that the co-existence of toxic metals and AO II not only enhanced the fungal biomineralization of toxic metals but also accelerated the removal of AO II. We hypothesize that the fungus and in situ mycogenic biominerals (toxic metal oxalates) constituted a quasi-bioreactor, where the biominerals removed organic pollutants by catalyzing reactive oxygen species (ROS) generation resulting from oxidative stress. We have therefore demonstrated that a fungal/biomineral system can successfully achieve the goal of toxic metal immobilization and organic pollutant decomposition. Such findings inform the potential development of fungal-biomineral hybrid systems for mixed pollutant bioremediation as well as provide further understanding of fungal organic-inorganic pollutant transformations in the environment and their importance in biogeochemical cycles.

The impact of biomembranes and their dynamics on organismic aging: insights from a fungal aging model

Biomembranes fulfill several essential functions. They delimitate cells and control the exchange of compounds between cells and the environment. They generate specialized cellular reaction spaces, house functional units such as the respiratory chain (RC), and are involved in content trafficking. Biomembranes are dynamic and able to adjust their properties to changing conditions and requirements. An example is the inner mitochondrial membrane (IMM), which houses the RC involved in the formation of adenosine triphosphate (ATP) and the superoxide anion as a reactive oxygen species (ROS). The IMM forms a characteristic ultrastructure that can adapt to changing physiological situations. In the fungal aging model Podospora anserina, characteristic age-related changes of the mitochondrial ultrastructure occur. More recently, the impact of membranes on aging was extended to membranes involved in autophagy, an important pathway involved in cellular quality control (QC). Moreover, the effect of oleic acid on the lifespan was linked to basic biochemical processes and the function of membranes, providing perspectives for the elucidation of the mechanistic effects of this nutritional component, which positively affects human health and aging.

Tacrolimus (FK506) Exhibits Fungicidal Effects against Candida parapsilosis Sensu Stricto via Inducing Apoptosis

Tacrolimus (FK506), an immunosuppressant and calcineurin inhibitor, has fungicidal effects. However, its fungicidal effect is thought to be limited to basidiomycetes, such as Cryptococcus and Malassezia, and not to ascomycetes. FK506 had no fungicidal effect on Candida albicans, C. auris, C. glabrata, C. guilliermondii, C. kefyr, C. krusei, and C. tropicalis (>8 µg/mL); however, C. parapsilosis was susceptible to it at low concentrations of 0.125-0.5 µg/mL. C. metapsilosis and C. orthopsils, previously classified as C. parapsilosis, are molecularly and phylogenetically closely related to C. parapsilosis, but neither species was sensitive to FK506. FK506 increased the mitochondrial reactive oxygen species production and cytoplasmic and mitochondrial calcium concentration and activated metacaspases, nuclear condensation, and DNA fragmentation, suggesting that it induced mitochondria-mediated apoptosis in C. parapsilosis. Elucidating why FK506 exhibits fungicidal activity only against C. parapsilosis will provide new information for developing novel antifungal drugs.

Protection of postharvest grains from fungal spoilage by biogenic volatiles

Fungal spoilage of postharvest grains poses serious problems with respect to food safety, human health, and the economic value of grains. The protection of cereal grains from deleterious fungi is a critical aim in postharvest grain management. Considering the bulk volume of grain piles in warehouses or bins and food safety, fumigation with natural gaseous fungicides is a promising strategy to control fungal contamination on postharvest grains. Increasing research has focused on the antifungal properties of biogenic volatiles. This review summarizes the literature related to the effects of biogenic volatiles from microbes and plants on spoilage fungi on postharvest grains and highlights the underlying antifungal mechanisms. Key areas for additional research on fumigation with biogenic volatiles in postharvest grains are noted. The research described in this review supports the protective effects of biogenic volatiles against grain spoilage by fungi, providing a basis for their expanded application in the management of postharvest grains.

Impact of Volatile Organic Compounds on the Growth of Aspergillus flavus and Related Aflatoxin B1 Production: A Review

Volatile organic compounds (VOCs) are secondary metabolites of varied chemical nature that are emitted by living beings and participate in their interactions. In addition, some VOCs called bioactive VOCs cause changes in the metabolism of other living species that share the same environment. In recent years, knowledge on VOCs emitted by Aspergillus flavus, the main species producing aflatoxin B1 (AFB1), a highly harmful mycotoxin, has increased. This review presents an overview of all VOCs identified as a result of A. flavus toxigenic (AFB1-producing) and non-toxigenic (non AFB1-producing) strains growth on different substrates, and the factors influencing their emissions. We also included all bioactive VOCs, mixes of VOCs or volatolomes of microbial species that impact A. flavus growth and/or related AFB1 production. The modes of action of VOCs impacting the fungus development are presented. Finally, the potential applications of VOCs as biocontrol agents in the context of mycotoxin control are discussed.

Recombinant phage displaying ToAP2D peptide with antifungal activity against Sporothrix globosa

We designed and synthesized recombinant phage nanofibers displaying ToAP2D peptide and investigated their antifungal effect on Sporothrix and the corresponding mechanism. Antimicrobial peptide, ToAP2D, was used as the template. The effect of synthesized recombinant phages on the immune function of CD4+ T lymphocytes in mice was tested using an enzyme-linked immunosorbent assay. The therapeutic effect and safety of recombinant phage administration on Sporothrix-infected BALB/c mice were evaluated based on survival analysis, histopathological changes, and renal and liver functions. The successfully prepared recombinant phage displaying ToAP2D peptides significantly inhibited Sporothrix growth. According to the scanning electron microscopy results, the recombinant phage caused shrinkage and rupture of Sporothrix globosa, leading to leakage of the contents. The Hoechst/propidium iodide double staining test indicated that the recombinant phage could induce cell apoptosis of Sporothrix globosa. The apoptotic pathway might be due to the accumulation of reactive oxygen species in large quantities in cells, activating caspase dependence; this reduced inflammation, prolonged the survival time, and enhanced levels of IFN-γ and IL-17 in mice. We believe that recombinant phage inhibits Sporothrix growth by adjusting the immune response of mice, inducing Sporothrix apoptosis and improving animal survival. This study offers a new approach to preparing antimicrobial peptides.

The antifungal mechanisms of plant volatile compound 1-octanol against Aspergillus flavus growth

The exploitation of active ingredients from plant volatile organic compounds as natural gaseous fungicides shows remarkable potential for controlling fungal decay in postharvest agroproducts. Although 1-octanol is a common component of cereal volatiles, its antifungal potency against spoilage fungi in postharvest grains remains unclear. In this study, we studied the effectiveness of 1-octanol against Aspergillus flavus growth in postharvest grains and its mechanisms of action. 1-Octanol vapor and liquid contact dose-dependently inhibited A. flavus spore germination and mycelial growth at a low concentration. The simulated storage experiment demonstrated that 300 μL/L of 1-octanol vapor completely controlled A. flavus growth in wheat, corn, and paddy grains with 20% moisture content. 1-Octanol treatment irreversibly damaged the conidial and mycelial morphology of A. flavus and caused electrolyte leakage due to reduced plasma membrane integrity. It induced apoptosis along with morphological abnormalities, phosphatidylserine externalization, mitochondrial membrane potential depolarization, intracellular reactive oxygen species accumulation, and DNA fragmentation in A. flavus cells. Metabolomic analysis revealed that 1-octanol treatment disrupted the biosynthesis of unsaturated fatty acids, ATP-binding cassette transporters, amino acid metabolism, and glycerophospholipid metabolism. This study demonstrated the promising application potential of 1-octanol as a biofumigant for preventing fungal spoilage of postharvest cereal grains. KEY POINTS: • (1) 1-Octanol inhibits Aspergillus flavus growth in the vapor phase and liquid contact; • (2) 1-Octanol damages membrane integrity and induces apoptosis of A. flavus; • (3) Metabolomic changes in A. flavus mycelia were analyzed after 1-octanol treatment.

Biocontrol potential and antifungal mechanism of a novel Streptomyces sichuanensis against Fusarium oxysporum f. sp. cubense tropical race 4 in vitro and in vivo

Most commercial banana cultivars are highly susceptible to Fusarium wilt caused by soilborne fungus Fusarium oxysporum f. sp. cubense (Foc), especially tropical race 4 (TR4). Biological control using antagonistic microorganism has been considered as an alternative method to fungicide. Our previous study showed that Streptomyces sp. SCA3-4 ^T had a broad-spectrum antifungal activity from the rhizosphere soil of Opuntia stricta in a dry hot valley. Here, the sequenced genome of strain SCA3-4 ^T contained 6614 predicted genes with 72.38% of G + C content. A polymorphic tree was constructed using the multilocus sequence analysis (MLSA) of five house-keeping gene alleles (atpD, gyrB, recA, rpoB, and trpB). Strain SCA3-4 ^T formed a distinct clade with Streptomyces mobaraensis NBRC 13819 ^T with 71% of bootstrap. Average nucleotide identity (ANI) values between genomes of strain SCA3-4 ^T and S. mobaraensis NBRC 13819 ^T was 85.83% below 95-96% of the novel species threshold, and named after Streptomyces sichuanensis sp. nov. The type strain is SCA3-4 ^T (= GDMCC 4.214 ^T = JCM 34964 ^T). Genomic analysis revealed that strain SCA3-4 ^T contained 36 known biosynthetic gene clusters of secondary metabolites. Antifungal activity of strain SCA3-4 ^T was closely associated with the production of siderophore and its extracts induced the apoptosis of Foc TR4 cells. A total of 12 potential antifungal metabolites including terpenoids, esters, acid, macrolides etc. were obtained by the gas chromatography-mass spectrometry (GC-MS). Greenhouse experiment indicated that strain SCA3-4 ^T could significantly inhibit infection of Foc TR4 in the roots and corms of banana seedlings and reduce disease index. Therefore, strain SCA3-4 ^T is an important microbial resource for exploring novel natural compounds and developing biopesticides to manage Foc TR4. KEY POINTS: • Strain SCA3-4 ^T was identified as a novel species of Streptomyces. • Siderophore participates in the antifungal regulation. • Secondary metabolites of strain SCA3-4 ^T improves the plant resistance to Foc TR4.

Novel 3-chloro-6-nitro-1H-indazole derivatives as promising antileishmanial candidates: synthesis, biological activity, and molecular modelling studies

An efficient pathway was disclosed for the synthesis of 3-chloro-6-nitro-1H-indazole derivatives by 1,3-dipolar cycloaddition on dipolarophile compounds 2 and 3. Faced the problem of separation of two regioisomers, a click chemistry method has allowed us to obtain regioisomers of triazole-1,4 with good yields from 82 to 90% were employed. Also, the antileishmanial biological potency of the compounds was achieved using an MTT assay that reported compound 13 as a promising growth inhibitor of Leishmania major. Molecular docking demonstrated highly stable binding with the Leishmania trypanothione reductase enzyme and produced a network of hydrophobic and hydrophilic interactions. Molecular dynamics simulations were performed for TryR-13 complex to understand its structural and intermolecular affinity stability in a biological environment. The studied complex remained in good equilibrium with a structure deviation of ∼1-3 Å. MM/GBSA binding free energies illustrated the high stability of TryR-13 complex. The studied compounds are promising leads for structural optimisation to enhance the antileishmanial activity.

Antifungal mechanism of 1-nonanol against Aspergillus flavus growth revealed by metabolomic analyses

Chemical control of fungal spoilage of postharvest cereal grains is an important strategy for the management of grain storage. Here, the potential antifungal activity of 1-nonanol, a main component of cereal volatiles, against Aspergillus flavus was studied. The growth of A. flavus was completely inhibited by 0.11 and 0.20 μL/mL 1-nonanol at vapor and liquid contact phases, respectively. Metabolomic analysis identified 135 metabolites whose expression was significantly different between 1-nonanol-treated and untreated A. flavus. These metabolites were involved in the tricarboxylic acid cycle, amino acid biosynthesis, protein degradation and absorption, aminoacyl-tRNA biosynthesis, mineral absorption, and in interactions with ABC transporters. Biochemical validation confirmed the disruptive effect of 1-nonanol on A. flavus growth, as indicated by the leakage of intracellular electrolytes, decreased succinate dehydrogenase, mitochondrial dehydrogenase, and ATPase activity, and the accumulation of reactive oxygen species. We speculated that 1-nonanol could disrupt cell membrane integrity and mitochondrial function and might induce apoptosis of A. flavus mycelia. Simulated grain storage experiments showed that 1-nonanol vapor, at a concentration of 264 μL/L, completely inhibited A. flavus growth in wheat, corn, and paddy grain with an 18% moisture content. This study provides new insights into the antifungal mechanism of 1-nonanol against A. flavus, indicating that it has a promising potential as a bio-preservative to prevent fungal spoilage of postharvest grains. KEY POINTS: • 1-Nonanol showed higher antifungal activity against A. flavus. • The antifungal mechanisms of 1-nonanol against A. flavus were revealed. • 1-Nonanol could damage cell membrane integrity and mitochondrial function.

Mining RNA-Seq Data to Depict How Penicillium digitatum Shapes Its Transcriptome in Response to Nanoemulsion

Penicillium digitatum is the most severe pathogen that infects citrus fruits during storage. It can cause fruit rot and bring significant economic losses. The continuous use of fungicides has resulted in the emergence of drug-resistant strains. Consequently, there is a need to develop naturally and efficiently antifungal fungicides. Natural antimicrobial agents such as clove oil, cinnamon oil, and thyme oil can be extracted from different plant parts. They exhibited broad-spectrum antimicrobial properties and have great potential in the food industry. Here, we exploit a novel cinnamaldehyde (CA), eugenol (EUG), or carvacrol (CAR) combination antifungal therapy and formulate it into nanoemulsion form to overcome lower solubility and instability of essential oil. In this study, the antifungal activity evaluation and transcriptional profile of Penicillium digitatum exposed to compound nanoemulsion were evaluated. Results showed that compound nanoemulsion had a striking inhibitory effect on P. digitatum in a dose-dependent manner. According to RNA-seq analysis, there were 2,169 differentially expressed genes (DEGs) between control and nanoemulsion-treated samples, including 1,028 downregulated and 1,141 upregulated genes. Gene Ontology (GO) analysis indicated that the DEGs were mainly involved in intracellular organelle parts of cell component: cellular respiration, proton transmembrane transport of biological process, and guanyl nucleotide-binding molecular function. KEGG analysis revealed that metabolic pathway, biosynthesis of secondary metabolites, and glyoxylate and dicarboxylate metabolism were the most highly enriched pathways for these DEGs. Taken together, we can conclude the promising antifungal activity of nanoemulsion with multiple action sites against P. digitatum. These outcomes would deepen our knowledge of the inhibitory mechanism from molecular aspects and exploit naturally, efficiently, and harmlessly antifungal agents in the citrus postharvest industry.

Hexanal induces early apoptosis of Aspergillus flavus conidia by disrupting mitochondrial function and expression of key genes

Aspergillus flavus is a notorious saprophytic fungus that compromises the quantity and quality of postharvest grains and produces carcinogenic aflatoxins. The natural compound hexanal disrupts cell membrane synthesis and mitochondrial function and induces apoptosis in A. flavus; here, we investigated the molecular mechanisms underlying these effects. The minimum inhibition and fungicidal concentration (MIC and MFC) of hexanal against A. flavus spores were 3.2 and 9.6 μL/mL, respectively. Hexanal exposure resulted in abnormal spore morphology and early spore apoptosis. These changes were accompanied by increased reactive oxygen species production, reduced mitochondrial membrane potential, and DNA fragmentation. Transcriptomic analysis revealed that hexanal treatment greatly altered the metabolism of A. flavus spores, including membrane permeability, mitochondrial function, energy metabolism, DNA replication, oxidative stress, and autophagy. This study provides novel insights into the mechanism underlying the antifungal activity of hexanal, suggesting that hexanal can be used an anti-A. flavus agent for agricultural applications. KEY POINTS: • Hexanal exposure resulted in abnormal spore morphology. • The apoptotic characteristics of A. flavus were induced after hexanal treatment. • Hexanal could change the expression of key A. flavus growth-related genes.

Quorum Sensing in Fungal Species

Quorum sensing (QS) is one of the most studied cell-cell communication mechanisms in fungi. Research in the last 20 years has explored various fungal QS systems that are involved in a wide range of biological processes, especially eukaryote- or fungus-specific behaviors, mirroring the significant contribution of QS regulation to fungal biology and evolution. Based on recent progress, we summarize in this review fungal QS regulation, with an emphasis on its functional role in behaviors unique to fungi or eukaryotes. We suggest that using fungi as genetically amenable eukaryotic model systems to address why and how QS regulation is integrated into eukaryotic reproductive strategies and molecular or cellular processes could be an important direction for QS research. Expected final online publication date for the Annual Review of Microbiology, Volume 75 is October 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Apoptosis-Like Cell Death in Leishmania major Treated with HESA-A: An Herbal Marine Compound

Background: The first drug for the treatment of leishmaniasis is pentavalent antimony compounds which have great side effects. Objectives: This study aimed to assess apoptosis induction by HESA-A, an herbal marine compound in Leishmania major promastigotes. Methods: Leishmania major promastigotes were treated with HESA-A in different increasing concentrations ranged 1.625 - 120 µg/mL, and amphotericin B and the phenomenon of apoptosis in the parasite were evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), flow cytometry, and DNA fragmentation tests. Results: The IC50 value of the compound and amphotericin B at 72 h were estimated at 2.81 µg/mL and 40 µg/mL, respectively. After 72 h of the adjacency of Leishmania major promastigotes with IC50 dose (2.81 µg/mL), the percentage of promastigotes in early and late apoptosis phases in the treated group was 5.4% and 60.4%, respectively. DNA fragmentation of Leishmania major promastigotes treated with 2.81 µg/mL for 72 h was observed. Conclusions: HESA-A, with significant induction of apoptosis in Leishmania major promastigotes, can be plausible in the treatment of cutaneous Leishmaniasis.

Impaired F1Fo-ATP-Synthase Dimerization Leads to the Induction of Cyclophilin D-Mediated Autophagy-Dependent Cell Death and Accelerated Aging

Mitochondrial F1Fo-ATP-synthase dimers play a critical role in shaping and maintenance of mitochondrial ultrastructure. Previous studies have revealed that ablation of the F1Fo-ATP-synthase assembly factor PaATPE of the ascomycete Podospora anserina strongly affects cristae formation, increases hydrogen peroxide levels, impairs mitochondrial function and leads to premature cell death. In the present study, we investigated the underlying mechanistic basis. Compared to the wild type, we observed a slight increase in non-selective and a pronounced increase in mitophagy, the selective vacuolar degradation of mitochondria. This effect depends on the availability of functional cyclophilin D (PaCYPD), the regulator of the mitochondrial permeability transition pore (mPTP). Simultaneous deletion of PaAtpe and PaAtg1, encoding a key component of the autophagy machinery or of PaCypD, led to a reduction of mitophagy and a partial restoration of the wild-type specific lifespan. The same effect was observed in the PaAtpe deletion strain after inhibition of PaCYPD by its specific inhibitor, cyclosporin A. Overall, our data identify autophagy-dependent cell death (ADCD) as part of the cellular response to impaired F1Fo-ATP-synthase dimerization, and emphasize the crucial role of functional mitochondria in aging.

Fungal evolution: cellular, genomic and metabolic complexity

The question of how phenotypic and genomic complexity are inter-related and how they are shaped through evolution is a central question in biology that historically has been approached from the perspective of animals and plants. In recent years, however, fungi have emerged as a promising alternative system to address such questions. Key to their ecological success, fungi present a broad and diverse range of phenotypic traits. Fungal cells can adopt many different shapes, often within a single species, providing them with great adaptive potential. Fungal cellular organizations span from unicellular forms to complex, macroscopic multicellularity, with multiple transitions to higher or lower levels of cellular complexity occurring throughout the evolutionary history of fungi. Similarly, fungal genomes are very diverse in their architecture. Deep changes in genome organization can occur very quickly, and these phenomena are known to mediate rapid adaptations to environmental changes. Finally, the biochemical complexity of fungi is huge, particularly with regard to their secondary metabolites, chemical products that mediate many aspects of fungal biology, including ecological interactions. Herein, we explore how the interplay of these cellular, genomic and metabolic traits mediates the emergence of complex phenotypes, and how this complexity is shaped throughout the evolutionary history of Fungi.

Dynamic modelling of the killing mechanism of action by virus-infected yeasts

Killer yeasts are microorganisms, which can produce and secrete proteinaceous toxins, a characteristic gained via infection by a virus. These toxins are able to kill sensitive cells of the same or a related species. From a biotechnological perspective, killer yeasts are beneficial due to their antifungal/antimicrobial activity, but also regarded as problematic for large-scale fermentation processes, whereby those yeasts would kill starter cultures species and lead to stuck fermentations. Here, we propose a mechanistic model of the toxin-binding kinetics pertaining to the killer population coupled with the toxin-induced death kinetics of the sensitive population to study toxic action. The dynamic model captured the transient toxic activity starting from the introduction of killer cells into the culture at the time of inoculation through to induced cell death. The kinetics of K1/K2 activity via its primary pathway of toxicity was 5.5 times faster than its activity at low concentration inducing the apoptotic pathway in sensitive cells. Conversely, we showed that the primary pathway for K28 was approximately three times slower than its equivalent apoptotic pathway, indicating the particular relevance of K28 in biotechnological applications where the toxin concentration is rarely above those limits to trigger the primary pathway of killer activity.

Functions of reactive oxygen species in apoptosis and ganoderic acid biosynthesis in Ganoderma lucidum

Ganoderma lucidum is a medicinal fungus that is widely used in traditional medicine. Fungal PacC is recognized as an important transcription factor that functions during adaptation to environmental pH, fungal development and secondary metabolism. Previous studies have revealed that GlPacC plays important roles in mycelial growth, fruiting body development and ganoderic acid (GA) biosynthesis. In this study, using a terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling (TUNEL) assay, we found that the apoptosis level was increased when PacC was silenced. The transcript and activity levels of caspase-like proteins were significantly increased in the PacC-silenced (PacCi) strains compared with the control strains. Silencing PacC also resulted in an increased reactive oxygen species (ROS) levels (∼2-fold) and decreased activity levels of enzymes involved in the antioxidant system. Further, we found that the intracellular ROS levels contributed to apoptosis and GA biosynthesis. Adding N-acetyl-cysteine and vitamin C decreased intracellular ROS and resulted in the inhibition of apoptosis in the PacCi strains. Additionally, the GA biosynthesis was different between the control strains and the PacCi strains after intracellular ROS was eliminated. Taken together, the findings showed that silencing PacC can result in an intracellular ROS burst, which increases cell apoptosis and GA biosynthesis levels. Our study provides novel insight into the functions of PacC in filamentous fungi.

The Bax inhibitor UvBI-1, a negative regulator of mycelial growth and conidiation, mediates stress response and is critical for pathogenicity of the rice false smut fungus Ustilaginoidea virens

Bax inhibitor-1 (BI-1), an evolutionarily conserved protein, is a suppressor of cell death induced by the proapoptotic protein Bax and is involved in the response to biotic and abiotic stress in animals, plants and yeast. Rice false smut caused by Ustilaginoidea virens is one of the destructive rice diseases worldwide. Although BI-1 proteins are widely distributed across filamentous fungi, few of them are functionally characterized. In this study, we identified a BI-1 protein in U. virens, UvBI-1, which contains a predicted Bax inhibitor-1-like family domain and could suppress the cell death induced by Bax. By co-transformation of the CRISPR/Cas9 construct along with donor DNA fragment containing the hygromycin resistance gene, we successfully generated Uvbi-1 deletion mutants. The UvBI-1 deletion showed an increase in mycelia vegetative growth and conidiation, suggesting this gene acts as a negative regulator of the growth and conidiation. In addition, the Uvbi-1 mutants exhibited higher sensitivity to osmotic and salt stress, hydrogen peroxide stress, and cell wall or membrane stress than the wild-type strain. Furthermore, UvBI-1 deletion was found to cause increased production of secondary metabolites and loss of pathogenicity of U. virens. Taken together, our results demonstrate that UvBI-1 plays a negative role in mycelial growth and conidiation, and is critical for stress tolerance, cell wall integrity, secondary metabolites production and pathogenicity of U. virens. Therefore, this study provides new evidence on the conserved function of BI-1 among fungal organisms and other species.

A morphological, enzymatic and metabolic approach to elucidate apoptotic-like cell death in fungi exposed to h- and α-molybdenum trioxide nanoparticles

The present study compares for the first time the effects of h-MoO3 and α-MoO3 against two fungal strains: Aspergillus niger and Aspergillus flavus. The h-MoO3 nanoparticles were more toxic to both fungi than α-MoO3. The toxic effects of h-MoO3 were more pronounced toward A. flavus, which presented a growth inhibition of 67.4% at 200 mg L-1. The presence of the nanoparticles affected drastically the hyphae morphology by triggering nuclear condensation and compromising the hyphae membrane. Further analysis of the volatile organic compounds (VOCs) produced by both fungi in the presence of the nanomaterials indicated important metabolic changes related to programmed cell death. These nanomaterials induced the production of specific antifungal VOCs, such as β-Elemene and t-Cadinol, by the fungi. The production of essential enzymes involved in fungal metabolism, such as acid phosphatase, naphthol-As-BI-phosphohydrolase, β-galactosidase, β-glucosidase and N-acetyl-β-glucosaminidase, reduced significantly in the presence of the nanomaterials. The changes in enzymatic production and VOCs corroborate the fact that these nanoparticles, especially h-MoO3, exert changes in the fungal metabolism, triggering apoptotic-like cell death responses in these fungi.

The genomic tool-kit of the truffle Tuber melanosporum programmed cell death

A survey of the truffle Tuber melanosporum genome has shown the presence of 67 programmed cell death (PCD)-related genes. The 67 genes are all expressed during fruit body (FB) development of T. melanosporum development; their expression has been detected by DNA microarrays and qPCR. A set of 14 PCD-related genes have been chosen, those with the highest identities to the homologs of other species, for a deeper investigation. That PCD occurs during T. melanosporum development has been demonstrated by the TUNEL reaction and transmission electron microscopy. The findings of this work, in addition to the discovery of PCD-related genes in the T. melanosporum genome and their expression during the differentiation and development of the FB, would suggest that one of the PCD subroutines, maybe autophagy, is involved in the FB ripening, i.e., sporogenesis.

Impact of F1Fo-ATP-synthase dimer assembly factors on mitochondrial function and organismic aging

In aerobic organisms, mitochondrial F₁F_o-ATP-synthase is the major site of ATP production. Beside this fundamental role, the protein complex is involved in shaping and maintenance of cristae. Previous electron microscopic studies identified the dissociation of F₁F_o-ATP-synthase dimers and oligomers during organismic aging correlating with a massive remodeling of the mitochondrial inner membrane. Here we report results aimed to experimentally proof this impact and to obtain further insights into the control of these processes. We focused on the role of the two dimer assembly factors PaATPE and PaATPG of the aging model Podospora anserina. Ablation of either protein strongly affects mitochondrial function and leads to an accumulation of senescence markers demonstrating that the inhibition of dimer formation negatively influences vital functions and accelerates organismic aging. Our data validate a model that links mitochondrial membrane remodeling to aging and identify specific molecular components triggering this process.

The synthesis, antifungal and apoptotic effects of triazole-oxadiazoles against Candida species

In search of potent and safe antifungal agents, herein, we report the synthesis, characterization and biological activities of triazole-oxadiazole compounds. The structural verification of the molecules was carried out by ¹H NMR, ¹³C NMR and mass spectral data. The in vitro antifungal and apoptotic activity were investigated against C. albicans, C. parapsilosis, C. krusei and C. glabrata. The compounds namely N-(4-nitrophenyl)-2-[(5-(2-((4-methyl-4H-1,2,4-triazol-3-yl)thio)ethyl)-1,3,4-oxadiazol-2-yl)thio]acetamide (4e) and N-(6-fluorobenzothiazol-2-yl)-2-[(5-(2-((4-methyl-4H-1,2,4-triazol-3-yl)thio)ethyl)-1,3,4-oxadiazol-2-yl)thio]acetamide (4i) were detected as the most potent compounds against C. albicans and C. glabrata (MIC₉₀ = 62.5 μg/mL). According to studies on their mechanism of action, it was confirmed that compound 4i has apoptotic effect on four Candida via Annexin V-PI with flow cytometry. The MTT assay revealed that all compounds were determined to be non-toxic against healthy cells in the tested concentrations.

Scolopendin, an antimicrobial peptide from centipede, attenuates mitochondrial functions and triggers apoptosis in Candida albicans

Centipedes, a type of arthropod, reportedly produce antimicrobial peptides as part of an innate immune response. Scolopendin (SPSEKAGLQPVGRIGRMLKK) is a novel antimicrobial peptide derived from Scolopendra subspinipes mutilans Many antifungal agents have more than one type of cell death mechanism. Although scolopendin is involved in membrane perturbation, the corresponding intracellular changes require further investigation. Therefore, we assessed the cell morphology and calcium ion concentration of the cytosol and mitochondria of scolopendin-treated cells. The treated cells were shrunken, and calcium ion homeostasis was disrupted in both the cytosol and mitochondria. These conditions attenuated mitochondrial homeostasis, disrupting mitochondrial membrane potential and cytochrome c levels. Fungal cells treated with scolopendin exhibited various apoptotic phenotypes such as reactive oxygen species accumulation, phosphatidylserine exposure, chromatin condensation, and nuclear fragmentation. Scolopendin-induced cell death also triggered metacaspase activation. In conclusion, treatment of Candida albicans with scolopendin induced the apoptotic response, which in turn led to mitochondrial dysfunction, metacaspase activation, and cell death. The antimicrobial peptide scolopendin from the centipede S.s. mutilans demonstrated a novel apoptotic mechanism as an antifungal agent.

Silibinin triggers yeast apoptosis related to mitochondrial Ca2+ influx in Candida albicans

Candida albicans is a common yeast that resides in the human body, but can occasionally cause systemic fungal infection, namely candidiasis. As this infection rate is gradually increasing, it is becoming a major problem to public health. Accordingly, we for the first time investigated the antifungal activity and mode of action of silibinin, a natural product extracted from Silybum marianum (milk thistle), against C. albicans. On treatment with 100μM silibinin, generation of reactive oxygen species (ROS) from mitochondria, which can cause yeast apoptosis via oxidative stress, was increased by 24.17% compared to that in untreated cells. Subsequently, we found disturbances in ion homeostasis such as release of intracellular K+ and accumulation of cytoplasmic and mitochondrial Ca2+. Among these phenomena, mitochondrial Ca2+ overload particularly plays a crucial role in the process of apoptosis, promoting the activation of pro-apoptotic factors. Therefore, we investigated the significance of mitochondrial Ca2+ in apoptosis by employing 20mM ruthenium red (RR). Additional apoptosis hallmarks such as mitochondrial membrane depolarization, cytochrome c release, caspase activation, phosphatidylserine (PS) exposure, and DNA damage were observed in response to silibinin treatment, whereas RR pre-treatment seemed to block these responses. In summary, our results suggest that silibinin induces yeast apoptosis mediated by mitochondrial Ca2+ signaling in C. albicans.

Plant phenolic acids induce programmed cell death of a fungal pathogen: MAPK signaling and survival of Cochliobolus heterostrophus

Plant aromatic compounds provide signals and a nutrient source to pathogens, and also act as stressors. Structure-activity relationships suggest two pathways sensing these compounds in the maize pathogen Cochliobolus heterostrophus, one triggering a stress response, and one inducing enzymes for their degradation. Focusing on the stress pathway, we found that ferulic acid causes rapid appearance of TUNEL-positive nuclei, dispersion of histone H1:GFP, hyphal shrinkage, and eventually membrane damage. These hallmarks of programmed cell death (PCD) were not seen upon exposure to caffeic acid, a very similar compound. Exposure to ferulic acid dephosphorylated two MAP kinases: Hog1 (stress activated) and Chk1 (pathogenicity related), while increasing phosphorylation of Mps1 (cell integrity related). Mutants lacking Hog1 or Chk1 are hypersensitive to ferulic acid while Mps1 mutants are not. These results implicate three MAPK pathways in the stress response. Ferulic acid and the antifungal fludioxonil have opposite additive effects on survival and on dephosphorylation of Hog1, which is thus implicated in survival. The results may explain why some fungal pathogens of plants undergo cell death early in host invasion, when phenolics are released from plant tissue.

Galleria mellonella lysozyme induces apoptotic changes in Candida albicans cells

The greater wax moth Galleria mellonella has been increasingly used as a model host to determine Candida albicans virulence and efficacy of antifungal treatment. The G. mellonella lysozyme, similarly to its human counterpart, is a member of the c-type family of lysozymes that exhibits antibacterial and antifungal activity. However, in contrast to the relatively well explained bactericidal action, the mechanism of fungistatic and/or fungicidal activity of lysozymes is still not clear. In the present study we provide the direct evidences that the G. mellonella lysozyme binds to the protoplasts as well as to the intact C. albicans cells and decreases the survival rate of both these forms in a time-dependent manner. No enzymatic activity of the lysozyme towards typical chitinase and β-glucanase substrates was detected, indicating that hydrolysis of main fungal cell wall components is not responsible for anti-Candida activity of the lysozyme. On the other hand, pre-treatment of cells with tetraethylammonium, a potassium channel blocker, prevented them from the lysozyme action, suggesting that lysozyme acts by induction of programmed cell death. In fact, the C. albicans cells treated with the lysozyme exhibited typical apoptotic features, i.e. loss of mitochondrial membrane potential, phosphatidylserine exposure in the outer leaflet of the cell membrane, as well as chromatin condensation and DNA fragmentation.

Cyclophilin D Is Involved in the Regulation of Autophagy and Affects the Lifespan of P. anserina in Response to Mitochondrial Oxidative Stress

The mitochondrial permeability transition pore plays a key role in programmed cell death and the induction of autophagy. Opening of the pore is regulated by the mitochondrial peptidyl prolyl-cis, trans-isomerase cyclophilin D (CYPD). Previously it was shown in the aging model organism Podospora anserina that PaCYPD abundance increases during aging and that PaCypD overexpressors are characterized by accelerated aging. Here, we describe a role of PaCYPD in the regulation of autophagy. We found that the accelerated aging phenotype observed in a strain overexpressing PaCypD is not metacaspase-dependent but is accompanied by an increase of general autophagy and mitophagy, the selective autophagic degradation of mitochondria. It thus is linked to what has been defined as "autophagic cell death" or "type II" programmed cell death. Moreover, we found that the previously demonstrated age-related induction of autophagy in wild-type aging depends on the presence of PaCYPD. Deletion of PaCypD leads to a decrease in autophagy in later stages of age and under paraquat-mediated oxidative stress. Finally, we report that PaCYPD is also required for mitohormesis, the beneficial effect of mild mitochondrial stress. Thus, PaCYPD plays a key role in the context-dependent regulation of pathways leading to pro-survival and pro-death effects of autophagy.

Iron starvation induces apoptosis in Rhizopus oryzae in vitro

Mortality associated with mucormycosis remains high despite current antifungals. Iron-starvation strategies have been shown to have promising activity against Mucorales. We hypothesized that iron starvation enhances apoptosis in Rhizopus oryzae. Apoptosis was characterized in R. oryzae transformed with RNAi plasmid targeting FTR1 expression (iron permease mutant) or empty plasmid grown in iron rich (0.125% FeCl3) and iron depleted media (YNB+1mM ferrozine and 1 mM ascorbic acid). Increased apoptosis was observed with dihydrorhodamine-123 and rhodamine-123 staining in the iron starved mutant FTR1 when compared to empty plasmid, followed by increased extracellular ATP levels. In addition, DNA fragmentation and metacaspase activity were prominent in FTR1. In contrast, Rhizopus strains grown in iron-rich medium displayed minimal apoptosis. Our results demonstrate a metacaspase dependent apoptotic process in iron deprived condition and further support the role of iron starvation strategies as an adjunct treatment for mucormycosis, a mechanism by which iron starvation affects R. oryzae.

Identification of potential mitochondrial CLPXP protease interactors and substrates suggests its central role in energy metabolism

Maintenance of mitochondria is achieved by several mechanisms, including the regulation of mitochondrial proteostasis. The matrix protease CLPXP, involved in protein quality control, has been implicated in ageing and disease. However, particularly due to the lack of knowledge of CLPXP’s substrate spectrum, only little is known about the pathways and mechanisms controlled by this protease. Here we report the first comprehensive identification of potential mitochondrial CLPXP in vivo interaction partners and substrates using a combination of tandem affinity purification and differential proteomics. This analysis reveals that CLPXP in the fungal ageing model Podospora anserina is mainly associated with metabolic pathways in mitochondria, e.g. components of the pyruvate dehydrogenase complex and the tricarboxylic acid cycle as well as subunits of electron transport chain complex I. These data suggest a possible function of mitochondrial CLPXP in the control and/or maintenance of energy metabolism. Since bioenergetic alterations are a common feature of neurodegenerative diseases, cancer, and ageing, our data comprise an important resource for specific studies addressing the role of CLPXP in these adverse processes.

Hydrogen peroxide-induced secondary necrosis in conidia of Aspergillus fumigatus

Aspergillus fumigatus conidia have been linked to severe aspergillosis in immunocompromised patients. Recently, the cytotoxic effect of secondary metabolites from A. fumigatus conidia was reported. In the present work, a methodology used to detect cell death markers in fungal hyphae was adapted to study conidia cell death. Additionally, the mechanism of H2O2-induced cell death was studied in A. fumigatus conidia for the first time. Data presented in this work reveal that the H2O2-induced conidial cell death was associated with a marked increase of TUNEL- and PI-positive cells. It is therefore suggested that conidia cell death occurs in a dose-dependent manner through a secondary necrosis mechanism. The knowledge of conidia cell death machinery may provide insights into the molecular mechanism of conidia-mediated toxicity to the respiratory tract and may pave the way for improved therapeutic approaches against A. fumigatus conidia-mediated diseases.

Micafungin induced apoptosis in Candida parapsilosis independent of its susceptibility to micafungin

We hypothesized that the cell wall inhibitor micafungin (MICA) induces apoptosis in both MICA-susceptible (MICA-S) and MICA-non-susceptible (MICA-NS) Candida parapsilosis. Antifungal activity and apoptosis were analyzed in MICA-S and MICA-NS C. parapsilosis strains following exposure to micafungin for 3 h at 37°C in RPMI 1640 medium. Apoptosis was characterized by detecting phosphatidylserine externalization (PS), plasma membrane integrity, reactive oxygen species (ROS) generation, mitochondrial membrane potential changes, adenosine triphosphate (ATP) release, and caspase-like activity. Apoptosis was detected in MICA exposed (0.25 to 1 mg/L) susceptible C. parapsilosis strains and was associated with apoptosis of 20-52% of analyzed cells versus only 5-30% of apoptosis in MICA-NS cells exposed to micafungin (0.5 to 2 mg/L; P = 0.001). The MICA antifungal activity was correlated with apoptotic cells showing increased dihydrorhodamine-123 staining (indicating ROS production), Rh-123 staining (decreased mitochondrial membrane potential), elevated ATP, and increased metacaspase activity. In conclusion, MICA is pro-apoptotic in MICA-S cells, but still exerts apoptotic effects in MICA -NS C. parapsilosis.

Caspases in plants: metacaspase gene family in plant stress responses

Programmed cell death (PCD) is an ordered cell suicide that removes unwanted or damaged cells, playing a role in defense to environmental stresses and pathogen invasion. PCD is component of the life cycle of plants, occurring throughout development from embryogenesis to the death. Metacaspases are cysteine proteases present in plants, fungi, and protists. In certain plant-pathogen interactions, the PCD seems to be mediated by metacaspases. We adopted a comparative genomic approach to identify genes coding for the metacaspases in Viridiplantae. We observed that the metacaspase was divided into types I and II, based on their protein structure. The type I has a metacaspase domain at the C-terminus region, presenting or not a zinc finger motif in the N-terminus region and a prodomain rich in proline. Metacaspase type II does not feature the prodomain and the zinc finger, but has a linker between caspase-like catalytic domains of 20 kDa (p20) and 10 kDa (p10). A high conservation was observed in the zinc finger domain (type I proteins) and in p20 and p10 subunits (types I and II proteins). The phylogeny showed that the metacaspases are divided into three principal groups: type I with and without zinc finger domain and type II metacaspases. The algae and moss are presented as outgroup, suggesting that these three classes of metacaspases originated in the early stages of Viridiplantae, being the absence of the zinc finger domain the ancient condition. The study of metacaspase can clarify their assignment and involvement in plant PCD mechanisms.