Hydrogen peroxide acts on sensitive mitochondrial proteins to induce death of a fungal pathogen revealed by proteomic analysis

Superoxide Dismutase Premodulates Oxidative Stress in Plastids for Protection of Tobacco Plants from Cold Damage Ultrastructure Damage

ROS-dependent induction of oxidative damage can be used as a trigger initiating genetically determined non-specific protection in plant cells and tissues. Plants are potentially able to withstand various specific (toxic, osmotic) factors of abiotic effects, but do not have sufficient or specific sensitivity to form an adequate effective response. In this work, we demonstrate one of the possible approaches for successful cold acclimation through the formation of effective protection of photosynthetic structures due to the insertion of the heterologous FeSOD gene into the tobacco genome under the control of the constitutive promoter and equipped with a signal sequence targeting the protein to plastid. The increased enzymatic activity of superoxide dismutase in the plastid compartment of transgenic tobacco plants enables them to tolerate the oxidative factor of environmental stresses scavenging ROS. On the other hand, the cost of such resistance is quite high and, when grown under normal conditions, disturbs the arrangement of the intrachloroplastic subdomains leading to the modification of stromal thylakoids, probably significantly affecting the photosynthesis processes that regulate the efficiency of photosystem II. This is partially compensated for by the fact that, at the same time, under normal conditions, the production of peroxide induces the activation of ROS detoxification enzymes. However, a violation of a number of processes, such as the metabolism of accumulation, and utilization and transportation of sugars and starch, is significantly altered, which leads to a shift in metabolic chains. The expected step for further improvement of the applied technology could be both the use of inducible promoters in the expression cassette, and the addition of other genes encoding for hydrogen peroxide-scavenging enzymes in the genetic construct that are downstream in the metabolic chain.

Transcriptomic and metabolomic analysis unveils a negative effect of glutathione metabolism on laccase activity in Cerrena unicolor 87613

The white rot fungus Cerrena unicolor 87613 has been previously shown to be a promising resource in laccase production, an enzyme with significant biotechnological applications. Conventional methods face technical challenges in improving laccase activity. Attempts are still being made to develop novel approaches for further enhancing laccase activity. This study aimed to understand the regulation of laccase activity in C. unicolor 87613 for a better exploration of the novel approach. Transcriptomic and metabolomic analyses were performed to identify key genes and metabolites involved in extracellular laccase activity. The findings indicated a strong correlation between the glutathione metabolism pathway and laccase activity. Subsequently, experimental verifications were conducted by manipulating the pathway using chemical approaches. The additive reduced glutathione (GSH) dose-dependently repressed laccase activity, while the GSH inhibitors (APR-246) and reactive oxygen species (ROS) inducer (H2O2) enhanced laccase activity. Changes in GSH levels could determine the intracellular redox homeostasis in interaction with ROS and partially affect the expression level of laccase genes in C. unicolor 87613 in turn. In addition, GSH synthetase was found to mediate GSH abundance in a feedback loop. This study suggests that laccase activity is negatively influenced by GSH metabolism and provides a theoretical basis for a novel strategy to enhance laccase activity by reprogramming glutathione metabolism at a specific cultivation stage.IMPORTANCEThe production of laccase activity is limited by various conventional approaches, such as heterologous expression, strain screening, and optimization of incubation conditions. There is an urgent need for a new strategy to meet industrial requirements more effectively. In this study, we conducted a comprehensive analysis of the transcriptome and metabolome of Cerrena unicolor 87613. For the first time, we discovered a negative role played by reduced glutathione (GSH) and its metabolic pathway in influencing extracellular laccase activity. Furthermore, we identified a feedback loop involving GSH, GSH synthetase gene, and GSH synthetase within this metabolic pathway. These deductions were confirmed through experimental investigations. These findings not only advanced our understanding of laccase activity regulation in its natural producer but also provide a theoretical foundation for a strategy to enhance laccase activity by reprogramming glutathione metabolism at a specific cultivation stage.

Ozone treatment modulates reactive oxygen species levels in kiwifruit through the antioxidant system: Insights from transcriptomic analysis

Owing to its easy decomposition and residue-free properties, ozone has been used as an effective and environmentally friendly physical preservation method for maintaining the post-harvest quality of fruits. This study aimed to investigate the effects of ozone treatment on the levels of oxidative stress markers and the status of the antioxidant defense system in refrigerated kiwifruit. Additionally, the study aimed to identify the differences in gene expression levels and potential regulatory effects from the transcriptional level. The results showed that ozone treatment reduced the respiration rate, maintained the fruit hardness and storage quality, and inhibited the ripening and senescence of kiwifruit. Ozone treatment activated antioxidant enzymes (superoxide dismutase, peroxidase, and catalase) and ascorbate-glutathione cycle to prevent the increase of reactive oxygen species levels (H2O2, O2-•) and malonaldehyde content, maintaining lower membrane lipid peroxidation and reactive oxygen species (ROS) accumulation than the control treatment. Further analysis showed that the regulatory ability of ROS in kiwifruit treated with ozone was not only related to the synergistic effect of enzyme activity and gene expression related to the antioxidant oxidase system and the ascorbate-glutathione (ASA-GSH) cycle but also related to downstream hormone signaling. This study provides a foundation for understanding the potential effects of ozone treatment on the antioxidant cycle of kiwifruit and provides valuable insights into the molecular basis and related key genes involved in regulating ROS to delay aging in kiwifruit.

PeAP1-mediated oxidative stress response plays an important role in the growth and pathogenicity of Penicillium expansum

Penicillium expansum is the causal agent of post-harvest blue mold in various fruits and serves as a model for understanding fungal pathogenicity and mycotoxin production. The relevance of oxidative stress response in the growth and virulence of P. expansum has been largely unexplored. Here, we identify the transcriptional factor PeAP1 as a regulator of oxidative stress response in P. expansum. Gene expression and protein abundance of PeAP1, as well as its nuclear localization, are specifically induced by H2O2. Deletion of PeAP1 results in increased sensitivity to H2O2, and PeAP1 mutants exhibit a variety of defects in hyphal growth and virulence. PeAP1 prevents the accumulation of both intracellular H2O2 during vegetative growth and host-derived H2O2 during biotrophic growth. Application of an antioxidant glutathione and a NADPH oxidase inhibitor, diphenylene iodonium, to the PeAP1 mutant partially restored fungal growth and virulence. RNA sequencing analysis revealed 144 H2O2-induced PeAP1 target genes, including four antioxidant-related genes, PeGST1, PePrx1, PePrx2, and PeTRX2, that were also demonstrated to be involved in oxidative stress response and/or virulence. Collectively, our results demonstrate the global regulatory role of PeAP1 in response to oxidative stress and provide insights into the critical role of the PeAP1-mediated oxidative stress response to regulate growth and virulence of P. expansum. IMPORTANCE Reactive oxygen species are the core of host plant defense and also play a vital role in the successful invasion of host plants by pathogenic fungi. Despite its importance, the relevance of oxidative stress response in fungal growth and virulence is poorly understood in P. expansum. In this study, we reveal that the transcription factor PeAP1 acts as a central regulator of oxidative stress response in P. expansum and that there is a major link between PeAP1-mediated oxidative stress response and fungal growth and virulence. To explore the underlying mechanisms, we performed comparative transcriptomic studies and identified a number of H2O2-induced PeAP1 target genes, including four novel ones, PePrx1, PePrx2, PeGST1, and PeTRX2, whose functions were linked to PeAP1 and pathogenicity. These findings provide novel insights into the regulation mechanism of PeAP1 on growth and virulence, which might offer promising targets for control of blue mold and patulin contamination.

Cinnamaldehyde Inhibits Postharvest Gray Mold on Pepper Fruits via Inhibiting Fungal Growth and Triggering Fruit Defense

Gray mold infected with Botrytis cinerea frequently appears on fruits and vegetables throughout the supply chain after harvest, leading to economic losses. Biological control of postharvest disease with phytochemicals is a promising approach. CA (cinnamaldehyde) is a natural phytochemical with medicinal and antimicrobial activity. This study evaluated the effect of CA in controlling B. cinerea on fresh pepper fruit. CA inhibited B. cinerea growth in vitro significantly in a dose- (0.1-0.8 mM) and time-dependent (6-48 h) manner, with an EC50 (median effective concentration) of 0.5 mM. CA induced the collapse and breakdown of the mycelia. CA induced lipid peroxidation resulting from ROS (reactive oxygen species) accumulation in mycelia, further leading to cell leakage, evidenced by increased conductivity in mycelia. CA induced mycelial glycerol accumulation, resulting in osmotic stress possibly. CA inhibited sporulation and spore germination resulting from ROS accumulation and cell death observed in spores. Spraying CA at 0.5 mM induced a defense response in fresh pepper fruits, such as the accumulation of defense metabolites (flavonoid and total phenols) and an increase in the activity of defense enzymes (PAL, phenylalanine ammonia lyase; PPO, polyphenol oxidase; POD, peroxidase). As CA is a type of environmentally friendly compound, this study provides significant data on the activity of CA in the biocontrol of postharvest gray mold in peppers.

The ATP Synthase Subunits FfATPh, FfATP5, and FfATPb Regulate the Development, Pathogenicity, and Fungicide Sensitivity of Fusarium fujikuroi

ATP synthase catalyzes the synthesis of ATP by consuming the proton electrochemical gradient, which is essential for maintaining the life activity of organisms. The peripheral stalk belongs to ATP synthase and plays an important supporting role in the structure of ATP synthase, but their regulation in filamentous fungi are not yet known. Here, we characterized the subunits of the peripheral stalk, FfATPh, FfATP5, and FfATPb, and explored their functions on development and pathogenicity of Fusarium Fujikuroi. The FfATPh, FfATP5, and FfATPb deletion mutations (∆FfATPh, ∆FfATP5, and ∆FfATPb) presented deficiencies in vegetative growth, sporulation, and pathogenicity. The sensitivity of ∆FfATPh, ∆FfATP5, and ∆FfATPb to fludioxonil, phenamacril, pyraclostrobine, and fluazinam decreased. In addition, ∆FfATPh exhibited decreased sensitivity to ionic stress and osmotic stress, and ∆FfATPb and ∆FfATP5 were more sensitive to oxidative stress. FfATPh, FfATP5, and FfATPb were located on the mitochondria, and ∆FfATPh, ∆FfATPb, and ∆FfATP5 disrupted mitochondrial location. Furthermore, we demonstrated the interaction among FfATPh, FfATP5, and FfATPb by Bimolecular Fluorescent Complimentary (BiFC) analysis. In conclusion, FfATPh, FfATP5, and FfATPb participated in regulating development, pathogenicity, and sensitivity to fungicides and stress factors in F. fujikuroi.

A semi purified hydroalcoholic fraction from Caesalpinia bonduc seeds causes ergosterol biosynthesis inhibition in Candida albicans resulting in cell membrane damage

Candida species are currently developing resistance to prevailing commercially available drugs, which raises an instantaneous need to discover novel antifungals. To cope with this shocking situation, phytochemicals are the richest, safest, and most potent source of excellent antimicrobials with broad-spectrum activity. The aim of the current study is to explore the anticandidal potential of the various fractions purified from the hydroalcoholic extract of C. bonduc seed. Out of five fractions purified from the hydroalcoholic extract, fraction 3 (Fr. 3) recorded the best activity against C. albicans (8 μg/mL) and thus this species was chosen for further mechanism of action studies. The phytochemical examination reveals that Fr. 3 was found to contain steroids and triterpenoids. This was further supported by LC-QTOF-MS and GCMS analyses. Our findings show that Fr. 3 targets the ergosterol biosynthesis pathway in C. albicans by inhibiting the lanosterol 14-α demethylase enzyme and downregulating expression of its related gene ERG11. Molecular docking outcomes disclosed favorable structural dynamics of the compounds, implying that the compounds present in Fr. 3 would be able to successfully bind to the lanosterol 14-α demethylase, as evidenced by the docked compounds' strong interaction with the target enzyme's amino acid residues. Considering virulence factors, the Fr. 3 recorded significant antibiofilm activity as well as germ-tube reduction potential. Furthermore, Fr. 3 enhances the production of intracellular reactive oxygen species (ROS). This suggests that the antifungal activity of Fr. 3 was associated with membrane damage and the induction of ROS production, resulting in cell death. Fluorescence microscopic analysis of PI stained Candida further showed changes in the plasma membrane permeability, which causes severe loss of intracellular material and osmotic balance. This was demonstrated by the potassium ion leakage and release of genetic materials. Finally, the erythrocyte lysis assay confirmed the low cytotoxicity of Fr. 3. Both in silico and in vitro results suggest that Fr. 3 has the potential to propel forward novel antifungal drug discovery programmes.

Functional Analyses of the Bacillus velezensis HMB26553 Genome Provide Evidence That Its Genes Are Potentially Related to the Promotion of Plant Growth and Prevention of Cotton Rhizoctonia Damping-Off

Bacillus spp. is one kind of the important representative biocontrol agents against plant diseases and promoting plant growth. In this study, the whole genomic sequence of bacterial strain HMB26553 was obtained. A phylogenetic tree based on the genome and ANI (average nucleotide identity), as well as dDDH (digital DNA-DNA hybridization), was constructed, and strain HMB26553 was identified as Bacillus velezensis. Fourteen biosynthetic gene clusters responsible for secondary metabolite were predicted via anti-SMASH, and six secondary metabolites were identified by UHPLC-QTOF-MS/MS (ultra-high-performance liquid chromatography coupled to quadrupole-time-of-flight tandem mass spectrometry). When the phytopathogen Rhizoctonia solani was treated with B. velezensis HMB26553, the mycelial structure changed, ROS (reactive oxygen species) accumulated, and the mitochondrial membrane potential decreased. Characteristics of strain HMB26553 were predicted and confirmed by genomic information and experiments, such as producing IAA, siderophore, extracellular enzymes and biofilm, as well as moving and promoting cotton growth. All these results suggested the mechanisms by which B. velezensis HMB26553 inhibits pathogen growth and promotes cotton growth, which likely provided the potential biocontrol agent to control cotton Rhizoctonia damping-off.

Enzymatic and proteomic exploration into the inhibitory activities of lemongrass and lemon essential oils against Botrytis cinerea (causative pathogen of gray mold)

Introduction

Essential oils (EOs) have been demonstrated as efficacious against B. cinerea. However, the underpinning enzymatic and proteomic mechanism for these inhibitory effects is not entirely clear.

Methods

Thus, this study examined the effects of lemon (Le) and lemongrass (Lg) EOs (individually and in combination) against B. cinerea based on enzymatic and proteomic analyses. Proteomics data are available via ProteomeXchange with identifier PXD038894.

Results and discussion

Both EOs (individually and in combination) displayed abilities to induce scavenging as observed with the reduction of H2O2. Measured malondialdehyde (MDA) and superoxide dismutase (SOD) activity were increased in all EOs treated B. cinerea mycelia compared to the control. Ascorbate peroxidase (APX) activity was highest in Lg treated B. cinerea (206% increase), followed by combined (Le + Lg) treatment with 73% compared to the untreated control. Based on GC-MS analysis, the number of volatile compounds identified in lemon and lemongrass EOs were 7 and 10, respectively. Major chemical constituent of lemon EO was d-limonene (71%), while lemongrass EO was a-citral (50.1%). Based on the interrogated LC-MS data, 42 distinct proteins were identified, and 13 of these proteins were unique with 1, 8, and 4 found in Le-, Lg-, and (Le + Lg) EOs treated B. cinerea, respectively, and none in control. Overall, 72% of identified proteins were localized within cellular anatomical entity, and 28% in protein-complexes. Proteins involved in translation initiation, antioxidant activity, protein macromolecule adaptor activity and microtubule motor activity were only identified in the Lg and (Le + Lg) EOs treated B. cinerea mycelia, which was consistent with their APX activities.

Effect of selenium and methods of protein extraction on the proteomic profile of Saccharomyces yeast

Selenium may influence the biosynthesis of individual proteins in the yeast cell cytosol. In this study, we used two-dimensional (2D) electrophoresis to identify proteins that are differentially expressed by the enrichment of selenium in Saccharomyces cerevisiae yeast cells. We chose eight protein fractions for further proteomic analysis. A detailed analysis was performed using the Ultraflextreme matrix-assisted laser desorption/ionisation time-of-flight/time-of-flight mass spectrometer, which enables fast and accurate measurement of the molecular weight of the analysed proteins. This study, for the first time, provides evidence that selenium-enriched yeast contains higher levels of mitochondria malate dehydrogenase, adenosine-5'-triphosphate (ATP)-dependent RNA helicase dbp3, and tryptophan dimethylallyltransferase, and alanyl-tRNA editing protein AlaX than yeast without the addition of selenium. It should be emphasised that the proteomic variability obtained reflects the high biological and complexity of yeast metabolism under control and selenium-enriched conditions and can be properly used in the future as a model for further research aimed at determining the expression of appropriate metabolic genes.

Mechanism of Antifungal Action of Monoterpene Isoespintanol against Clinical Isolates of Candida tropicalis

The growing increase in infections by Candida spp., non-albicans, coupled with expressed drug resistance and high mortality, especially in immunocompromised patients, have made candidemia a great challenge. The efficacy of compounds of plant origin with antifungal potential has recently been reported as an alternative to be used. Our objective was to evaluate the mechanism of the antifungal action of isoespintanol (ISO) against clinical isolates of Candida tropicalis. Microdilution assays revealed fungal growth inhibition, showing minimum inhibitory concentration (MIC) values between 326.6 and 500 µg/mL. The eradication of mature biofilms by ISO was between 20.3 and 25.8% after 1 h of exposure, being in all cases higher than the effect caused by amphotericin B (AFB), with values between 7.2 and 12.4%. Flow cytometry showed changes in the permeability of the plasma membrane, causing loss of intracellular material and osmotic balance; transmission electron microscopy (TEM) confirmed the damage to the integrity of the plasma membrane. Furthermore, ISO induced the production of intracellular reactive oxygen species (iROS). This indicates that the antifungal action of ISO is associated with damage to membrane integrity and the induction of iROS production, causing cell death.

Antifungal mechanism of (E)-2-hexenal against Botrytis cinerea growth revealed by transcriptome analysis

Gray mold caused by Botrytis cinerea, a necrotrophic plant pathogen, is one of the most damaging diseases of tomato, resulting in both pre- and post-harvest losses. (E)-2-Hexenal dose-dependently inhibited the mycelial growth of B. cinerea, and caused distortion of mycelia and loss of the cytoplasm content, thus altering the morphology of B. cinerea hyphae. To understand molecular processes in response to (E)-2-hexenal, transcriptome sequencing was carried out using RNA-Seq technology. RNA-Seq results revealed that a total of 3,893 genes were differentially expressed in B. cinerea samples treated with (E)-2-hexenal fumigation. Among these genes, 1,949 were upregulated and 1,944 were downregulated. Moreover, further analysis results showed 2,113 unigenes were mapped onto 259 pathways in Kyoto Encyclopedia of Genes and Genomes (KEGG). Moreover, (E)-2-hexenal stress affected the expression of genes involved in the pathways of cell wall, cell membrane, and energy metabolism. KEGG pathway analysis showed that the terpenoid backbone biosynthesis and steroid biosynthesis were the most enriched in ergosterol biosynthetic process transcriptome data. Particularly, (E)-2-hexenal fumigation had influenced ergosterol biosynthetic gene expression levels (e.g., ERG1, ERG3, ERG4, ERG7, ERG12, ERG13, ERG24, ERG25, ERG26, and ERG27), which were in good agreement with the experimental measurement results, and the ergosterol content decreased. Collectively, the results of this study increase our current understanding of (E)-2-hexenal inhibition mechanisms in B. cinerea and provide relevant information on postharvest shelf life extension and preservation of fruits and vegetables.

Bioactivity of mefentrifluconazole against different Fusarium spp

Emergence and development of resistance to 14α-demethylase inhibitors (DMIs) have become a critical issue in both agriculture and medical fields. Mefentrifluconazole, the first isopropanol triazole fungicide belonging to a new subclass of DMIs, has been proposed to show high activity, minimal adverse side effects, and inconsistent cross resistance with other DMIs due to its high structural flexibility. In this study, mefentrifluconazole showed disparate inhibitory activity against the mycelium growth of seven tested Fusarium species. The most sensitive species included F. oxysporum, F. proliferatum, F. commuae, and F. fujikuroi, followed by F. equiseti and F. graminearum, while F. solani was most insensitive. Consistently, mefentrifluconazole presented the strongest inhibiting effects on conidium germination, cell membrane integrity, and ergosterol biosynthesis in F. fujikuroi, followed by F. graminearum, while F. solani ranked last. Further results indicated that all F. fujikuroi isolates causing rice bakanae disease (RBD) were sensitive to mefentrifluconazole regardless of their resistance to prochloraz, tebuconazole, carbendazim, and phenamacril. Additionally, the inoculation tests found that mefentrifluconazole presented a better protective efficacy on rice seedlings when applied 12 h before the F. fujikuroi inoculation, compared to applied 12 h post the inoculation. Overall, this study demonstrated the various bioactivity of mefentrifluconazole combating Fusarium spp. and put new insights into RBD management as well as the applications of DMIs.

Antimicrobial action of phenolic acids combined with violet 405-nm light for disinfecting pathogenic and spoilage fungi

The aim of this study is to investigate the fungicidal spectrum of six phenolic-cinnamic and -benzoic acid derivatives using four fungi, Aspergillus niger, Cladosporium cladosporioides, Trichophyton mentagrophytes and Candida albicans, in a photocombination system with violet 405-nm light. This is the first study to examine the fungicidal mechanism involving oxidative damage using the conidium of A. niger, as well as an assessment of cellular function and chemical characteristics. The results of the screening assay indicated that ferulic acid (FA) and vanillic acid (VA), which possess 4-hydroxyl and 3-methoxy groups in their phenolic acid structures, produced synergistic activity with 405-nm light irradiation. FA and VA (5.0 mM) significantly decreased the viability of A. niger by 2.4 to 2.6-logs under 90-min irradiation. The synergistic effects were attenuated by the addition of the radical scavenger dimethyl sulfoxide. Generation of reactive oxygen species (ROS), such as hydrogen peroxide and hydroxyl radicals, were confirmed in the phenolic acid solutions tested after irradiation with colorimetric and electron spin resonance analyses. Adsorption of FA and VA to conidia was greater than other tested phenolic acids, and produced 1.55- and 1.85-fold elevation of intracellular ROS levels, as determined using an oxidant-sensitive probe with flow cytometry analysis. However, cell wall or membrane damage was not the main mechanism by which the combination-induced fungal death was mediated. Intracellular ATP was drastically diminished (5% of control levels) following combined treatment with FA and light exposure, even under a condition that produced negligible decreases in viability, thereby resulting in pronounced growth delay. These results suggest that the first stage in the photofungicidal mechanism is oxidative damage to mitochondria or the cellular catabolism system associated with ATP synthesis, which is a result of the photoreaction of phenolic acids adsorbed and internalized by conidia. This photo-technology in combination with food-grade phenolic acids can aid in developing alternative approaches for disinfection of pathogenic and spoilage fungi in the fields of agriculture, food processing and medical care.

Bacillomycin D-C16 inhibits growth of Fusarium verticillioides and production of fumonisin B1 in maize kernels

Fusarium verticillioides causes ear and kernel rot in maize and produces mycotoxins, like fumonisin B₁ (FB₁). Bacillomycin D-C16 is a natural antimicrobial lipopeptide produced by Bacillus subtilis. In this study, the inhibitory effects of Bacillomycin D-C16 on the growth of F. verticillioides and on the production of FB₁ in maize were investigated. Bacillomycin D-C16 displayed strong fungicidal activity against F. verticillioides, with a minimum inhibitory concentration (MIC) of 32 g/L. Scanning electron microscopy (SEM) showed that Bacillomycin D-C16 altered the morphology of F. verticillioides mycelia. Bacillomycin D-C16 reduced the ergosterol content, increased the release of nucleic acids and proteins, and increased the levels of reactive oxygen species (ROS) in fungal mycelia. Bacillomycin D-C16 also significantly inhibited the production of FB₁ by inhibiting mycelial growth and decreasing the levels of fumonisin biosynthetic genes 1 (fum1), fum6 and fum14. The application of Bacillomycin D-C16 on maize kernels prior to storage inhibited the growth of F. verticillioides and the production of FB₁. Our results suggested that Bacillomycin D-C16 has a significant antifungal activity that could be used as a potential natural antimicrobial agent to control food contamination and to ensure food safety.

In Vitro Anti-Biofilm Activity of Hydrogen-Peroxide Generating Electrochemical Bandage Against Yeast Biofilms

Wound infections are caused by bacteria and/or fungi. The presence of fungal biofilms in wound beds presents a unique challenge, as fungal biofilms may be difficult to eradicate. The goal of this work was to assess the in vitro anti-biofilm activity of a H₂O₂-producing electrochemical bandage (e-bandage) against 15 yeast isolates representing commonly-encountered species. Time-dependent decreases in viable biofilm CFU counts of all isolates tested were observed, resulting in no visible colonies with 48 hours of exposure by plate culture. Fluorescence microscopic analysis showed extensive cell membrane damage of biofilm cells after e-bandage treatment. Reductions in intracellular ATP levels of yeast biofilm cells were recorded post e-bandage treatment. Our results suggest that exposure to H₂O₂-producing e-bandages reduce in vitro viable cell counts of yeast biofilms, making this a potential new topical treatment approach for fungal wound infections.

Antifungal action of the combination of ferulic acid and ultraviolet-A irradiation against Saccharomyces cerevisiae

AIMS

To examine the antifungal action of photocombination treatment with ferulic acid (FA) and ultraviolet-A (UV-A) light (wavelength, 365 nm) by investigating associated changes in cellular functions of Saccharomyces cerevisiae.

METHODS AND RESULTS

When pre-incubation of yeast cells with FA was extended from 0.5 to 10 min, its photofungicidal activity increased. Flow cytometry analysis of stained live and dead cells revealed that 10-min UV-A exposure combined with FA (1 mg ml^-1 ) induced a ~99.9% decrease in cell viability although maintaining cell membrane integrity when compared with pre-exposure samples. When morphological and biochemical analysis were performed, treated cells exhibited an intact cell surface and oxidative DNA damage similar to control cells. Photocombination treatment induced cellular proteins oxidation, as shown by 2.3-fold increasing in immunostaining levels of ~49-kDa carbonylated proteins compared with pre-irradiation samples. Pyruvate kinase 1 (PK1) was identified by proteomics analysis as a candidate protein whose levels was affected by photocombination treatment. Moreover, intracellular ATP levels decreased following FA treatment both in darkness and with UV-A irradiation, thus suggesting a possible FA-induced delay in cell growth.

CONCLUSIONS

FA functions within the cytoplasmic membrane; addition of UV-A exposure induces increased oxidative modifications of cytosolic proteins such as PK1, which functions in ATP generation, without causing detectable genotoxicity, thus triggering inactivation of yeast cells.

SIGNIFICANCE AND IMPACT OF THE STUDY

Microbial contamination is a serious problem that diminishes the quality of fruits and vegetables. Combining light exposure with food-grade phenolic acids such as FA is a promising disinfection technology for applications in agriculture and food processing. However, the mode of photofungicidal action of FA with UV-A light remains unclear. This study is the first to elucidate the mechanism using S. cerevisiae. Moreover, proteomics analyses identified a specific cytosolic protein, PK1, which is oxidatively modified by photocombination treatment.

Effects of Matrix pH on Spontaneous Transient Depolarization and Reactive Oxygen Species Production in Mitochondria

Reactive oxygen species (ROS) oxidize surrounding molecules and thus impair their functions. Since mitochondria are a major source of ROS, suppression of ROS overproduction in the mitochondria is important for cells. Spontaneous transient depolarization of individual mitochondria is a physiological phenomenon widely observed from plants to mammals. Mitochondrial uncoupling can reduce ROS production; therefore, it is conceivable that transient depolarization could reduce ROS production. However, transient depolarization has been observed with increased ROS production. Therefore, the exact contribution of transient depolarization to ROS production has not been elucidated. In this study, we examined how the spontaneous transient depolarization occurring in individual mitochondria affected ROS production. When the matrix pH increased after the addition of malate or exposure of the isolated mitochondria to a high-pH buffer, transient depolarization was stimulated. Similar stimulation by an increased matrix pH was also observed in the mitochondria in intact H9c2 cells. Modifying the mitochondrial membrane potential and matrix pH by adding K⁺ in the presence of valinomycin, a K⁺ ionophore, clarified that an increase in the matrix pH is a major cause of ROS generation. When we added ADP in the presence of oligomycin to suppress the transient depolarization without decreasing the matrix pH, we observed the suppression of mitochondrial respiration, increased matrix pH, and enhanced ROS production. Based on these results, we propose a model where spontaneous transient depolarization occurs during increased proton influx through proton channels opened by increased matrix pH, leading to the suppression of ROS production. This study improves our understanding of mitochondrial behavior.

Molecular basis of pathogenesis of postharvest pathogenic Fungi and control strategy in fruits: progress and prospect

The disease caused by pathogenic fungi is the main cause of postharvest loss of fresh fruits. The formulation of disease control strategies greatly depends on the understanding of pathogenic mechanism of fungal pathogens and control strategy. In recent years, based on the application of various combinatorial research methods, some pathogenic genes of important postharvest fungal pathogens in fruit have been revealed, and their functions and molecular regulatory networks of virulence have been explored. These progresses not only provide a new perspective for understanding the molecular basis and regulation mechanism of pathogenicity of postharvest pathogenic fungi, but also are beneficial to giving theoretical guidance for the creation of new technologies of postharvest disease control. Here, we synthesized these recent advances and illustrated conceptual frameworks, and identified several issues on the focus of future studies.

Transient Mitochondria Dysfunction Confers Fungal Cross-Resistance against Phagocytic Killing and Fluconazole

Loss or inactivation of antivirulence genes is an adaptive strategy in pathogen evolution. Candida glabrata is an important opportunistic pathogen related to baker’s yeast, with the ability to both quickly increase its intrinsic high level of azole resistance and persist within phagocytes. During C. glabrata’s evolution as a pathogen, the mitochondrial DNA polymerase CgMip1 has been under positive selection. We show that CgMIP1 deletion not only triggers loss of mitochondrial function and a petite phenotype, but increases C. glabrata’s azole and endoplasmic reticulum (ER) stress resistance and, importantly, its survival in phagocytes. The same phenotype is induced by fluconazole and by exposure to macrophages, conferring a cross-resistance between antifungals and immune cells, and can be found in clinical isolates despite a slow growth of petite strains. This suggests that petite constitutes a bet-hedging strategy of C. glabrata and, potentially, a relevant cause of azole resistance. Mitochondrial function may therefore be considered a potential antivirulence factor.

Naringin-generated ROS promotes mitochondria-mediated apoptosis in Candida albicans

Naringin is a flavonoid which has a therapeutic effect. However, the details of its antifungal mechanism have not yet been fully elucidated. This study focused on clarifying the relationship between naringin and Candida albicans, to understand its mode of antifungal action. In general, naringin is an antioxidant, but our results indicated that 1 mM naringin generates intracellular superoxide (O₂ ^- ) and hydroxyl radicals (OH^- ). Reactive oxygen species (ROS) have a serious impact on Ca²⁺ signaling and the production of mitochondrial ROS. After exposure to enhanced O₂ ^- and OH^- , mitochondrial Ca²⁺ overload and mitochondrial O₂ ^- generation were confirmed in C. albicans. It was verified that mitochondrial O₂ ^- transforms mitochondrial glutathione (GSH) to oxidized GSH (GSSG), leading to extreme oxidative stress in mitochondria. The previously observed Ca²⁺ accumulation and oxidative stress resulted in mitochondrial membrane potential (MMP) alteration and increased mitochondrial mass. In succession, cytochrome c release from the mitochondria to the cytosol was detected due to MMP loss. Cytochrome c promotes the initiation of apoptosis, and further experiments were performed to assess the apoptotic hallmarks. Metacaspases activation, chromosomal condensation, DNA fragmentation, and phosphatidylserine exposure were observed, indicating that naringin induces apoptosis in C. albicans. In conclusion, our findings manifested that naringin-generated O₂ ^- and OH^- damage the mitochondria and that mitochondrial dysfunction-mediated apoptosis is novel antifungal mechanism of naringin.

An image segmentation technique with statistical strategies for pesticide efficacy assessment

Image analysis is a useful technique to evaluate the efficacy of a treatment for weed control. In this study, we address two practical challenges in the image analysis. First, it is challenging to accurately quantify the efficacy of a treatment when an entire experimental unit is not affected by the treatment. Second, RGB codes, which can be used to identify weed growth in the image analysis, may not be stable due to various surrounding factors, human errors, and unknown reasons. To address the former challenge, the technique of image segmentation is considered. To address the latter challenge, the proportion of weed area is adjusted under a beta regression model. The beta regression is a useful statistical method when the outcome variable (proportion) ranges between zero and one. In this study, we attempt to accurately evaluate the efficacy of a 35% hydrogen peroxide (HP). The image segmentation was applied to separate two zones, where the HP was directly applied (gray zone) and its surroundings (nongray zone). The weed growth was monitored for five days after the treatment, and the beta regression was implemented to compare the weed growth between the gray zone and the control group and between the nongray zone and the control group. The estimated treatment effect was substantially different after the implementation of image segmentation and the adjustment of green area.

Reactive oxygen species: A generalist in regulating development and pathogenicity of phytopathogenic fungi

Reactive oxygen species (ROS) are small molecules with high oxidative activity, and are usually produced as byproducts of metabolic processes in organisms. ROS play an important role during the interaction between plant hosts and pathogenic fungi. Phytopathogenic fungi have evolved sophisticated ROS producing and scavenging systems to achieve redox homeostasis. Emerging evidences suggest that ROS derived from fungi are involved in various important aspects of the development and pathogenesis, including formation of conidia, sclerotia, conidial anastomosis tubes (CATs) and infectious structures. In this mini-review, we summarize the research progress on the redox homeostasis systems, the versatile functions of ROS in the development and pathogenesis of phytopathogenic fungi, and the regulation effects of exogenous factors on intercellular ROS and virulence of the fungal pathogens.

Luteolin-induced activation of the phenylpropanoid metabolic pathway contributes to quality maintenance and disease resistance of sweet cherry

Redox imbalance and fungal infection are major causes for quality deterioration and postharvest decay of fruit. Therefore, it is crucial to activate intrinsic antioxidative capacity and disease responses for fruit quality maintenance. Although plant-derived flavonoids have been reported for health-promoting benefits, their roles in the maintenance of fruit quality remains largely unexplored. Here, we exogenously applied luteolin, a flavonoid substance, and further examined its efficacy in maintaining fruit quality and inhibiting fungal diseases in sweet cherry. The results showed that 100 or 200 mg/L luteolin maintained better organoleptic quality and decreased disease incidence during storage. Biochemical assays revealed that luteolin activated the phenylpropanoid metabolic pathway and improved antioxidative capacity, thereby elevating total anthocyanin and flavonoid contents. Notably, luteolin inhibited mycelial growth of fungal pathogens and reduced patulin yield by Penicillium expansum. Collectively, these results suggest that luteolin is a promising alternative for maintaining better fruit quality and ameliorating disease resistance.

Allergenicity assessment of fungal species using immunoclinical and proteomic techniques: a study on Fusarium lateritium

Airborne fungal spores are extensively reported as the elicitors of respiratory allergies in human. Fusarium lateritium is one such fungal species reported for eliciting significant skin prick results from India. The present study aims to analyze the allergenic potential of F. lateritium followed by the identification of allergens. The total protein of F. lateritium was subjected to 1dimensional (1D) and 2D gel electrophoresis followed by corresponding IgE-specific immunoblots. We found 8 immunoreactive bands/zones in (1D) immunoblot using 11 F. lateritium-sensitised patient sera. In 1D immunoblot, a 34 kDa band was detected in >80% of the patients and hence considered as a potential allergen of F. lateritium. Corresponding 34 kDa spot in 2D-immunoblot was analyzed by mass spectrometric analysis and identified as Glyceraldehyde 3-phosphate dehydrogenase. The identified F. lateritium allergen holds the potential to instigate vaccine development for immunotherapy of F. lateritium sensitized patients.

Influence of Nonthermal Atmospheric Plasma-Activated Water on the Structural, Optical, and Biological Properties of Aspergillus brasiliensis Spores

Plasma-activated water (PAW) has emerged as a platform for sterilizing fungal pathogens. In this study, we investigated the influence of PAW on black melanized spores of Aspergillus brasiliensis to explore the mechanism of fungal spore inactivation. PAW was prepared by activating deionized water with a nonthermal atmospheric pressure air plasma jet (soft plasma jet). The concentrations of H2O2 and NOx in the PAW treated by the soft plasma jet for 3 min were 50 μM and 1.8 mM, respectively, and the pH of the PAW was 3.10. The reactive oxygen and nitrogen species (RONS) in the PAW increased with longer plasma activation time. After being treated for 30 min in the PAW with a plasma activation time of 3 min, the spore viability dramatically dropped to 15%. The viabilities of 0.3% H2O2- and 0.3% HNO3-treated spores were 22% and 42%, respectively. The breakage of the spore cell wall by the PAW was revealed in scanning electron microscope images and flow cytometry measurements. Disruption of cell wall integrity provides a path for intracellular components to escape and RONS of the PAW can attack intracellular components directly. Degradation of high molecular genomic DNA was also observed by agarose gel electrophoresis. These results suggest that long-lived reactive species generated in the PAW play an important role in the inactivation of melanized fungal spores. Consequently, PAW produced by a soft plasma jet can be applied to sterilize bioprotective walled fungal spores in a relatively large volume.

Photosynthesis is sensitive to nitric oxide and respiration sensitive to hydrogen peroxide: Studies with pea mesophyll protoplasts

Reports on the effect of nitric oxide (NO) or reactive oxygen species (ROS) on photosynthesis and respiration in leaf tissues are intriguing; therefore, the effects of exogenous addition of sodium nitroprusside (SNP, releases NO) or H2O2 on the photosynthetic O2 evolution and respiratory O2 uptake by mesophyll protoplasts in pea (Pisum sativum) were evaluated in the present study. Low concentrations of SNP or H2O2 were used to minimize nonspecific effects. The effects of NO or H2O2 on respiration and photosynthesis were different. The presence of NO decreased the rate of photosynthesis but caused a marginal stimulation of dark respiration. Conversely, externally administered H2O2 drastically decreased the rate of respiration but only slightly decreased photosynthesis. The PS I activity was more sensitive to NO than PS II. On the other hand, 100 μM H2O2 had no effect on the photochemical reactions of either PS I or PS II. The sensitivity of photosynthesis to antimycin A or SHAM (reflecting the interplay between chloroplasts and mitochondria) was not affected by NO. By contrast, H2O2 markedly decreased the sensitivity of photosynthesis to antimycin A and SHAM. It can be concluded that chloroplasts are the primary targets of NO, while mitochondria are the primary targets of ROS in plant cells. We propose that H2O2 can be an important signal to modulate the crosstalk between chloroplasts and mitochondria.

Ultra-Structural Alterations in Botrytis cinerea-The Causal Agent of Gray Mold-Treated with Salt Solutions

Potassium bicarbonate (PB), calcium chelate (CCh), and sodium silicate (SSi) have been extensively used as antifungal generally recognized as safe (GRAS) compounds against plant pathogenic fungi. In this research, in in vitro tests, the radial growth, conidial germination, and germ tube elongation of Botrytis cinerea was completely inhibited at 0.3% of PB, SSi, and CCh. In in vivo tests, application of PB, SSi, and CCh completely inhibited the occurrence of gray mold incidence of inoculated 'Italia' grape berries at concentrations of 1.0, 0.8, and 0.8%, respectively. In order to investigate the detailed mechanisms by which salts exhibited antifungal activity, we analyzed their influence on morphological changes by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and also on reactive species of oxygen (ROS), mitochondrial membrane potential (MMP), and adenosine triphosphate (ATP) content. Defects such as malformation and excessive septation were detected on salt-treated hyphae morphology observed by SEM. The internal structure of conidia treated or not with salt solutions was examined by TEM. In treated conidia, most of the conidia were affected and cellular vacuolization and cytoplasmic disorganization was observed. For ROS accumulation, a higher increase was observed in fluorescent conidia in presence of PB, SSi, and CCh by 75, 68, and 70% as compared to control, respectively. MMP was significantly decreased after salt application indicating a loss of mitochondria function. Also, luminescence showed that B. cinerea-conidia treated with salts contained less ATP than the untreated conidia. The results obtained herein are a step towards a comprehensive understanding of the mode of action by which salts act as antifungal agents against B. cinerea.

Synergistic effect of a novel chitosan/silica nanocomposites-based formulation against gray mold of table grapes and its possible mode of action

Ecofriendly nanostructured materials have been proposed as promising alternative control means to prevent plant diseases. Chitosan nanoparticles (CN), silica nanoparticles (SN) and chitosan-silica nanocomposites (CSN) were synthesized and their morphology and structure was characterized by transmission electron microscope (TEM), scanning electron microscopy (SEM), infrared spectra (FT-IR) and Raman spectroscopy. Their antifungal efficiency against Botrytis cinerea, the causal fungus of gray mold disease of table grapes, was tested in vitro and in vivo (under artificial and natural infections). In vitro tests showed that CN, SN and CSN reduced fungal growth by 72, 76 and 100%, respectively at 1% as compared to control. Under natural infection, at the end of cold storage, CSN was the most effective treatment, and reduced the development of gray mold by 59 and 83%, for 'Italia' and 'Benitaka' grapes, respectively as compared to the water control. Results indicate that a synergistic effect of CSN against gray mold was observed. The impact of tested nanocomposites on soluble solids - TSS, titratable acidity - TA, TSS/TA, berry color, mass loss, stem browning and shattered berries was investigated. No negative effect of tested nanomaterials in term of grape quality was observed. For 'Italia' table grape, CN and CSN can preserve bunches from mass loss as compared to control. Also, the effect of CSN on reactive species of oxygen (ROS), ATP content and mitochondrial membrane potential (MMP) of B. cinerea spores was determined to verify its mode of action. The obtained results suggested CSN, as alternative control means, to reduce/substitute the use of fungicides to control gray mold of table grapes while maintaining grape quality.

Production, Signaling, and Scavenging Mechanisms of Reactive Oxygen Species in Fruit-Pathogen Interactions

Reactive oxygen species (ROS) play a dual role in fruit–pathogen interaction, which largely depends on their different levels in cells. Fruit recognition of a pathogen immediately triggers an oxidative burst that is considered an integral part of the fruit defense response. ROS are also necessary for the virulence of pathogenic fungi. However, the accumulation of ROS in cells causes molecular damage and finally leads to cell death. In this review, on the basis of data regarding ROS production and the scavenging systems determining ROS homeostasis, we focus on the role of ROS in fruit defense reactions against pathogens and in fungi pathogenicity during fruit–pathogen interaction.

Early Defense Responses Involved in Mitochondrial Energy Metabolism and Reactive Oxygen Species Accumulation in Harvested Muskmelons Infected by Trichothecium roseum

Mitochondria play an essential part in fighting against pathogen infection in the defense responses of fruits. In this study, we investigated the reactive oxygen species (ROS) production, energy metabolism, and changes of mitochondrial proteins in harvested muskmelon fruits ( Cucumis melo cv. Yujinxiang) inoculated with Trichothecium roseum. The results indicated that the fungal infection obviously induced the H₂O₂ accumulation in mitochondria. Enzyme activities were inhibited in the first 6 h postinoculation (hpi), including succinic dehydrogenase, cytochrome c oxidase, H⁺-ATPase, and Ca²⁺-ATPase. However, the activities of Ca²⁺-ATPase and H⁺-ATPase and the contents of intracellular adenosine triphosphate (ATP) were improved to a higher level at 12 hpi. A total of 42 differentially expressed proteins were identified through tandem mass tags-based proteomic analyses, which are mainly involved in energy metabolism, stress responses and redox homeostasis, glycolysis and tricarboxylic acid cycle, and transporter and mitochondria dysfunction. Taken together, our results suggest that mitochondria play crucial roles in the early defense responses of muskmelons against T. roseum infection through regulation of ROS production and energy metabolism.

Sodium silicate prime defense responses in harvested muskmelon by regulating mitochondrial energy metabolism and reactive oxygen species production

The effects of postharvest treatment with sodium silicate (Si) (100 mM) on mitochondrial ROS production and energy metabolism of the muskmelon fruits (cv. Yujinxiang) on development of defense responses to Trichothecium roseum were studied. Si treatment decreased decay severity of inoculated muskmelons, enhanced the activities of energy metabolism of key enzymes and kept the intracellular ATP at a higher level; meanwhile, Si also induced the mtROS accumulation such as H₂O₂ and superoxide anion. TMT-based quantitative proteomics analysis revealed that a total of 24 proteins with significant differences in abundance involved in energy metabolism, defense and stress responses, glycolytic and TCA cycle, and oxidation-reduction process. It is suggested by our study that melon fruit mitochondria, when induced by Si treatments, play a key role in priming of host resistance against T. roseum infection through the regulation of energy metabolism and ROS production in the pathogen infected muskmelon fruits.

Comparative transcriptomic analysis unveils interactions between the regulatory CarS protein and light response in Fusarium

BACKGROUND

The orange pigmentation of the agar cultures of many Fusarium species is due to the production of carotenoids, terpenoid pigments whose synthesis is stimulated by light. The genes of the carotenoid pathway and their regulation have been investigated in detail in Fusarium fujikuroi. In this and other Fusarium species, such as F. oxysporum, deep-pigmented mutants affected in the gene carS, which encodes a protein of the RING-finger family, overproduce carotenoids irrespective of light. The induction of carotenogenesis by light and its deregulation in carS mutants are achieved on the transcription of the structural genes of the pathway. We have carried out global RNA-seq transcriptomics analyses to investigate the relationship between the regulatory role of CarS and the control by light in these fungi.

RESULTS

The absence of a functional carS gene or the illumination exert wide effects on the transcriptome of F. fujikuroi, with predominance of genes activated over repressed and a greater functional diversity in the case of genes induced by light. The number of the latter decreases drastically in a carS mutant (1.1% vs. 4.8% in the wild-type), indicating that the deregulation produced by the carS mutation affects the light response of many genes. Moreover, approximately 27% of the genes activated at least 2-fold by light or by the carS mutation are coincident, raising to 40% for an 8-fold activation threshold. As expected, the genes with the highest changes under both regulatory conditions include those involved in carotenoid metabolism. In addition, light and CarS strongly influence the expression of some genes associated with stress responses, including three genes with catalase domains, consistent with roles in the control of oxidative stress. The effects of the CarS mutation or light in the transcriptome of F. oxysporum were partially coincident with those of F. fujikuroi, indicating the conservation of the objectives of their regulatory mechanisms.

CONCLUSIONS

The CarS RING finger protein down-regulates many genes whose expression is up-regulated by light in wild strains of the two investigated Fusarium species, indicating a regulatory interplay between the mechanism of action of the CarS protein and the control by light.

Inhibitory effect and possible mechanism of a Pseudomonas strain QBA5 against gray mold on tomato leaves and fruits caused by Botrytis cinerea

The fungal pathogen Botrytis cinerea causes gray mold disease on various hosts, which results in serious economic losses. Over the past several decades, many kinds of fungicides have been used to successfully control the disease. Meanwhile, the uses of fungicides lead to environmental pollution as well as a potential threat to the human health by the chemical residues in tomato fruit. Also, the gray mold disease is difficult to control with fungicides. Therefore, exploring alternative measures such as biological controls could be the best choice to control the disease and alleviate damages caused by fungicides. In this study, we isolated and identified a novel Pseudomonas strain termed as QBA5 from healthy tomato plant based on the morphological, biochemical characteristics and molecular detection. The antifungal activity assays revealed that, in the presence of QBA5, conidia germination, germ tube elongation and mycelial growth of B. cinerea were significantly inhibited. Most importantly, QBA5 exerted a significant preventive effectiveness against gray mold on tomato fruits and plants. The possible mechanism of QBA5 involved in the inhibition of B. cinerea was investigated. It revealed that the conidia plasma membrane of B. cinerea was severely damaged by QBA5. Further, four different antifungal compounds in the supernatant of QBA5 were separated by preparative high performance liquid chromatography (PHPLC). Overall, the data indicate that there is a considerable potential for QBA5 to reduce the damage caused by gray mold disease on tomato.

Antifungal mechanism of cinnamaldehyde and citral combination against Penicillium expansum based on FT-IR fingerprint, plasma membrane, oxidative stress and volatile profile

Cinnamaldehyde (Cin) and citral (Cit) have been studied as antimicrobial agents and natural preservatives, but their action modes are controversial, and the knowledge of their antifungal mechanism against P. expansum is still incomplete.

The impact of the postharvest environment on the viability and virulence of decay fungi

Postharvest decay of fruits, vegetables, and grains by fungal pathogens causes significant economic losses. Infected produce presents a potential health risk since some decay fungi produce mycotoxins that are hazardous to human health. Infections are the result of the interplay between host resistance and pathogen virulence. Both of these processes, however, are significantly impacted by environmental factors, such as temperature, UV, oxidative stress, and water activity. In the present review, the impact of various physical postharvest treatments (e.g., heat and UV) on the viability and virulence of postharvest pathogens is reviewed and discussed. Oxidative injury, protein impairment, and cell wall degradation have all been proposed as the mechanisms by which these abiotic stresses reduce fungal viability and pathogenicity. The response of decay fungi to pH and the ability of pathogens to modulate the pH of the host environment also affect pathogenicity. The effects of the manipulation of the postharvest environment by ethylene, natural edible coatings, and controlled atmosphere storage on fungal viability are also discussed. Lastly, avenues of future research are proposed.

Comparative Proteomics Reveals the Potential Targets of BcNoxR, a Putative Regulatory Subunit of NADPH Oxidase of Botrytis cinerea

The NADPH oxidase (NOX) complex has been shown to play a crucial role in stress response and in the virulence of various fungal pathogens. The underlying molecular mechanisms of NOX, however, remain largely unknown. In the present study, a comparative proteomic analysis compared changes in protein abundance in wild-type Botrytis cinerea and ΔbcnoxR mutants in which the regulatory subunit of NOX was deleted. The ΔbcnoxR mutants exhibited reduced growth, sporulation, and impaired virulence. A total of 60 proteins, representing 49 individual genes, were identified in ΔbcnoxR mutants that exhibited significant differences in abundance relative to wild-type. Reverse transcription-quantitative polymerase chain reaction analysis demonstrated that the differences in transcript levels for 36 of the genes encoding the identified proteins were in agreement with the proteomic analysis, while the remainder exhibited reverse levels. Functional analysis of four proteins that decreased abundance in the ΔbcnoxR mutants indicated that 6-phosphogluconate dehydrogenase (BcPGD) played a role in the growth and sporulation of B. cinerea. The Δbcpgd mutants also displayed impaired virulence on various hosts, such as apple, strawberry, and tomato fruit. These results suggest that NOX can influence the expression of BcPGD, which has an impact on growth, sporulation, and virulence of B. cinerea.

Aquaporin8 regulates cellular development and reactive oxygen species production, a critical component of virulence in Botrytis cinerea

Aquaporins (AQPs) are ubiquitous in nearly all organisms, mediating selective and rapid flux of water across biological membranes. The role of AQPs in phytopathogenic fungi is poorly understood. Orthologs of AQP genes in Botrytis cinerea were identified and knocked out. The effects of AQPs on hyphal growth and conidiation, formation of infection structures and virulence on plant hosts were examined. The role of AQP8 in reactive oxygen species (ROS) production, distribution and transport were further determined. Among eight AQPs, only AQP8 was essential for the ability of B. cinerea to infect plants. AQP8 was demonstrated to be an intrinsic plasma membrane protein, which may function as a channel and mediate hydrogen peroxide uptake. Deletion of AQP8 in B. cinerea completely inhibited the development of conidia and infection structures, and significantly affected noxR expression. Further observations revealed that both AQP8 and noxR impacted ROS distribution in the hyphal tips of B. cinerea. Moreover, AQP8 affected the expression of a mitochondrial protein, NQO1. A knockout mutant of NQO1 was observed to display reduced virulence. These data lead to a better understanding of the important role of AQP8 in the development and pathogenesis of plant pathogens.

Deciphering the mode of action of a mutant Allium sativum Leaf Agglutinin (mASAL), a potent antifungal protein on Rhizoctonia solani

Background

Mutant Allium sativum leaf agglutinin (mASAL) is a potent, biosafe, antifungal protein that exhibits fungicidal activity against different phytopathogenic fungi, including Rhizoctonia solani.

Methods

The effect of mASAL on the morphology of R.solani was monitored primarily by scanning electron and light microscopic techniques. Besides different fluorescent probes were used for monitoring various intracellular changes associated with mASAL treatment like change in mitochondrial membrane potential (MMP), intracellular accumulation of reactive oxygen species (ROS) and induction of programmed cell death (PCD). In addition ligand blot followed by LC-MS/MS analyses were performed to detect the putative interactors of mASAL.

Results

Knowledge on the mode of function for any new protein is a prerequisite for its biotechnological application. Detailed morphological analysis of mASAL treated R. solani hyphae using different microscopic techniques revealed a detrimental effect of mASAL on both the cell wall and the plasma membrane. Moreover, exposure to mASAL caused the loss of mitochondrial membrane potential (MMP) and the subsequent intracellular accumulation of reactive oxygen species (ROS) in the target organism. In conjunction with this observation, evidence of the induction of programmed cell death (PCD) was also noted in the mASAL treated R. solani hyphae.

Furthermore, we investigated its interacting partners from R. solani. Using ligand blots followed by liquid chromatography tandem mass spectrometry (LC-MS/MS) analyses, we identified different binding partners including Actin, HSP70, ATPase and 14-3-3 protein.

Conclusions

Taken together, the present study provides insight into the probable mode of action of the antifungal protein, mASAL on R. solani which could be exploited in future biotechnological applications.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-015-0549-7) contains supplementary material, which is available to authorized users.