Quantitative proteomics reveals that tea tree oil effects Botrytis cinerea mitochondria function

Inhibitory Effect of L-Methionine on Alternaria alternata Based on Metabolomics Analysis

Alternaria alternata is the main pathogenic fungus of postharvest black spots in fruits and vegetables. This study aimed to explore the antifungal activity of methionine on A. alternata in vitro and to reveal related antifungal mechanisms through a metabolomics analysis. The results showed that the inhibitory effects of L-methionine (Met) treatment on mycelium growth, spore germination, and the germ tube elongation of A. alternata were enhanced with an increase in the Met concentration, but the inhibitory effects decreased when the Met concentration was higher than 50 mmolL-1. The results of propidium iodide staining and scanning electron microscopy showed that the Met treatment damaged the plasma membrane integrity of the A. alternata spores and caused an irreversible deformation of mycelium. In addition, after the Met treatment, the leakage of electrolytes, nucleic acid, and proteins in the A. alternata cells was significantly higher than that in the control group, indicating that the Met treatment increased the permeability of the cell membranes. Eighty-one different metabolites, divided into seven categories, were identified through the metabolomics analysis, including forty-three downregulated metabolites and thirty-eight upregulated metabolites. Among them, these differential metabolites were mainly involved in amino acid synthesis and metabolism, the pentose phosphate pathway, and the TCA cycle. Therefore, the antifungal effect of the Met treatment on A. alternata was mainly to damage the integrity of the cell membranes, make nucleic acid and protein contents leak, and affect the TCA cycle, carbohydrate metabolism, amino acid synthesis metabolism, and the metabolic pathways associated with cell membrane biosynthesis. Thus, the growth and development of A. alternata were inhibited. The research enriched the investigation of the effect of the antifungal mechanism of Met treatment on A. alternata and provided a theoretical basis for the application of Met to prevent and treat postharvest black spots in fruits and vegetables.

TMT-Based Proteomic Analysis Reveals the Molecular Mechanisms of Sodium Pheophorbide A against Black Spot Needle Blight Caused by Pestalotiopsis neglecta in Pinus sylvestris var. mongolica

Black spot needle blight is a minor disease in Mongolian Scots pine (Pinus sylvestris var. mongolica) caused by Pestalotiopsis neglecta, but it can cause economic losses in severe cases. Sodium pheophorbide a (SPA), an intermediate product of the chlorophyll metabolism pathway, is a compound with photoactivated antifungal activity, which has been previously shown to inhibit the growth of P. neglecta. In this study, SPA significantly reduced the incidence and disease index and enhanced the chlorophyll content and antioxidant enzyme activities of P. sylvestris var. mongolica. To further study the molecular mechanism of the inhibition, we conducted a comparative proteomic analysis of P. neglecta mycelia with and without SPA treatment. The cellular proteins were obtained from P. neglecta mycelial samples and subjected to a tandem mass tag (TMT)-labelling LC-MS/MS analysis. Based on the results of de novo transcriptome assembly, 613 differentially expressed proteins (DEPs) (p < 0.05) were identified, of which 360 were upregulated and 253 downregulated. The 527 annotated DEPs were classified into 50 functional groups according to Gene Ontology and linked to 256 different pathways using the Kyoto Encyclopedia of Genes and Genomes database as a reference. A joint analysis of the transcriptome and proteomics results showed that the top three pathways were Amino acid metabolism, Carbohydrate metabolism, and Lipid metabolism. These results provide new viewpoints into the molecular mechanism of the inhibition of P. neglecta by SPA at the protein level and a theoretical basis for evaluating SPA as an antifungal agent to protect forests.

Comprehensive Analysis of the Complete Mitochondrial Genome of Rehmannia chingii: An Autotrophic Species in the Orobanchaceae Family

Rehmannia chingii is an important medicinal plant with immense value in scientific research. However, its mitochondrial genome (mitogenome) has not yet been characterized. Herein, based on whole-genome Illumina short reads and PacBio HiFi reads, we obtained the complete mitogenome of R. chingii through a de novo assembly strategy. We carried out comparative genomic analyses and found that, in comparison with the plastid genome (plastome) showing a high degree of structural conservation, the R. chingii mitogenome structure is relatively complex, showing an intricate ring structure with 16 connections, owing to five repetitive sequences. The R. chingii mitogenome was 783,161 bp with a GC content of 44.8% and contained 77 genes, comprising 47 protein-coding genes (CDS), 27 tRNA genes, and 3 rRNA genes. We counted 579 RNA editing events in 47 CDS and 12,828 codons in all CDSs of the R. chingii mitogenome. Furthermore, 24 unique sequence transfer fragments were found between the mitogenome and plastome, comprising 8 mitogenome CDS genes and 16 plastome CDS genes, corresponding to 2.39% of the R. chingii mitogenome. Mitogenomes had shorter but more collinear regions, evidenced by a comparison of the organelles of non-parasitic R. chingii, hemiparasitic Pedicularis chinensis, and holoparasitic Aeginetia indica in the Orobanchaceae family. Moreover, from non-parasitic to holoparasitic species, the genome size in the mitogenomes of Orobanchaceae species did not decrease gradually. Instead, the smallest mitogenome was found in the hemiparasitic species P. chinensis, with a size of 225,612 bp. The findings fill the gap in the mitogenome research of the medicinal plant R. chingii, promote the progress of the organelle genome research of the Orobanchaceae family, and provide clues for molecular breeding.

Effects and mechanisms of plant bioactive compounds in preventing fungal spoilage and mycotoxin contamination in postharvest fruits: A review

Spoilage and mycotoxin contamination of fruits cause significant economic losses and food safety issues. Synthetic chemical fungicide treatment as primary postharvest management has attracted increasing public concern in recent years, because it may cause negative effects on the environment and human health. Numerous bioactive compounds from plants have demonstrated excellent control effects on fruit spoilage and mycotoxin contamination. Plant bioactive compounds have been considered one of the most promising alternatives, because they are generally regarded as safe and environmentally friendly. Here, we reviewed the most recent advances in plant bioactive compounds in the prevention of fungal spoilage and mycotoxin contamination in fruits. The control effects of these compounds and the mechanisms involved were summarized, and current limitations and future perspectives were discussed.

Comparative physiological and transcriptome analysis provide insights into the inhibitory effect of 6-pentyl-2H-pyran-2-one on Clarireedia jacksonii

Clarireedia spp. is a destructive phytopathogenic fungus that causes turf dollar spot of bent-grass, leading to widespread lawn death. In this study, we explored the antifungal capability of 6-pentyl-2H-pyran-2-one (6PP), a natural metabolite volatilized by microorganisms, which plays an important role in the biological control of turfgrass dollar spot. However, the mechanisms by which 6PP inhibits Clarireedia jacksonii remain unknown. In the present study, C. jacksonii mycelial growth was inhibited by the 6PP treatment and the 6PP treatment damaged cell membrane integrity, causing an increase in relative conduc-tivity. Furthermore, physiological and biochemistry assay showed that 6PP treatment can enhance reactive oxygen species (ROS) levels, malondialdehyde (MDA) content obviously increased with 6PP exposure, increased alchohol dehydrogenase (ADH) and depleted acetalde-hyde dehydrogenase (ALDH), and activated the activities of many antioxidant enzymes in C. jacksonii. Gen Ontology and Kyoto Encyclopedia of Genes and Genomes analysis revealed that some genes in C. jacksonii after 6PP treatment related to integrity of the cell wall and membrane, and oxidative stress were significantly downregulated. It is worth mentioning that the fatty acid degradation pathway is significantly upregulated, with an increase in ATP content and ATP synthase activity, which may promote fungal cell apoptosis. Moreover, we found that the expression of ABC transporters, and glutathione metabolism encoding genes were increased to respond to external stimuli. Taken together, these findings revealed the potential antifungal mechanism of 6PP against Clarireedia spp., which also provides a theoretical basis for the commercial utilization of 6PP as a green pesticide in the future.

Proteomics as a New-Generation Tool for Studying Moulds Related to Food Safety and Quality

Mould development in foodstuffs is linked to both spoilage and the production of mycotoxins, provoking food quality and food safety concerns, respectively. The high-throughput technology proteomics applied to foodborne moulds is of great interest to address such issues. This review presents proteomics approaches useful for boosting strategies to minimise the mould spoilage and the hazard related to mycotoxins in food. Metaproteomics seems to be the most effective method for mould identification despite the current problems related to the bioinformatics tool. More interestingly, different high resolution mass spectrometry tools are suitable for evaluating the proteome of foodborne moulds able to unveil the mould's response under certain environmental conditions and the presence of biocontrol agents or antifungals, being sometimes combined with a method with limited ability to separate proteins, the two-dimensional gel electrophoresis. However, the matrix complexity, the high ranges of protein concentrations needed and the performing of multiple steps are some of the proteomics limitations for the application to foodborne moulds. To overcome some of these limitations, model systems have been developed and proteomics applied to other scientific fields, such as library-free data independent acquisition analyses, the implementation of ion mobility, and the evaluation of post-translational modifications, are expected to be gradually implemented in this field for avoiding undesirable moulds in foodstuffs.

Inhibitory effect of (E)-2-heptenal on Aspergillus flavus growth revealed by metabolomics and biochemical analyses

The prevention of fungal proliferation in postharvest grains is critical for maintaining grain quality and reducing mycotoxin contamination. Fumigation with natural gaseous fungicides is a promising and sustainable approach to protect grains from fungal spoilage. In this study, the antifungal activities of (E)-2-alkenals (C₅-C₁₀) on Aspergillus flavus were tested in the vapor phase, and (E)-2-heptenal showed the highest antifungal activity against A. flavus. (E)-2-Heptenal completely inhibited A. flavus growth at 0.0125 µL/mL and 0.2 µL/mL in the vapor phase and liquid contact, respectively. (E)-2-Heptenal can disrupt the plasma membrane integrity of A. flavus via leakage of intracellular electrolytes. Scanning electron microscopy indicated that the mycelial morphology of A. flavus was remarkably affected by (E)-2-heptenal. Metabolomic analyses indicated that 49 metabolites were significantly differentially expressed in A. flavus mycelia exposed to 0.2 µL/mL (E)-2-heptenal; these metabolites were mainly involved in galactose metabolism, starch and sucrose metabolism, the phosphotransferase system, and ATP-binding cassette transporters. ATP production was reduced in (E)-2-heptenal-treated A. flavus, and Janus Green B staining showed reduced cytochrome c oxidase activity. (E)-2-Heptenal treatment induced oxidative stress in A. flavus mycelia with an accumulation of superoxide anions and hydrogen peroxide and increased activities of superoxide dismutase and catalase. Simulated storage experiments showed that fumigation with 400 µL/L of (E)-2-heptenal vapor could completely inhibit A. flavus growth in wheat grains with 20% moisture; this demonstrates its potential use in preventing grain spoilage. This study provides valuable insights into understanding the antifungal effects of (E)-2-heptenal on A. flavus. KEY POINTS : • (E)-2-Heptenal vapor showed the highest antifungal activity against A. flavus among (C₅-C₁₀) (E)-2-alkenals. • The antifungal effects of (E)-2-heptenal against A. flavus were determined. • The antifungal actions of (E)-2-heptenal on A. flavus were revealed by metabolomics and biochemical analyses.

Mechanisms underlying the inhibitory effects of linalool on Aspergillus flavus spore germination

Biogenic volatile organic compounds hold remarkable potential for controlling fungal decay in agro- and food products. Recently, we reported that linalool, the major volatile component of the Zanthoxylum schinifolium pericarp, showed great potential as a biofumigant to control Aspergillus flavus growth in postharvest grains. In this study, the inhibitory effects of linalool on A. flavus growth in stored grains and its underlying mechanism were investigated through transcriptomic and biochemical analyses. Linalool vapor at 800 μL/L can effectively prevent A. flavus growth in 22% moisture wheat grains. Linalool at 2 μL/mL completely inhibited the germination of A. flavus spores, and 10 μL/mL caused spore death. Scanning electron microscopy revealed that linalool treatment caused wrinkling and spore breakage. Transcriptomics showed that 3806 genes were significantly differentially expressed in A. flavus spores exposed to 2 μL/mL linalool, predominantly showing enrichment regarding the ribosome, DNA replication, glutathione metabolism, peroxisome, and MAPK signaling pathways. Flow cytometry showed that linalool treatment caused hyperpolarization of mitochondrial membrane potential. 4,6-Diamidino-2-phenylindole staining indicated that linalool caused DNA fragmentation in A. flavus spores, and monodansylcadaverine staining confirmed that linalool induced autophagy in A. flavus spores. We thus propose that linalool can damage the plasma membrane, cause mitochondrial dysfunction and DNA damage, and induce autophagy in A. flavus spores. These findings considerably improve our understanding of the mechanisms underlying the inhibitory effects of linalool on A. flavus, which is crucial regarding the development of applications to prevent postharvest grain spoilage due to A. flavus infestations. KEY POINTS: • The inhibitory potency of linalool on A. flavus spore germination was determined. • Transcriptomic analyses were performed to identify differentially expressed genes of A. flavus exposed to linalool. • A functional mechanism underlying the inhibitory effects of linalool on A. flavus spore germination is proposed.

iTRAQ proteomic analysis of the inhibitory effect of 1,6-O,O-diacetylbritannilactone on the plant pathogenic oomycete Phytophthora capsici

Phytophthora capsici is a highly destructive oomycete of vegetables; its management is challenging due to its broad host range, rapid dispersion, resilient spores and severe fungicide resistance. Identifying an effective alternative fungicide is important for the control of P. capsici. 1,6-O,O-diacetylbritannilactone (ABLOO), one of the secondary metabolites of Inula Britannica, showed a favorable inhibitory activity against P. capsici at different developmental stages, with a sensitivity order as follows: sporangia formation (30.45 mg/L) > zoospore discharge (77.69 mg/L) > mycelial growth (93.18 mg/L) > cystospore germination (591.48 mg/L). To investigate the mode of action of ABLOO in P. capsici, iTRAQ-based quantitative proteomic analysis was performed by comparing the expression levels of proteins in the control and ABLOO-treated (400 mg/L, inhibition rate of 80%) mycelial groups. A total of 65 downregulated and 75 upregulated proteins were identified in the proteomic analysis. Functional enrichment analyses showed that proteins with transmembrane transport activity were significantly inhibited, while proteins involved in energy production were significantly increased, including proteins involved in ubiquinone and other terpenoid-quinone biosynthesis, oxidative phosphorylation, and glycolysis/gluconeogenesis. The morphological results indicated that ABLOO treatment could decrease the thickness of the cell walls of P. capsici mycelia. Correspondingly, biochemical results showed that ABLOO treatment reduced the β-1,3-glucan contents (the key component of the cell wall of P. capsici) and increased the cell membrane permeability of P. capsici. ABLOO may exhibit antioomycete activity by destroying the cell membrane of P. capsici. This study provides new evidence regarding the inhibitory mechanisms of ABLOO against P. capsici.

Transcriptomics analyses and biochemical characterization of Aspergillus flavus spores exposed to 1-nonanol

The exploitation of plant volatile organic compounds as biofumigants to control postharvest decaying of agro-products has received considerable research attention. Our previous study reported that 1-nonanol, the main constituent of cereal volatiles, can inhibit Aspergillus flavus growth and has the potential as a biofumigant to control the fungal spoilage of cereal grains. However, the antifungal mechanism of 1-nonanol against A. flavus is still unclear at the molecular level. In this study, the minimum inhibitory concentration and minimum fungicidal concentration of 1-nonanol against A. flavus spores were 2 and 4 μL/mL, respectively. Scanning electron microscopy revealed that the 1-nonanol can distort the morphology of A. flavus spore. Annexin V-FITC/PI double staining showed that 1-nonanol induced phosphatidylserine eversion and increased membrane permeability of A. flavus spores. Transcriptional profile analysis showed that 1-nonanol treatment mainly affected the expression of genes related to membrane damage, oxidative phosphorylation, blockage of DNA replication, and autophagy in A. flavus spores. Flow cytometry analysis showed that 1-nonanol treatment caused hyperpolarization of mitochondrial membrane potential and accumulation of reactive oxygen species in A. flavus spores. 4',6-diamidino-2-phenylindole staining showed that treatment with 1-nonanol destroyed the DNA. Biochemical analysis results confirmed that 1-nonanol exerted destructive effects on A. flavus spores by decreasing intracellular adenosine triphosphate content, reducing mitochondrial ATPase activity, accumulating hydrogen peroxide and superoxide anions, and increasing catalase and superoxide dismutase enzyme activities. This study provides new insights into the antifungal mechanisms of 1-nonanol against A. flavus. KEY POINTS: • 1-Nonanol treatment resulted in abnormal morphology of A. flavus spores. • 1-Nonanol affects the expression of key growth-related genes of A. flavus. • The apoptosis of A. favus spores were induced after exposed to 1-nonanol.

Active compound identification by screening 33 essential oil monomers against Botryosphaeria dothidea from postharvest kiwifruit and its potential action mode

The antifungal activity of postharvest kiwifruit against the pathogen Botryosphaeria dothidea was evaluated for 33 essential oil monomers. The possible mechanism for the known active compounds were further assessed in this study. The results show all the EO components exhibit inhibitory effects on the pathogen to different degrees except for Farnesol. Carbon chain length and C₂-C₃ double bonds had a great effect on the antifungal activities of aldehydes. Of all of these, carvacrol had the strongest antifungal activity with EC₅₀ of 12.58 μL/L and EC₉₀ of 22.08 μL/L. Carvacrol also exhibits significant inhibitory effects on the pathogen, both in vivo and in vitro. Carvacrol evidently alters the hyphal morphology of B. dothidea and severely damages cell membrane and inhibits the formation of lipid components on the membrane. As cell membrane permeability increases, intracellular homeostasis including ion and biomacromolecules were destroyed by carvacrol. Furthermore, carvacrol appears to significantly inhibit mitochondrial activity and respiration rates, resulting in cell death of B. dothidea. Our results provide evidence that carvacrol could be a very useful compound for controlling postharvest rot soft in kiwifruit.

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.

Antifungal mechanisms of lavender essential oil in the inhibition of rot disease caused by Monilinia fructicola in postharvest flat peaches

As a natural antimicrobial agent, lavender essential oil (LEO) is generally recognized to be safe and effective in the inhibition of phytopathogenic fungi. Direct contact and fumigation (in vivo and in vitro) were used to study the fungistatic effect of LEO on Monilinia fructicola. Additionally, the effect on the ultrastructure of cells and degree of destruction of the cell membrane of M. fructicola were revealed. In addition, the effects of LEO on the expression levels of particular apoptosis-related genes in M. fructicola cells were detected and GC-MS was used to analyse the main components of LEO. LEO had a good inhibitory efficacy against M. fructicola in flat peaches, with almost complete growth inhibition with 800 μL / L. These effects were associated with leakage of cytoplasm contents, hyphal distortion and spore disruption. Moreover, the expression of apoptosis RTG1 and RLM1 genes increased on LEO treatment. These results demonstrate that LEO can inhibit M. fructicola by inducing cytoplasmic membrane damage and cell apoptosis of fungi and that the major ingredients of LEO are monoterpenes and sesquiterpenes which are presumed to contribute to the inhibitory effects.