Cinnamaldehyde inhibits the growth of Phytophthora capsici through disturbing metabolic homoeostasis

Transcriptome Analysis of mfs2-Defective Penicillium digitatum Mutant to Reveal Importance of Pdmfs2 in Developing Fungal Prochloraz Resistance

Demethylation inhibitors (DMIs), including prochloraz, are popular fungicides to control citrus postharvest pathogens such as Penicillium digitatum (green mold). However, many P. digitatum strains have developed prochloraz resistance, which decreases drug efficacy. Specific major facilitator superfamily (MFS) transporter gene mfs2, encoding drug-efflux pump protein MFS2, has been identified in P. digitatum strain F6 (PdF6) to confer fungal strain prochloraz resistance. However, except for the drug-efflux pump function of MFS2, other mechanisms relating to the Pdmfs2 are not fully clear. The present study reported a transcriptome investigation on the mfs2-defective P. digitatum strain. Comparing to the wild-type strain, the mfs2-defective strain showed 717 differentially expressed genes (DEGs) without prochloraz induction, and 1221 DEGs with prochloraz induction. The obtained DEGs included multiple isoforms of MFS transporter-encoding genes, ATP-binding cassette (ABC) transporter-encoding genes, and multidrug and toxic compound extrusion (MATE) family protein-encoding genes. Many of these putative drug-efflux pump protein-encoding genes had significantly lower transcript abundances in the mfs2-defective P. digitatum strain at prochloraz induction, as compared to the wild-type strain, including twenty-two MFS transporter-encoding genes (MFS1 to MFS22), two ABC transporter-encoding genes (ABC1 and ABC2), and three MATE protein-encoding genes (MATE1 to MATE3). The prochloraz induction on special drug-efflux pump protein genes in the wild-type strain was not observed in the mfs2-defective strain, including MFS21, MFS22, ABC2, MATE1, MATE2, and MATE3. On the other hand, the up-regulation of other drug-efflux pump protein genes in the mfs2-defective strain cannot recover the fungal prochloraz resistance, including MFS23, MFS26, MFS27, MFS31, MFS33, and ABC3 to ABC8. The functional enrichment of DEGs based on Kyoto Encyclopedia of Genes and Genomes (KEGG), Clusters of Orthologous Groups (COG), and euKaryotic Orthologous Groups (KOG) database resources suggested some essential contributors to the mfs2-relating prochloraz resistance, including ribosome biosynthesis-related genes, oxidative phosphorylation genes, steroid biosynthesis-related genes, fatty acid and lipid metabolism-related genes, and carbon- and nitrogen-metabolism-related genes. The results indicated that the MFS2 transporter might be involved in the regulation of multiple drug-efflux pump protein gene expressions and multiple metabolism-related gene expressions, thus playing an important role in developing P. digitatum prochloraz resistance.

Transcriptional Response of Pectobacterium carotovorum to Cinnamaldehyde Treatment

Cinnamaldehyde is a natural compound extracted from cinnamon bark essential oil, acclaimed for its versatile properties in both pharmaceutical and agricultural fields, including antimicrobial, antioxidant, and anticancer activities. Although potential of cinnamaldehyde against plant pathogenic bacteria like Agrobacterium tumefaciens and Pseudomonas syringae pv. actinidiae causative agents of crown gall and bacterial canker diseases, respectively has been documented, indepth studies into cinnamaldehyde's broader influence on plant pathogenic bacteria are relatively unexplored. Particularly, Pectobacterium spp., gram-negative soil-borne pathogens, notoriously cause soft rot damage across a spectrum of plant families, emphasizing the urgency for effective treatments. Our investigation established that the Minimum Inhibitory Concentrations (MICs) of cinnamaldehyde against strains P. odoriferum JK2, P. carotovorum BP201601, and P. versatile MYP201603 were 250 μg/ml, 125 μg/ml, and 125 μg/ml, respectively. Concurrently, their Minimum Bactericidal Concentrations (MBCs) were found to be 500 μg/ml, 250 μg/ml, and 500 μg/ml, respectively. Using RNA-sequencing analysis, we identified 1,907 differentially expressed genes in P. carotovorum BP201601 treated with 500 μg/ml cinnamaldehyde. Notably, our results indicate that cinnamaldehyde upregulated nitrate reductase pathways while downregulating the citrate cycle, suggesting a potential disruption in the aerobic respiration system of P. carotovorum during cinnamaldehyde exposure. This study serves as a pioneering exploration of the transcriptional response of P. carotovorum to cinnamaldehyde, providing insights into the bactericidal mechanisms employed by cinnamaldehyde against this bacterium.

Unveiling molecular mechanisms of pepper resistance to Phytophthora capsici through grafting using iTRAQ-based proteomic analysis

Phytophthora blight severely threatens global pepper production. Grafting bolsters plant disease resistance, but the underlying molecular mechanisms remain unclear. In this study, we used P. capsici-resistant strain 'ZCM334' and susceptible strain 'Early Calwonder' for grafting. Compared to self-rooted 'Early Calwonder' plants, 'ZCM334' grafts exhibited delayed disease onset, elevated resistance, and reduced leaf cell damage, showcasing the potential of grafting in enhancing pepper resistance to P. capsici. Proteomic analysis via the iTRAQ technology unveiled 478 and 349 differentially expressed proteins (DEPs) in the leaves and roots, respectively, between the grafts and self-rooted plants. These DEPs were linked to metabolism and cellular processes, stimulus responses, and catalytic activity and were significantly enriched in the biosynthesis of secondary metabolites, carbon fixation in photosynthetic organizations, and pyruvate metabolism pathways. Twelve DEPs exhibiting consistent expression trends in both leaves and roots, including seven related to P. capsici resistance, were screened. qRT-PCR analysis confirmed a significant correlation between the protein and transcript levels of DEPs after P. capsici inoculation. This study highlights the molecular mechanisms whereby grafting enhances pepper resistance to Phytophthora blight. Identification of key genes provides a foundation for studying the regulatory network governing the resistance of pepper to P. capsici.

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.

Antifungal activity of Ligusticum chuanxiong essential oil and its active composition butylidenephthalide against Sclerotium rolfsii

BACKGROUND

Peanut stem rot caused by Sclerotium rolfsii is an epidemic disastrous soil-borne disease. Recently, natural products tend to be safe alternative antifungal agents to combat pathogens.

RESULTS

This work determined the preliminary antifungal activity of 29 essential oils against S. rolfsii and found that Ligusticum chuanxiong essential oil (LCEO) showed the best antifungal activity, with an EC50 value of 81.79 mg L-1 . Sixteen components (98.78%) were identified in LCEO by gas chromatography-mass spectrometry analysis, the majority by volume comprising five phthalides (93.14%). Among these five phthalides, butylidenephthalide was the most effective compound against S. rolfsii. Butylidenephthalide not only exhibited favorable in vitro antifungal activity against the mycelial growth, sclerotia production and germination of S. rolfsi, but also presented efficient in vivo efficacy in the control of peanut stem rot. Seven days after application in the glasshouse, the protective and curative efficacy of butylidenephthalide at 300 mg L-1 (52.02%, 44.88%) and LCEO at 1000 mg L-1 (49.60%, 44.29%) against S. rolfsii were similar to that of the reference fungicide polyoxin at 300 mg L-1 (54.61%, 48.28%). Butylidenephthalide also significantly decreased the oxalic acid and polygalacturonase content of S. rolfsii, suggesting a decreased infection ability on plants. Results of biochemical actions indicated that butylidenephthalide did not have any effect on the cell membrane integrity and permeability but significantly decreased nutrient contents, disrupted the mitochondrial membrane, inhibited energy metabolism and induced reactive oxygen species (ROS) accumulation of S. rolfsii.

CONCLUSION

Our results could provide an important reference for understanding the application potential and mechanisms of butylidenephthalide in the control of S. rolfsii. © 2023 Society of Chemical Industry.

Antifungal Activity and Action Mechanisms of 2,4-Di-tert-butylphenol against Ustilaginoidea virens

Ustilaginoidea virens is a destructive phytopathogenic fungus that causes false smut disease in rice. In this study, the natural product 2,4-di-tert-butylphenol (2,4-DTBP) was found to be an environmentally friendly and effective agent for the first time, which exhibited strong antifungal activity against U. virens, with an EC50 value of 0.087 mmol/L. The scanning electron microscopy, fluorescence staining, and biochemical assays indicated that 2,4-DTBP could destroy the cell wall, cell membrane, and cellular redox homeostasis of U. virens, ultimately resulting in fungal cell death. Through the transcriptomic analysis, a total of 353 genes were significantly upregulated and 367 genes were significantly downregulated, focusing on the spindle microtubule assembly, cell wall and membrane, redox homeostasis, mycotoxin biosynthesis, and intracellular metabolism. These results enhanced the understanding of the antifungal activity and action mechanisms of 2,4-DTBP against U. virens, supporting it to be a potential antifungal agent for the control of false smut disease.

Towards Phytopathogen Diagnostics? Coconut Bud Rot Pathogen Phytophthora palmivora Mycelial Proteome Analysis Informs Genome Annotation

Planetary agriculture stands to benefit immensely from phytopathogen diagnostics, which would enable early detection of pathogens with harmful effects on crops. For example, Phytophthora palmivora is one of the most destructive phytopathogens affecting many economically important tropical crops such as coconut. P. palmivora causes diseases in over 200 host plants, and notably, the bud rot disease in coconut and oil palm, which is often lethal because it is usually detected at advanced stages of infection. Limited availability of large-scale omics datasets for P. palmivora is an important barrier for progress toward phytopathogen diagnostics. We report here the mycelial proteome of P. palmivora using high-resolution mass spectrometry analysis. We identified 8073 proteins in the mycelium. Gene Ontology-based functional classification of detected proteins revealed 4884, 4981, and 3044 proteins, respectively, with roles in biological processes, molecular functions, and cellular components. Proteins such as P-loop, NTPase, and WD40 domains with key roles in signal transduction pathways were identified. KEGG pathway analysis annotated 2467 proteins to various signaling pathways, such as phosphatidylinositol, Ca²⁺, and mitogen-activated protein kinase, and autophagy and cell cycle. These molecular substrates might possess vital roles in filamentous growth, sporangia formation, degradation of damaged cellular content, and recycling of nutrients in P. palmivora. This large-scale proteomics data and analyses pave the way for new insights on biology, genome annotation, and vegetative growth of the important plant pathogen P. palmivora. They also can help accelerate research on future phytopathogen diagnostics and preventive interventions.

The Inflammatory Response in Human Keratinocytes Exposed to Cinnamaldehyde Is Regulated by Nrf2

Keratinocytes (KC) play a crucial role in epidermal barrier function, notably through their metabolic activity and the detection of danger signals. Chemical sensitizers are known to activate the transcription factor nuclear factor (erythroid-derived 2)-like 2 (Nrf2), leading to cellular detoxification and suppressed proinflammatory cytokines such as IL-1β, a key cytokine in skin allergy. We investigated the role of Nrf2 in the control of the proinflammatory response in human KC following treatment with Cinnamaldehyde (CinA), a well-known skin sensitizer. We used the well-described human KC cell line KERTr exposed to CinA. Our results showed that 250 μM of CinA did not induce any Nrf2 accumulation but increased the expression of proinflammatory cytokines. In contrast, 100 μM of CinA induced a rapid accumulation of Nrf2, inhibited IL-1β transcription, and downregulated the zymosan-induced proinflammatory response. Moreover, Nrf2 knockdown KERTr cells (KERTr ko) showed an increase in proinflammatory cytokines. Since the inhibition of Nrf2 has been shown to alter cellular metabolism, we performed metabolomic and seahorse analyses. The results showed a decrease in mitochondrial metabolism following KERTr ko exposure to CinA 100 µM. In conclusion, the fate of Nrf2 controls proinflammatory cytokine production in KCs that could be linked to its capacity to preserve mitochondrial metabolism upon chemical sensitizer exposure.