Sodium pheophorbide a has photoactivated fungicidal activity against Pestalotiopsis neglecta

The photoactivated antifungal activity and possible mode of action of sodium pheophorbide a on Diaporthe mahothocarpus causing leaf spot blight in Camellia oleifera

Introduction

Sodium pheophorbide a (SPA) is a natural plant-derived photosensitizer, with high photoactivated antifungal activity against some phytopathogenic fungi. However, its fungicidal effect on Diaporthe mahothocarpus, a novel pathogen that causes Camellia oleifera leaf spot blight, is unclear.

Methods

In the present study, we explored its inhibitory effects on spore germination and mycelial growth of D. mahothocarpus. Then we determined its effects on the cell membrane, mycelial morphology, redox homeostasis, and cell death through bioassay. Finally, RNA-seq was used further to elucidate its mode of action at the transcriptional level.

Results

We found that SPA effectively inhibited the growth of D. mahothocarpus, with half-maximal effective concentrations to inhibit mycelial growth and spore germination of 1.059 and 2.287 mg/mL, respectively. After 1.0 mg/mL SPA treatment, the conductivity and malondialdehyde content of D. mahothocarpus were significantly increased. Scanning electron microscopy and transmission electron microscopy indicated that SPA significantly affected the morphology and ultrastructure of D. mahothocarpus hyphae, revealing that SPA can destroy the mycelial morphology and cell structure, especially the cell membrane of D. mahothocarpus. Furthermore, transcriptome analysis revealed that SPA significantly suppressed the expression of genes involved in morphology, cell membrane permeability, and oxidative stress. Then, we also found that SPA significantly promoted the accumulation of reactive oxygen species (ROS) in of D. mahothocarpus, while it decreased the content of reduced glutathione, inhibited the enzyme activities of superoxide dismutase and catalase, and exacerbated DNA damage. Annexin V-FITC/PI staining also confirmed that 1.0 mg/mL SPA could significantly induce apoptosis and necrosis.

Discussion

Generally, SPA can induce ROS-mediated oxidative stress and cell death, thus destroying the cell membrane and hyphal morphology, and ultimately inhibiting mycelial growth, which indicates that SPA has multiple modes of action, providing a scientific basis for the use of SPA as an alternative plant-derived photoactivated fungicide against C. oleifera leaf spot blight.

Biocontrol activity and potential mechanism of volatile organic compounds from Aspergillus niger strain La2 against pear Valsa canker

BACKGROUND

Valsa canker caused by Valsa pyri is one of the most destructive diseases of pear, leading to severe yield and economic losses. Volatile organic compounds (VOCs) from endophytes have important roles in the regulation of plant disease. In this study, we investigated the biocontrol activity of the endophytic fungus Aspergillus niger strain La2 and its antagonistic VOCs against pear Valsa canker.

RESULTS

Strain La2 exhibited an obvious inhibitory effect against V. pyri. A colonization assay suggested that strain La2 could complete its life cycle on pear twigs. The symptoms of pear Valsa canker were weakened on detached pear twigs after treatment with strain La2. In addition, VOCs from strain La2 also significantly suppressed mycelial growth in V. pyri. Based on the results of headspace solid-phase microextraction/gas chromatography-mass spectrometry analysis, six possible VOCs produced by strain La2 were detected, of which 2,4-di-tert-butylphenol and 4-methyl-1-pentanol were the main antagonistic VOCs in terms of their effect on pear Valsa canker in vitro and in vivo. Further results showed that 4-methyl-1-pentanol could destroy the V. pyri hyphal structure and cell membrane integrity. Importantly, the activities of pear defense-related enzymes (polyphenol oxidase, phenylalanine ammonia lyase and superoxide dismutase) were enhanced after 4-methyl-1-pentanol treatment in pear twigs, suggesting that 4-methyl-1-pentanol might induce a plant disease resistance response.

CONCLUSION

Aspergillus niger strain La2 and its VOCs 2,4-di-tert-butylphenol and 4-methyl-1-pentanol have potential as novel biocontrol agents of pear Valsa canker. © 2024 Society of Chemical Industry.

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 Mechanism of Phenazine-1-Carboxylic Acid against Pestalotiopsis kenyana

Pestalotiopsis sp. is an important class of plant pathogenic fungi that can infect a variety of crops. We have proved the pathogenicity of P. kenyana on bayberry leaves and caused bayberry blight. Phenazine-1-carboxylic acid (PCA) has the characteristics of high efficiency, low toxicity, and environmental friendliness, which can prevent fungal diseases on a variety of crops. In this study, the effect of PCA on the morphological, physiological, and molecular characteristics of P. kenyana has been investigated, and the potential antifungal mechanism of PCA against P. kenyana was also explored. We applied PCA on P. kenyana in vitro and in vivo to determine its inhibitory effect on PCA. It was found that PCA was highly efficient against P. kenyana, with EC₅₀ around 2.32 μg/mL, and the in vivo effect was 57% at 14 μg/mL. The mechanism of PCA was preliminarily explored by transcriptomics technology. The results showed that after the treatment of PCA, 3613 differential genes were found, focusing on redox processes and various metabolic pathways. In addition, it can also cause mycelial development malformation, damage cell membranes, reduce mitochondrial membrane potential, and increase ROS levels. This result expanded the potential agricultural application of PCA and revealed the possible mechanism against P. kenyana.

Pheophorbide-a as a Light-Triggered Liposomal Switch: For the Controlled Release of Alpinia galanga (A. galanga) Essential Oil and Its Stability, Antioxidant, and Antibacterial Activity Assessment

In this study, Alpinia galanga essential oil liposomes (EO-Lip) were prepared with soybean lecithin and cholesterol as wall materials. A light-responsive liposome (EO-PLip) was designed for the controlled release of A. galanga oil based on the light-responsive properties of Pheophorbide-a. The dependence of Pheophorbide-a on illumination time was proved by UV spectroscopy. Characterization techniques such as UV spectroscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy demonstrated that the essential oils were successfully encapsulated in liposomes. Moreover, the particle size of EO-PLip was 166.30 nm, the polydispersity index was 0.22, the zeta potential was -49.50 mV, and the encapsulation efficiency was 30.83%. Both EO-Lip and EO-Plip have high sustained-release effects on essential oil and showed light-responsive release characteristics under infrared stimulation. The prepared liposomes had good storage stability at 4 °C for 28 d. EO-PLip showed excellent transient antioxidant and bacteriostatic properties based on the ability to respond to light and slow release. This EO-PLip provided a platform for essential oils and might be used as a potent and controllable solution.

OsGLP participates in the regulation of lignin synthesis and deposition in rice against copper and cadmium toxicity

Copper (Cu) and cadmium (Cd) are common heavy metal pollutants. When Cd and excessive Cu accumulate in plants, plant growth is reduced. Our previous study showed that Germin-like proteins (GLPs), which exist in tandem on chromosomes, are a class of soluble glycoproteins that respond to Cu stress. In this study, hydroponic cultures were carried out to investigate the effect of GLP on Cd and Cu tolerance and accumulation in rice. The results showed that knockout of a single OsGLP8-2 gene or ten OsGLP genes (OsGLP8-2 to OsGLP8-11) resulted in a similar sensitivity to Cd and Cu toxicity. When subjected to Cu and Cd stress, the glp8-2 and glp8-(2-11) mutants displayed a more sensitive phenotype based on the plant height, root length, and dry biomass of the rice seedlings. Correspondingly, Cu and Cd concentrations in the glp8-2 and glp8-(2-11) mutants were significantly higher than those in the wild-type (WT) and OsGLP8-2-overexpressing line. However, Cu and Cd accumulation in the cell wall was the opposite. Furthermore, we determined lignin accumulation. The overexpressing-OsGLP8-2 line had a higher lignin accumulation in the shoot and root cell walls than those of the WT, glp8-2, and glp8-(2-11). The expression of lignin synthesis genes in the OsGLP8-2-overexpressing line was significantly higher than that in the WT, glp8-2, and glp8-(2-11). The SOD activity of OsGLP8-2, Diaminobe-nzidine (DAB), propidium iodide (PI) staining, and Malondialdehyde (MDA) content determination suggested that OsGLP8-2 is involved in heavy metal-induced antioxidant defense in rice. Our findings clearly suggest that OsGLPs participate in responses to heavy metal stress by lignin deposition and antioxidant defense capacity in rice, and OsGLP8-2 may play a major role in the tandem repeat gene clusters of chromosome 8 under heavy metal stress conditions.

Antifungal Activity of 6-Methylcoumarin against Valsa mali and Its Possible Mechanism of Action

Valsa canker of apple (VCA) caused by Valsa mali severely affected apple production in east Asia. With the increase in drug resistance, there is an urgent need for efficient and environmentally friendly antifungal agents. Coumarins have attracted much attention due to their excellent antimicrobial activity against plant pathogens. In this study, the antifungal activity of several coumarins against phytopathogenic fungi was evaluated, and then the antifungal activity of the screened 6-MCM against V. mali and its underlying mechanism was further investigated. The results of the in vitro antifungal activity assay showed that some coumarins had significant inhibitory effects on V. mali. Notably, 400 mg/L of 6-MCM had the best antifungal activity of 94.6%. Further experiments showed that 6-MCM slowed down the growth of V. mali mycelia and the germination of spores in a concentration-dependent manner, with EC₅₀ of 185.49 and 54.62 mg/L, respectively. In addition, 6-MCM treatment increased mycelial conductivity, extracellular protein leakage, and MDA content, resulting in damage to the cell membrane. Moreover, 6-MCM significantly reduced the cell wall degrading enzymes secreted by V. mali, including EG, PG and PL, thereby limiting its pathogenic capacity. SEM and TEM results showed that 6-MCM treatment had a significant effect on the morphology and ultrastructure of mycelial cells. Inoculation of isolated apple branches found that the application of 6-MCM effectively inhibited the development of VCA and significantly reduced the incidence. All these results suggest that 6-MCM has the potential as a green substitute for VCA control.

Inhibitory effect and mechanism of action of juniper essential oil on gray mold in cherry tomatoes

Juniper essential oil (JEO), which is mostly known as an immune system booster and effective detoxifier, has substantial antimicrobial activity. A comparison of the inhibitory effects of three plant essential oils from juniper (Juniperus rigida), cedarwood (Juniperus virginiana), and cypress (Crupressus sempervirens) on four plant pathogenic fungi indicated that JEO was the most effective at inhibiting the growth of gray mold (Botrytis cinerea). Additional studies were subsequently conducted to explore the in vivo and in vitro antifungal activity and possible mechanism of JEO against B. cinerea. The results show that JEO inhibited the germination of spores and mycelial growth of B. cinerea in a concentration-dependent manner and exhibited strong inhibition when its concentration exceeded 10 μL/mL. JEO also significantly inhibited the incidence of disease and diameters of gray mold lesions on cherry tomato fruit (Solanum lycopersicum). After 12 h of treatment with JEO, the extracellular conductivity, and the contents of soluble protein, malondialdehyde, and hydrogen peroxide were 3.1, 1.2, 7.2, and 4.7 folds higher than those of the control group, respectively (P < 0.05), which indicated that JEO can damage membranes. Scanning electron microscopy observations revealed that JEO affected the morphology of mycelia, causing them to shrivel, twist and distort. Furthermore, JEO significantly improved the activities of the antioxidant-related enzymes superoxide dismutase and catalase but reduced the pathogenicity-related enzymes polygalacturonase (PG), pectin lyase and endoglucanase of B. cinerea (P < 0.05). In particular, PG was reduced by 93% after treatment with JEO for 12 h. Moreover, the 18 constituents of JEO were identified by gas chromatography/mass spectrometry (GC-MS) analysis, mainly limonene (15.17%), γ-terpinene (8.3%), β-myrcene (4.56%), terpinen-4-ol (24.26%), linalool (8.73%), α-terpineol (1.03%), o-cymene (8.35%) and other substances with antimicrobial activity. Therefore, JEO can be an effective alternative to prevent and control gray mold on cherry tomato fruit.

Unraveling the polypharmacology of a natural antifungal product, eugenol, against Rhizoctonia solani

BACKGROUND

Rice sheath blight caused by Rhizoctonia solani is a devastating disease of rice in China. However, indiscriminate use of chemical fungicides applied to control the disease raise major environmental and food safety issues. Ecofriendly biocontrol alternatives are urgently needed. Eugenol, one of the main ingredients in Syzygium aromaticum, has attracted much attention owing to its antifungal properties. However, its mode of action is still not clear. Herein, the antifungal activity and mode of action of eugenol against R. solani were investigated.

RESULTS

Results confirmed that the mycelia of R. solani treated with eugenol shrank and became dehydrated, the cytoplasmic wall separated, and the vacuoles and mitochondria decreased or dissolved. Moreover, we found that eugenol downregulated expression of C-4 methyl sterol oxidase, inhibited synthesis of ergosterol, increased membrane permeability and impaired the transportation of amino acids and glucose across the cell membrane. In addition, eugenol decreased the mitochondrial membrane potential and initiated an oxidative stress reaction by increasing reactive oxygen species and malondialdehyde, which together with membrane damage contribute to the antifungal activity of eugenol. Meanwhile, eugenol might inhibit R. solani by affecting oxidative phosphorylation and the tricarboxylic acid cycle (TCA cycle).

CONCLUSION

In view of its multitarget properties against R. solani, eugenol provides an alternative approach to chemical control strategies against rice sheath blight. © 2021 Society of Chemical Industry.

Inhibitory effects and mechanisms of vanillin on gray mold and black rot of cherry tomatoes

Vanillin is a natural antimicrobial agent; however, there are few reports on its antifungal effect on postharvest pathogenic fungi. This study aimed to investigate the in vivo and in vitro antifungal activities of vanillin against gray mold (caused by B. cinerea) and black rot (caused by A. alternata) of cherry tomato fruit and to explain its possible mechanism of action. Vanillin strongly inhibits Botrytis cinerea and Alternaria alternata mycelial growth, spore germination, and germ tube elongation in a concentration-dependent manner (P<0.05). In vivo experiments showed that 4000 mg L^-1 vanillin treatment inhibited cherry tomato gray mold and black rot occurrence. Besides, intercellular electrolytes, soluble proteins, and soluble sugars leakage indicated that 50 or 100 mg L^-1 vanillin treatment increased Botrytis cinerea and Alternaria alternata membrane permeability. The increase of malondialdehyde and hydrogen peroxide contents confirmed that 50 or 100 mg L^-1 vanillin treatment damages the pathogen membranes. Importantly, vanillin treatment inhibited the pathogenicity-related enzyme activities of the two pathogens to reduce their infection ability, among them PL enzyme activity in A. alternata was most inhibited, reducing by 94.7 % at 6 h treated with 100 mg L^-1 vanillin. The hyphae morphology of the two pathogens changed, the mycelia were severely damaged, and the hyphae surface was deformed, shrunk, or even broken after 100 mg L^-1 vanillin treatment. In summary, vanillin had a substantial inhibitory effect on postharvest gray mold and black rot in cherry tomato fruit. Therefore, vanillin can be an effective alternative to prevent and control cherry tomato postharvest diseases.

Transcriptome and cell wall degrading enzyme-related gene analysis of Pestalotiopsis neglecta in response to sodium pheophorbide a

Sodium pheophorbide a (SPA) is a new alternative fungicide with low toxicity and high efficiency, which has high fungicidal activity against Pestalotiopsis neglecta, a pathogen that causes black spot needle blight of Pinus sylvestris var. mongolica. To utilize SPA for plant disease control, understanding its antifungal mechanism is essential. Six cDNA libraries were constructed from 3 d-old P. neglecta mycelia (three SPA-infected and three untreated groups) and 29,850 expressed genes were obtained by Illumina HiSeq4000 sequencing. Compared with controls, 3268 differentially expressed genes (DEGs) were identified in SPA-treated groups, including 1879 upregulated and 1389 downregulated genes. Most DEGs were involved in the metabolism of amino acids, carbohydrates, and lipids, as well as cell structure and genetic information processing. These findings were further confirmed by decreased conductivity, RNA and protein content, and activities of nicotinamide adenine dinucleotide-dependent malate dehydrogenase, citrate synthase, isocitrate dehydrogenase, and succinate dehydrogenase. Moreover, qRT-PCR verified the reliability of the transcriptome results. After treatment with SPA at different concentrations for 60 min, the expressions of three cell wall degrading enzyme-related genes (PnEG, PnBG, and PnPG) were all suppressed. Overall, this study provided insights into the molecular mechanisms through which SPA inhibits P. neglecta, increasing the possibility of developing SPA into an effective fungicide in the future.

Key factors affecting photoactivated fungicidal activity of sodium pheophorbide a against Pestalotiopsis neglecta

Recently, photodynamic therapy (PDT) and photoactivated pesticides have attracted considerable research attention. In the present study, we aimed to investigate the photodynamic activity of a chlorophyllous derivative, sodium pheophorbide a (SPA), and to evaluate its potential as a photoactivated fungicide. The singlet oxygen quantum yield, the photoreaction process, the anti-photobleaching ability in sterile water (H₂O), the effect of light conditions on its antifungal activity, and its stability were all investigated. SPA showed significant fungicidal activity and photostability, during which Type I and Type II photodynamic reactions occurred simultaneously on Pestalotiopsis neglecta, and the influence of Type I was slightly larger than that of Type II. In addition, light promoted the antifungal activity of SPA. In particular, the antifungal activity was enhanced with increasing light intensity, and was strongest under 8000 lx conditions. Under monochromatic light sources, antifungal activity was strongest under green light s; however, the effect of monochromatic light was not as good as that of white light. From 0 to 24 h, the antifungal effect of the SPA solution was enhanced; however, the activity of the solution began to weaken after 24 h. Furthermore, our study confirmed that the antifungal activity of SPA was stable under different temperatures, pH values, and UV irradiation durations.

Sodium pheophorbide a controls cherry tomato gray mold (Botrytis cinerea) by destroying fungal cell structure and enhancing disease resistance-related enzyme activities in fruit

Sodium pheophorbide a (SPA) is a natural photosensitizer. The present study investigated the antifungal activity and mechanism of SPA against Botrytis cinerea in vitro and in vivo. Its inhibitory effect was studied on the spore germination and mycelial growth of B. cinerea. The effects of SPA on cell wall integrity, cell membrane permeability, and mycelial morphology of B. cinerea were also determined. Additionally, how SPA effected B. cinerea in vivo was evaluated using cherry tomato fruit. The results showed that SPA effectively inhibited the spore germination and mycelial growth of B. cinerea under light conditions (4000 lx). SPA significantly affected both cell wall integrity and cell membrane permeability (P < .05). In addition, SEM analysis suggested that B. cinerea treated with SPA (12.134 mg/mL) showed abnormal mycelial morphology, including atrophy, collapse, flattening, and mycelial wall dissolution. In vivo tests showed that SPA could increase the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) significantly (P < .05); however, SPA had no significant effect on phenylalanine ammonia lyase (PAL) activity. In short, SPA could destroy the fungal cell structure and enhance disease resistance-related enzyme activity in cherry tomatoes, thereby controlling cherry tomato gray mold.