Biological and biorational management of blast diseases in cereals caused by Magnaporthe oryzae

The link between changing in host carbon allocation and resistance to Magnaporthe oryzae: a possible tactic for mitigating the rice blast fungus

One of the most destructive diseases affecting rice is rice blast, which is brought on by the rice blast fungus Magnaporthe oryzae. The preventive measures, however, are not well established. To effectively reduce the negative effects of rice blasts on crop yields, it is imperative to comprehend the dynamic interactions between pathogen resistance and patterns of host carbon allocation. This review explores the relationship between variations in carbon allocation and rice plants' ability to withstand the damaging effects of M. oryzae. The review highlights potential strategies for altering host carbon allocation including transgenic, selective breeding, crop rotation, and nutrient management practices as a promising avenue for enhancing rice blast resistance. This study advances our knowledge of the interaction between plants' carbon allocation and M. oryzae resistance and provides stakeholders and farmers with practical guidance on mitigating the adverse effects of the rice blast globally. This information may be used in the future to create varieties that are resistant to M. oryzae.

Unveiling the mechanism of broad-spectrum blast resistance in rice: The collaborative role of transcription factor OsGRAS30 and histone deacetylase OsHDAC1

Rice blast, caused by Magnaporthe oryzae, significantly impacts grain yield, necessitating the identification of broad-spectrum resistance genes and their functional mechanisms for disease-resistant crop breeding. Here, we report that rice with knockdown OsHDAC1 gene expression displays enhanced broad-spectrum blast resistance without effects on plant height and tiller numbers compared to wild-type rice, while rice overexpressing OsHDAC1 is more susceptible to M. oryzae. We identify a novel blast resistance transcription factor, OsGRAS30, which genetically acts upstream of OsHDAC1 and interacts with OsHDAC1 to suppress its enzymatic activity. This inhibition increases the histone H3K27ac level, thereby boosting broad-spectrum blast resistance. Integrating genome-wide mapping of OsHDAC1 and H3K27ac targets with RNA sequencing analysis unveils how OsHDAC1 mediates the expression of OsSSI2, OsF3H, OsRLR1 and OsRGA5 to regulate blast resistance. Our findings reveal that the OsGRAS30-OsHDAC1 module is critical to rice blast control. Therefore, targeting either OsHDAC1 or OsGRAS30 offers a promising approach for enhancing crop blast resistance.

Characterization of a broad-spectrum antifungal strain, Streptomyces graminearus STR-1, against Magnaporthe oryzae

Fungal diseases such as the devastating rice blast pose severe threats to crop production worldwide. Biological control of crop diseases caused by fungal pathogens is an environment-friendly approach for safeguarding crop production. But the insufficient availability of microbial agents effective against various fungal diseases has hampered the development of green production in crops. In this study, we identified a broad-spectrum antifungal bacterium, Streptomyces graminearus STR-1, showing antagonistic activity to diverse fungal pathogens including Magnaporthe oryzae, Rhizoctonia solani, Fusarium graminearum, Ustilaginoidea virens, and Bipolaris maydis. Its antifungal activity was relatively stable and less affected by temperature and pH. Evaluation of the biocontrol activity of STR-1 revealed that STR-1 prevented and controlled rice blast disease via eliciting plant immunity and suppressing fungal infection-structure development. STR-1 broth extract inhibited spore germination, likely through inhibiting protein synthesis. Combining LC-MS and chromatography analysis of the antimicrobial compounds purified from STR-1 broth extract, together with decoding STR-1 genomic sequence, we identified 4-oxo-4-[(1-phenylethyl)amino]but-2-enoic acid, 1,3,5-Trimethylpyrazole and SMA-1 as the potential main STR-1 secondary metabolites associated with its antifungal effects. This study suggests that bacterial strain STR-1 could be used for identifying highly effective and broad-spectrum secondary metabolites for containing rice blast and other crop diseases. The application of the active compounds offers a promising measure to tackle fungal disease.

Lipopeptides from Bacillus velezensis induced apoptosis-like cell death in the pathogenic fungus Fusarium concentricum

AIMS

Stem rot caused by Fusarium concentricum is a new disease of Paris polyphylla reported by our research group. The present study investigates the growth inhibitory and apoptotic effects of Bacillus velezensis FJAT-54560 lipopeptide against F. concentricum.

METHODS AND RESULTS

HPLC preparation and LC-MS analysis results show that the crude lipopeptides secreted by Bacillus velezensis FJAT-54560 isolated from Jasminum sambac consist of C14-17 iturin A, C14 fengycin B, C16 fengycin A/A2, C18 fengycin A, C20 fengycin B2, C21 fengycin A2, C22-23 fengycin A, C12-16 surfactin A, and C15 surfactin A derivatives. The mass ratios (g/g) of iturin, fengycin, and surfactin in lipopeptides are 2.40, 67.51, and 30.08%, respectively. Through inhibition zone and inhibition rate experiments, we found that crude lipopeptides and purified fengycin exhibit strong antifungal activity against F. concentricum, including accumulation of reactive oxygen species, loss of mitochondrial membrane potential, DNA fragmentation, Ca2+ accumulation, chromatin condensation, and phosphatidylserine externalization. Transcriptomic analysis indicates that crude lipopeptide-induced apoptosis in F. concentricum cells may be mediated by apoptosis-inducing factors and apoptosis mediators and can serve as a metacaspase-independent model.

CONCLUSION

Lipopeptides from Bacillus velezensis FJAT-54560 can control the pathogenic fungus F. concentricum by inducing apoptosis.

Beneficial Microorganisms as Bioprotectants against Foliar Diseases of Cereals: A Review

Cereal production plays a major role in both animal and human diets throughout the world. However, cereal crops are vulnerable to attacks by fungal pathogens on the foliage, disrupting their biological cycle and photosynthesis, which can reduce yields by 15-20% or even 60%. Consumers are concerned about the excessive use of synthetic pesticides given their harmful effects on human health and the environment. As a result, the search for alternative solutions to protect crops has attracted the interest of scientists around the world. Among these solutions, biological control using beneficial microorganisms has taken on considerable importance, and several biological control agents (BCAs) have been studied, including species belonging to the genera Bacillus, Pseudomonas, Streptomyces, Trichoderma, Cladosporium, and Epicoccum, most of which include plants of growth-promoting rhizobacteria (PGPRs). Bacillus has proved to be a broad-spectrum agent against these leaf cereal diseases. Interaction between plant and beneficial agents occurs as direct mycoparasitism or hyperparasitism by a mixed pathway via the secretion of lytic enzymes, growth enzymes, and antibiotics, or by an indirect interaction involving competition for nutrients or space and the induction of host resistance (systemic acquired resistance (SAR) or induced systemic resistance (ISR) pathway). We mainly demonstrate the role of BCAs in the defense against fungal diseases of cereal leaves. To enhance a solution-based crop protection approach, it is also important to understand the mechanism of action of BCAs/molecules/plants. Research in the field of preventing cereal diseases is still ongoing.

Discovery of novel isopropanolamine inhibitors against MoTPS1 as potential fungicides with unique mechanisms

The resistance and ecotoxicity of fungicides seriously restrict our ability to effectively control Magnaporthe oryzae. Discovering fungicidal agents based on novel targets, including MoTPS1, could efficiently address this situation. Here, we identified a hit VS-10 containing an isopropanolamine fragment as a novel MoTPS1 inhibitor through virtual screening, and forty-four analogs were synthesized by optimizing the structure of VS-10. Utilizing our newly established ion-pair chromatography (IPC) and leaf inoculation methods, we found that compared to VS-10, its analog j11 exhibited substantially greater inhibitory activity against both MoTPS1 and the pathogenicity of M. oryzae. Molecular simulations clarified that the electrostatic interactions between the bridging moiety of isopropanolamine and residue Glu396 of contributed significantly to the binding of j11 and MoTPS1. We preliminarily revealed the unique fungicidal mechanism of j11, which mainly impeded the infection of M. oryzae by decreasing sporulation, killing a small portion of conidia and interfering with the accumulation of turgor pressure in appressoria. Thus, in this study, a novel fungicide candidate with a unique mechanism targeting MoTPS1 was screened and discovered.

Recent Advances in Effector Research of Magnaporthe oryzae

Recalcitrant rice blast disease is caused by Magnaporthe oryzae, which has a significant negative economic reverberation on crop productivity. In order to induce the disease onto the host, M. oryzae positively generates many types of small secreted proteins, here named as effectors, to manipulate the host cell for the purpose of stimulating pathogenic infection. In M. oryzae, by engaging with specific receptors on the cell surface, effectors activate signaling channels which control an array of cellular activities, such as proliferation, differentiation and apoptosis. The most recent research on effector identification, classification, function, secretion, and control mechanism has been compiled in this review. In addition, the article also discusses directions and challenges for future research into an effector in M. oryzae.

A newly identified glycosyltransferase AsRCOM provides resistance to purple curl leaf disease in agave

BACKGROUND

Purple curl leaf disease brings a significant threat to the development of agave industry, the underlying mechanism of disease-resistant Agave sisalana. hybrid 11648 (A. H11648R) is still unknown.

RESULTS

To excavate the crucial disease-resistant genes against purple curl leaf disease, we performed an RNA-seq analysis for A.H11648R and A.H11648 during different stages of purple curl leaf disease. The DEGs (differentially expressed genes) were mainly enriched in linolenic acid metabolism, starch and sucrose mechanism, phenylpropanoid biosynthesis, hypersensitive response (HR) and systemic acquired resistance. Further analysis suggested that eight candidate genes (4'OMT2, ACLY, NCS1, GTE10, SMO2, FLS2, SQE1 and RCOM) identified by WGCNA (weighted gene co-expression network analysis) may mediate the resistance to agave purple curl disease by participating the biosynthesis of benzylisoquinoline alkaloids, steroid, sterols and flavonoids, and the regulation of plant innate immunity and systemic acquired resistance. After qPCR verification, we found that AsRCOM, coding a glycosyltransferase and relevant to the regulation of plant innate immunity and systemic acquired resistance, may be the most critical disease-resistant gene. Finally, the overexpression of AsRCOM gene in agave could significantly enhance the resistance to purple curl disease with abundant reactive oxygen species (ROS) accumulations.

CONCLUSIONS

Integrative RNA-seq analysis found that HR may be an important pathway affecting the resistance to purple curl leaf disease in agave, and identified glycosyltransferase AsRCOM as the crucial gene that could significantly enhance the resistance to purple curl leaf disease in agave, with obvious ROS accumulations.

Induction of systemic resistance in Solanum lycopersicum and Capsicum annum seedlings against Fusarium wilt by Streptomyces bioformulations

Plant diseases induced by various phytopathogens pose a significant threat to contemporary agricultural systems around the world. In modern agriculture, the use of pesticides is still a valuable and effective method to control plant diseases. However, agrochemicals are becoming less popular because of the accretion of toxic compounds perilous and potentially hazardous to humans and the environment. Taking into consideration these aspects, the present study was conducted to explore the biocontrol potential of an endophytic Streptomyces sp. SP5 bioformulations against Fusarium wilt. Three bioformulations were prepared using cell biomass and different carriers, i.e., B1 (talc-kaolin), B2 (MgSO4/glycerol/Na-alginate/talc/Ca-lignosulfonate), and B3 (calcium carbonate/CMC/talc). Apart from antagonistic action against Fusarium wilt, the influence of bioformulations on plant growth and systemic resistance was investigated by analyzing morphological parameters (root length, shoot length, root weight, shoot weight), biochemical parameters (photosynthetic pigments, non-enzymatic antioxidants), and induction of antioxidative enzymes, e.g., catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GPX), and superoxide dismutase (SOD), in S. lycopersicum and C. annum seedlings. The results revealed that Streptomyces bioformulations effectively controlled Fusarium wilt in S. lycopersicum and C. annum (82.6-83.4% and 81.8-100%, respectively). Besides reducing disease prevalence, bioformulations significantly increased all the morphological parameters and increased the activity of antioxidative enzymes, i.e., CAT, APX, GPX, and SOD, in plants. The current findings display that bioformulations can be utilized as environment-friendly biocontrol agents against Fusarium wilt and also as plant growth promoters.

Involvement of the Cell Wall-Integrity Pathway in Signal Recognition, Cell-Wall Biosynthesis, and Virulence in Magnaporthe oryzae

The fungal cell wall is the first layer exposed to the external environment. The cell wall has key roles in regulating cell functions, such as cellular stability, permeability, and protection against stress. Understanding the structure of the cell wall and the mechanism of its biogenesis is important for the study of fungi. Highly conserved in fungi, including Magnaporthe oryzae, the cell wall-integrity (CWI) pathway is the primary signaling cascade regulating cell-wall structure and function. The CWI pathway has been demonstrated to correlate with pathogenicity in many phytopathogenic fungi. In the synthesis of the cell wall, the CWI pathway cooperates with multiple signaling pathways to regulate cell morphogenesis and secondary metabolism. Many questions have arisen regarding the cooperation of different signaling pathways with the CWI pathway in regulating cell-wall synthesis and pathogenicity. In this review, we summarized the latest advances in the M. oryzae CWI pathway and cell-wall structure. We discussed the CWI pathway components and their involvement in different aspects, such as virulence factors, the possibility of the pathway as a target for antifungal therapies, and crosstalk with other signaling pathways. This information will aid in better understanding the universal functions of the CWI pathway in regulating cell-wall synthesis and pathogenicity in M. oryzae. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

In-silico prediction of highly promising natural fungicides against the destructive blast fungus Magnaporthe oryzae

Magnaporthe oryzae causes destructive blast disease in more than 50 species of the major cereal crops rice, wheat and maize and destroys food of millions of people worldwide. Application of synthetic chemical fungicides are environmentally hazardous and unreliable in controlling M. oryzae. Conversely, naturally occurring biofungicides with multiple modes of actions are needed to be discovered for combatting the blast fungus. To find the effective biofungicides, we performed molecular docking study of some potential antifungal natural compounds targeting two proteins including a single-stranded DNA binding protein MoSub1 (4AGH), and an effector protein AVR-Pik (5E9G) of M. oryzae that regulates transcription in fungus and/or suppresses the host cell immunity. The thirty-nine natural compounds previously shown to inhibit M. oryzae growth and reproduction were put under molecular docking against these two proteins followed by simulation, free energy, and interaction analysis of protein-ligand complexes. The virtual screening revealed that two alkaloidal metabolites, camptothecin and GKK1032A2 showed excellent binding energy with any of these target proteins compared to reference commercial fungicides, azoxystrobin and strobilurin. Of the detected compounds, GKK1032A2 bound to both target proteins of M. oryzae. Both compounds showed excellent bioactivity scores as compared to the reference fungicides. Results of our computational biological study suggest that both camptothecin and GKK1032A2 are potential fungicides that could also be considered as lead compounds to design novel fungicides against the blast fungus. Furthermore, the GKK1032A2 acted as a multi-site mode of action fungicide against M. oryzae.

Burkholderia gladioli strain KJ-34 exhibits broad-spectrum antifungal activity

INTRODUCTION

Plant pathogens are one of the major constraints on worldwide food production. The antibiotic properties of microbes identified as effective in managing plant pathogens are well documented.

METHODS

Here, we used antagonism experiments and untargeted metabolomics to isolate the potentially antifungal molecules produced by KJ-34.

RESULTS

KJ-34 is a potential biocontrol bacterium isolated from the rhizosphere soil of rice and can fight multiple fungal pathogens (i.e. Ustilaginoidea virens, Alternaria solani, Fusarium oxysporum, Phytophthora capsica, Corynespora cassiicola). The favoured fermentation conditions are determined and the fermentation broth treatment can significantly inhibit the infection of Magnaporthe oryzae and Botryis cinerea. The fermentation broth suppression ratio is 75% and 82%, respectively. Fermentation broth treatment disrupted the spore germination and led to malformation of hyphae. Additionally, we found that the molecular weight of antifungal products were less than 1000 Da through semipermeable membranes on solid medium assay. To search the potentially antifungal molecules that produce by KJ-34, we used comparative and bioinformatics analyses of fermentation broth before and after optimization by mass spectrometry. Untargeted metabolomics analyses are presumed to have a library of antifungal agents including benzoylstaurosporine, morellin and scopolamine.

DISCUSSION

These results suggest that KJ-34 produced various biological control agents to suppress multiple phytopathogenic fungi and showed a strong potential in the ecological technologies of prevention and protection.

New Insights on Endophytic Microbacterium-Assisted Blast Disease Suppression and Growth Promotion in Rice: Revelation by Polyphasic Functional Characterization and Transcriptomics

Plant growth-promoting endophytic microbes have drawn the attention of researchers owing to their ability to confer fitness benefits in many plant species. Here, we report agriculturally beneficial traits of rice-leaf-adapted endophytic Microbacterium testaceum. Our polyphasic taxonomic investigations revealed its identity as M. testaceum. The bacterium displayed typical endophytism in rice leaves, indicated by the green fluorescence of GFP-tagged M. testaceum in confocal laser scanning microscopy. Furthermore, the bacterium showed mineral solubilization and production of IAA, ammonia, and hydrolytic enzymes. Tobacco leaf infiltration assay confirmed its non-pathogenic nature on plants. The bacterium showed antifungal activity on Magnaporthe oryzae, as exemplified by secreted and volatile organic metabolome-mediated mycelial growth inhibition. GC-MS analysis of the volatilome of M. testaceum indicated the abundance of antimicrobial compounds. Bacterization of rice seedlings showed phenotypic traits of MAMP-triggered immunity (MTI), over-expression of OsNPR1 and OsCERK, and the consequent blast suppressive activity. Strikingly, M. testaceum induced the transcriptional tradeoff between physiological growth and host defense pathways as indicated by up- and downregulated DEGs. Coupled with its plant probiotic features and the defense elicitation activity, the present study paves the way for developing Microbacterium testaceum-mediated bioformulation for sustainably managing rice blast disease.

Effects of rice blast biocontrol strain Pseudomonas alcaliphila Ej2 on the endophytic microbiome and proteome of rice under salt stress

Introduction

Soil salinity is a prevalent environmental stress in agricultural production. Microbial inoculants could effectively help plants to alleviate salt stress. However, there is little knowledge of the biocontrol strain Pseudomonas alcaliphila Ej2 mechanisms aiding rice plants to reduce the adverse effects caused by salt stress.

Methods

We performed integrated field and greenhouse experiments, microbial community profiling, and rice proteomic analysis to systematically investigate the Ej2 mechanism of action.

Results

The results displayed that biocontrol strain Ej2 increased shoot/root length and fresh/dry weight compared with control under salt stress. Meanwhile, strain Ej2 has the ability to control rice blast disease and promote rice growth. Furthermore, the microbial community analysis revealed that the alpha-diversity of Ej2-inoculated plants was higher than the control plants, expect the Shannon index of the bacterial microbiome and the Ej2-inoculated samples clustered and separated from the control samples based on beta-diversity analysis. Importantly, the enriched and specific OTUs after Ej2 inoculation at the genus level were Streptomyces, Pseudomonas, Flavobacterium, and Bacillus. Moreover, we observed that Ej2 inoculation influenced the rice proteomic profile, including metabolism, plant-pathogen interactions, and biosynthesis of unsaturated fatty acids. These results provide comprehensive evidence that Ej2 inoculation induced the rice endophytic microbiome and proteomic profiles to promote plant growth under salt stress.

Discussion

Understanding the biocontrol strain effects on the endophytic microbiome and rice proteomics will help us better understand the complex interactions between plants and microorganisms under salt stress. Furthermore, unraveling the mechanisms underlying salt tolerance will help us more efficiently ameliorate saline soils.

Highly potent natural fungicides identified in silico against the cereal killer fungus Magnaporthe oryzae

Magnaporthe oryzae is one of the most notorious fungal pathogens that causes blast disease in cereals, and results in enormous loss of grain production. Many chemical fungicides are being used to control the pathogen but none of them are fully effective in controlling blast disease. Therefore, there is a demand for the discovery of a new natural biofungicide to manage the blast disease efficiently. A large number of new natural products showed inhibitory activities against M. oryzae in vitro. To find out effective biofungicides, we performed in silico molecular docking analysis of some of the potent natural compounds targeting four enzymes namely, scytalone dehydratase, SDH1 (PDB ID:1STD), trihydroxynaphthalene reductase, 3HNR (PDB ID:1YBV), trehalose-6-phosphate synthase, Tps1 (PDB ID:6JBI) and isocitrate lyase, ICL1 (PDB ID:5E9G) of M. oryzae fungus that regulate melanin biosynthesis and/or appresorium formation. Thirty-nine natural compounds that were previously reported to inhibit the growth of M. oryzae were subjected to rigid and flexible molecular docking against aforementioned enzymes followed by molecular dynamic simulation. The results of virtual screening showed that out of 39, eight compounds showed good binding energy with any one of the target enzymes as compared to reference commercial fungicides, azoxystrobin and strobilurin. Among the compounds, camptothecin, GKK1032A2 and chaetoviridin-A bind with more than one target enzymes of M. oryzae. All of the compounds except tricyclazole showed good bioactivity score. Taken together, our results suggest that all of the eight compounds have the potential to develop new fungicides, and remarkably, camptothecin, GKK1032A2 and chaetoviridin-A could act as multi-site mode of action fungicides against the blast fungus M. oryzae.

Characterization of a Bacillus velezensis strain isolated from Bolbostemmatis Rhizoma displaying strong antagonistic activities against a variety of rice pathogens

Biological control is an effective measure in the green control of rice diseases. To search for biocontrol agents with broad-spectrum and high efficiency against rice diseases, in this study, a strain of antagonistic bacterium BR-01 with strong inhibitory effect against various rice diseases was isolated from Bolbostemmatis Rhizoma by plate confrontation method. The strain was identified as Bacillus velezensis by morphological observation, physiological and biochemical identification, and molecular characterization by 16S rDNA and gyrB gene sequencing analysis. The confrontation test (dual culture) and Oxford cup assays demonstrated that B. velezensis BR-01 had strong antagonistic effects on Magnaporthe oryzae, Ustilaginoidea virens, Fusarium fujikuroi, Xanthomonas oryzae pv. Oryzicola, and Xanthomonas oryzae pv. oryzae, the major rice pathogens. The genes encoding antimicrobial peptides (ituA, ituD, bmyB, bmyC, srfAA, fenB, fenD, bacA, and bacD) were found in B. velezensis BR-01 by PCR amplification with specific primers. B. velezensis BR-01 could produce protease, cellulase, β-1,3-glucanase, chitinase, indoleacetic acid, siderophore, and 1-aminocyclopropane-1-carboxylate (ACC) deaminase, and might produce three lipopeptide antibiotics, surfactin, iturin, and fengycin based on Liquid chromatography–mass spectrometry (LC-MS) results. Furthermore, the plant assays showed that B. velezensis BR-01 had significant control effects on rice bacterial blight and bacterial leaf streak by pot experiments in greenhouse. In conclusion, B. velezensis BR-01 is a broad-spectrum antagonistic bacterium and has the potential as the ideal biocontrol agent in controlling multiple rice diseases with high efficiency.

Bonactin and Feigrisolide C Inhibit Magnaporthe oryzae Triticum Fungus and Control Wheat Blast Disease

Wheat blast caused by the Magnaporthe oryzaeTriticum (MoT) pathotype is one of the most damaging fungal diseases of wheat. During the screening of novel bioactive secondary metabolites, we observed two marine secondary metabolites, bonactin and feigrisolide C, extracted from the marine bacteria Streptomyces spp. (Act 8970 and ACT 7619), remarkably inhibited the hyphal growth of an MoT isolate BTJP 4 (5) in vitro. In a further study, we found that bonactin and feigrisolide C reduced the mycelial growth of this highly pathogenic isolate in a dose-dependent manner. Bonactin inhibited the mycelial development of BTJP 4 (5) more effectively than feigrisolide C, with minimal concentrations for inhibition being 0.005 and 0.025 µg/disk, respectively. In a potato dextrose agar (PDA) medium, these marine natural products greatly reduced conidia production in the mycelia. Further bioassays demonstrated that these secondary metabolites could inhibit the MoT conidia germination, triggered lysis, or conidia germinated with abnormally long branched germ tubes that formed atypical appressoria (low melanization) of BTJP 4 (5). Application of these natural products in a field experiment significantly protected wheat from blast disease and increased grain yield compared to the untreated control. As far as we are aware, this is the first report of bonactin and feigrisolide C that inhibited mycelial development, conidia production, conidial germination, and morphological modifications in the germinated conidia of an MoT isolate and suppressed wheat blast disease in vivo. To recommend these compounds as lead compounds or biopesticides for managing wheat blast, more research is needed with additional MoT isolates to identify their exact mode of action and efficacy of disease control in diverse field conditions.

Genomic and Biocontrol Potential of the Crude Lipopeptide by Streptomyces bikiniensis HD-087 Against Magnaporthe oryzae

Rice blast caused by Magnaporthe oryzae is one of the most destructive plant diseases. The secondary metabolites of Streptomyces have potential as biological control agents against M. oryzae. However, no commercial secondary antimicrobial products of Streptomyces have been found by gene prediction, and, particularly relevant for this study, a biocontrol agent obtained from Streptomyces bikiniensis has yet to be found. In this research, genomic analysis was used to predict the secondary metabolites of Streptomyces, and the ability to develop biocontrol pharmaceuticals rapidly was demonstrated. The complete genome of the S. bikiniensis HD-087 strain was sequenced and revealed a number of key functional gene clusters that contribute to the biosynthesis of active secondary metabolites. The crude extract of lipopeptides (CEL) predicted by NRPS gene clusters was extracted from the fermentation liquid of S. bikiniensis HD-087 by acid precipitation followed by methanol extraction, and surfactins, iturins, and fengycins were identified by liquid chromatography-mass spectrometry (LC–MS). In vitro, the CEL of this strain inhibited spore germination and appressorial formation of M. oryzae by destroying membrane integrity and through the leakage of cellular components. In vivo, this CEL reduced the disease index of rice blast by approximately 76.9% on detached leaves, whereas its control effect on leaf blast during pot experiments was approximately 60%. Thus, the S. bikiniensis CEL appears to be a highly suitable alternative to synthetic chemical fungicides for controlling M. oryzae.

Transcriptome and Quasi-Targeted Metabolome Analyze Overexpression of 4-Hydroxyphenylpyruvate Dioxygenase Alleviates Fungal Toxicity of 9-Phenanthrol in Magnaporthe oryzae

Magnaporthe oryzae, the causal agent of rice blast disease, produces devastating damage to global rice production. It is urgent to explore novel strategies to overcome the losses caused by this disease. 9-phenanthrol is often used as a transient receptor potential melastatin 4 (TRPM4) channel inhibitor for animals, but we found its fungal toxicity to M. oryzae. Thus, we explored the antimicrobial mechanism through transcriptome and metabolome analyses. Moreover, we found that overexpression of a gene encoding 4-hydroxyphenylpyruvate dioxygenase involved in the tyrosine degradative pathway enhanced the tolerance of 9-phenanthrol in M. oryzae. Thus, our results highlight the potential fungal toxicity mechanism of 9-phenanthrol at metabolic and transcriptomic levels and identify a gene involving 9-phenanthrol alleviation. Importantly, our results demonstrate the novel mechanism of 9-phenanthrol on fungal toxicity that will provide new insights of 9-phenanthrol for application on other organisms.

Natural Protein Kinase Inhibitors, Staurosporine, and Chelerythrine Suppress Wheat Blast Disease Caused by Magnaporthe oryzae Triticum

Protein kinases (PKs), being key regulatory enzymes of a wide range of signaling pathways, are potential targets for antifungal agents. Wheat blast disease, caused by Magnaporthe oryzae Triticum (MoT), is an existential threat to world food security. During the screening process of natural metabolites against MoT fungus, we find that two protein kinase inhibitors, staurosporine and chelerythrine chloride, remarkably inhibit MoT hyphal growth. This study further investigates the effects of staurosporine and chelerythrine chloride on MoT hyphal growth, conidia production, and development as well as wheat blast inhibition in comparison to a commercial fungicide, Nativo^®75WG. The growth of MoT mycelia is significantly inhibited by these compounds in a dose-dependent manner. These natural compounds greatly reduce conidia production in MoT mycelia along with suppression of conidial germination and triggered lysis, resulting in deformed germ tubes and appressoria. These metabolites greatly suppress blast development in artificially inoculated wheat plants in the field. This is the first report of the antagonistic effect of these two natural PKC inhibitory alkaloids on MoT fungal developmental processes in vitro and suppression of wheat blast disease on both leaves and spikes in vivo. Further research is needed to identify their precise mechanism of action to consider them as biopesticides or lead compounds for controlling wheat blast.

Exploring the Common Mechanism of Fungal sRNA Transboundary Regulation of Plants Based on Ensemble Learning Methods

Studies have found that pathogenic fungi and plants have sRNA transboundary regulation mechanisms. However, no researchers have used computer methods to carry out comprehensive studies on whether there is a more remarkable similarity in the transboundary regulation of plants by pathogenic fungi. In this direction, high-throughput non-coding sRNA data of three types of fungi and fungi-infected plants for 72 h were obtained. These include the Magnaporthe, Magnaporthe oryzae infecting Oryza sativa, Botrytis cinerea, Botrytis cinerea infecting Solanum lycopersicum, Phytophthora infestans and Phytophthora infestans infecting Solanum tuberosum. Research on these data to explore the commonness of fungal sRNA transboundary regulation of plants. First, using the big data statistical analysis method, the sRNA whose expression level increased significantly after infection was found as the key sRNA for pathogenicity, including 355 species of Magnaporthe oryzae, 399 species of Botrytis cinerea, and 426 species of Phytophthora infestans. Secondly, the target prediction was performed on the key sRNAs of the above three fungi, and 96, 197, and 112 core nodes were screened out, respectively. After functional enrichment analysis, multiple GO and KEGG_Pathway were obtained. It is found that there are multiple identical GO and KEGG_Pathway that can participate in plant gene expression regulation, metabolism, and other life processes, thereby affecting plant growth, development, reproduction, and response to the external environment. Finally, the characteristics of key pathogenic sRNAs and some non-pathogenic sRNAs are mined and extracted. Five Ensemble learning algorithms of Gradient Boosting Decision Tree, Random Forest, Adaboost, XGBoost, and Light Gradient Boosting Machine are used to construct a binary classification prediction model on the data set. The five indicators of accuracy, recall, precision, F1 score, and AUC were used to compare and analyze the models with the best parameters obtained by training, and it was found that each model performed well. Among them, XGBoost performed very well in the five models, and the AUC of the validation set was 0.86, 0.93, and 0.90. Therefore, this model has a reference value for predicting other fungi’s key sRNAs that transboundary regulation of plants.

Biologicals and New Generation Fungicides in the Management of Blast Disease in Rice

Background: Blast is a devastating disease in rice production. The current research tested the efficacy of biologicals and fungicides against blast. Aqueous extracts of Azadirachta indica, Ocimum basalicum, Cymbopogan flexousus, Thymus vulgaris, Aloe vera, Tagetes patula, Cordia curassavica, Aegle marmelos, Allium fistulosum, Syzygium aromaticum, and Calotropis gigantea were tested in vitro at 5, 10, and 15% concentrations against Magnaporthe oryzae. Also, two isolates, Bacillus cereus OG2L and B. subtilis OG2A, and one isolate, Azotobacter SAG19, and, similarly, five new generation fungicides were evaluated at three different doses against blast pathogen M. oryzae in vitro. The treatments that exhibited the best performance in vitro were further evaluated against blast disease under field conditions.

Results: Extracts of T. patula (5%), C. gigantea (5%), C. curassavica (10%), A. fistulosum (10%), and A. marmelos (15%) showed greater than 81% inhibition to M. oryzae in vitro. Likewise, all three biocontrol agents, viz. B. cereus OG2L, B. subtilis OG2A, and Azotobacter SAG19, demonstrated more than 50% inhibition of mycelial growth of pathogen in vitro, and the commercial formulations of fungicides Propineb, Trifloxystrobin+Tebuconazole, Tebuconazol+Triadimenol, Bacillus subtilis Strain QST 713, and Cinnamon Oil 8%+Clove Oil 2% also significantly inhibited M. oryzae. Under field conditions, C. curassavica (10%), A. marmelos (15%), C. gigantea (5%); B.cereus OG2L; B.subtilis OG2A; Proineb and Trifloxystrobin+Tebuconazole were effective in reducing disease in addition to yield enhancement.

Conclusion: Overall, the plant extracts (C. curassavica at 10%, A. marmelos at 15%, C. gigantea at 5%); bio-agents (B. cereus OG2L, B. subtilis OG2A both at 2g/l), and new generation fungicides Antracol 70WP (Proineb) at 2.5 g/l and Nativo 75 WG (Trifloxystrobin+Tebuconazole) at 0.5 g/l provided effective control against blast disease and superior plant growth and yield compared with other treatments and untreated control.

Prospect and Challenges for Sustainable Management of Climate Change-Associated Stresses to Soil and Plant Health by Beneficial Rhizobacteria

Climate change imposes biotic and abiotic stresses on soil and plant health all across the planet. Beneficial rhizobacterial genera, such as Bacillus, Pseudomonas, Paraburkholderia, Rhizobium, Serratia, and others, are gaining popularity due to their ability to provide simultaneous nutrition and protection of plants in adverse climatic conditions. Plant growth-promoting rhizobacteria are known to boost soil and plant health through a variety of direct and indirect mechanisms. However, various issues limit the wider commercialization of bacterial biostimulants, such as variable performance in different environmental conditions, poor shelf-life, application challenges, and our poor understanding on complex mechanisms of their interactions with plants and environment. This study focused on detecting the most recent findings on the improvement of plant and soil health under a stressful environment by the application of beneficial rhizobacteria. For a critical and systematic review story, we conducted a non-exhaustive but rigorous literature survey to assemble the most relevant literature (sorting of a total of 236 out of 300 articles produced from the search). In addition, a critical discussion deciphering the major challenges for the commercialization of these bioagents as biofertilizer, biostimulants, and biopesticides was undertaken to unlock the prospective research avenues and wider application of these natural resources. The advancement of biotechnological tools may help to enhance the sustainable use of bacterial biostimulants in agriculture. The perspective of biostimulants is also systematically evaluated for a better understanding of the molecular crosstalk between plants and beneficial bacteria in the changing climate towards sustainable soil and plant health.