Magnaporthe as a model for understanding host-pathogen interactions

The role of the poly(A) binding protein-binding protein MoPbp1 as a regulator of the TOR signaling pathway in growth, autophagy, and pathogenicity of the rice blast fungus

The target of the rapamycin (TOR) signaling pathway is crucial for biological function in plant pathogenic fungi, yet its regulatory mechanisms remain limited. In this study, the biological functions of MoPbp1 were identified and characterized, and the findings indicate that MoPbp1 contributes to hyphal growth, conidiation, appressoria formation, metabolism of glycogen and lipid droplets, responses to stress, and pathogenicity in Magnaporthe oryzae. Further investigation revealed that MoPBP1 acts as a negative regulator of TOR activity and influences autophagy. In addition, transcriptome data revealed that MoPBP1 mainly regulates amino acid metabolism pathways, components of membrane, and oxidation-reduction process. Our results suggest that MoPbp1 is required for autophagy and pathogenicity in M. oryzae. Overall, we first revealed the relationship between Pbp1 and TOR activity in plant pathogenic fungi.

Mechanisms of regulated cell death during plant infection by the rice blast fungus Magnaporthe oryzae

Fungi are the most important group of plant pathogens, responsible for many of the world's most devastating crop diseases. One of the reasons they are such successful pathogens is because several fungi have evolved the capacity to breach the tough outer cuticle of plants using specialized infection structures called appressoria. This is exemplified by the filamentous ascomycete fungus Magnaporthe oryzae, causal agent of rice blast, one of the most serious diseases affecting rice cultivation globally. M. oryzae develops a pressurized dome-shaped appressorium that uses mechanical force to rupture the rice leaf cuticle. Appressoria form in response to the hydrophobic leaf surface, which requires the Pmk1 MAP kinase signalling pathway, coupled to a series of cell-cycle checkpoints that are necessary for regulated cell death of the fungal conidium and development of a functionally competent appressorium. Conidial cell death requires autophagy, which occurs within each cell of the spore, and is regulated by components of the cargo-independent autophagy pathway. This results in trafficking of the contents of all three cells to the incipient appressorium, which develops enormous turgor of up to 8.0 MPa, due to glycerol accumulation, and differentiates a thickened, melanin-lined cell wall. The appressorium then re-polarizes, re-orienting the actin and microtubule cytoskeleton to enable development of a penetration peg in a perpendicular orientation, that ruptures the leaf surface using mechanical force. Re-polarization requires septin GTPases which form a ring structure at the base of the appressorium, which delineates the point of plant infection, and acts as a scaffold for actin re-localization, enhances cortical rigidity, and forms a lateral diffusion barrier to focus polarity determinants that regulate penetration peg formation. Here we review the mechanism of regulated cell death in M. oryzae, which requires autophagy but may also involve ferroptosis. We critically evaluate the role of regulated cell death in appressorium morphogenesis and examine how it is initiated and regulated, both temporally and spatially, during plant infection. We then use this synopsis to present a testable model for control of regulated cell death during appressorium-dependent plant infection by the blast fungus.

Protein PARylation: a novel regulator of fungal virulence

Protein PARylation is a reversible post-translational modification; however, its role in fungal virulence has remained elusive. Recently, Gao et al. demonstrated that PARylation of two 14-3-3 regulatory proteins by poly(ADP-ribose) polymerase is essential for the virulence of rice blast fungus, highlighting the critical regulatory function of PARylation in fungal pathogenicity.

From Natural Hosts to Agricultural Threats: The Evolutionary Journey of Phytopathogenic Fungi

Since the domestication of plants, pathogenic fungi have consistently threatened crop production, evolving genetically to develop increased virulence under various selection pressures. Understanding their evolutionary trends is crucial for predicting and designing control measures against future disease outbreaks. This paper reviews the evolution of fungal pathogens from natural habitats to agricultural settings, focusing on eight significant phytopathogens: Pyricularia oryzae, Botrytis cinerea, Puccinia spp., Fusarium graminearum, F. oxysporum, Blumeria graminis, Zymoseptoria tritici, and Colletotrichum spp. Also, we explore the mechanism used to understand evolutionary trends in these fungi. The studied pathogens have evolved in agroecosystems through either (1) introduction from elsewhere; or (2) local origins involving co-evolution with host plants, host shifts, or genetic variations within existing strains. Genetic variation, generated via sexual recombination and various asexual mechanisms, often drives pathogen evolution. While sexual recombination is rare and mainly occurs at the center of origin of the pathogen, asexual mechanisms such as mutations, parasexual recombination, horizontal gene or chromosome transfer, and chromosomal structural variations are predominant. Farming practices like mono-cropping resistant cultivars and prolonged use of fungicides with the same mode of action can drive the emergence of new pathotypes. Furthermore, host range does not necessarily impact pathogen adaptation and evolution. Although halting pathogen evolution is impractical, its pace can be slowed by managing selective pressures, optimizing farming practices, and enforcing quarantine regulations. The study of pathogen evolution has been transformed by advancements in molecular biology, genomics, and bioinformatics, utilizing methods like next-generation sequencing, comparative genomics, transcriptomics and population genomics. However, continuous research remains essential to monitor how pathogens evolve over time and to develop proactive strategies that mitigate their impact on agriculture.

The serine palmitoyltransferase core subunit StLcb2 regulates sphingolipid metabolism and promotes Setosphaeria turcica pathogenicity by modulating appressorium development

The fungal pathogen Setosphaeria turcica (S. turcica) causes northern corn leaf blight (NCLB), resulting in significant yield and economic losses in maize. To elucidate the metabolic pathways essential for its pathogenicity, we investigated the metabolome of S. turcica during appressorium development, a critical stage for host infection. Our analysis indicated a substantial enrichment of sphingosine and related compounds during this phase. The application of chemical inhibitors to disrupt sphingolipid metabolism confirmed their pivotal role in appressorium formation and pathogenicity. Additionally, silencing of the serine palmitoyl transferase (Spt) core subunit gene StLCB2 led to significant alterations in fungal morphology and growth, accompanied by changes in cell membrane integrity, surface hydrophobicity, melanin, and sphingosine synthesis. These findings underscore the importance of sphingolipids in the pathogenicity of S. turcica and suggest that targeting specific components of the sphingolipid pathway could aid in developing novel fungicides or genetically engineered maize varieties with increased resistance to NCLB.

Synthesis and biological evaluation of MS-347a derivatives against plant pathogenic fungi based on a strategy of laeA gene introduction

Our group previously identified MS-347a (1) as a new fungicide candidate from the culture broth of the mutant strain, Aspergillus sp. KTF-0058, which had the laeA gene inserted. This mutant strain was able to produce a sufficient supply of 1, allowing for its use to investigate the structure-activity relationship. To this end, we synthesized 11 derivatives and evaluated their antifungal activity. Among these derivatives, the aldehyde derivative exhibited superior antifungal potency as compared to 1, and some acyl derivatives were able to maintain the antifungal activity of 1 despite significant structural changes. From these results, it is found that the aldehyde derivative is one of the most promising fungicidal candidates, and the introduction of acyl groups could be utilized to create chemical probes for target-identification experiments.

The nucleolin MoNsr1 plays pleiotropic roles in the pathogenicity and stress adaptation in the rice blast fungus Magnaporthe oryzae

The rice blast disease, caused by the fungus Magnaporthe oryzae, is a significant agricultural problem that adversely impacts rice production and food security. Understanding the precise molecular pathways involved in the interaction between the pathogen and its host is crucial for developing effective disease management strategies. This study examines the crucial function of the nucleolin MoNsr1 in regulating M. oryzae physiological functions. ΔMoNsr1 deletion mutants showed reduced fungal growth, asexual sporulation, and pathogenicity compared to the wild-type. Mutants exhibited impaired conidial germination and appressoria formation, reducing infection progression. Additionally, ΔMoNsr1 deletion mutant had less turgor pressure, confirming that MoNsr1 is essential for cell wall biogenesis and resistant to external stresses. Furthermore, ΔMoNsr1 deletion mutant showed enhanced sensitivity to oxidative stress, reactive oxygen species, and cold tolerance. Our results offer a thorough understanding of the function of MoNsr1 in the virulence and stress-resilient capability in M. oryzae. These findings provide insights into the novel targets and contribute to the emergence of innovative approaches for managing rice blast disease.

Ammonium enhances rice resistance to Magnaporthe oryzae through H2O2 accumulation

Nitrogen (N) is essential for the physiological processes of plants. However, the specific mechanisms by which different nitrogen forms influence rice blast pathogenesis remain poorly understood. This study used hydroponic assays to explore how ammonium (NH4+) and nitrate (NO3-) affect rice after inoculation with Magnaporthe oryzae (M. oryzae). The results showed that NH4+, compared to NO3-, significantly reduced disease severity, fungal growth, fungal hyphae number, the expansion capacity of infectious hyphae, and disease-related loss of photosynthesis. Additionally, NH4+ enhanced the expression of defense-related genes, including OsPBZ1, OsCHT1, OsPR1a, and OsPR10. NH4+-treated rice also exhibited higher hydrogen peroxide (H2O2) accumulation and increased antioxidant enzyme activities. Moreover, susceptibility to rice blast disease increased when H2O2 was scavenged, while a reduction in susceptibility was observed with the application of exogenous H2O2. These results suggest that ammonium enhances rice resistance to M. oryzae, potentially through H2O2 accumulation. The findings provide valuable insights into how different nitrogen forms affect plant immunity in rice, which is crucial for controlling rice blast and ensuring stable food production.

The dual-specificity kinase MoLKH1-mediated cell cycle, autophagy, and suppression of plant immunity is critical for development and pathogenicity of Magnaporthe oryzae

Cell cycle progression, autophagic cell death during appressorium development, and ROS degradation at the infection site are important for the development of rice blast disease. However, the association of cell cycle, autophagy and ROS detoxification remains largely unknown in M. oryzae. Here, we identify the dual-specificity kinase MoLKH1, which serves as an important cell cycle regulator required for appressorium formation by regulating cytokinesis and cytoskeleton in M. oryzae. MoLKH1 is transcriptionally activated by H2O2 and required for H2O2-induced autophagic cell death and suppression of ROS-activated plant defense during plant invasion of M. oryzae. In addition, the Molkh1 mutant also showed several phenotypic defects, including delayed growth, abnormal conidiation, damaged cell wall integrity, impaired glycogen and lipid transport, reduced secretion of extracellular enzymes and effectors, and attenuated virulence of M. oryzae. Nuclear localization of MoLKH1 requires the nuclear localization sequence, Lammer motif, as well as the kinase active site and ATP-binding site in this protein. Site-directed mutagenesis showed that each of them plays crucial roles in fungal growth and pathogenicity of M. oryzae. In conclusion, our results demonstrate that MoLKH1-mediated cell cycle, autophagy, and suppression of plant immunity play crucial roles in development and pathogenicity of M. oryzae.

MoRgs3 functions in intracellular reactive oxygen species perception-integrated cAMP signaling to promote appressorium formation in Magnaporthe oryzae

Regulator of G-protein signaling (RGS) proteins exhibit GTPase-accelerating protein activities to govern G-protein function. In the rice blast fungus Magnaporthe oryzae, there is a family of at least eight RGS and RGS-like proteins (MoRgs1 to MoRgs8), each exhibiting distinct or shared functions in the growth, appressorium formation, and pathogenicity. MoRgs3 recently emerged as one of the crucial regulators that senses intracellular oxidation during appressorium formation. To explore this unique regulatory mechanism of MoRgs3, we identified the nucleoside diphosphate kinase MoNdk1 that interacts with MoRgs3. MoNdk1 phosphorylates MoRgs3 under induced intracellular reactive oxygen species levels, and MoRgs3 phosphorylation is required for appressorium formation and pathogenicity. In addition, we showed that MoRgs3 phosphorylation determines its interaction with MoCrn1, a coronin-like actin-binding protein homolog, which regulates MoRgs3 internalization. Finally, we provided evidence demonstrating that MoRgs3 functions in MoMagA-mediated cAMP signaling to regulate normal appressorium induction. By revealing a novel signal perception mechanism, our studies highlighted the complexity of regulation during the appressorium function and pathogenicity of the blast fungus.

IMPORTANCE

We report that MoRgs3 becomes phosphorylated in an oxidative intracellular environment during the appressorium formation stage. We found that this phosphorylation is carried out by MoNdk1, a nucleoside diphosphate kinase. In addition, this phosphorylation leads to a higher binding affinity between MoRgs3 and MoCrn1, a coronin-like actin-binding protein that was implicated in the endocytic transport of several other RGS proteins of Magnaporthe oryzae. We further found that the internalization of MoRgs3 is indispensable for its GTPase-activating protein function toward the Gα subunit MoMagA. Importantly, we characterized how such cellular regulatory events coincide with cAMP signaling-regulated appressorium formation and pathogenicity in the blast fungus. Our studies uncovered a novel intracellular reactive oxygen species signal-transducing mechanism in a model pathogenic fungus with important basic and applied implications.

Comprehensive Review of COVID-19: Epidemiology, Pathogenesis, Advancement in Diagnostic and Detection Techniques, and Post-Pandemic Treatment Strategies

At present, COVID-19 remains a public health concern due to the ongoing evolution of SARS-CoV-2 and its prevalence in particular countries. This paper provides an updated overview of the epidemiology and pathogenesis of COVID-19, with a focus on the emergence of SARS-CoV-2 variants and the phenomenon known as 'long COVID'. Meanwhile, diagnostic and detection advances will be mentioned. Though many inventions have been made to combat the COVID-19 pandemic, some outstanding ones include multiplex RT-PCR, which can be used for accurate diagnosis of SARS-CoV-2 infection. ELISA-based antigen tests also appear to be potential diagnostic tools to be available in the future. This paper also discusses current treatments, vaccination strategies, as well as emerging cell-based therapies for SARS-CoV-2 infection. The ongoing evolution of SARS-CoV-2 underscores the necessity for us to continuously update scientific understanding and treatments for it.

A novel MAP kinase-interacting protein MoSmi1 regulates development and pathogenicity in Magnaporthe oryzae

The cell wall is the first barrier against external adversity and plays roles in maintaining normal physiological functions of fungi. Previously, we reported a nucleosome assembly protein, MoNap1, in Magnaporthe oryzae that plays a role in cell wall integrity (CWI), stress response, and pathogenicity. Moreover, MoNap1 negatively regulates the expression of MoSMI1 encoded by MGG_03970. Here, we demonstrated that deletion of MoSMI1 resulted in a significant defect in appressorium function, CWI, cell morphology, and pathogenicity. Further investigation revealed that MoSmi1 interacted with MoOsm1 and MoMps1 and affected the phosphorylation levels of MoOsm1, MoMps1, and MoPmk1, suggesting that MoSmi1 regulates biological functions by mediating mitogen-activated protein kinase (MAPK) signalling pathway in M. oryzae. In addition, transcriptome data revealed that MoSmi1 regulates many infection-related processes in M. oryzae, such as membrane-related pathway and oxidation reduction process. In conclusion, our study demonstrated that MoSmi1 regulates CWI by mediating the MAPK pathway to affect development and pathogenicity of M. oryzae.

Re-discovery of MS-347a as a fungicide candidate through a new drug discovery platform with a multidrug-sensitive Saccharomyces cerevisiae screening system and the introduction of a global secondary metabolism regulator, laeA gene

We found that the culture broth of fungi showed anti-fungal activity against multidrug-sensitive budding yeast. However, we could not identify the anti-fungal compound due to the small quantity. Therefore, we attempted to increase the productivity of the target compound by the introduction of a global secondary metabolism regulator, laeA to the strain, which led to the successful isolation of 10-folds greater amount of MS-347a (1) than Aspergillus sp. FKI-5362. Compound 1 was not effective against Candida albicans and the detailed anti-fungal activity of 1 remains unverified. After our anti-fungal activity screening, 1 was found to inhibit the growth of broad plant pathogenic fungal species belonging to the Ascomycota. It is noteworthy that 1 showed little insecticidal activity against silkworms, suggesting its selective biological activity against plant pathogenic fungi. Our study implies that the combination strategy of multidrug-sensitive yeast and the introduction of laeA is useful for new anti-fungal drug discovery.

Hyperspectral imaging for quantifying Magnaporthe oryzae sporulation on rice genotypes

BACKGROUND

Precise evaluation of fungal conidia production may facilitate studies on resistance mechanisms and plant breeding for disease resistance. In this study, hyperspectral imaging (HSI) was used to quantify the sporulation of Magnaporthe oryzae on the leaves of rice cultivars grown under controlled conditions. Three rice genotypes (CO 39, Nipponbare, IR64) differing in susceptibility to blast were inoculated with M. oryzae isolates Guy 11 and Li1497. Spectral information (450-850 nm, 140 wavebands) of typical leaf blast symptoms was recorded before and after induction of sporulation of the pathogen.

RESULTS

M. oryzae produced more conidia on the highly susceptible genotype than on the moderately susceptible genotype, whereas the resistant genotype resulted in no sporulation. Changes in reflectance spectra recorded before and after induction of sporulation were significantly higher in genotype CO 39 than in Nipponbare. The spectral angle mapper algorithm for supervised classification allowed for the classification of blast symptom subareas and the quantification of lesion areas with M. oryzae sporulation. The correlation between the area under the difference spectrum (viz. spectral difference without and with sporulation) and the number of conidia per lesion and the number of conidia per lesion area was positive and count-based differences in rice - M. oryzae interaction could be reproduced in the spectral data.

CONCLUSIONS

HSI provided a precise and objective method of assessing M. oryzae conidia production on infected rice plants, revealing differences that could not be detected visually.

First telomere-to-telomere gapless assembly of the rice blast fungus Pyricularia oryzae

Rice blast caused by Pyricularia oryzae (syn., Magnaporthe oryzae) was one of the most destructive diseases of rice throughout the world. Genome assembly was fundamental to genetic variation identification and critically impacted the understanding of its ability to overcome host resistance. Here, we report a gapless genome assembly of rice blast fungus P. oryzae strain P131 using PacBio, Illumina and high throughput chromatin conformation capture (Hi-C) sequencing data. This assembly contained seven complete chromosomes (43,237,743 bp) and a circular mitochondrial genome (34,866 bp). Approximately 14.31% of this assembly carried repeat sequences, significantly greater than its previous assembled version. This assembly had a 99.9% complement in BUSCO evaluation. A total of 14,982 genes protein-coding genes were predicted. In summary, we assembled the first telomere-to-telomere gapless genome of P. oryzae, which would be a valuable genome resource for future research on the genome evolution and host adaptation.

Pyricularia oryzae: Lab star and field scourge

Pyricularia oryzae (syn. Magnaporthe oryzae), is a filamentous ascomycete that causes a major disease called blast on cereal crops, as well as on a wide variety of wild and cultivated grasses. Blast diseases have a tremendous impact worldwide particularly on rice and on wheat, where the disease emerged in South America in the 1980s, before spreading to Asia and Africa. Its economic importance, coupled with its amenability to molecular and genetic manipulation, have inspired extensive research efforts aiming at understanding its biology and evolution. In the past 40 years, this plant-pathogenic fungus has emerged as a major model in molecular plant-microbe interactions. In this review, we focus on the clarification of the taxonomy and genetic structure of the species and its host range determinants. We also discuss recent molecular studies deciphering its lifecycle.

TAXONOMY

Kingdom: Fungi, phylum: Ascomycota, sub-phylum: Pezizomycotina, class: Sordariomycetes, order: Magnaporthales, family: Pyriculariaceae, genus: Pyricularia.

HOST RANGE

P. oryzae has the ability to infect a wide range of Poaceae. It is structured into different host-specialized lineages that are each associated with a few host plant genera. The fungus is best known to cause tremendous damage to rice crops, but it can also attack other economically important crops such as wheat, maize, barley, and finger millet.

DISEASE SYMPTOMS

P. oryzae can cause necrotic lesions or bleaching on all aerial parts of its host plants, including leaf blades, sheaths, and inflorescences (panicles, spikes, and seeds). Characteristic symptoms on leaves are diamond-shaped silver lesions that often have a brown margin and whose appearance is influenced by numerous factors such as the plant genotype and environmental conditions. USEFUL WEBSITES Resources URL Genomic data repositories http://genome.jouy.inra.fr/gemo/ Genomic data repositories http://openriceblast.org/ Genomic data repositories http://openwheatblast.net/ Genome browser for fungi (including P. oryzae) http://fungi.ensembl.org/index.html Comparative genomics database https://mycocosm.jgi.doe.gov/mycocosm/home T-DNA mutant database http://atmt.snu.kr/ T-DNA mutant database http://www.phi-base.org/ SNP and expression data https://fungidb.org/fungidb/app/.

The Microtubule End Binding Protein Mal3 Is Essential for the Dynamic Assembly of Microtubules during Magnaporthe oryzae Growth and Pathogenesis

Cytoskeletal microtubules (MTs) play crucial roles in many aspects of life processes in eukaryotic organisms. They dynamically assemble physiologically important MT arrays under different cell conditions. Currently, aspects of MT assembly underlying the development and pathogenesis of the model plant pathogenic fungus Magnaporthe oryzae (M. oryzae) are unclear. In this study, we characterized the MT plus end binding protein MoMal3 in M. oryzae. We found that knockout of MoMal3 results in defects in hyphal polar growth, appressorium-mediated host penetration and nucleus division. Using high-resolution live-cell imaging, we further found that the MoMal3 mutant assembled a rigid MT in parallel with the MT during hyphal polar growth, the cage-like network in the appressorium and the stick-like spindle in nuclear division. These aberrant MT organization patterns in the MoMal3 mutant impaired actin-based cell growth and host infection. Taken together, these findings showed that M. oryzae relies on MoMal3 to assemble elaborate MT arrays for growth and infection. The results also revealed the assembly mode of MTs in M. oryzae, indicating that MTs are pivotal for M. oryzae growth and host infection and may be new targets for devastating fungus control.

Tiny but mighty: metal nanoparticles as effective antimicrobial agents for plant pathogen control

Metal nanoparticles (MNPs) have gained significant attention in recent years for their potential use as effective antimicrobial agents for controlling plant pathogens. This review article summarizes the recent advances in the role of MNPs in the control of plant pathogens, focusing on their mechanisms of action, applications, and limitations. MNPs can act as a broad-spectrum antimicrobial agent against various plant pathogens, including bacteria, fungi, and viruses. Different types of MNPs, such as silver, copper, zinc, iron, and gold, have been studied for their antimicrobial properties. The unique physicochemical properties of MNPs, such as their small size, large surface area, and high reactivity, allow them to interact with plant pathogens at the molecular level, leading to disruption of the cell membrane, inhibition of cellular respiration, and generation of reactive oxygen species. The use of MNPs in plant pathogen control has several advantages, including their low toxicity, selectivity, and biodegradability. However, their effectiveness can be influenced by several factors, including the type of MNP, concentration, and mode of application. This review highlights the current state of knowledge on the use of MNPs in plant pathogen control and discusses the future prospects and challenges in the field. Overall, the review provides insight into the potential of MNPs as a promising alternative to conventional chemical agents for controlling plant pathogens.

The bZIP transcription factor BIP1 of the rice blast fungus is essential for infection and regulates a specific set of appressorium genes

The rice blast fungus Magnaporthe oryzae differentiates specialized cells called appressoria that are required for fungal penetration into host leaves. In this study, we identified the novel basic leucine zipper (bZIP) transcription factor BIP1 (B-ZIP Involved in Pathogenesis-1) that is essential for pathogenicity. BIP1 is required for the infection of plant leaves, even if they are wounded, but not for appressorium-mediated penetration of artificial cellophane membranes. This phenotype suggests that BIP1 is not implicated in the differentiation of the penetration peg but is necessary for the initial establishment of the fungus within plant cells. BIP1 expression was restricted to the appressorium by both transcriptional and post-transcriptional control. Genome-wide transcriptome analysis showed that 40 genes were down regulated in a BIP1 deletion mutant. Most of these genes were specifically expressed in the appressorium. They encode proteins with pathogenesis-related functions such as enzymes involved in secondary metabolism including those encoded by the ACE1 gene cluster, small secreted proteins such as SLP2, BAS2, BAS3, and AVR-Pi9 effectors, as well as plant cuticle and cell wall degrading enzymes. Interestingly, this BIP1 network is different from other known infection-related regulatory networks, highlighting the complexity of gene expression control during plant-fungal interactions. Promoters of BIP1-regulated genes shared a GCN4/bZIP-binding DNA motif (TGACTC) binding in vitro to BIP1. Mutation of this motif in the promoter of MGG_08381.7 from the ACE1 gene cluster abolished its appressorium-specific expression, showing that BIP1 behaves as a transcriptional activator. In summary, our findings demonstrate that BIP1 is critical for the expression of early invasion-related genes in appressoria. These genes are likely needed for biotrophic invasion of the first infected host cell, but not for the penetration process itself. Through these mechanisms, the blast fungus strategically anticipates the host plant environment and responses during appressorium-mediated penetration.

In silico characterization, molecular docking, and dynamic simulation of a novel fungal cell-death suppressing effector, MoRlpA as potential cathepsin B-like cysteine protease inhibitor during rice blast infection

The blast fungus Magnaporthe oryzae is one of the most notorious pathogens affecting rice production worldwide. The cereal killer employs a special class of small secreted proteins called effectors to manipulate and perturb the host metabolism. In turn, the host plants trigger effector-triggered immunity (ETI) via localized cell death and hypersensitive response (HR). We have identified and characterized a novel secreted effector MoRlpA from M. oryzae by extensive in silico methods. The localization studies suggested that it is exclusively secreted in the host apoplasts. Interestingly, MoRlpA interacts with a protease, cathepsin B from rice with highest affinity. The 3D structural models of both the proteins were generated. Cathepsin B-like cysteine proteases are usually involved in programmed cell death (PCD) and autophagy in plants which lead to generation of HR upon infection. Our results suggest that MoRlpA interacts with rice cathepsin B-like cysteine protease and demolish the host counter-attack by suppressing cell death and HR during an active blast infection. This was further validated by molecular docking and molecular dynamic simulation analyses. The important residues involved in the rice-blast pathogen interactions were deciphered. Overall, this research highlights stable interactions between MoRlpA-OsCathB during rice blast pathogenesis and providing an insight into how this novel RlpA protease inhibitor-cum-effector modulates the host's apoplast to invade the host tissues and establish a successful infection. Thus, this research will help to develop potential fungicide to block the binding region of MoRlpA target so that the cryptic pathogen would be recognized by the host. HIGHLIGHTSFor the first time, a novel secreted effector protein, MoRlpA has been identified and characterised from M. oryzae in silicoMoRlpA contains a rare lipoprotein A-like DPBB domain which is often an enzymatic domain in other systemsMoRlpA as an apoplastic effector interacts with the rice protease OsCathB to suppress the cell death and hypersensitive response during rice blast infectionThe three-dimensional structures of both the MoRlpA and OsCathB proteins were predictedMoRlpA-OsCathB interactions were analysed by molecular docking and molecular dynamic simulation studiesCommunicated by Ramaswamy H. Sarma.

MIF-like domain containing protein orchestrates cellular differentiation and virulence in the fungal pathogen Magnaporthe oryzae

Macrophage migration inhibitory factor (MIF) is a pleiotropic protein with chemotactic, pro-inflammatory, and growth-promoting activities first discovered in mammals. In parasites, MIF homologs are involved in immune evasion and pathogenesis. Here, we present the first comprehensive analysis of an MIF protein from the devastating plant pathogen Magnaporthe oryzae (Mo). The fungal genome encodes a single MIF protein (MoMIF1) that, unlike the human homolog, harbors multiple low-complexity regions (LCRs) and is unique to Ascomycota. Following infection, MoMIF1 is expressed in the biotrophic phase of the fungus, and is strongly down-regulated during subsequent necrotrophic growth in leaves and roots. We show that MoMIF1 is secreted during plant infection, affects the production of the mycotoxin tenuazonic acid and inhibits plant cell death. Our results suggest that MoMIF1 is a novel key regulator of fungal virulence that maintains the balance between biotrophy and necrotrophy during the different phases of fungal infection.

Plant immunity suppression by an exo-β-1,3-glucanase and an elongation factor 1α of the rice blast fungus

Fungal cell walls undergo continual remodeling that generates β-1,3-glucan fragments as products of endo-glycosyl hydrolases (GHs), which can be recognized as pathogen-associated molecular patterns (PAMPs) and trigger plant immune responses. How fungal pathogens suppress those responses is often poorly understood. Here, we study mechanisms underlying the suppression of β-1,3-glucan-triggered plant immunity by the blast fungus Magnaporthe oryzae. We show that an exo-β-1,3-glucanase of the GH17 family, named Ebg1, is important for fungal cell wall integrity and virulence of M. oryzae. Ebg1 can hydrolyze β-1,3-glucan and laminarin into glucose, thus suppressing β-1,3-glucan-triggered plant immunity. However, in addition, Ebg1 seems to act as a PAMP, independent of its hydrolase activity. This Ebg1-induced immunity appears to be dampened by the secretion of an elongation factor 1 alpha protein (EF1α), which interacts and co-localizes with Ebg1 in the apoplast. Future work is needed to understand the mechanisms behind Ebg1-induced immunity and its suppression by EF1α.

Improvement of resistance to rice blast and bacterial leaf streak by CRISPR/Cas9-mediated mutagenesis of Pi21 and OsSULTR3;6 in rice (Oryza sativa L.)

Rice (Oryza sativa L.) is a staple food in many countries around the world, particularly in China. The production of rice is seriously affected by the bacterial leaf streak and rice blast, which can reduce rice yield or even cause it to fail to be harvested. In this study, susceptible material 58B was edited by CRISPR/Cas9, targeting a target of the Pi21 gene and a target of the effector-binding element (EBE) of the OsSULTR3;6 gene, and the mutants 58b were obtained by Agrobacterium-mediated method. The editing efficiency of the two targets in the T₀ generation was higher than 90.09%, the homozygous mutants were successfully selected in the T₀ generation, and the homozygous mutation rate of each target was higher than 26.67%. The expression of the edited pi21 and EBE of Ossultr3;6 was significantly reduced, and the expression of defense responsive genes was significantly upregulated after infected with rice blast. The lesion areas of rice blast and bacterial leaf streak were significantly reduced in 58b, and the resistance of both was effectively improved. Furthermore, the gene editing events did not affect the agronomic traits of rice. In this study, the resistance of 58b to rice blast and bacterial leaf streak was improved simultaneously. This study provides a reference for using Clustered Regularly Interspaced Short Palindromic Repeats/Cas9 (CRISPR/Cas9) to accelerate the improvement of rice varieties and the development of new materials for rice breeding.

Sakuranetin protects rice from brown planthopper attack by depleting its beneficial endosymbionts

Plants produce chemical defenses that poison insect herbivores or deter their feeding, but herbivores are also accompanied by microbial endosymbionts crucial for their nutrition, reproduction, and fitness. Hence, plant defenses could target a herbivore's beneficial endosymbionts, but this has not yet been demonstrated. Here, we studied flavonoids that are induced when rice is attacked by a phloem-feeding pest, the brown planthopper (BPH), which harbors beneficial yeast-like symbionts (YLS) essential for insect nutrition, such as by remedying deficiencies in sterols. BPH attack dramatically increased sakuranetin accumulations in leaf sheaths and phloem exudates. Sakuranetin is an antifungal phytoalexin derived from the antibacterial precursor, naringenin, via catalysis of naringenin-O-methyltransferase (NOMT). When added to artificial diets, sakuranetin decreased BPH survivorship, suggesting that it functions as an induced defense. Mutation of NOMT abolished sakuranetin accumulation and increased BPH oviposition and hatching rates. High-throughput amplicon sequencing revealed that BPH fed on sakuranetin-deficient nomt lines were enriched in YLS with only minor changes in the bacterial endosymbionts, compared to those feeding on sakuranetin-rich wild-type (WT) plants. In-vitro feeding of sakuranetin suggested that this flavonoid directly inhibited the growth of YLS. BPH feeding on nomt lines accumulated higher cholesterol levels, which might be attributed to increases in the supply of sterol precursors from the YLS, while nomt lines suffered more damage than WT plants did from BPH herbivory. BPH-elicited accumulation of sakuranetin requires intact jasmonate (JA) signaling. This study reveals that rice uses a JA-induced antifungal flavonoid phytoalexin in defense against BPH by inhibiting its beneficial endosymbionts.

A lipid droplet-associated protein Nem1 regulates appressorium function for infection of Magnaporthe oryzae

Lipid droplets are important storages in fungal conidia and can be used by plant pathogenic fungi for infection. However, the regulatory mechanism of lipid droplets formation and the utilization during fungal development and infection are largely unknown. Here, in Magnaporthe oryzae, we identified a lipid droplet-associated protein Nem1 that played a key role in lipid droplets biogenesis and utilization. Nem1 was highly expressed in conidia, but lowly expressed in appressoria, and its encoded protein was localized to lipid droplets. Deletion of NEM1 resulted in reduced numbers of lipid droplets and decreased content of diacylglycerol (DAG) or triacylglycerol (TAG). NEM1 was required for asexual development especially conidia production. The Δnem1 mutant was nearly loss of virulence to host plants due to defects in appressorial penetration and invasive growth. Remarkably, Nem1 was regulated by the TOR signaling pathway and involved in the autophagy process. The Ser303 residue of Nem1 could be phosphorylated by the cAMP-PKA signaling pathway and was important for biological function of Nem1. Together, our study revealed a regulatory mechanism of lipid biogenesis and metabolism during the conidium and appressorium formation of the rice blast fungus.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42994-023-00098-5.

Metabolic efficiency reshapes the seminal relationship between pathogen growth rate and virulence

A cornerstone of classical virulence evolution theories is the assumption that pathogen growth rate is positively correlated with virulence, the amount of damage pathogens inflict on their hosts. Such theories are key for incorporating evolutionary principles into sustainable disease management strategies. Yet, empirical evidence raises doubts over this central assumption underpinning classical theories, thus undermining their generality and predictive power. In this paper, we identify a key component missing from current theories which redefines the growth-virulence relationship in a way that is consistent with data. By modifying the activity of a single metabolic gene, we engineered strains of Magnaporthe oryzae with different nutrient acquisition and growth rates. We conducted in planta infection studies and uncovered an unexpected non-monotonic relationship between growth rate and virulence that is jointly shaped by how growth rate and metabolic efficiency interact. This novel mechanistic framework paves the way for a much-needed new suite of virulence evolution theories.

Isolation of Bacillus siamensis B-612, a Strain That Is Resistant to Rice Blast Disease and an Investigation of the Mechanisms Responsible for Suppressing Rice Blast Fungus

Rice yield can be significantly impacted by rice blast disease. In this investigation, an endophytic strain of Bacillus siamensis that exhibited a potent inhibitory effect on the growth of rice blast was isolated from healthy cauliflower leaves. 16S rDNA gene sequence analysis showed that it belongs to the genus Bacillus siamensis. Using the rice OsActin gene as an internal control, we analyzed the expression levels of genes related to the defense response of rice. Analysis showed that the expression levels of genes related to the defense response in rice were significantly upregulated 48 h after treatment. In addition, peroxidase (POD) activity gradually increased after treatment with B-612 fermentation solution and peaked 48 h after inoculation. These findings clearly demonstrated that the 1-butanol crude extract of B-612 retarded and inhibited conidial germination as well as the development of appressorium. The results of field experiments showed that treatment with B-612 fermentation solution and B-612 bacterial solution significantly reduced the severity of the disease before the seedling stage of Lijiangxintuan (LTH) was infected with rice blast. Future studies will focus on exploring whether Bacillus siamensis B-612 produces new lipopeptides and will apply proteomic and transcriptomic approaches to investigate the signaling pathways involved in its antimicrobial effects.

Doxorubicin inhibits phosphatidylserine decarboxylase and confers broad-spectrum antifungal activity

As phospholipids of cell membranes, phosphatidylethanolamine (PE) and phosphatidylserine (PS) play crucial roles in glycerophospholipid metabolism. Broadly, some phospholipid biosynthesis enzymes serve as potential fungicide targets. Therefore, revealing the functions and mechanism of PE biosynthesis in plant pathogens would provide potential targets for crop disease control. We performed analyses including phenotypic characterizations, lipidomics, enzyme activity, site-directed mutagenesis, and chemical inhibition assays to study the function of PS decarboxylase-encoding gene MoPSD2 in rice blast fungus Magnaporthe oryzae. The Mopsd2 mutant was defective in development, lipid metabolism, and plant infection. The PS level increased while PE decreased in Mopsd2, consistent with the enzyme activity. Furthermore, chemical doxorubicin inhibited the enzyme activity of MoPsd2 and showed antifungal activity against 10 phytopathogenic fungi including M. oryzae and reduced disease severity of two crop diseases in the field. Three predicted doxorubicin-interacting residues are important for MoPsd2 functions. Our study demonstrates that MoPsd2 is involved in de novo PE biosynthesis and contributes to the development and plant infection of M. oryzae and that doxorubicin shows broad-spectrum antifungal activity as a fungicide candidate. The study also implicates that bacterium Streptomyces peucetius, which biosynthesizes doxorubicin, could be potentially used as an eco-friendly biocontrol agent.

MoRts1, a regulatory subunit of PP2A, is required for fungal development and pathogenicity of Magnaporthe oryzae

Protein phosphatase 2 A (PP2A) is a major heterotrimeric serine/threonine protein phosphatase comprised of three subunits, including structural subunits (A), regulatory subunits (B), and catalytic subunits (C). PP2A has been widely shown to involve in a series of cell signal transduction processes such as cell metabolism, cell cycle regulation, DNA replication, gene transcription and protein translation in yeast and mammalian. However, the roles of PP2A in pathogenic fungi Magnaporthe oryzae still remain unclear. We here found that MoRts1, a gene encoding B regulatory subunit of PP2A homologous to Saccharomyces cerevisiae Rts1, showed up-regulated transcription during conidia and initially infectious stage. Subcellular localization revealed that MoRts1-eGFP was localized to the cytoplasm and septum. Targeted disruption of MoRts1 leads to a reduction of mycelial growth and sporulation, as well as the defects of hydrophobicity, melanin pigmentation and cell wall integrity (CWI). The MoRts1 mutants were less pathogenic to the host plants, compared to the Ku80 strain, and the transcriptional levels of several pathogenicity-related Rho GTPase genes, including MoCdc42, MoRho2, MoRho3, MoRho4, MoRhoX and MoRac1, were significantly decreased in the MoRts1 mutants. Besides, two splicing variants of MoRts1 with unique functions of regulating the growth and pathogenicity were identified, and the B56 domain is vital for determining the sporulation and pathogenicity of M. oryzae. Furthermore, MoRts1 was identified to interact with PP2A catalytic subunit MoPPG1 in vivo in M. oryzae. In summary, our results showed that MoRts1 is an important regulator contributing to the fungal development, and pathogenicity of M. oryzae.

Two nucleotide sugar transporters are important for cell wall integrity and full virulence of Magnaporthe oryzae

Cell wall polysaccharides play key roles in fungal development, virulence, and resistance to the plant immune system, and are synthesized from many nucleotide sugars in the endoplasmic reticulum (ER)-Golgi secretory system. Nucleotide sugar transporters (NSTs) are responsible for transporting cytosolic-derived nucleotide sugars to the ER lumen for processing, but their roles in plant-pathogenic fungi remain to be revealed. Here, we identified two important NSTs, NST1 and NST2, in the rice blast fungus Magnaporthe oryzae. Both NSTs were localized in the ER, which was consistent with a function in transporting nucleotide sugar for processing in the ER. Sugar transport property analysis suggested that NST1 is involved in transportation of mannose and glucose, while NST2 is only responsible for mannose transportation. Accordingly, deletion of NSTs resulted in a significant decrease in corresponding soluble saccharides abundance and defect in sugar utilization. Moreover, both NSTs played important roles in cell wall integrity, were involved in asexual development, and were required for full virulence. The NST mutants exhibited decreasing external glycoproteins and exposure of inner chitin, which resulted in activation of the host defence response. Altogether, our results revealed that two sugar transporters are required for fungal cell wall polysaccharides accumulation and full virulence of M. oryzae.

Population structure of Pyricularia oryzae on rice in Vietnam reveals diversified populations with four pandemic and two endemic clusters

We characterized the genetic structure of 609 strains of Pyricularia oryzae, the fungal pathogen causing rice blast disease, in three main regions in Vietnam using microsatellites (SSR) markers. From the 447 distinct multilocus genotypes identified, six genetic clusters were defined, all of them showing elevated genetic and genotypic diversities. Four of these clusters were related to rice-attacking lineages already described at the worldwide scale, whereas the two remaining clusters were endemic to Vietnam. Strains were unevenly distributed into the six clusters depending on their groups of rice variety (indica / japonica) or type of varieties (traditional / modern) of origin, but none of the clusters was specifically related to these two factors. The highest diversity of blast population was found in Northern mountainous area, and the lowest in Red River Delta in both term of genetic diversity and gene diversity. Hierarchical AMOVAs confirmed that all three factors considered (rice variety group, type of variety origin and geography) significantly contributed to the population structure of P. oryzae in Vietnam, with highest contribution from rice variety group. Mating types were unevenly distributed among clusters. Combined with results of female fertility and linkage disequilibirum, we hypothesized that clonal reproduction probably occurred in all clusters, but that sexual reproduction likely took place at least in some restricted areas in the Northern mountainous area for strains belonging to the cluster related to the previously described recombinant lineage (worldwide lineage 1). Our study pictures the genetic diversity, population structure and reproductive mode of the blast fungus in central and north Vietnam, and shows that the observed population structure is explained by several factors, the most important one being the variability of rice variety. All these new information might help for elaborating appropriate strategies to controlling the blast disease.

MoMih1 is indispensable for asexual development, cell wall integrity, and pathogenicity of Magnaporthe oryzae

Asexual spore serves as essential inoculum of rice blast during the disease cycle, and differentiation of young conidium from conidiophore is intimately regulated by cell cycle. Mih1 encodes a dual-specificity phosphatase that involved in the G2/M transition of the mitotic cell cycle by regulating the Cdk1 activity in eukaryotes. Till now, the roles of Mih1 homologue, however, remain unclear in Magnaporthe oryzae. We here functionally characterized the Mih1 homologue MoMih1 in M. oryzae. MoMih1 is localized to both the cytoplasm and nucleus and can physically interact with the CDK protein MoCdc28 in vivo. Loss of MoMih1 led to delayed nucleus division and a high level of Tyr15 phosphorylation of MoCdc28. The MoMih1 mutants showed retarded mycelial growth with a defective polar growth, less fungal biomass, and shorter distance between diaphragms, compared with the KU80. Asexual reproduction altered in MoMih1 mutants, with both abnormal conidial morphogenesis and decreased conidiation. The MoMih1 mutants severely attenuated the virulence to host plants due to the impaired ability of penetration and biotrophic growth. The incapability of scavenging of host-derived reactive oxygen species, which was possibly ascribed to the severely decreased extracellular enzymes activities, were partially associated with deficiency of pathogenicity. Besides, the MoMih1 mutants displayed also improper localization of retromer protein MoVps26 and polarisome component MoSpa2, and defects of cell wall integrity (CWI), melanin pigmentation, chitin synthesis, and hydrophobicity. In conclusion, our results demonstrate that MoMih1 plays pleiotropic roles during fungal development and plant infection of M. oryzae.

Management of mung bean leaf spot disease caused by Phoma herbarum through Penicillium janczewskii metabolites mediated by MAPK signaling cascade

Vigna radiata L., an imperative legume crop of Pakistan, faces hordes of damage due to fungi; infecting host tissues by the appressorium. The use of natural compounds is an innovative concern to manage mung-bean fungal diseases. The bioactive secondary metabolites of Penicillium species are well documented for their strong fungi-static ability against many pathogens. Presently, one-month-old aqueous culture filtrates of Penicillium janczewskii, P. digitatum, P. verrucosum, P. crustosum, and P. oxalicum were evaluated to check the antagonistic effect of different dilutions (0, 10, 20, … and 60%). There was a significant reduction of around 7-38%, 46-57%, 46-58%, 27-68%, and 21-51% in Phoma herbarum dry biomass production due to P. janczewskii, P. digitatum, P. verrucosum, P. crustosum, and P. oxalicum, respectively. Inhibition constants determined by a regression equation demonstrated the most significant inhibition by P. janczewskii. Finally, using real-time reverse transcription PCR (qPCR) the effect of P. Janczewskii metabolites was determined on the transcript level of StSTE12 gene involved in the development and penetration of appressorium. The expression pattern of the StSTE12 gene was determined by percent Knockdown (%KD) expression that was found to be decreased i.e. 51.47, 43.22, 40.67, 38.01, 35.97, and 33.41% for P. herbarum with an increase in metabolites concentrations viz., 10, 20, 30, 40, 50 and 60% metabolites, respectively. In silico studies were conducted to analyze the role of Ste12 a transcriptional factor in the MAPK signaling pathway. The present study concludes a strong fungicidal potential of Penicillium species against P. herbarum. Further studies to isolate the effective fungicidal constituents of Penicillium species through GCMS analysis and determination of their role in signaling pathways are requisite.

Appressoria-Small but Incredibly Powerful Structures in Plant-Pathogen Interactions

Plant-pathogenic fungi are responsible for many of the most severe crop diseases in the world and remain very challenging to control. Improving current protection strategies or designating new measures based on an overall understanding of molecular host-pathogen interaction mechanisms could be helpful for disease management. The attachment and penetration of the plant surface are the most important events among diverse plant-fungi interactions. Fungi evolved as small but incredibly powerful infection structure appressoria to facilitate attachment and penetration. Appressoria are indispensable for many diseases, such as rusts, powdery mildews, and blast diseases, as well as devastating oomycete diseases. Investigation into the formation of plant-pathogen appressoria contributes to improving the understanding of the molecular mechanisms of plant-pathogen interactions. Fungal host attachment is a vital step of fungal pathogenesis. Here, we review recent advances in the molecular mechanisms regulating the formation of appressoria. Additionally, some biocontrol agents were revealed to act on appressorium. The regulation of fungal adhesion during the infective process by acting on appressoria formation is expected to prevent the occurrence of crop disease caused by some pathogenic fungi.

The power of the smallest: The inhibitory activity of microbial volatile organic compounds against phytopathogens

Plant diseases caused by phytopathogens result in huge economic losses in agriculture. In addition, the use of chemical products to control such diseases causes many problems to the environment and to human health. However, some bacteria and fungi have a mutualistic relationship with plants in nature, mainly exchanging nutrients and protection. Thus, exploring those beneficial microorganisms has been an interesting and promising alternative for mitigating the use of agrochemicals and, consequently, achieving a more sustainable agriculture. Microorganisms are able to produce and excrete several metabolites, but volatile organic compounds (VOCs) have huge biotechnology potential. Microbial VOCs are small molecules from different chemical classes, such as alkenes, alcohols, ketones, organic acids, terpenes, benzenoids and pyrazines. Interestingly, volatilomes are species-specific and also change according to microbial growth conditions. The interaction of VOCs with other organisms, such as plants, insects, and other bacteria and fungi, can cause a wide range of effects. In this review, we show that a large variety of plant pathogens are inhibited by microbial VOCs with a focus on the in vitro and in vivo inhibition of phytopathogens of greater scientific and economic importance in agriculture, such as Ralstonia solanacearum, Botrytis cinerea, Xanthomonas and Fusarium species. In this scenario, some genera of VOC-producing microorganisms stand out as antagonists, including Bacillus, Pseudomonas, Serratia and Streptomyces. We also highlight the known molecular and physiological mechanisms by which VOCs inhibit the growth of phytopathogens. Microbial VOCs can provoke many changes in these microorganisms, such as vacuolization, fungal hyphal rupture, loss of intracellular components, regulation of metabolism and pathogenicity genes, plus the expression of proteins important in the host response. Furthermore, we demonstrate that there are aspects to investigate by discussing questions that are still not very clear in this research area, especially those that are essential for the future use of such beneficial microorganisms as biocontrol products in field crops. Therefore, we bring to light the great biotechnological potential of VOCs to help make agriculture more sustainable.

Magnaporthe oryzae pathotype Triticum (MoT) can act as a heterologous expression system for fungal effectors with high transcript abundance in wheat

Plant pathogens deliver effector proteins to reprogramme a host plants circuitry, supporting their own growth and development, whilst thwarting defence responses. A subset of these effectors are termed avirulence factors (Avr) and can be recognised by corresponding host resistance (R) proteins, creating a strong evolutionary pressure on pathogen Avr effectors that favours their modification/deletion to evade the immune response. Hence, identifying Avr effectors and tracking their allele frequencies in a population is critical for understanding the loss of host recognition. However, the current systems available to confirm Avr effector function, particularly for obligate biotrophic fungi, remain limited and challenging. Here, we explored the utility of the genetically tractable wheat blast pathogen Magnaporthe oryzae pathotype Triticum (MoT) as a suitable heterologous expression system in wheat. Using the recently confirmed wheat stem rust pathogen (Puccina graminis f. sp. tritici) avirulence effector AvrSr50 as a proof-of-concept, we found that delivery of AvrSr50 via MoT could elicit a visible Sr50-dependant cell death phenotype. However, activation of Sr50-mediated cell death correlated with a high transgene copy number and transcript abundance in MoT transformants. This illustrates that MoT can act as an effective heterologous delivery system for fungal effectors from distantly related fungal species, but only when enough transgene copies and/or transcript abundance is achieved.

Phosphocholine cytidylyltransferase MoPct1 is crucial for vegetative growth, conidiation, and appressorium-mediated plant infection by Magnaporthe oryzae

Phosphatidylcholine (PC) plays crucial biological roles in eukaryotic cells. In Saccharomyces cerevisiae, apart from phosphatidylethanolamine (PE) methylation pathway, PC is also synthesized via CDP-choline pathway. Phosphocholine cytidylyltransferase Pct1 is the rate-limiting enzyme to catalyze the conversion from phosphocholine to CDP-choline in this pathway. Here, we report the identification and functional characterization of an ortholog of the budding yeast PCT1 in Magnaporthe oryzae, named MoPCT1. Targeted gene deletion mutants of MoPCT1 were impaired in vegetative growth, conidiation, appressorium turgor accumulation and cell wall integrity. Also, the mutants were severely compromised in appressorium-mediated penetration, infectious growth and pathogenicity. Western blot analysis revealed that cell autophagy was activated by the deletion of MoPCT1 under nutrient-rich conditions. Moreover, we found several key genes in PE methylation pathway, such as MoCHO2, MoOPI3, and MoPSD2, were significantly up-regulated in the ΔMopct1 mutants, indicating that a pronounced compensation effect exists between the two PC biosynthesis pathways in M. oryzae. Interestingly, in the ΔMopct1 mutants, histone H3 was hypermethylated and expression levels of several methionine cycling-related genes were significantly up-regulated, suggesting that MoPCT1 is involved in histone H3 methylation and methionine metabolism. Taken together, we conclude that the phosphocholine cytidylyltransferase coding gene MoPCT1 plays important roles in vegetative growth, conidiation and appressorium-mediated plant infection by M. oryzae.

Acyl-coenzyme A binding protein MoAcb1 regulates conidiation and pathogenicity in Magnaporthe oryzae

Magnaporthe oryzae is a filamentous fungus that causes rice blast. Rice blast seriously threatens the safety of food production. The normal synthesis and metabolism of fatty acids are extremely important for eukaryotes, and acyl-CoA is involved in fatty acid metabolism. Acyl-CoA binding (ACB) proteins specifically bind both medium-chain and long-chain acyl-CoA esters. However, the role of the Acb protein in plant-pathogenic fungi has not yet been investigated. Here, we identified MoAcb1, a homolog of the Acb protein in Saccharomyces cerevisiae. Disruption of MoACB1 causes delayed hyphal growth, significant reduction in conidial production and delayed appressorium development, glycogen availability, and reduced pathogenicity. Using immunoblotting and chemical drug sensitivity analysis, MoAcb1 was found to be involved in endoplasmic reticulum autophagy (ER-phagy). In conclusion, our results suggested that MoAcb1 is involved in conidia germination, appressorium development, pathogenicity and autophagy processes in M. oryzae.

Benzyl Alcohol/Salicylaldehyde-Type Polyketide Metabolites of Fungi: Sources, Biosynthesis, Biological Activities, and Synthesis

Marine microorganisms are an important source of natural polyketides, which have become a significant reservoir of lead structures for drug design due to their diverse biological activities. In this review, we provide a summary of the resources, structures, biological activities, and proposed biosynthetic pathways of the benzyl alcohol/salicylaldehyde-type polyketides. In addition, the total syntheses of these secondary metabolites from their discoveries to the present day are presented. This review could be helpful for researchers in the total synthesis of complex natural products and the use of polyketide bioactive molecules for pharmacological purposes and applications in medicinal chemistry.

Transcriptome Analysis of Protein Kinase MoCK2, which Affects Acetyl-CoA Metabolism and Import of CK2-Interacting Mitochondrial Proteins into Mitochondria in the Rice Blast Fungus Magnaporthe oryzae

The rice pathogen Magnaporthe oryzae causes severe losses to rice production. Previous studies have shown that the protein kinase MoCK2 is essential for pathogenesis, and this ubiquitous eukaryotic protein kinase might affect several processes in the fungus that are needed for infection. To better understand which cellular processes are affected by MoCK2 activity, we performed a detailed transcriptome sequencing analysis of deletions of the MoCK2 b1 and b2 components in relation to the background strain Ku80 and connected this analysis with the abundance of substrates for proteins in a previous pulldown of the essential CKa subunit of CK2 to estimate the effects on proteins directly interacting with CK2. The results showed that MoCK2 seriously affected carbohydrate metabolism, fatty acid metabolism, amino acid metabolism, and the related transporters and reduced acetyl-CoA production. CK2 phosphorylation can affect the folding of proteins and especially the effective formation of protein complexes by intrinsically disordered or mitochondrial import by destabilizing soluble alpha helices. The upregulated genes found in the pulldown of the b1 and b2 mutants indicate that proteins directly interacting with CK2 are compensatorily upregulated depending on their pulldown. A similar correlation was found for mitochondrial proteins. Taken together, the classes of proteins and the changes in regulation in the b1 and b2 mutants suggest that CK2 has a central role in mitochondrial metabolism, secondary metabolism, and reactive oxygen species (ROS) resistance, in addition to its previously suggested role in the formation of new ribosomes, all of which are processes central to efficient nonself responses as innate immunity. IMPORTANCE The protein kinase CK2 is highly expressed and essential for plants, animals, and fungi, affecting fatty acid-related metabolism. In addition, it directly affects the import of essential mitochondrial proteins into mitochondria. These effects mean that CK2 is essential for lipid metabolism and mitochondrial function and, as shown previously, is crucial for making new translation machinery proteins. Taken together, our new results combined with previously reported results indicate that CK2 is an essential protein necessary for the capacities to launch efficient innate immunity responses and withstand the negative effects of such responses necessary for general resistance against invading bacteria and viruses as well as to interact with plants, withstand plant immunity responses, and kill plant cells.

Genome-Wide Analysis of AGC Kinases Reveals that MoFpk1 Is Required for Development, Lipid Metabolism, and Autophagy in Hyperosmotic Stress of the Rice Blast Fungus Magnaporthe oryzae

During eukaryotic evolution, the TOR-AGC kinase signaling module is involved in the coordinated regulation of cell growth and survival. However, the AGC kinases in plant-pathogenic fungi remain poorly understood. In this study, we have identified 20 members of the AGC family of protein kinases. Evolutionary and biological studies have revealed that AGC kinases are highly conserved and involved in the growth (8 genes), conidiation (13 genes), conidial germination (9 genes), appressorium formation (9 genes), and pathogenicity (5 genes) of Magnaporthe oryzae, in which a subfamily protein of the AGC kinases, MoFpk1, the activator of flippase, specifically exhibited diverse roles. Two kinase sites were screened and found to be critical for MoFpk1: 230K and 326D. Moreover, MoFpk1 is involved in cell wall integrity through the negative regulation of MoMps1 phosphorylation. The deletion of MoFpk1 resulted in defective phosphatidylacetamide (PE) and phosphatidylserine (PS) turnover and a series of lipid metabolism disorders. Under hyperosmotic stress, since the ΔMofpk1 mutant is unable to maintain membrane asymmetry, MoYpk1 phosphorylation and MoTor activity were downregulated, thus enhancing autophagy. Our results provide insights into the evolutionary and biological relationships of AGC kinases and new insight into plasma membrane (PM) homeostasis, i.e., responses to membrane stress and autophagy through lipid asymmetry maintenance. IMPORTANCE Our identification and analysis of evolutionary and biological relationships provide us with an unprecedented high-resolution view of the flexible and conserved roles of the AGC family in the topmost fungal pathogens that infect rice, wheat, barley, and millet. Guided by these insights, an AGC member, MoFpk1, was found to be indispensable for M. oryzae development. Our study defined a novel mechanism of plasma membrane homeostasis, i.e., adaptation to stress through the asymmetric distribution of phospholipids. Furthermore, defects in the asymmetric distribution of phospholipids in the membrane enhanced autophagy under hyperosmotic stress. This study provides a new mechanism for the internal linkage between lipid metabolism and autophagy, which may help new fungicide target development for controlling this devastating disease.

Type 2C Protein Phosphatases MoPtc5 and MoPtc7 Are Crucial for Multiple Stress Tolerance, Conidiogenesis and Pathogenesis of Magnaporthe oryzae

Protein kinases and phosphatases catalyze the phosphorylation and dephosphorylation of their protein substrates, respectively, and these are important mechanisms in cellular signal transduction. The rice blast fungus Magnaporthe oryzae possesses 6 protein phosphatases of type 2C class, including MoPtc1, 2, 5, 6, 7 and 8. However, only very little is known about the roles of these phosphatases in filamentous fungi. Here in, we deployed genetics and molecular biology techniques to identify, characterize and establish the roles of MoPtc5 and MoPtc7 in M. oryzae development and pathogenicity. We found that during pathogen-host interaction, MoPTC7 is differentially expressed. Double deletion of MoPTC7 and MoPTC5 suppressed the fungal vegetative growth, altered its cell wall integrity and reduced its virulence. The two genes were found indispensable for stress tolerance in the phytopathogen. We also demonstrated that disruption of any of the two genes highly affected appressorium turgor generation and Mps1 and Osm1 phosphorylation levels. Lastly, we demonstrated that both MoPtc5 and MoPtc7 are localized to mitochondria of different cellular compartments in the blast fungus. Taken together, our study revealed synergistic coordination of M. oryzae development and pathogenesis by the type 2C protein phosphatases.

The Calcium Chloride Responsive Type 2C Protein Phosphatases Play Synergistic Roles in Regulating MAPK Pathways in Magnaporthe oryzae

Reversible protein phosphorylation is essential in cellular signal transduction. The rice blast fungus Magnaporthe oryzae contains six putative type 2C protein phosphatases, namely MoPtc1, MoPtc2, MoPtc5, MoPtc6, MoPtc7, and MoPtc8. The major functions of MoPtc1 and MoPtc2 have been reported recently. In this communication, we found that MoPtc1 and MoPtc2 were induced by calcium chloride. We also found that the deletion of both MoPtc1 and MoPtc2 resulted in the overstimulation of both the high-osmolarity glycerol (Hog1) and pathogenicity MAP kinase 1 (Pmk1) pathways in M. oryzae. MoPtc1 was recruited directly to Osm1 (the osmotic stress-sensitive mutant) by the adaptor protein MoNbp2 to inactivate the Osm1 during hypoosmotic stress, distinct from the budding yeast. Moreover, we showed that MoPtc1 and MoPtc2 were localized in different cellular compartments in the fungal development. Taken together, we added some new findings of type 2C protein phosphatases MoPtc1 and MoPtc2 functions to the current knowledge on the regulation of MAPK signaling pathways in M. oryzae.

The target site of the novel fungicide quinofumelin, Pyricularia oryzae class II dihydroorotate dehydrogenase

The target site of the novel fungicide quinofumelin was investigated in the rice blast fungus Pyricularia oryzae. Quinofumelin-induced mycelial growth inhibition was reversed by orotate but not by dihydroorotate. Recovery tests suggested that the target site of quinofumelin was dihydroorotate dehydrogenase (DHODH), which catalyzes the oxidation of dihydroorotate to orotate. Quinofumelin strongly inhibited P. oryzae class 2 DHODH (DHODH II) (IC₅₀: 2.8 nM). The inhibitory activities of mycelial growth and DHODH II were strongly positively correlated, indicating that DHODH II inhibition by quinofumelin lead to antifungal activity. A P. oryzae DHODH II gene (PoPYR4) disruption mutant (ΔPopyr4), showing the same tendency as the quinofumelin-treated wild strain in recovery tests, was constructed, and disease symptoms were not observed in rice plants infected by ΔPopyr4. Thus, DHODH II, which plays an important role in pathogenicity and mycelial growth, is found to be the target site of quinofumelin.

The G143A/S substitution of mitochondrially encoded cytochrome b (Cytb) in Magnaporthe oryzae confers resistance to quinone outside inhibitors

BACKGROUND

Rice blast, caused by Magnaporthe oryzae, is a destructive disease threatening the production of staple foods worldwide. Quinone outside inhibitors (QoIs) are a group of chemicals exhibiting excellent activity against a majority of plant pathogens, with the disadvantage that pathogens can easily develop resistance to QoIs.

RESULTS

Here, we investigated the activity of picoxystrobin against M. oryzae, which showed a great inhibitory effect on 100 strains of M. oryzae with half-maximal effective concentrations (EC₅₀ ) ranging from 0.0251 to 0.1337 μg ml^-1 . The EC₅₀ values showed a continuous unimodal distribution that was identical to the normal distribution, suggesting the potency of our study to represent baseline sensitivity. In addition, nine resistant mutants were obtained by exposing M. oryzae to a high dosage of picoxystrobin in the laboratory; all of them showed cross-resistance to the other five QoI fungicides. Although some mutants showed a decreased resistance factor after ten successive cultures on fungicide-free medium, the resistance to picoxystrobin was still inheritable. Amino acid substitution of G143S was detected in eight of nine picoxystrobin-resistant mutants, and G143A was detected in only one of nine mutants. A fitness penalty was found in the mutants carrying G143S rather than G143A.

CONCLUSION

Our findings suggested that M. oryzae had a mid to high risk of resistance to picoxystrobin. Considering this, we should be vigilant to the resistance risk and apply picoxystrobin sensibly in the field. © 2022 Society of Chemical Industry.

Role of the cAMP signaling pathway in the dissemination and development on pepper fruit anthracnose disease caused by Colletotrichum scovillei

The ascomycete fungus Colletotrichum scovillei causes severe anthracnose disease on the fruit of sweet pepper and chili pepper (Capsicum annuum L.) worldwide. Understanding the biology of C. scovillei would improve the management of fruit anthracnose diseases. The cyclic adenosine monophosphate (cAMP) signaling pathway regulates diverse cellular and physiological processes in several foliar fungal pathogens. We investigated the roles of the cAMP signaling pathway in C. scovillei using pharmaceutical and genetic approaches. Exogenous cAMP was found to increase conidiation, appressorium formation, and anthracnose disease development in C. scovillei. CsAc1, CsCap1, and CsPdeH, which regulate the intracellular cAMP level, were deleted by homology-dependent gene replacement. Expectedly, the intracellular cAMP level was significantly decreased in ΔCsac1 and ΔCscap1 but increased in ΔCspdeh. All three deletion mutants exhibited serious defects in multiple fungal developments and pathogenicity, suggesting regulation of the intracellular cAMP level is important for C. scovillei. Notably, exogenous cAMP recovered the defect of ΔCsac1 in appressorium development, but not penetration, which was further recovered by adding CaCl2. This result suggests that CsAc1 is associated with both the cAMP and Ca2+ signaling pathways in C. scovillei. ΔCscap1 produced morphologically abnormal conidia with reduced tolerance to thermal stress. ΔCspdeh was completely defective in conidiation in C. scovillei, unlike other foliar pathogens. Taken together, these results demonstrate the importance of cAMP signaling in anthracnose disease caused by C. scovillei.

Functional characterization of MoSdhB in conferring resistance to pydiflumetofen in blast fungus Magnaporthe oryzae

BACKGROUND

Rice (Oryza sativa) is an important cereal crop around the world, and has constantly been threaten by the most destructive fungus Magnaporthe oryzae. Pydiflumetofen, a novel succinate dehydrogenase inhibitor (SDHI), is currently being used for controlling various fungal diseases. However, the potential resistance risk of M. oryzae to pydiflumetofen has remained unclear to date, and finding the resistance mechanism is critical for the usage of this fungicide.

RESULTS

The M. oryzae strain Guy11 is sensitive to pydiflumetofen, with EC₅₀ value of 1.24 μg mL^-1 . 58 pydiflumetofen-resistant (PR) mutants were obtained through pydiflumetofen-induced spontaneous mutation, with a mean EC₅₀ value >500 μg mL ^-1 , and the resistance factor (RF) >400. The PR mutants displayed positive cross-resistance to carboxin, but were more sensitive to fluopyram. Sequencing analysis showed that all PR mutants presented a cytosine-to-thymine transition at nucleotide position +1218, resulting in a replacement of histidine 245 by tyrosine (H245Y) on MoSdhB. The mutation of MoSdhB exhibited strong resistant phenotype, but no detectable growth deficits in fungal development, including vegetative growth and pathogenicity of M. oryzae. An allele-specific PCR for rapid detection of the H245Y mutants was established in M. oryzae.

CONCLUSION

The M. oryzae is sensitive to pydiflumetofen, and shows a medium to high resistance risk to pydiflumetofen. A point mutation of MoSdhB (H245Y) is responsible for the fungal resistance to pydiflumetofen in M. oryzae. © 2022 Society of Chemical Industry.

Distinctive phosphorylation pattern during mitotic exit network (MEN) regulation is important for the development and pathogenicity of Magnaporthe oryzae

The mitotic exit network (MEN) pathway is a vital kinase cascade regulating the timely and correct progress of cell division. In the rice blast fungus Magnaporthe oryzae, the MEN pathway, consisting of conserved protein kinases MoSep1 and MoMob1-MoDbf2, is important in the development and pathogenicity of the fungus. We found that deletion of MoSEP1 affects the phosphorylation of MoMob1, but not MoDbf2, in contrast to what was found in the buddy yeast Saccharomyces cerevisiae, and verified this finding by in vitro phosphorylation assay and mass spectrometry (MS) analysis. We also found that S43 residue is the critical phosphor-site of MoMob1 by MoSep1, and proved that MoSep1-dependent MoMob1 phosphorylation is essential for cell division during the development of M. oryzae. We further provided evidence demonstrating that MoSep1 phosphorylates MoMob1 to maintain the cell cycle during vegetative growth and infection. Taken together, our results revealed that the MEN pathway has both distinct and conservative functions in regulating the cell cycle during the development and pathogenesis of M. oryzae.

Transcriptome analysis of maize pathogen Fusarium verticillioides revealed FvLcp1, a secreted protein with type-D fungal LysM and chitin-binding domains, that plays important roles in pathogenesis and mycotoxin production

Fusarium verticillioides is a key maize pathogen and produces fumonisins, a group of mycotoxins detrimental to humans and animals. Unfortunately, our understanding on how this fungus interacts with maize to trigger mycotoxin biosynthesis is limited. We performed a systematic computational network-based analysis of large-scale F. verticillioides RNA-seq datasets to identify gene subnetwork modules associated with virulence and fumonisin regulation. F. verticillioides was inoculated on two different maize lines, moderately resistant line hybrid 33K44 and highly susceptible line maize inbred line B73, to generate time-course RNA-Seq data. Among the highly discriminative subnetwork modules, we identified a putative hub gene FvLCP1, which encodes a putative a type-D fungal LysM protein with a signal peptide, three LysM domains, and two chitin binding domains. FvLcp1 is a unique protein that harbors these domains amongst five representative Fusarium species. FvLcp1 is a secreted protein important for fumonisin production with the LysM domain playing a critical role. The chitin-binding domain was essential for in vitro chitin binding. Using Magnaporthe oryzae, we learned that FvLcp1 accumulates in appressoria, suggesting that FvLcp1 is involved in host recognition and infection. Full length FvLcp1 suppressed BAX-triggered plant cell death in Nicotiana benthamiana. This unique type-D LysM secreted protein with a chitin-binding domain in F. verticillioides was shown to be potentially involved in suppressing host cell death and promoting fumonisin biosynthesis while the pathogen colonizes maize kernels.

Signal and regulatory mechanisms involved in spore development of Phytophthora and Peronophythora

Oomycetes cause hundreds of destructive plant diseases, threatening agricultural production and food security. These fungus-like eukaryotes show multiple sporulation pattern including the production of sporangium, zoospore, chlamydospore and oospore, which are critical for their survival, dispersal and infection on hosts. Recently, genomic and genetic technologies have greatly promoted the study of molecular mechanism of sporulation in the genus Phytophthora and Peronophythora. In this paper, we characterize the types of asexual and sexual spores and review latest progress of these two genera. We summarize the genes encoding G protein, mitogen-activated protein kinase (MAPK) cascade, transcription factors, RNA-binding protein, autophagy-related proteins and so on, which function in the processes of sporangium production and cleavage, zoospore behaviors and oospore formation. Meanwhile, various molecular, chemical and electrical stimuli in zoospore behaviors are also discussed. Finally, with the molecular mechanism of sporulation in Phytophthora and Peronophythora is gradually being revealed, we propose some thoughts for the further research and provide the alternative strategy for plant protection against phytopathogenic oomycetes.