A carnitine–acylcarnitine carrier protein, MoCrc1, is essential for pathogenicity in Magnaporthe oryzae

Decarboxylase mediated oxalic acid metabolism is important to antioxidation and detoxification rather than pathogenicity in Magnaporthe oryzae

Oxalic acid (OA), an essential pathogenic factor, has been identified in several plant pathogens, and researchers are currently pursuing studies on interference with OA metabolism as a treatment for related diseases. However, the metabolic route in Magnaporthe oryzae remains unknown. In this study, we describe D-erythroascorbic acid-mediated OA synthesis and its metabolic and clearance pathways in rice blast fungus. By knocking out the D-arabino-1,4-lactone oxidase gene (Moalo1), one-third of oxalic acid remained in M. oryzae, indicating a main pathway for oxalic acid production. M. oryzae OxdC (MoOxdC) is an oxalate decarboxylase that appears to play a role in relieving oxalic acid toxicity. Loss of Mooxdc does not affect mycelial growth, conidiophore development, or appressorium formation in M. oryzae; however, the antioxidant and pathogenic abilities of the mutant were enhanced. This is owing to Mooxdc deletion upregulated a series of OA metabolic genes, including the oxalate oxidase gene (Mooxo) and Moalo1, as well as both OA transporter genes. Simultaneously, as feedback to the tricarboxylic acid (TCA) cycle, the decrease of formic acid in ΔMooxdc leads to the reduction of acetyl-CoA content, and two genes involved in the β-oxidation of fatty acids were also upregulated, which enhanced the fatty acid metabolism of the ΔMooxdc. Overall, this work reveals the role of OA in M. oryzae. We found that OA metabolism was mainly involved in the growth and development of M. oryzae, OA as a byproduct of D-erythroascorbic acid after removing H2O2, the OA-associated pathway ensures the TCA process and ATP supply.

Isoflavones extracted from Millettia pachyloba prevent the infection of the rice blast fungus by inhibiting its conidial germination and appressorium formation

BACKGROUND

The ascomycete Magnaporthe oryzae is a destructive phytopathogenic fungus that causes rice blast disease and can greatly reduce rice yields. Due to the widespread use of synthesized chemical fungicides and the frequent occurrence of fungicide resistance and environmental pollution as a result, it has become increasingly urgent to develop environmentally friendly biocontrol alternatives, including plant crude extracts.

RESULTS

In this study, the crude extracts of the tropical plant Millettia pachyloba were screened out and exhibited excellent preventive effects against M. oryzae at 200 μg mL-1. Bio-guided isolation of M. pachyloba was conducted and three isoflavonoids, rotenolone, durmillone, and durallone, whose chemical structures were determined using spectroscopic and spectrometric analyses, were obtained. The three isoflavonoids exhibited antifungal activities on conidial germination and appressorium formation in M. oryzae. Rotenolone had the strongest effect, with EC50 values of 57.81 μg mL-1 on conidial germination and 19.14 μg mL-1 on appressorium formation. Comparative metabolomics showed that differential metabolites were enriched in ABC transporter pathways and amino acid metabolic pathways when M. oryzae conidia were treated with rotenolone, suggesting that rotenolone interferes with amino acid transportation. Moreover, the M. pachyloba crude extract also effectively inhibited the infection of other fungal pathogens on tomato, apple, wheat, and maize.

CONCLUSION

The results suggest that isoflavones extracted from M. pachyloba prevent rice blast by inhibiting the infection-related morphogenesis of M. oryzae and may interfere with amino acid transport, demonstrating that M. pachyloba crude extract exhibits potential as a bio-fungicide for controlling fungal diseases in plants. © 2025 Society of Chemical Industry.

Transcriptional Landscapes of Long Non-coding RNAs and Alternative Splicing in Pyricularia oryzae Revealed by RNA-Seq

Pyricularia oryzae causes the rice blast, which is one of the most devastating crop diseases worldwide, and is a model fungal pathogen widely used for dissecting the molecular mechanisms underlying fungal virulence/pathogenicity. Although the whole genome sequence of P. oryzae is publicly available, its current transcriptomes remain incomplete, lacking the information on non-protein coding genes and alternative splicing. Here, we performed and analyzed RNA-Seq of conidia and hyphae, resulting in the identification of 3,374 novel genes. Interestingly, the vast majority of these novel genes likely transcribed long non-coding RNAs (lncRNAs), and most of them were localized in the intergenic regions. Notably, their expressions were concomitant with the transcription of neighboring genes thereof in conidia and hyphae. In addition, 2,358 genes were found to undergo alternative splicing events. Furthermore, we exemplified that a lncRNA was important for hyphal growth likely by regulating the neighboring protein-coding gene and that alternative splicing of the transcription factor gene CON7 was required for appressorium formation. In summary, results from this study indicate that lncRNA transcripts and alternative splicing events are two important mechanisms for regulating the expression of genes important for conidiation, hyphal growth, and pathogenesis, and provide new insights into transcriptomes and gene regulation in the rice blast fungus.

Prp19-associated splicing factor Cwf15 regulates fungal virulence and development in the rice blast fungus

The splicing factor Cwf15 is an essential component of the Prp19-associated component of the spliceosome and regulates intron splicing in several model species, including yeasts and human cells. However, the roles of Cwf15 remain unexplored in plant pathogenic fungi. Here, we report that MoCWF15 in the rice blast fungus Magnaporthe oryzae is non-essential to viability and important to fungal virulence, growth and conidiation. MoCwf15 contains a putative nuclear localization signal (NLS) and is localized into the nucleus. The NLS sequence but not the predicted phosphorylation site or two sumoylation sites was essential for the biological functions of MoCwf15. Importantly, MoCwf15 physically interacted with the Prp19-associated splicing factors MoCwf4, MoSsa1 and MoCyp1, and negatively regulated protein accumulations of MoCyp1 and MoCwf4. Furthermore, with the deletion of MoCWF15, aberrant intron splicing occurred in near 400 genes, 20 of which were important to the fungal development and virulence. Taken together, MoCWF15 regulates fungal growth and infection-related development by modulating the intron splicing efficiency of a subset of genes in the rice blast fungus.

Regulatory network of genes associated with stimuli sensing, signal transduction and physiological transformation of appressorium in Magnaporthe oryzae

Rice blast caused by Magnaporthe oryzae is the most destructive disease affecting the rice production (Oryza sativa), with an average global loss of 10-30% per annum. Recent reports have indicated that the fungus also inflicts blast disease on wheat (Triticum aestivum) posing a serious threat to the wheat production. Due to its easily detected infectious process and manoeuvrable genetic manipulation, M. oryzae is considered a model organism for exploring the molecular mechanism underlying fungal pathogenicity during the pathogen-host interaction. M. oryzae utilises an infectious structure called appressorium to breach the host surface by generating high turgor pressure. The appressorium development is induced by physical and chemical cues which are coordinated by the highly conserved cAMP/PKA, MAPK and calcium signalling cascades. Genes involved in the appressorium development have been identified and well studied in M. oryzae, a summary of the working gene network linking stimuli sensing and physiological transformation of appressorium is needed. This review provides a comprehensive discussion regarding the regulatory networks underlying appressorium development with particular emphasis on sensing of appressorium inducing stimuli, signal transduction, transcriptional regulation and the corresponding developmental and physiological responses. We also discussed the crosstalk and interaction of various pathways during the appressorium development.

Glutamate synthase MoGlt1-mediated glutamate homeostasis is important for autophagy, virulence and conidiation in the rice blast fungus

Glutamate homeostasis plays a vital role in central nitrogen metabolism and coordinates several key metabolic functions. However, its function in fungal pathogenesis and development has not been investigated in detail. In this study, we identified and characterized a glutamate synthase gene MoGLT1 in the rice blast fungus Magnaporthe oryzae that was important to glutamate homeostasis. MoGLT1 was constitutively expressed, but showed the highest expression level in appressoria. Deletion of MoGLT1 resulted in a significant reduction in conidiation and virulence. The ΔMoglt1 mutants were defective in appressorial penetration and the differentiation and spread of invasive hyphae in penetrated plant cells. The addition of exogenous glutamic acid partially rescued the defects of the ΔMoglt1 mutants in conidiation and plant infection. Assays for MoAtg8 expression and localization showed that the ΔMoglt1 mutants were defective in autophagy. The ΔMoglt1 mutants were delayed in the mobilization of glycogens and lipid bodies from conidia to developing appressoria. Taken together, our results show that glutamate synthase MoGlt1-mediated glutamate homeostasis is important for pathogenesis and development in the rice blast fungus, possibly via the regulation of autophagy.

The D-lactate dehydrogenase MoDLD1 is essential for growth and infection-related development in Magnaporthe oryzae

Rice blast disease caused by Magnaporthe oryzae is initiated by the attachment of conidia to plant surfaces. Germ tubes emerging from conidia develop melanized appressoria to physically penetrate the host surface. Previous studies revealed that appressorium development requires the breakdown of storage lipids and glycogen that occur in peroxisomes and the cytosol respectively, culminating in production of pyruvate. However, the downstream product(s) entering the mitochondria for further oxidation is unclear. In this study, we aimed to investigate the molecular basis underlying the metabolic flux towards the mitochondria associated with the infectious-related development in M. oryzae. We showed that D-lactate is a key intermediate metabolite of the mobilization of lipids and glycogen, and its oxidative conversion to pyruvate is catalysed by a mitochondrial D-lactate dehydrogenase MoDLD1. Deletion of MoDLD1 caused defects in conidiogenesis and appressorium formation, and subsequently the loss of fungal pathogenicity. Further analyses demonstrated that MoDLD1 activity is involved in the maintenance of redox homeostasis during conidial germination. Thus, MoDLD1 is a critical modulator that channels metabolite flow to the mitochondrion coupling cellular redox state, and contributes to development and virulence of M. oryzae.

Peroxisomal fission is induced during appressorium formation and is required for full virulence of the rice blast fungus

Peroxisomes are involved in various metabolic processes and are important for virulence in different pathogenic fungi. How peroxisomes rapidly emerge in the appressorium during fungal infection is poorly understood. Here, we describe a gene, PEF1, which can regulate peroxisome formation in the appressorium by controlling peroxisomal fission, and is required for plant infection in the rice blast fungus Magnaporthe oryzae. Targeted deletion of PEF1 resulted in a reduction in virulence and a delay in penetration and invasive growth in host cells. PEF1 was particularly expressed during appressorial development, and its encoding protein was co-localized with peroxisomes during appressorial development. Compared with the massive vesicle-shaped peroxisomes formed in the wild-type appressorium, the Δpef1 mutant could only form stringy linked immature peroxisomes, suggesting that PEF1 was involved in peroxisomal fission during appressorium formation. We also found that the Δpef1 mutant could not utilize fatty acids efficiently, which can improve significantly the expression level of PEF1 and induce peroxisomal fission. As expected, the Δpef1 mutant showed reduced intracellular production of reactive oxygen species (ROS) during appressorium formation and induced ROS accumulation in host cells during infection. Taken together, PEF1-mediated peroxisomal fission is important for fungal infection by controlling the number of peroxisomes in the appressorium.

An Ash1-Like Protein MoKMT2H Null Mutant Is Delayed for Conidium Germination and Pathogenesis in Magnaporthe oryzae

Ash1 is a known H3K36-specific histone demethylase that is required for normal Hox gene expression and fertility in Drosophila and mammals. However, little is known about the expression and function of the fungal ortholog of Ash1 in phytopathogenic fungus Magnaporthe oryzae. Here we report that MoKMT2H, an Ash1-like protein, is required for conidium germination and virulence in rice. We obtained MoKMT2H null mutant (ΔMoKMT2H) using a target gene replacement strategy. In the ΔMoKMT2H null mutants, global histone methyltransferase modifications (H3K4me3, H3K9me3, H3K27me3, and H3K36me2/3) of the genome were unaffected. The ΔMoKMT2H mutants showed no defect in vegetative hyphal growth, conidium morphology, conidiation, or disease lesion formation on rice leaves. However, the MoKMT2H deletion mutants were delayed for conidium germination and consequently had decreased virulence. Taken together, our results indicated that MoKMT2H plays an important role in conidium germination during appressorium formation in the rice blast fungus and perhaps other pathogenic plant fungi.

Roles of Peroxisomes in the Rice Blast Fungus

The rice blast fungus, Magnaporthe oryzae, is a model plant pathogenic fungus and is a severe threat to global rice production. Over the past two decades, it has been found that the peroxisomes play indispensable roles during M. oryzae infection. Given the importance of the peroxisomes for virulence, we review recent advances of the peroxisomes roles during M. oryzae infection processes. We firstly introduce the molecular mechanisms and life cycles of the peroxisomes. And then, metabolic functions related to the peroxisomes are also discussed. Finally, we provide an overview of the relationship between peroxisomes and pathogenicity.

Crosstalk between SNF1 pathway and the peroxisome-mediated lipid metabolism in Magnaporthe oryzae

The SNF1/AMPK pathway has a central role in response to nutrient stress in yeast and mammals. Previous studies on SNF1 function in phytopathogenic fungi mostly focused on the catalytic subunit Snf1 and its contribution to the derepression of cell wall degrading enzymes (CWDEs). However, the MoSnf1 in Magnaporthe oryzae was reported not to be involved in CWDEs regulation. The mechanism how MoSnf1 functions as a virulence determinant remains unclear. In this report, we demonstrate that MoSnf1 retains the ability to respond to nutrient-free environment via its participation in peroxisomal maintenance and lipid metabolism. Observation of GFP-tagged peroxisomal targeting signal-1 (PTS1) revealed that the peroxisomes of ΔMosnf1 were enlarged in mycelia and tended to be degraded before conidial germination, leading to the sharp decline of peroxisomal amount during appressorial development, which might impart the mutant great retard in lipid droplets mobilization and degradation. Consequently, ΔMosnf1 exhibited inability to maintain normal appressorial cell wall porosity and turgor pressure, which are key players in epidermal infection process. Exogenous glucose could partially restore the appressorial function and virulence of ΔMosnf1. Toward a further understanding of SNF1 pathway, the β-subunit MoSip2, γ-subunit MoSnf4, and two putative Snf1-activating kinases, MoSak1 and MoTos3, were additionally identified and characterized. Here we show the null mutants ΔMosip2 and ΔMosnf4 performed multiple disorders as ΔMosnf1 did, suggesting the complex integrity is essential for M. oryzae SNF1 kinase function. And the upstream kinases, MoSak1 and MoTos3, play unequal roles in SNF1 activation with a clear preference to MoSak1 over MoTos3. Meanwhile, the mutant lacking both of them exhibited a severe phenotype comparable to ΔMosnf1, uncovering a cooperative relationship between MoSak1 and MoTos3. Taken together, our data indicate that the SNF1 pathway is required for fungal development and facilitates pathogenicity by its contribution to peroxisomal maintenance and lipid metabolism in M. oryzae.

Pleiotropic function of the putative zinc-finger protein MoMsn2 in Magnaporthe oryzae

The mitogen-activated protein kinase MoOsm1-mediated osmoregulation pathway plays crucial roles in stress responses, asexual and sexual development, and pathogenicity in Magnaporthe oryzae. Utilizing an affinity purification approach, we identified the putative transcriptional activator MoMsn2 as a protein that interacts with MoOsm1 in vivo. Disruption of the MoMSN2 gene resulted in defects in aerial hyphal growth, conidial production, and infection of host plants. Quantitative reverse transcription-polymerase chain reaction analysis showed that the expression of several genes involved in conidiophore formation was reduced in ΔMomsn2, suggesting that MoMsn2 might function as a transcriptional regulator of these genes. Subsequently, MoCos1 was identified as one of the MoMsn2 targets through yeast one-hybrid analysis in which MoMsn2 binds to the AGGGG and CCCCT motif of the MoCOS1 promoter region. Phenotypic characterization showed that MoMsn2 was required for appressorium formation and penetration and pathogenicity. Although the ΔMomsn2 mutant was tolerant to the cell-wall stressor Calcofluor white, it was sensitive to common osmotic stressors. Further analysis suggests that MoMsn2 is involved in the regulation of the cell-wall biosynthesis pathway. Finally, transcriptome data revealed that MoMsn2 modulates numerous genes participating in conidiation, infection, cell-wall integrity, and stress response. Collectively, our results led to a model in which MoMsn2 mediates a series of downstream genes that control aerial hyphal growth, conidiogenesis, appressorium formation, cell-wall biosynthesis, and infection and that also offer potential targets for the development of new disease management strategies.

N-glycosylation of effector proteins by an α-1,3-mannosyltransferase is required for the rice blast fungus to evade host innate immunity

Plant pathogenic fungi deploy secreted effectors to suppress plant immunity responses. These effectors operate either in the apoplast or within host cells, so they are putatively glycosylated, but the posttranslational regulation of their activities has not been explored. In this study, the ASPARAGINE-LINKED GLYCOSYLATION3 (ALG3)-mediated N-glycosylation of the effector, Secreted LysM Protein1 (Slp1), was found to be essential for its activity in the rice blast fungus Magnaporthe oryzae. ALG3 encodes an α-1,3-mannosyltransferase for protein N-glycosylation. Deletion of ALG3 resulted in the arrest of secondary infection hyphae and a significant reduction in virulence. We observed that Δalg3 mutants induced massive production of reactive oxygen species in host cells, in a similar manner to Δslp1 mutants, which is a key factor responsible for arresting infection hyphae of the mutants. Slp1 sequesters chitin oligosaccharides to avoid their recognition by the rice (Oryza sativa) chitin elicitor binding protein CEBiP and the induction of innate immune responses, including reactive oxygen species production. We demonstrate that Slp1 has three N-glycosylation sites and that simultaneous Alg3-mediated N-glycosylation of each site is required to maintain protein stability and the chitin binding activity of Slp1, which are essential for its effector function. These results indicate that Alg3-mediated N-glycosylation of Slp1 is required to evade host innate immunity.

Cells in cells: morphogenetic and metabolic strategies conditioning rice infection by the blast fungus Magnaporthe oryzae

The rice blast fungus Magnaporthe oryzae is a global food security threat due to its destruction of cultivated rice. Of the world's rice harvest, 10-30 % is lost each year to this pathogen, and changing climates are likely to favor its spread into new areas. Insights into how the fungus might be contained could come from the wealth of molecular and cellular studies that have been undertaken in order to shed light on the biological underpinnings of blast disease, aspects of which we review herein. Infection begins when a three-celled spore lands on the surface of a leaf, germinates, and develops the specialized infection structure called the appressorium. The mature appressorium develops a high internal turgor that acts on a thin penetration peg, forcing it through the rice cuticle and into the underlying epidermal cells. Primary then invasive hyphae (IH) elaborate from the peg and grow asymptomatically from one living rice cell to another for the first few days of infection before host cells begin to die and characteristic necrotic lesions form on the surface of the leaf, from which spores are produced to continue the life cycle. To gain new insights into the biology of rice blast disease, we argue that, conceptually, the infection process can be viewed as two discrete phases occurring in markedly different environments and requiring distinct biochemical pathways and morphogenetic regulation: outside the host cell, where the appressorium develops in a nutrient-free environment, and inside the host cell, where filamentous growth occurs in a glucose-rich, nitrogen-poor environment, at least from the perspective of the fungus. Here, we review the physiological and metabolic changes that occur in M. oryzae as it transitions from the surface to the interior of the host, thus enabling us to draw lessons about the strategies that allow M. oryzae cells to thrive in rice cells.

Function of peroxisomes in plant-pathogen interactions

Peroxisomes are ubiquitous organelles of eukaryotic cells that accomplish a variety of biochemical functions, including β-oxidation of fatty acids, glyoxylate cycle, etc. Many reports have been accumulating that indicate peroxisome related metabolic functions are essential for pathogenic development of plant pathogenic fungi. They include peroxisome biogenesis proteins, peroxins and preferential destruction of peroxisomes, pexophagy. Gene disrupted mutants of anthracnose disease pathogen Colletotrichum orbiculare or rice blast pathogen Magnaporthe oryzae defective in peroxins or pexophagy showed deficiency in pathogenesis. Woronin body, a peroxisome related cellular organelle that is related to endurance of fungal cells against environmental damage has essential roles in pathogenesis of M. oryzae. Also, peroxisome related metabolisms such as β-oxidation and glyoxylate cycle are essential for pathogenesis in several plant pathogenic fungi. In addition, secondary metabolisms including polyketide melanin biosynthesis of C. orbiculare and M. oryzae, and host selective toxins produced by necrotrophic pathogen Alternaria alternata have pivotal roles in fungal pathogenesis. Every such factor was listed and their functions for pathogenesis were demonstrated (Table 18.1 and Fig. 18.1).

A serine/threonine-protein phosphatase PP2A catalytic subunit is essential for asexual development and plant infection in Magnaporthe oryzae

Protein phosphatase 2A is a subgroup of widely conserved serine/threonine phosphatases and plays diverse roles in transcription, translation, differentiation, cell cycle, and signal transduction in many organisms. However, its roles in biotrophic and hemi-biotrophic phytopathogenic fungi remain to be investigated. In this study, we isolated an insertional mutant of the rice blast fungus Magnaporthe oryzae that was defective in vegetative hyphal growth. In the mutant, the T-DNA fragment was found to be inserted in the promoter region of a putative serine/threonine protein phosphatase 2A catalytic subunit (PP2Ac) gene MoPPG1. Deletion of MoPPG1 leads to severe defects in vegetative hyphal growth and conidiation. Conidia of the ∆Moppg1 null mutants were misshaped, and most of them were two-celled. The deletion mutants of MoPPG1 did not penetrate into host plant cells and failed to cause any disease lesions on rice leaves. Interestingly, significant reduction was found in the ∆Moppg1 null mutants in expression levels of several Rho GTPase family genes including MgCDC42, MgRHO3, and MgRAC1, which were important for pathogenesis of M. oryzae. Taken together, our results indicated that PP2Ac plays vital roles in asexual development and plant infection by regulating Rho GTPases in the rice blast fungus and perhaps other plant pathogenic fungi.