Pleiotropic roles of O-mannosyltransferase MoPmt4 in development and pathogenicity of Magnaporthe oryzae

O-Mannosyltransferase CfPmt4 Regulates the Growth, Development and Pathogenicity of Colletotrichum fructicola

Camellia oleifera is a woody, edible-oil plant native to China. Anthracnose is the major disease of Ca. oleifera, and Colletotrichum fructicola is the main epidemic pathogen. Our previous research indicated that CfHac1 (homologous to ATF/CREB1) and CfGcn5 (general control nonderepressible 5, Gcn5) are integral to key cellular processes that govern fungal development and pathogenesis. Further transcriptomic analyses of the CfHac1 and CfGcn5 mutants, particularly under conditions of endoplasmic reticulum (ER) stress, hold the potential to unveil additional genes implicated in this critical cellular response. We identified all OST/PMT (oligosaccharyltransferase/Protein O-Mannosyltransferases) genes in C. fructicola and analyzed their expression levels. To elucidate novel glycosylation-related genes that may be important for the virulence of C. fructicola, we took an unbiased transcriptomic approach comparing wild-type and the ∆Cfhac1 mutant. Notably, all OST/PMT genes were induced by dithiothreitol and down-regulated in the ΔCfhac1 mutant, yet only the CfPMT4 (Protein O-Mannosyltransferases 4) gene (A04626) was unaffected in the ΔCfgcn5. The results of targeted gene deletion experiments indicate that CfPMT4 plays a crucial role in both vegetative growth and conidiation. Additionally, our investigation revealed that the ΔCfpmt4 exhibits deficiencies in appressorium formation, as well as in its response to cell wall integrity and endoplasmic reticulum stresses. Furthermore, the mutant displayed impaired glycogen metabolism, which may contribute to reduced penetration ability. Overall, CfPmt4, an O-mannosyltransferase, controls the growth, development, and pathogenicity of Colletotrichum fructicola. Understanding the function of the CfPMT4 homolog could provide a potential molecular target for controlling Ca. oleifera anthracnose.

Effector secretion and stability in the maize anthracnose pathogen Colletotrichum graminicola requires N-linked protein glycosylation and the ER chaperone pathway

N-linked protein glycosylation is a conserved and essential modification mediating protein processing and quality control in the endoplasmic reticulum (ER), but how this contributes to the infection cycle of phytopathogenic fungi is largely unknown. In this study, we discovered that inhibition of protein N-glycosylation severely affected vegetative growth, hyphal tip development, conidial germination, appressorium formation, and, ultimately, the ability of the maize (Zea mays) anthracnose pathogen Colletotrichum graminicola to infect its host. Quantitative proteomics analysis showed that N-glycosylation can coordinate protein O-glycosylation, glycosylphosphatidylinositol anchor modification, and endoplasmic reticulum quality control (ERQC) by directly targeting the proteins from the corresponding pathway in the ER. We performed a functional study of the N-glycosylation pathway-related protein CgALG3 and of the ERQC pathway-related protein CgCNX1, which demonstrated that N-glycosylation of ER chaperone proteins is essential for effector stability, secretion, and pathogenicity of C. graminicola. Our study provides concrete evidence for the regulation of effector protein stability and secretion by N-glycosylation.

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

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

Extension of O-Linked Mannosylation in the Golgi Apparatus Is Critical for Cell Wall Integrity Signaling and Interaction with Host Cells in Cryptococcus neoformans Pathogenesis

The human-pathogenic yeast Cryptococcus neoformans assembles two types of O-linked glycans on its proteins. In this study, we identified and functionally characterized the C. neoformans CAP6 gene, encoding an α1,3-mannosyltransferase responsible for the second mannose addition to minor O-glycans containing xylose in the Golgi apparatus. Two cell surface sensor proteins, Wml1 (WSC/Mid2-like) and Wml2, were found to be independent substrates of Cap6-mediated minor or Ktr3-mediated major O-mannosylation, respectively. The double deletion of KTR3 and CAP6 (ktr3Δ cap6Δ) completely blocked the mannose addition at the second position of O-glycans, resulting in the accumulation of proteins with O-glycans carrying only a single mannose. Tunicamycin (TM)-induced phosphorylation of the Mpk1 mitogen-activated protein kinase (MAPK) was greatly decreased in both ktr3Δ cap6Δ and wml1Δ wml2Δ strains. Transcriptome profiling of the ktr3Δ cap6Δ strain upon TM treatment revealed decreased expression of genes involved in the Mpk1-dependent cell wall integrity (CWI) pathway. Consistent with its defective growth under several stress conditions, the ktr3Δ cap6Δ strain was avirulent in a mouse model of cryptococcosis. Associated with this virulence defect, the ktr3Δ cap6Δ strain showed decreased adhesion to lung epithelial cells, decreased proliferation within macrophages, and reduced transcytosis of the blood-brain barrier (BBB). Notably, the ktr3Δ cap6Δ strain showed reduced induction of the host immune response and defective trafficking of ergosterol, an immunoreactive fungal molecule. In conclusion, O-glycan extension in the Golgi apparatus plays critical roles in various pathobiological processes, such as CWI signaling and stress resistance and interaction with host cells in C. neoformans. IMPORTANCE Cryptococcus neoformans assembles two types of O-linked glycans on its surface proteins, the more abundant major O-glycans that do not contain xylose residues and minor O-glycans containing xylose. Here, we demonstrate the role of the Cap6 α1,3-mannosyltransferase in the synthesis of minor O-glycans. Previously proposed to be involved in capsule biosynthesis, Cap6 works with the related Ktr3 α1,2-mannosyltransferase to synthesize O-glycans on their target proteins. We also identified two novel C. neoformans stress sensors that require Ktr3- and Cap6-mediated posttranslational modification for full function. Accordingly, the ktr3Δ cap6Δ double O-glycan mutant strain displays defects in stress signaling pathways, CWI, and ergosterol trafficking. Furthermore, the ktr3Δ cap6Δ strain is completely avirulent in a mouse infection model. Together, these results demonstrate critical roles for O-glycosylation in fungal pathogenesis. As there are no human homologs for Cap6 or Ktr3, these fungus-specific mannosyltransferases are novel targets for antifungal therapy.

Endoplasmic reticulum membrane protein MoScs2 is important for asexual development and pathogenesis of Magnaporthe oryzae

Most secretory proteins are folded and modified in the endoplasmic reticulum (ER). In Saccharomyces cerevisiae, the absence of Scs2 protein will lead to the separation of the endoplasmic reticulum and plasma membrane, resulting in endoplasmic reticulum dysfunction, but its function is not clear in rice blast fungus or even filamentous fungus. In this study, we report the identification and characterization of MoSCS2 in the pathogenesis of the rice blast fungus Magnaporthe oryzae. Protein subcellular localization showed that MoSCS2 is mainly localized in the endoplasmic reticulum. Compared to the wild-type strain Guy11, the deletion mutant ΔMoscs2 showed a significant reduction in growth and conidiation. MoSCS2 deficiency also resulted in abnormal conidial morphology and septum formation. The ΔMoscs2 mutant shows delayed appressorium formation, and the appressorium of ΔMoscs2 mutant could not form huge turgor pressure to penetrate the host epidermal cell wall. Pathogenicity and plant leave infection assays showed that knockout of MoSCS2 significantly inhibited the expansion of the invasive hyphae in host cells, ultimately leading to the decline of pathogenicity. Moreover, MoSCS2 gene is also involved in the regulation of cell wall and endoplasmic reticulum stress response. In conclusion, MoSCS2 plays an important role in the growth, asexual production, conidia morphogenesis, infection-related morphogenesis and pathogenicity of M. oryzae.

Comparative Secretome Analysis of Magnaporthe oryzae Identified Proteins Involved in Virulence and Cell Wall Integrity

Plant fungal pathogens secrete numerous proteins into the apoplast at the plant-fungus contact sites to facilitate colonization. However, only a few secretory proteins were functionally characterized in Magnaporthe oryzae, the fungal pathogen causing rice blast disease worldwide. Asparagine-linked glycosylation 3 (Alg3) is an α-1,3-mannosyltransferase functioning in the N-glycan synthesis of N-glycosylated secretory proteins. Fungal pathogenicity and cell wall integrity are impaired in Δalg3 mutants, but the secreted proteins affected in Δalg3 mutants are largely unknown. In this study, we compared the secretomes of the wild-type strain and the Δalg3 mutant and identified 51 proteins that require Alg3 for proper secretion. These proteins were predicted to be involved in metabolic processes, interspecies interactions, cell wall organization, and response to chemicals. Nine proteins were selected for further validation. We found that these proteins were localized at the apoplastic region surrounding the fungal infection hyphae. Moreover, the N-glycosylation of these proteins was significantly changed in the Δalg3 mutant, leading to the decreased protein secretion and abnormal protein localization. Furthermore, we tested the biological functions of two genes, INV1 (encoding invertase 1, a secreted invertase) and AMCase (encoding acid mammalian chinitase, a secreted chitinase). The fungal virulence was significantly reduced, and the cell wall integrity was altered in the Δinv1 and Δamcase mutant strains. Moreover, the N-glycosylation was essential for the function and secretion of AMCase. Taken together, our study provides new insight into the role of N-glycosylated secretory proteins in fungal virulence and cell wall integrity.

Genome-Wide Identification and Expression Analysis of the Basic Leucine Zipper (bZIP) Transcription Factor Gene Family in Fusarium graminearum

The basic leucine zipper (bZIP) is a widely found transcription factor family that plays regulatory roles in a variety of cellular processes including cell growth and development and various stress responses. However, the bZIP gene family has not been well studied at a genome-wide scale in Fusarium graminearum (Fg), a potent pathogen of cereal grains. In the present study, we conducted a genome-wide identification, characterization, and expression profiling of 22 F. graminearum bZIP (FgbZIP) genes at different developmental stages and under various abiotic stresses. All identified FgbZIPs were categorized into nine groups based on their sequence similarity and phylogenetic tree analysis. Furthermore, the gene structure analysis, conserved motif analysis, chromosomal localization, protein network studies, and synteny analysis were performed. The symmetry of the exon and intron varied with the phylogenetic groups. The post-translational modifications (PTMs) analysis also predicted several phosphorylation sites in FgbZIPs, indicating their functional diversity in cellular processes. The evolutionary study identified many orthogroups among eight species and also predicted several gene duplication events in F. graminearum. The protein modeling indicated the presence of a higher number of α-helices and random coils in their structures. The expression patterns of FgbZIP genes showed that 5 FgbZIP genes, including FgbZIP_1.1, FgbZIP_1.3, FgbZIP_2.6 FgbZIP_3.1 and FgbZIP_4.3, had high expression at different growth and conidiogenesis stages. Similarly, eight genes including FgbZIP_1.1, FgbZIP_1.6, FgbZIP_2.3, FgbZIP_2.4, FgbZIP_4.1, FgbZIP_4.2, FgbZIP_4.3 and FgbZIP_4.6 demonstrated their putative role in response to various abiotic stresses. In summary, these results provided basic information regarding FgbZIPs which are helpful for further functional analysis.

Protein O-mannosylation across kingdoms and related diseases: From glycobiology to glycopathology

The post-translational glycosylation of proteins by O-linked α-mannose is conserved from bacteria to humans. Due to advances in high-throughput mass spectrometry-based approaches, a variety of glycoproteins are identified to be O-mannosylated. Various proteins with O-mannosylation are involved in biological processes, providing essential necessity for proper growth and development. In this review, we summarize the process and regulation of O-mannosylation. The multi-step O-mannosylation procedures are quite dynamic and complex, especially when considering the structural and functional inspection of the involved enzymes. The widely studied O-mannosylated proteins in human include α-Dystroglycan (α-DG), cadherins, protocadherins, and plexin, and their aberrant O-mannosylation are associated with many diseases. In addition, O-mannosylation also contributes to diverse functions in lower eukaryotes and prokaryotes. Finally, we present the relationship between O-mannosylation and gut microbiota (GM), and elucidate that O-mannosylation in microbiome is of great importance in the dynamic balance of GM. Our study provides an overview of the processes of O-mannosylation in mammalian cells and other organisms, and also associated regulated enzymes and biological functions, which could contribute to the understanding of newly discovered O-mannosylated glycoproteins.

Emerging Roles of Posttranslational Modifications in Plant-Pathogenic Fungi and Bacteria

Posttranslational modifications (PTMs) play crucial roles in regulating protein function and thereby control many cellular processes and biological phenotypes in both eukaryotes and prokaryotes. Several recent studies illustrate how plant fungal and bacterial pathogens use these PTMs to facilitate development, stress response, and host infection. In this review, we discuss PTMs that have key roles in the biological and infection processes of plant-pathogenic fungi and bacteria. The emerging roles of PTMs during pathogen-plant interactions are highlighted. We also summarize traditional tools and emerging proteomics approaches for PTM research. These discoveries open new avenues for investigating the fundamental infection mechanisms of plant pathogens and the discovery of novel strategies for plant disease control.

Protein glycosylation during infection by plant pathogenic fungi

Glycosylation is a conserved set of post-translational modifications that exists in all eukaryotic cells. During the last decade, the role of glycosylation in plant pathogenic fungi has received significant attention and considerable progress has been made especially in Ustilago maydis and Magnaporthe oryzae. Here, we review recent advances in our understanding of the role of N-glycosylation, O-glycosylation and glycosylphosphatidylinositol (GPI) anchors during plant infection by pathogenic fungi. We highlight the roles of these processes in regulatory mechanisms associated with appressorium formation, host penetration, biotrophic growth and immune evasion. We argue that improved knowledge of glycosylation pathways and the impact of these modifications on fungal pathogenesis is overdue and could provide novel strategies for disease control.

Structural, Evolutionary, and Functional Analysis of the Protein O-Mannosyltransferase Family in Pathogenic Fungi

Protein O-mannosyltransferases (Pmts) comprise a group of proteins that add mannoses to substrate proteins at the endoplasmic reticulum. This post-translational modification is important for the faithful transfer of nascent glycoproteins throughout the secretory pathway. Most fungi genomes encode three O-mannosyltransferases, usually named Pmt1, Pmt2, and Pmt4. In pathogenic fungi, Pmts, especially Pmt4, are key factors for virulence. Although the importance of Pmts for fungal pathogenesis is well established in a wide range of pathogens, questions remain regarding certain features of Pmts. For example, why does the single deletion of each pmt gene have an asymmetrical impact on host colonization? Here, we analyse the origin of Pmts in fungi and review the most important phenotypes associated with Pmt mutants in pathogenic fungi. Hence, we highlight the enormous relevance of these glycotransferases for fungal pathogenic development.

Comparative Genomic Data Provide New Insight on the Evolution of Pathogenicity in Sporothrix Species

Sporothrix species are commonly isolated from environmental and clinical samples. As common causes of zoonotic mycosis, Sporothrix species may result in localized or disseminated infections, posing considerable threat to animal and human health. However, the pathogenic profiles of different Sporothrix species varied, in virulence, geographic location and host ranges, which have yet to be explored. Analysing the genomes of Sporothrix species are useful for understanding their pathogenicity. In this study, we analyzed the whole genome of 12 Sporothrix species and six S. globosa isolates from different clinical samples in China. By combining comparative analyses with Kyoto Encyclopedia of Genes and Genomes (KEGG), Carbohydrate-Active enZymes (CAZy), antiSMASH, Pfam, and PHI annotations, Sporothrix species showed exuberant primary and secondary metabolism processes. The genome sizes of four main clinical species, i.e., S. brasiliensis, S. schenckii, S. globosa, and S. luriei were significantly smaller than other environmental and clinical Sporothrix species. The contracted genes included mostly CAZymes and peptidases genes that were usually associated with the decay of plants, as well as the genes that were associated with the loss of pathogenicity and the reduced virulence. Our results could, to some extent, explain a habitat shift of Sporothrix species from a saprobic life in plant materials to a pathogenic life in mammals and the increased pathogenicity during the evolution. Gene clusters of melanin and clavaric acid were identified in this study, which improved our understanding on their pathogenicity and possible antitumor effects. Moreover, our analyses revealed no significant genomic variations among different clinical isolates of S. globosa from different regions in China.

PoMet3 and PoMet14 associated with sulfate assimilation are essential for conidiogenesis and pathogenicity in Pyricularia oryzae

Pyricularia oryzae is the causal agent of blast disease on staple gramineous crops. Sulphur is an essential element for the biosynthesis of cysteine and methionine in fungi. Here, we targeted the P. oryzae PoMET3 encoding the enzyme ATP sulfurylase, and PoMET14 encoding the APS (adenosine-5'-phosphosulphate) kinase that are involved in sulfate assimilation and sulphur-containing amino acids biosynthesis. In P. oryzae, deletion of PoMET3 or PoMET14 separately results in defects of conidiophore formation, significant impairments in conidiation, methionine and cysteine auxotrophy, limited invasive hypha extension, and remarkably reduced virulence on rice and barley. Furthermore, the defects of the null mutants could be restored by supplementing with exogenous cysteine or methionine. Our study explored the biological functions of sulfur assimilation and sulphur-containing amino acids biosynthesis in P. oryzae.

Quantitative proteomics analysis reveals important roles of N-glycosylation on ER quality control system for development and pathogenesis in Magnaporthe oryzae

Genetic studies have shown essential functions of N-glycosylation during infection of the plant pathogenic fungi, however, systematic roles of N-glycosylation in fungi is still largely unknown. Biological analysis demonstrated N-glycosylated proteins were widely present at different development stages of Magnaporthe oryzae and especially increased in the appressorium and invasive hyphae. A large-scale quantitative proteomics analysis was then performed to explore the roles of N-glycosylation in M. oryzae. A total of 559 N-glycosites from 355 proteins were identified and quantified at different developmental stages. Functional classification to the N-glycosylated proteins revealed N-glycosylation can coordinate different cellular processes for mycelial growth, conidium formation, and appressorium formation. N-glycosylation can also modify key components in N-glycosylation, O-glycosylation and GPI anchor pathways, indicating intimate crosstalk between these pathways. Interestingly, we found nearly all key components of the endoplasmic reticulum quality control (ERQC) system were highly N-glycosylated in conidium and appressorium. Phenotypic analyses to the gene deletion mutants revealed four ERQC components, Gls1, Gls2, GTB1 and Cnx1, are important for mycelial growth, conidiation, and invasive hyphal growth in host cells. Subsequently, we identified the Gls1 N-glycosite N497 was important for invasive hyphal growth and partially required for conidiation, but didn’t affect colony growth. Mutation of N497 resulted in reduction of Gls1 in protein level, and localization from ER into the vacuole, suggesting N497 is important for protein stability of Gls1. Our study showed a snapshot of the N-glycosylation landscape in plant pathogenic fungi, indicating functions of this modification in cellular processes, developments and pathogenesis.

The fungal pathogen Magnaporthe oryzae can cause rice blast and wheat blast diseases, which threatens worldwide food production. During infection, M. oryzae follows a sequence of distinct developmental stages adapted to survival and invasion of the host environment. M. oryzae attaches onto the host by the conidium, and then develops an appressorium to breach the host cuticle. After penetrating, it forms invasive hyphae to quickly spread in the host cells. Numerous genetic studies have focused on the mechanisms underlying each step in the infection process, but systemic approaches are needed for a broader, integrated understanding of regulatory events during M. oryzae pathogenesis. Many infection-related signaling events are regulated through post-translational protein modifications within the pathogen. N-linked glycosylation, in which a glycan moiety is added to the amide group of an asparagine residue, is an abundant modification known to be essential for M. oryzae infection. In this study, we employed a quantitative proteomics analysis to unravel the overall regulatory mechanisms of N-glycosylation at different developmental stages of M. oryzae. We detected changes in N-glycosylation levels at 559 glycosylated residues (N-glycosites) in 355 proteins during different stages, and determined that the ER quality control system is elaborately regulated by N-glycosylation. The insights gained will help us to better understand the regulatory mechanisms of infection in pathogenic fungi. These findings may be also important for developing novel strategies for fungal disease control.

Effects of Elevated Root-Zone CO2 on Root Morphology and Nitrogen Metabolism Revealed by Physiological and Transcriptome Analysis in Oriental Melon Seedling Roots

Rhizosphere CO2 is vital for crop growth, development, and productivity. However, the mechanisms of plants' responses to root-zone CO2 are unclear. Oriental melons are sensitive to root-zone gas, often encountering high root-zone CO2 during cultivation. We investigated root growth and nitrogen metabolism in oriental melons under T1 (0.5%) and T2 (1.0%) root-zone CO2 concentrations using physiology and comparative transcriptome analysis. T1 and T2 increased root vigor and the nitrogen content in the short term. With increased treatment time and CO2 concentration, root inhibition increased, characterized by decreased root absorption, incomplete root cell structure, accelerated starch accumulation and hydrolysis, and cell aging. We identified 1280 and 1042 differentially expressed genes from T1 and T2, respectively, compared with 0.037% CO2-grown plants. Among them, 683 co-expressed genes are involved in stress resistance and nitrogen metabolism (enhanced phenylpropanoid biosynthesis, hormone signal transduction, glutathione metabolism, and starch and sucrose metabolism). Nitrogen metabolism gene expression, enzyme activity, and nitrogen content analyses showed that short-term elevated root-zone CO2 mainly regulated plant nitrogen metabolism post-transcriptionally, and directly inhibited it transcriptionally in the long term. These findings provided a basis for further investigation of nitrogen regulation by candidate genes in oriental melons under elevated root-zone CO2.

The putative deubiquitinating enzyme MoUbp4 is required for infection-related morphogenesis and pathogenicity in the rice blast fungus Magnaporthe oryzae

Ubiquitination is a key regulatory mechanism that affects numerous important biological processes, including cellular differentiation and pathogenesis in eukaryotic cells. Attachment of proteins to ubiquitin is reversed by specialized proteases, deubiquitinating enzymes (DUBs), which are essential for precursor processing, maintaining ubiquitin homeostasis and promoting protein degradation by recycling ubiquitins. Here, we report the identification of a novel non-pathogenic T-DNA-tagged mutant T612 of Magnaporthe oryzae with a single insertion in the second exon of MoUBP4, which encodes a putative ubiquitin carboxyl-terminal hydrolase. Targeted gene deletion mutants of MoUBP4 are significantly reduced in mycelial growth, conidiation, and increased in tolerance to SDS and CR (Congo red) cell-wall damage. The ΔMoubp4 mutants are blocked in penetration and invasive growth, which results in the loss of pathogenicity. Many conidia produced by the ΔMoubp4 mutants are unable to form appressoria and mobilization and degradation of glycogen and lipid droplets are significantly delayed. Moreover, immunohybridization analysis revealed that total protein ubiquitination levels of the null mutants were significantly increased, indicating that MoUbp4 functions as a deubiquitination enzyme. Taken together, we conclude that MoUbp4 is required for deubiquitination, infection-related morphogenesis and pathogenicity in M. oryzae.

N-glycosylation of the protein disulfide isomerase Pdi1 ensures full Ustilago maydis virulence

Fungal pathogenesis depends on accurate secretion and location of virulence factors which drive host colonization. Protein glycosylation is a common posttranslational modification of cell wall components and other secreted factors, typically required for correct protein localization, secretion and function. Thus, the absence of glycosylation is associated with animal and plant pathogen avirulence. While the relevance of protein glycosylation for pathogenesis has been well established, the main glycoproteins responsible for the loss of virulence observed in glycosylation-defective fungi have not been identified. Here, we devise a proteomics approach to identify such proteins and use it to demonstrate a role for the highly conserved protein disulfide isomerase Pdi1 in virulence. We show that efficient Pdi1 N-glycosylation, which promotes folding into the correct protein conformation, is required for full pathogenic development of the corn smut fungus Ustilago maydis. Remarkably, the observed virulence defects are reminiscent of those seen in glycosylation-defective cells suggesting that the N-glycosylation of Pdi1 is necessary for the full secretion of virulence factors. All these observations, together with the fact that Pdi1 protein and RNA expression levels rise upon virulence program induction, suggest that Pdi1 glycosylation is important for normal pathogenic development in U. maydis. Our results provide new insights into the role of glycosylation in fungal pathogenesis.

MoGT2 Is Essential for Morphogenesis and Pathogenicity of Magnaporthe oryzae

The ascomycete fungus Magnapothe oryzae is the causal agent of rice blast disease, leading to severe loss in cultivated rice production worldwide. In this study, we identified a conserved type 2 glycosyltransferase named MoGt2 in M. oryzae. The mogt2Δ targeted gene deletion mutants exhibited pleiotropic defects in vegetative growth, conidiation, stress response, hyphal appressorium-mediated penetration, and pathogenicity. Furthermore, conserved glycosyltransferase domains are critical for MoGt2 function. The comparative transcriptome analysis revealed potential target genes under MoGt2 regulation in M. oryzae conidiation. Identification of potential glycoproteins modified by MoGt2 provided information on its regulatory mechanism of gene expression and biological functions. Overall, our study represents the first report of type 2 glycosyltransferase function in M. oryzae infection-related morphogenesis and pathogenesis.

Magnaporthe oryzae causes the rice blast disease, which is one of the most serious diseases of cultivated rice worldwide. Glycosylation is an important posttranslational modification of secretory and membrane proteins in all eukaryotes, catalyzed by glycosyltransferases (GTs). In this study, we identified and characterized a type 2 glycosyltransferase, MoGt2, in M. oryzae. Targeted gene deletion mutants of MoGT2 (mogt2Δ strains) were nonpathogenic and were impaired in vegetative growth, conidiation, and appressorium formation at hyphal tips. Moreover, MoGT2 plays an important role in stress tolerance and hydrophobin function of M. oryzae. Site-directed mutagenesis analysis showed that conserved glycosyltransferase domains (DxD and QxxRW) are critical for biological functions of MoGt2. MoGT2 deletion led to altered glycoproteins during M. oryzae conidiation. By liquid chromatography-tandem mass spectrometry (LC-MS/MS), we identified several candidate proteins as potential substrates of MoGt2, including several heat shock proteins, two coiled-coil domain-containing proteins, aminopeptidase 2, and nuclease domain-containing protein 1. On the other hand, we found that a conidiation-related gene, genes involved in various metabolism pathways, and genes involved in cell wall integrity and/or osmotic response were differentially regulated in the mogt2Δ mutant, which may potentially contribute to its condiation defects. Taken together, our results show that MoGt2 is important for infection-related morphogenesis and pathogenesis in M. oryzae.

IMPORTANCE The ascomycete fungus Magnapothe oryzae is the causal agent of rice blast disease, leading to severe loss in cultivated rice production worldwide. In this study, we identified a conserved type 2 glycosyltransferase named MoGt2 in M. oryzae. The mogt2Δ targeted gene deletion mutants exhibited pleiotropic defects in vegetative growth, conidiation, stress response, hyphal appressorium-mediated penetration, and pathogenicity. Furthermore, conserved glycosyltransferase domains are critical for MoGt2 function. The comparative transcriptome analysis revealed potential target genes under MoGt2 regulation in M. oryzae conidiation. Identification of potential glycoproteins modified by MoGt2 provided information on its regulatory mechanism of gene expression and biological functions. Overall, our study represents the first report of type 2 glycosyltransferase function in M. oryzae infection-related morphogenesis and pathogenesis.

The P5-type ATPase Spf1 is required for development and virulence of the rice blast fungus Pyricularia oryzae

Pyricularia oryzae (synonym Magnaporthe oryzae) is a plant pathogen causing major yield losses in cultivated rice and wheat. The P-type ATPases play important roles in cellular processes of fungi, plants, and animals via transporting specific substrates through ATP hydrolysis. Here, we characterized the roles of a P5-ATPase, Spf1, in the development and virulence of P. oryzae. Deletion of SPF1 led to decreased hyphal growth and conidiation, delayed spore germination and appressorium formation, reduced penetration and invasive hyphal extension, and attenuated virulence. Appressorium turgor, however, was not affected by deletion of SPF1. The co-localization of Spf1-GFP and an endoplasmic reticulum (ER) marker protein, Lhs1-DsRed2, indicated that Spf1 is an ER-localized P5-ATPase. An ER stress factor, 0.5 μg/ml tunicamycin (TUNI), inhibited the growth of ∆spf1, but another ER stress factor, 5 mM dithiothreitol (DTT), promoted the growth of ∆spf1. Treatment with chemicals for oxidative stress (5 mM H₂O₂ and 0.8 mM paraquat) also promoted the growth of ∆spf1. Gene expression assays showed that unfolded protein response (UPR) components KAR2, OST1, PMT1, ERV29, PDI1, SCJ1, SEC61, a Ca²⁺ channel-related P-type ATPase gene PMR1, and a calcineurin-dependent transcription factor CRZ1 were significantly up-regulated in ∆spf1, suggesting activation of UPR in the mutant. These lines of experimental evidence indicate that SPF1 is involved in some basal ER mechanisms of P. oryzae including UPR pathway and responses to ER related stresses, therefore, affecting fungal development and virulence. However, the detailed mechanism between Spf1 and virulence still awaits future researches.

Every Coin Has Two Sides: Reactive Oxygen Species during Rice⁻Magnaporthe oryzae Interaction

Reactive oxygen species (ROS) are involved in many important processes, including the growth, development, and responses to the environments, in rice (Oryza sativa) and Magnaporthe oryzae. Although ROS are known to be critical components in rice⁻M. oryzae interactions, their regulations and pathways have not yet been completely revealed. Recent studies have provided fascinating insights into the intricate physiological redox balance in rice⁻M. oryzae interactions. In M. oryzae, ROS accumulation is required for the appressorium formation and penetration. However, once inside the rice cells, M. oryzae must scavenge the host-derived ROS to spread invasive hyphae. On the other side, ROS play key roles in rice against M. oryzae. It has been known that, upon perception of M. oryzae, rice plants modulate their activities of ROS generating and scavenging enzymes, mainly on NADPH oxidase OsRbohB, by different signaling pathways to accumulate ROS against rice blast. By contrast, the M. oryzae virulent strains are capable of suppressing ROS accumulation and attenuating rice blast resistance by the secretion of effectors, such as AvrPii and AvrPiz-t. These results suggest that ROS generation and scavenging of ROS are tightly controlled by different pathways in both M. oryzae and rice during rice blast. In this review, the most recent advances in the understanding of the regulatory mechanisms of ROS accumulation and signaling during rice⁻M. oryzae interaction are summarized.

Correction to: Pleiotropic roles of O-mannosyltransferase MoPmt4 in development and pathogenicity of Magnaporthe oryzae

In the original publication, Fig. 1 panel (b), the photo of MoPmt2-6 was incorrect. The correct Fig. 1 is shown below.