Roles of Peroxisomes in the Rice Blast Fungus

Peroxin MoPex22 Regulates the Import of Peroxisomal Matrix Proteins and Appressorium-Mediated Plant Infection in Magnaporthe oryzae

Magnaporthe oryzae, the pathogen responsible for rice blast disease, utilizes specialized infection structures known as appressoria to breach the leaf cuticle and establish intracellular, infectious hyphae. Our study demonstrates that the peroxin MoPex22 is crucial for appressorium function, specifically for the development of primary penetration hyphae. The ∆Mopex22 mutant exhibited slow growth, reduced aerial hyphae, and almost complete loss of virulence. Specifically, despite the mutant's capability to form appressoria, it showed abnormalities during appressorium development, including reduced turgor, increased permeability of the appressorium wall, failure to form septin rings, and significantly decreased ability to penetrate host cells. Additionally, there was a delay in the degradation of lipid droplets during conidial germination and appressorium development. Consistent with these findings, the ΔMopex22 mutant showed an inefficient utilization of long-chain fatty acids and defects in cell wall integrity. Moreover, our findings indicate that MoPex22 acts as an anchor for MoPex4, facilitating the localization of MoPex4 to peroxisomes. Together with MoPex4, it affects the function of MoPex5, thus regulating the import of peroxisomal matrix proteins. Overall, these results highlight the essential role of MoPex22 in regulating the transport of peroxisomal matrix proteins, which affect fatty acid metabolism, glycerol accumulation, cell wall integrity, growth, appressorium development, and the pathogenicity of M. oryzae. This study provides valuable insights into the significance of peroxin functions in fungal biology and appressorium-mediated plant infection.

StRAB4 gene is required for filamentous growth, conidial development, and pathogenicity in Setosphaeria turcica

Setosphaeria turcica, the fungal pathogen responsible for northern corn leaf blight in maize, forms specialized infectious structures called appressoria that are critical for fungal penetration of maize epidermal cells. The Rab family of proteins play a crucial role in the growth, development, and pathogenesis of many eukaryotic species. Rab4, in particular, is a key regulator of endocytosis and vesicle trafficking, essential for filamentous growth and successful infection by other fungal pathogens. In this study, we silenced StRAB4 in S. turcica to gain a better understanding the function of Rab4 in this plant pathogen. Phenotypically, the mutants exhibited a reduced growth rate, a significant decline in conidia production, and an abnormal conidial morphology. These phenotypes indicate that StRab4 plays an instrumental role in regulating mycelial growth and conidial development in S. turcica. Further investigations revealed that StRab4 is a positive regulator of cell wall integrity and melanin secretion. Functional enrichment analysis of differentially expressed genes highlighted primary enrichments in peroxisome pathways, oxidoreductase and catalytic activities, membrane components, and cell wall organization processes. Collectively, our findings emphasize the significant role of StRab4 in S. turcica infection and pathogenicity in maize and provide valuable insights into fungal behavior and disease mechanisms.

GUN Mutants: New Weapons To Unravel Ascospore Germination Regulation in the Model Fungus Podospora anserina

In Podospora anserina as in many other Ascomycetes, ascospore germination is a regulated process that requires the breaking of dormancy. Despite its importance in survival and dispersal, ascospore germination in filamentous fungi has been poorly investigated, and little is known about its regulation and genetic control. We have designed a positive genetic screen that led to the isolation of mutants showing uncontrolled germination, the GUN (Germination UNcontrolled) mutants. Here, we report on the characterization of the gun1SG (Spontaneous Germination) mutant. We show that gun1SG is mutated in Pa_6_1340, the ortholog of Magnaporthe oryzae Pth2, which encodes a carnitine-acetyltransferase (CAT) involved in the shuttling of acetyl coenzyme A between peroxisomes and mitochondria and which is required for appressorium development. Bioinformatic analysis revealed that the mutated residue (I441) is highly conserved among Fungi and that the mutation has a deleterious impact on the protein function. We show that GUN1 is essential for ascospore germination and that the protein is localized both in mitochondria and in peroxisomes. Finally, epistasis studies allowed us to place GUN1 together with the PaMpk2 MAPK pathway upstream of the PaNox2/PaPls1 complex in the regulation of ascospore germination. In addition, we show that GUN1 plays a role in appressorium functioning. The pivotal role of GUN1, the ortholog of Pth2, in ascospore germination and in appressorium functioning reinforces the idea of a common genetic regulation governing both appressorium development and melanized ascospore germination. Furthermore, we characterize the second CAT encoded in P. anserina genome, Pa_3_7660/GUP1, and we show that the function of both CATs is conserved in P. anserina. IMPORTANCE The regulation of ascospore germination in filamentous fungi has been poorly investigated so far. To unravel new genes involved in this regulation pathway, we conducted a genetic screen in Podospora anserina, and we isolated 57 mutants affected in ascospore germination. Here, we describe the Germination UNcontrolled One (gun1SG) mutant, and we characterize the gene affected. GUN1 is a peroxisomal/mitochondrial carnitine-acetyltransferase required for acetyl coenzyme A shuttling between both organelles, and we show that GUN1 is a pleiotropic gene also involved in appressorium functioning similarly to its ortholog, the pathogenesis factor Pth2, in the plant pathogen Magnaporthe oryzae. Given the similarities in the regulation of appressorium development and ascospore germination, we speculate that discovering new genes controlling ascospore germination in P. anserina may lead to the discovery of new pathogenesis factors in pathogenic fungi. The characterization of GUN1, the ortholog of M. oryzae Pth2, represents a proof of concept.

Histidine 19 Residue Is Essential for Cell Internalization of Antifungal Peptide SmAPα1-21 Derived from the α-Core of the Silybum marianum Defensin DefSm2-D in Fusarium graminearum

The synthetic peptide SmAP_α1-21 (KLCEKPSKTWFGNCGNPRHCG) derived from DefSm2-D defensin α-core is active at micromolar concentrations against the phytopathogenic fungus Fusarium graminearum and has a multistep mechanism of action that includes alteration of the fungal cell wall and membrane permeabilization. Here, we continued the study of this peptide’s mode of action and explored the correlation between the biological activity and its primary structure. Transmission electron microscopy was used to study the ultrastructural effects of SmAP_α1-21 in conidial cells. New peptides were designed by modifying the parent peptide SmAP_α1-21 (SmAPH19R and SmAPH19A, where His19 was replaced by Arg or Ala, respectively) and synthesized by the Fmoc solid phase method. Antifungal activity was determined against F. graminearum. Membrane permeability and subcellular localization in conidia were studied by confocal laser scanning microscopy (CLSM). Reactive oxygen species (ROS) production was assessed by fluorescence spectroscopy and CLSM. SmAP_α1-21 induced peroxisome biogenesis and oxidative stress through ROS production in F. graminearum and was internalized into the conidial cells’ cytoplasm. SmAPH19R and SmAPH19A were active against F. graminearum with minimal inhibitory concentrations (MICs) of 38 and 100 µM for SmAPH19R and SmAPH19A, respectively. The replacement of His19 by Ala produced a decrease in the net charge with a significant increase in the MIC, thus evidencing the importance of the positive charge in position 19 of the antifungal peptide. Like SmAP_α1-21, SmAP2H19A and SmAP2H19R produced the permeabilization of the conidia membrane and induced oxidative stress through ROS production. However, SmAPH19R and SmAPH19A were localized in the conidia cell wall. The replacement of His19 by Ala turned all the processes slower. The extracellular localization of peptides SmAPH19R and SmAPH19A highlights the role of the His19 residue in the internalization.

The Peroxisomal-CoA Synthetase MoPcs60 Is Important for Fatty Acid Metabolism and Infectious Growth of the Rice Blast Fungus

Fatty acid metabolism is important for the maintenance of fatty acid homeostasis. Free fatty acids, which are toxic in excess, are activated by esterification with coenzyme A (CoA) and then subjected to β-oxidization. Fatty acid β-oxidation-related genes play critical roles in the development and virulence of several phytopathogens. In this study, we identified and characterized a peroxisomal-CoA synthetase in the rice blast fungus Magnaporthe oryzae, MoPCS60, which is a homolog of PCS60 in budding yeast. MoPCS60 was highly expressed during the conidial and early infectious stages and was induced under oleate treatment. Targeted deletion of MoPCS60 resulted in a significant reduction in growth rate when oleate and olive oil were used as the sole carbon sources. Compared with the wild-type strain Guy11, the ΔMopcs60 mutant exhibited fewer peroxisomes, more lipid droplets, and decreased pathogenicity. The distribution of MoPcs60 varied among developmental stages and was mainly localized to peroxisomes in the hyphae, conidia, and appressoria when treated with oleate. Our results suggest that MoPcs60 is a key peroxisomal-CoA synthetase involved in fatty acid β-oxidation and pathogenicity in rice blast fungi.

Peroxin FgPEX22-Like Is Involved in FgPEX4 Tethering and Fusarium graminearum Pathogenicity

Peroxisomes are essential organelles that play important roles in a variety of biological processes in eukaryotic cells. To understand the synthesis of peroxisomes comprehensively, we identified the gene FgPEX22-like, encoding FgPEX22-like, a peroxin, in Fusarium graminearum. Our results showed that although FgPEX22-like was notably different from other peroxins (PEX) in Saccharomyces cerevisiae, it contained a predicted PEX4-binding site and interacted with FgPEX4 as a rivet protein of FgPEX4. To functionally characterize the roles of FgPEX22-like in F. graminearum, we performed homologous recombination to construct a deletion mutant (ΔPEX22-like). Analysis of the mutant showed that FgPEX22-like was essential for sexual and asexual reproduction, fatty acid utilization, pathogenicity, and production of the mycotoxin deoxynivalenol. Deletion of FgPEX22-like also led to increased production of lipid droplets and decreased elimination of reactive oxygen species. In addition, FgPEX22-like was required for the biogenesis of Woronin bodies. Taken together, our data demonstrate that FgPEX22-like is a peroxin in F. graminearum that interacts with PEX4 by anchoring PEX4 at the peroxisomal membrane and contributes to the peroxisome function in F. graminearum.

Functional analysis of seven regulators of G protein signaling (RGSs) in the nematode-trapping fungus Arthrobotrys oligospora

Regulators of G protein signaling (RGSs) are proteins that negatively regulate G protein signal transduction. In this study, seven putative RGSs were characterized in the nematode-trapping (NT) fungus, Arthrobotrys oligospora. Deleting Rgs genes significantly increased intracellular cAMP levels, and caused defects in mycelia growth, stress resistance, conidiation, trap formation, and nematocidal activity. In particular, the ΔAoFlbA mutant was unable to produce conidia and traps. Transcriptomic analysis showed that amino acid metabolic and biosynthetic processes were significantly enriched in the ΔAoFlbA mutant compared to WT. Interestingly, Gas1 family genes are significantly expanded in A. oligospora and other NT fungi that produce adhesive traps, and are differentially expressed during trap formation in A. oligospora. Disruption of two Gas1 genes resulted in defective conidiation, trap formation, and pathogenicity. Our results indicate that RGSs play pleiotropic roles in regulating A. oligospora mycelial growth, development, and pathogenicity. Further, AoFlbA is a prominent member and required for conidiation and trap formation, possibly by regulating amino acid metabolism and biosynthesis. Our results provide a basis for elucidating the signaling mechanism of vegetative growth, lifestyle transition, and pathogenicity in NT fungi.

The Aspergillus niger Major Allergen (Asp n 3) DNA-Specific Sequence Is a Reliable Marker to Identify Early Fungal Contamination and Postharvest Damage in Mangifera indica Fruit

The aim of this work was to study the value of the main allergen Asp n 3 of Aspergillus niger as a molecular marker of allergenicity and pathogenicity with the potential to be used in the identification of A. niger as a contaminant and cause of spoilage of Mangifera indica. Real-time polymerase chain reaction (RT-PCR) was used for the amplification of Asp n 3 gene. Two pairs of primers were designed: one for the amplification of the entire sequence and another one for the amplification of the most conserved region of this peroxisomal protein. The presence of A. niger was demonstrated by the early detection of the allergenic protein Asp n 3 coding gene, which could be considered a species-specific marker. The use of primers designed based on the conserved region of the Asp n 3 encoding gene allowed us to identify the presence of the closely related fungal species Aspergillus fumigatus by detecting Asp n 3 homologous protein, which can be cross-reactive. The use of conserved segments of the Asp n 3 gene or its entire sequence allows us to detect phylogenetically closely related species within the Aspergilaceae family or to identify species-specific contaminating fungi.

MrPEX33 is involved in infection-related morphogenesis and pathogenicity of Metarhizium robertsii

Peroxisomes, being indispensable organelles, play an important role in different biological processes in eukaryotes. PEX33, a filamentous fungus-specific peroxin of the docking machinery of peroxisomes, is involved in the virulence and development of other fungal pathogens. However, it is not clear whether PEX33 is necessary for the pathogenicity and development of an insect pathogenic fungus. In the present study, we report the presence of homologs of PEX33, namely MrPEX33 (MAA_05331), in the entomopathogenic fungus, Metarhizium robertsii. An M. robertsii transgenic strain expressing the fusion protein with MrPEX33-GFP and mCherry-PTS1 showed that MrPEX33 localizes to peroxisomes. The results also demonstrated that MrPEX33 is involved in the peroxisomal import pathway by peroxisomal targeting signals. Targeted gene deletion of MrPEX33 led to a significant decline in the asexual sporulation capacity, which was accompanied by downregulation of several conidiation-associated genes, such as wetA, abaA, and brlA. More importantly, our bioassay results showed that the virulence of ∆MrPEX33 mutants, against Galleria mellonella through cuticle infection, was greatly reduced. This was further accompanied by a significant drop in appressorium formation and cuticle penetration. Additionally, ∆MrPEX33 mutants showed a significant decrease in tolerance to cell wall integrity and oxidative stress. Taken together, our results suggest that MrPEX33 is involved in the cuticle infection-related morphogenesis and pathogenicity. KEY POINTS: • MrPEX33 is a specific peroxin of the docking machinery of peroxisomes. • MrPEX33 localizes to peroxisomes and is involved in the import of matrix proteins. • MrPEX33 is involved in the pathogenicity associated with cuticle infections.

Fungal effectors, the double edge sword of phytopathogens

Phyto-pathogenic fungi can cause huge damage to crop production. During millions of years of coexistence, fungi have evolved diverse life-style to obtain nutrients from the host and to colonize upon them. They deploy various proteinaceous as well as non-proteinaceous secreted molecules commonly referred as effectors to sabotage host machinery during the infection process. The effectors are important virulence determinants of pathogenic fungi and play important role in successful pathogenesis, predominantly by avoiding host-surveillance system. However, besides being important for pathogenesis, the fungal effectors end-up being recognized by the resistant cultivars of the host, which mount a strong immune response to ward-off pathogens. Various recent studies involving different pathosystem have revealed the virulence/avirulence functions of fungal effectors and their involvement in governing the outcome of host-pathogen interactions. However, the effectors and their cognate resistance gene in the host remain elusive for several economically important fungal pathogens. In this review, using examples from some of the biotrophic, hemi-biotrophic and necrotrophic pathogens, we elaborate the double-edged functions of fungal effectors. We emphasize that knowledge of effector functions can be helpful in effective management of fungal diseases in crop plants.

Transcriptome analysis of the plant pathogen Sclerotinia sclerotiorum interaction with resistant and susceptible canola (Brassica napus) lines

Sclerotinia stem rot is an economically important disease of canola (Brassica napus) and is caused by the fungal pathogen Sclerotinia sclerotiorum. This study evaluated the differential gene expression patterns of S. sclerotiorum during disease development on two canola lines differing in susceptibility to this pathogen. Sequencing of the mRNA libraries derived from inoculated petioles and mycelium grown on liquid medium generated approximately 164 million Illumina reads, including 95 million 75-bp-single reads, and 69 million 50-bp-paired end reads. Overall, 36% of the quality filter-passed reads were mapped to the S. sclerotiorum reference genome. On the susceptible line, 1301 and 1214 S. sclerotiorum genes were differentially expressed at early (8-16 hours post inoculation (hpi)) and late (24-48 hpi) infection stages, respectively, while on the resistant line, 1311 and 1335 genes were differentially expressed at these stages, respectively. Gene ontology (GO) categories associated with cell wall degradation, detoxification of host metabolites, peroxisome related activities like fatty acid ß-oxidation, glyoxylate cycle, oxidoreductase activity were significantly enriched in the up-regulated gene sets on both susceptible and resistant lines. Quantitative RT-PCR of six selected DEGs further validated the RNA-seq differential gene expression analysis. The regulation of effector genes involved in host defense suppression or evasion during the early infection stage, and the expression of effectors involved in host cell death in the late stage of infection provide supporting evidence for a two-phase infection model involving a brief biotrophic phase during early stages of infection. The findings from this study emphasize the role of peroxisome related pathways along with cell wall degradation and detoxification of host metabolites as the key mechanisms underlying pathogenesis of S. sclerotiorum on B. napus.

Network analysis exposes core functions in major lifestyles of fungal and oomycete plant pathogens

Background

Genomic studies demonstrate that components of virulence mechanisms in filamentous eukaryotic pathogens (FEPs, fungi and oomycetes) of plants are often highly conserved, or found in gene families that include secreted hydrolytic enzymes (e.g., cellulases and proteases) and secondary metabolites (e.g., toxins), central to the pathogenicity process. However, very few large-scale genomic comparisons have utilized complete proteomes from dozens of FEPs to reveal lifestyle-associated virulence mechanisms. Providing a powerful means for exploration, and the discovery of trends in large-scale datasets, network analysis has been used to identify core functions of the primordial cyanobacteria, and ancient evolutionary signatures in oxidoreductases.

Results

We used a sequence-similarity network to study components of virulence mechanisms of major pathogenic lifestyles (necrotroph (ic), N; biotroph (ic), B; hemibiotroph (ic), H) in complete pan-proteomes of 65 FEPs and 17 saprobes. Our comparative analysis highlights approximately 190 core functions found in 70% of the genomes of these pathogenic lifestyles. Core functions were found mainly in: transport (in H, N, B cores); carbohydrate metabolism, secondary metabolite synthesis, and protease (H and N cores); nucleic acid metabolism and signal transduction (B core); and amino acid metabolism (H core). Taken together, the necrotrophic core contains functions such as cell wall-associated degrading enzymes, toxin metabolism, and transport, which are likely to support their lifestyle of killing prior to feeding. The biotrophic stealth growth on living tissues is potentially controlled by a core of regulatory functions, such as: small G-protein family of GTPases, RNA modification, and cryptochrome-based light sensing. Regulatory mechanisms found in the hemibiotrophic core contain light- and CO₂-sensing functions that could mediate important roles of this group, such as transition between lifestyles.

Conclusions

The selected set of enriched core functions identified in our work can facilitate future studies aimed at controlling FEPs. One interesting example would be to facilitate the identification of the pathogenic potential of samples analyzed by metagenomics. Finally, our analysis offers potential evolutionary scenarios, suggesting that an early-branching saprobe (identified in previous studies) has probably evolved a necrotrophic lifestyle as illustrated by the highest number of shared gene families between saprobes and necrotrophs.

FgPex3, a Peroxisome Biogenesis Factor, Is Involved in Regulating Vegetative Growth, Conidiation, Sexual Development, and Virulence in Fusarium graminearum

Peroxisomes are involved in a wide range of important cellular functions. Here, the role of the peroxisomal membrane protein PEX3 in the plant-pathogen and mycotoxin producer Fusarium graminearum was studied using knock-out and complemented strains. To fluorescently label peroxisomes’ punctate structures, GFP and RFP fusions with the PTS1 and PTS2 localization signal were transformed into the wild type PH-1 and ΔFgPex3 knock-out strains. The GFP and RFP transformants in the ΔFgPex3 background showed a diffuse fluorescence pattern across the cytoplasm suggesting the absence of mature peroxisomes. The ΔFgPex3 strain showed a minor, non-significant reduction in growth on various sugar carbon sources. In contrast, deletion of FgPex3 affected fatty acid β-oxidation in F. graminearum and significantly reduced the utilization of fatty acids. Furthermore, the ΔFgPex3 mutant was sensitive to osmotic stressors as well as to cell wall-damaging agents. Reactive oxygen species (ROS) levels in the mutant had increased significantly, which may be linked to the reduced longevity of cultured strains. The mutant also showed reduced production of conidiospores, while sexual reproduction was completely impaired. The pathogenicity of ΔFgPex3, especially during the process of systemic infection, was strongly reduced on both tomato and on wheat, while to production of deoxynivalenol (DON), an important factor for virulence, appeared to be unaffected.

Advances of Metabolomics in Fungal Pathogen-Plant Interactions

Plant disease caused by fungus is one of the major threats to global food security, and understanding fungus-plant interactions is important for plant disease control. Research devoted to revealing the mechanisms of fungal pathogen-plant interactions has been conducted using genomics, transcriptomics, proteomics, and metabolomics. Metabolomics research based on mass spectrometric techniques is an important part of systems biology. In the past decade, the emerging field of metabolomics in plant pathogenic fungi has received wide attention. It not only provides a qualitative and quantitative approach for determining the pathogenesis of pathogenic fungi but also helps to elucidate the defense mechanisms of their host plants. This review focuses on the methods and progress of metabolomics research in fungal pathogen-plant interactions. In addition, the prospects and challenges of metabolomics research in plant pathogenic fungi and their hosts are addressed.

The AP-1-like transcription factor ChAP1 balances tolerance and cell death in the response of the maize pathogen Cochliobolus heterostrophus to a plant phenolic

Fungal pathogens need to contend with stresses including oxidants and antimicrobial chemicals resulting from host defenses. ChAP1 of Cochliobolus heterostrophus, agent of Southern corn leaf blight, encodes an ortholog of yeast YAP1. ChAP1 is retained in the nucleus in response to plant-derived phenolic acids, in addition to its well-studied activation by oxidants. Here, we used transcriptome profiling to ask which genes are regulated in response to ChAP1 activation by ferulic acid (FA), a phenolic abundant in the maize host. Nuclearization of ChAP1 in response to phenolics is not followed by strong expression of genes needed for oxidative stress tolerance. We, therefore, compared the transcriptomes of the wild-type pathogen and a ChAP1 deletion mutant, to study the function of ChAP1 in response to FA. We hypothesized that if ChAP1 is retained in the nucleus under plant-related stress conditions yet in the absence of obvious oxidant stress, it should have additional regulatory functions. The transcriptional signature in response to FA in the wild type compared to the mutant sheds light on the signaling mechanisms and response pathways by which ChAP1 can mediate tolerance to ferulic acid, distinct from its previously known role in the antioxidant response. The ChAP1-dependent FA regulon consists mainly of two large clusters. The enrichment of transport and metabolism-related genes in cluster 1 indicates that C. heterostrophus degrades FA and removes it from the cell. When this fails at increasing stress levels, FA provides a signal for cell death, indicated by the enrichment of cell death-related genes in cluster 2. By quantitation of survival and by TUNEL assays, we show that ChAP1 promotes survival and mitigates cell death. Growth rate data show a time window in which the mutant colony expands faster than the wild type. The results delineate a transcriptional regulatory pattern in which ChAP1 helps balance a survival response for tolerance to FA, against a pathway promoting cell death in the pathogen. A general model for the transition from a phase where the return to homeostasis dominates to a phase leading to the onset of cell death provides a context for understanding these findings.

FgPEX1 and FgPEX10 are required for the maintenance of Woronin bodies and full virulence of Fusarium graminearum

Peroxisomes are ubiquitous single-membrane-bound organelles that perform a variety of biochemical functions in eukaryotic cells. Proteins involved in peroxisomal biogenesis are collectively called peroxins. Currently, functions of most peroxins in phytopathogenic fungi are poorly understood. Here, we report identification of PEX1 and PEX10 in the phytopathogenic fungus, Fusarium graminearum, namely FgPEX1 and FgPEX10, the orthologs of yeast ScPEX1 and ScPEX10. To functionally characterize FgPEX1 and FgPEX10, we constructed deletion mutants of FgPEX1 and FgPEX10 (ΔPEX1 and ΔPEX10) by targeting gene-replacement strategies. Our data demonstrate that both mutants displayed reduced mycelial growth, conidiation, and production of perithecia. Deletion of FgPEX1 and FgPEX10 resulted in a shortage of acetyl-CoA, which is an important reason for the reduced deoxynivalenol production and inhibited virulence of F. graminearum. Moreover, ΔPEX1 and ΔPEX10 showed an increased accumulation of lipid droplets and endogenous reactive oxygen species. In addition, FgPEX1 and FgPEX10 were found to be involved in the maintenance of cell wall integrity and Woronin bodies.

MoMCP1, a Cytochrome P450 Gene, Is Required for Alleviating Manganese Toxin Revealed by Transcriptomics Analysis in Magnaporthe oryzae

Manganese, as an essential trace element, participates in many physiological reactions by regulating Mn associated enzymes. Magnaporthe oryzae is a serious pathogen and causes destructive losses for rice production. We identified a cytochrome P450 gene, MoMCP1, involving the alleviation of manganese toxin and pathogenicity. To identify the underlying mechanisms, transcriptomics were performed. The results indicated that many pathogenicity related genes were regulated, especially hydrophobin related genes in ∆Momcp1. Furthermore, the Mn²⁺ toxicity decreased the expressions of genes involved in the oxidative phosphorylation and energy production, and increased the reactive oxygen species (ROS) levels, which might impair the functions of mitochondrion and vacuole, compromising the pathogenicity and development in ∆Momcp1. Additionally, our results provided further information about Mn associated the gene network for Mn metabolism in cells.

FgPEX4 is involved in development, pathogenicity, and cell wall integrity in Fusarium graminearum

Peroxisomes are indispensable organelles that play critical roles in various biological processes in eukaryotic cells. PEX4, one of the peroxins, is the ubiquitin-conjugating enzyme. To functionally characterize roles of FgPEX4 in the phytopathogenic fungus, Fusarium graminearum, we constructed a deletion mutant of FgPEX4 (ΔPEX4) through homologous recombination. ΔPEX4 displayed reduced mycelial growth, conidiation, and the production of perithecia. ΔPEX4 was defective in pathogenicity and production of the mycotoxin deoxynivalenol (DON). In addition, FgPEX4 was involved in cell wall integrity, lipid droplet accumulation, and the elimination of reactive oxygen species. Western blot analysis revealed reduced phosphorylation of Mgv1 in the ∆PEX4 mutant. Importantly, proteomics analysis indicated that protein expression levels related to protein biosynthesis, fatty acid metabolism, cell wall synthesis, and oxidation-reduction reactions were downregulated in ΔPEX4 compared with the wild type. Taken together, these results demonstrate that FgPEX4 is important for development, pathogenicity, and cell wall integrity.

Contribution of peroxisomal protein importer AflPex5 to development and pathogenesis in the fungus Aspergillus flavus

Peroxisomes are important organelles that have diverse metabolic functions and participate in the pathogenicity of fungal pathogens. Previous studies indicate that most functions of peroxisomes are dependent on peroxisomal matrix proteins, which are delivered from the cytoplasm into peroxisomes by peroxisomal protein importers. In this study, the roles of peroxisomal protein importer AflPex5 were investigated in Aspergillus flavus with the application of gene disruption. AflPex5 deletion mutants failed to localize the fluorescently fused peroxisomal targeting signal 1 (PTS1) proteins to peroxisomes. Deletion of AflPex5 caused defects in sporulation, sclerotial formation, aflatoxin biosynthesis, stress response, and plant infection. Moreover, AflPex5 null mutants exhibited a significant defect in carbon metabolism and oxidants' clearance. These results indicate that the PTS1 pathway mediated by AflPex5 serves as an important role in the development, metabolism, and pathogenesis of A. flavus.