Colletotrichum higginsianum Mitogen-Activated Protein Kinase ChMK1: Role in Growth, Cell Wall Integrity, Colony Melanization, and Pathogenicity

Novel cellular functions of Cys2-His2 zinc finger proteins in anthracnose development and dissemination on pepper fruits by Colletotrichum scovillei

Colletotrichum species are notorious for causing anthracnose on many fruits, leading to significant economic losses worldwide. As a model, we functionally characterized cys2-his2 (C2H2) zinc finger proteins (CsCZFs) in Colletotrichum scovillei, a major causal agent of pepper fruit anthracnose in many countries. In all, 62 CsCZFs were identified by in silico genomic analysis. Twelve were selected based on their expression profiles to generate targeted deletion mutants for functional investigation. ΔCsczf1 markedly reduced conidiation and constitutive expression of CsCZF1 partially recovered conidiation in an asexual reproduction-defective mutant, ΔCshox2. Deletion of CsCZF12, orthologous to the calcineurin-responsive transcription factor Crz1, impaired autophagy in C. scovillei. ΔCsczf9 was defective in surface recognition, appressorium formation, and suppression of host defenses. CsCZF9 was identified as an essential and novel regulator under the control of the mitogen-activated protein kinase (CsPMK1) in an early step of appressorium development in C. scovillei. This study provides novel insights into CsCZF-mediated regulation of differentiation and pathogenicity in C. scovillei, contributing to understanding the regulatory mechanisms governing fruit anthracnose epidemics.IMPORTANCEThe phytopathogenic fungus Colletotrichum scovillei is known to cause serious anthracnose on chili pepper. However, the molecular mechanism underlying anthracnose caused by this fungus remains largely unknown. Here, we systematically analyzed the functional roles of cys2-his2 zinc finger proteins (CsCZFs) in the dissemination and pathogenic development of this fungus. Our results showed that CsCZF1 plays an important role in conidiation and constitutive expression of CsCZF1 restored conidiation in an asexual reproduction-defective mutant, ΔCshox2. The CsCZF9, a novel target of the mitogen-activated protein kinase (CsPMK1), is essential for surface recognition to allow appressorium formation and suppression of host defenses in C. scovillei. The CsCZF12, orthologous to the calcineurin-responsive transcription factor Crz1, is involved in the autophagy of C. scovillei. Our findings reveal a comprehensive mechanism underlying CsCZF-mediated regulation of differentiation and pathogenicity of C. scovillei, which contributes to the understanding of fruit anthracnose epidemics and the development of novel strategies for disease management.

Role of Pmk1, Mpk1, or Hog1 in the mitogen-activated protein kinase pathway of Aspergillus cristatus

Aspergillus cristatus is a probiotic fungus known for its safety and abundant secondary metabolites, making it a promising candidate for various applications. However, limited progress has been made in researching A. cristatus due to challenges in genetic manipulation. The mitogen-activated protein kinase (MAPK) signaling pathway is involved in numerous physiological processes, but its specific role in A. cristatus remains unclear. In this study, we successfully developed an efficient polyethylene glycol (PEG)-mediated protoplast transformation method for A. cristatus, enabling us to investigate the function of Pmk1, Mpk1, and Hog1 in the MAPK signaling pathway. Our findings revealed that Pmk1, Mpk1, and Hog1 are crucial for sexual reproduction, melanin synthesis, and response to external stress in A. cristatus. Notably, the deletion of Pmk1, Mpk1, or Hog1 resulted in the loss of sexual reproduction capability in A. cristatus. Overall, this research on MAPK will contribute to the continued understanding of the reproductive strategy and melanin synthesis mechanism of A. cristatus.

Aabrm1-mediated melanin synthesis is essential to growth and development, stress adaption, and pathogenicity in Alternaria alternata

Scytalone dehydratase (brm1) is one of the key enzymes in 1, 8-dihydroxynaphthalene (DHN) melanin synthesis, which mediates melanin biosythesis and regulates cell biological process of plant fungi, but its function in Alternaria alternata, the causal agent of pear black spot, is unclear. Brm1 in A. alternata was cloned, identified, and named as Aabrm1. An Aabrm1-deletion mutant was generated and revealed that the deletion of Aabrm1 leads to a significant decrease in melanin production and forms orange colony smooth spores. In addition, the deletion of Aabrm1 gene impaired infection structure information and penetration. The external stress resistance of ΔAabrm1 was significantly weakened, and, in particular, it is very sensitive to oxidative stress, and the contents of H2O2 and O2.- in ΔAabrm1 were significantly increased. Virulence of ΔAabrm1 was reduced in non-wound-inoculated pear leaves but not changed in wound-inoculated pear fruit. These results indicated that Aabrm1-mediated melanin synthesis plays an important role in the pathogenicity of A. alternata.

Genomic analysis of Colletotrichum camelliae responsible for tea brown blight disease

BACKGROUND

Colletotrichum camelliae, one of the most important phytopathogenic fungi infecting tea plants (Camellia sinensis), causes brown blight disease resulting in significant economic losses in yield of some sensitive cultivated tea varieties. To better understand its phytopathogenic mechanism, the genetic information is worth being resolved.

RESULTS

Here, a high-quality genomic sequence of C. camelliae (strain LT-3-1) was sequenced using PacBio RSII sequencing platform, one of the most advanced Three-generation sequencing platforms and assembled. The result showed that the fungal genomic sequence is 67.74 Mb in size (with the N50 contig 5.6 Mb in size) containing 14,849 putative genes, of which about 95.27% were annotated. The data revealed a large class of genomic clusters potentially related to fungal pathogenicity. Based on the Pathogen Host Interactions database, a total of 1698 genes (11.44% of the total ones) were annotated, containing 541 genes related to plant cell wall hydrolases which is remarkably higher than those of most species of Colletotrichum and others considered to be hemibiotrophic and necrotrophic fungi. It's likely that the increase in cell wall-degrading enzymes reflects a crucial adaptive characteristic for infecting tea plants.

CONCLUSION

Considering that C. camelliae has a specific host range and unique morphological and biological traits that distinguish it from other species of the genus Colletotrichum, characterization of the fungal genome will improve our understanding of the fungus and its phytopathogenic mechanism as well.

Glucose-6-phosphate 1-Epimerase CrGlu6 Contributes to Development and Biocontrol Efficiency in Clonostachys chloroleuca

Clonostachys chloroleuca (formerly classified as C. rosea) is an important mycoparasite active against various plant fungal pathogens. Mitogen-activated protein kinase (MAPK) signaling pathways are vital in mycoparasitic interactions; they participate in responses to diverse stresses and mediate fungal development. In previous studies, the MAPK-encoding gene Crmapk has been proven to be involved in mycoparasitism and the biocontrol processes of C. chloroleuca, but its regulatory mechanisms remain unclear. Aldose 1-epimerases are key enzymes in filamentous fungi that generate energy for fungal growth and development. By protein-protein interaction assays, the glucose-6-phosphate 1-epimerase CrGlu6 was found to interact with Crmapk, and expression of the CrGlu6 gene was significantly upregulated when C. chloroleuca colonized Sclerotinia sclerotiorum sclerotia. Gene deletion and complementation analyses showed that CrGlu6 deficiency caused abnormal morphology of hyphae and cells, and greatly reduced conidiation. Moreover, deletion mutants presented much lower antifungal activities and mycoparasitic ability, and control efficiency against sclerotinia stem rot was markedly decreased. When the CrGlu6 gene was reinserted, all biological characteristics and biocontrol activities were recovered. These findings provide new insight into the mechanisms of glucose-6-phosphate 1-epimerase in mycoparasitism and help to further reveal the regulation of MAPK and its interacting proteins in the biocontrol of C. chloroleuca.

The MAP Kinase PvMK1 Regulates Hyphal Development, Autophagy, and Pathogenesis in the Bayberry Twig Blight Fungus Pestalotiopsis versicolor

Bayberry twig blight caused by the ascomycete fungus Pestalotiopsis versicolor is a devastating disease threatening worldwide bayberry production. However, the molecular basis underlying the pathogenesis of P. versicolor is largely unknown. Here, we identified and functionally characterized the MAP kinase PvMk1 in P. versicolor through genetic and cellular biochemical approaches. Our analysis reveals a central role of PvMk1 in regulating P. versicolor virulence on bayberry. We demonstrate that PvMk1 is involved in hyphal development, conidiation, melanin biosynthesis, and cell wall stress responses. Notably, PvMk1 regulates P. versicolor autophagy and is essential for hyphal growth under nitrogen-depleting conditions. These findings suggest the multifaceted role of PvMk1 in regulating P. versicolor development and virulence. More remarkably, this evidence of virulence-involved cellular processes regulated by PvMk1 has paved a fundamental way for further understanding the impact of P. versicolor pathogenesis on bayberry.

Comparative Transcriptomic Analysis of MAPK-Mediated Regulation of Pathogenicity, Stress Responses, and Development in Cytospora chrysosperma

Mitogen-activated protein kinase (MAPK) cascades are highly conserved signal transduction pathways that mediate cellular responses to various biotic and abiotic signals in plant-pathogenic fungi. Generally, there are three MAPKs in filamentous pathogenic fungi: Pmk1/Fus3/Kss1, Hog1, and Stl2. Our previous studies have shown that CcPmk1 is a core regulator of fungal pathogenicity in Cytospora chrysosperma, the causal agent of canker disease in a wide range of woody plants. Here, we identified and functionally characterized the other two MAPK genes (CcHog1 and CcSlt2) and then compared the transcriptional differences among these three MAPKs in C. chrysosperma. We found that the MAPKs shared convergent and distinct roles in fungal development, stress responses, and virulence. For example, CcHog1, CcSlt2, and CcPmk1 were all involved in conidiation and response to stresses, including hyperosmotic pressure, cell wall inhibition agents, and H₂O₂, but only CcPmk1 and CcSlt2 were required for hyphal growth and fungal pathogenicity. Transcriptomic analysis showed that numerous hyperosmosis- and cell wall-related genes significantly reduced their expression levels in ΔCcHog1 and ΔCcSlt2, respectively. Interestingly, RNA- and ribosome-related processes were significantly enriched in the upregulated genes of ΔCcSlt2, whereas they were significantly enriched in the downregulated genes of ΔCcPmk1. Moreover, two secondary metabolite gene clusters were significantly downregulated in ΔCcPmk1, ΔCcSlt2, and/or ΔCcHog1. Importantly, some virulence-associated genes were significantly downregulated in ΔCcPmk1 and/or ΔCcSlt2, such as candidate effector genes. Collectively, these results suggest that the similar and distinct phenotypes of each MAPK deletion mutant may result from the transcriptional regulation of a series of common or specific downstream genes, which provides a better understanding of the regulation network of MAPKs in C. chrysosperma.

Phosphoproteomic and Metabolomic Profiling Uncovers the Roles of CcPmk1 in the Pathogenicity of Cytospora chrysosperma

Pmk1, a highly conserved pathogenicity-related mitogen-activated protein kinase (MAPK) in pathogenic fungi, is phosphorylated and activated by MAP2K and acts as a global regulator of fungal infection and invasive growth by modulating downstream targets. However, the hierarchical CcPmk1 regulatory network in Cytospora chrysosperma, the main causal agent of canker disease in many woody plant species, is still unclear. In this study, we analyzed and compared the phosphoproteomes and metabolomes of ΔCcPmk1 and wild-type strains and identified pathogenicity-related downstream targets of CcPmk1. We found that CcPmk1 could interact with the downstream homeobox transcription factor CcSte12 and affect its phosphorylation. In addition, the ΔCcSte12 displayed defective phenotypes that were similar to yet not identical to that of the ΔCcPmk1 and included significantly reduced fungal growth, conidiation, and virulence. Remarkably, CcPmk1 could phosphorylate proteins translated from a putative secondary metabolism-related gene cluster, which is specific to C. chrysosperma, and the phosphorylation of several peptides was completely abolished in the ΔCcPmk1. Functional analysis of the core gene (CcPpns1) in this gene cluster revealed its essential roles in fungal growth and virulence. Metabolomic analysis showed that amino acid metabolism and biosynthesis of secondary metabolites, lipids, and lipid-like molecules significantly differed between wild type and ΔCcPmk1. Importantly, most of the annotated lipids and lipid-like molecules were significantly downregulated in the ΔCcPmk1 compared to the wild type. Collectively, these findings suggest that CcPmk1 may regulate a small number of downstream master regulators to control fungal growth, conidiation, and virulence in C. chrysosperma. IMPORTANCE Understanding the pathogenic mechanisms of plant pathogens is a prerequisite to developing effective disease-control methods. The Pmk1 MAPK is highly conserved among phytopathogenic fungi and acts as a global regulator of fungal pathogenicity by modulating downstream transcription factors or other components. However, the regulatory network of CcPmk1 from C. chrysosperma remains enigmatic. The present data provide evidence that the core pathogenicity regulator CcPmk1 modulates a few downstream master regulators to control fungal virulence in C. chrysosperma through transcription or phosphorylation and that CcPmk1 may be a potential target for disease control.

SsAGM1-Mediated Uridine Diphosphate-N-Acetylglucosamine Synthesis Is Essential for Development, Stress Response, and Pathogenicity of Sclerotinia sclerotiorum

The necrotrophic fungus Sclerotinia sclerotiorum is a devastating pathogen. S. sclerotiorum can cause Sclerotinia stem rot in more than 600 species of plants, which results in serious economic losses every year. Chitin is one of the most important polysaccharides in fungal cell walls. Chitin and β-Glucan form a scaffold that wraps around the cell and determines the vegetative growth and pathogenicity of pathogens. UDP-GlcNAc is a direct precursor of chitin synthesis. During the synthesis of UDP-GlcNAc, the conversion of GlcNAc-6P to GlcNAc-1P that is catalyzed by AGM1 (N-acetylglucosamine-phosphate mutase) is a key step. However, the significance and role of AGM1 in phytopathogenic fungus are unclear. We identified a cytoplasm-localized SsAGM1 in S. sclerotiorum, which is homologous to AGM1 of Saccharomyces cerevisiae. We utilized RNA interference (RNAi) and overexpression to characterize the function of SsAGM1 in S. sclerotiorum. After reducing the expression of SsAGM1, the contents of chitin and UDP-GlcNAc decreased significantly. Concomitantly, the gene-silenced transformants of SsAGM1 slowed vegetative growth and, importantly, lost the ability to produce sclerotia and infection cushion; it also lost virulence, even on wounded leaves. In addition, SsAGM1 was also involved in the response to osmotic stress and inhibitors of cell wall synthesis. Our results revealed the function of SsAGM1 in the growth, development, stress response, and pathogenicity in S. sclerotiorum.

Screening and characterisation of proteins interacting with the mitogen-activated protein kinase Crmapk in the fungus Clonostachys chloroleuca

Clonostachys chloroleuca 67-1 (formerly C. rosea 67-1) is a promising mycoparasite with great potential for controlling various plant fungal diseases. The mitogen-activated protein kinase (MAPK)-encoding gene Crmapk is of great importance to the mycoparasitism and biocontrol activities of C. chloroleuca. To investigate the molecular mechanisms underlying the role of Crmapk in mycoparasitism, a high-quality yeast two hybrid (Y2H) library of C. chloroleuca 67-1 was constructed, and proteins interacting with Crmapk were characterised. The library contained 1.6 × 107 independent clones with a recombination rate of 96%, and most inserted fragments were > 1 kb. The pGBKT7-Crmapk bait vector with no self-activation or toxicity to yeast cells was used to screen interacting proteins from the Y2H library, resulting in 60 candidates, many linked to metabolism, cellular processes and signal transduction. Combined bioinformatics and transcriptome analyses of C. chloroleuca 67-1 and ΔCrmapk mutant mycoparasitising Sclerotinia sclerotiorum sclerotia, 41 differentially expressed genes were identified, which might be the targets of the Fus3/Kss1-MAPK pathway. The results provide a profile of potential protein interactions associated with MAPK enzymes in mycoparasites, and are of great significance for understanding the mechanisms of Crmapk regulating C. chloroleuca mycoparasitism.

AaHog1 Regulates Infective Structural Differentiation Mediated by Physicochemical Signals from Pear Fruit Cuticular Wax, Stress Response, and Alternaria alternata Pathogenicity

The high-osmolarity glycerol response kinase, Hog1, affects several cellular responses, but the precise regulatory role of the Hog1 mitogen-activated protein (MAP) kinase in the differentiation of the infective structure of Alternariaalternata induced by pear cuticular wax and hydrophobicity has not yet clarified. In this study, the AaHog1 in A. alternata was identified and functionally characterized. AaHog1 has threonine-glycine-tyrosine (TGY) phosphorylation sites. Moreover, the expression level of AaHog1 was significantly upregulated during the stages of appressorium formation of A. alternata on the fruit-wax-extract-coated GelBond hydrophobic film surface. Importantly, our results showed that the appressorium and infection hyphae formation rates were significantly reduced in ΔAaHog1 mutants. Furthermore, AaHog1 is beneficial for the growth and development, stress tolerance, virulence, and cell-wall-degrading enzyme activity of A. alternata. These findings may be useful for dissecting the AaHog1 regulatory mechanism in relation to the pathogenesis of A. alternata.

Mitogen-Activated Protein Kinase CsPMK1 Is Essential for Pepper Fruit Anthracnose by Colletotrichum scovillei

The phytopathogenic fungus Colletotrichum scovillei, belonging to the Colletotrichum acutatum species complex, causes severe anthracnose disease on several fruits, including chili pepper (Capsicum annuum). However, the molecular mechanisms underlying the development and pathogenicity of Colletotrichum scovillei are unclear. The conserved Fus3/Kss1-related MAPK regulates fungal development and pathogenicity. Here, the role of CsPMK1, orthologous to Fus3/Kss1, was characterized by phenotypic comparison of a target deletion mutant (ΔCspmk1). The mycelial growth and conidiation of ΔCspmk1 were normal compared to that of the wild type. ΔCspmk1 produced morphologically abnormal conidia, which were delayed in conidial germination. Germinated conidia of ΔCspmk1 failed to develop appressoria on inductive surfaces of hydrophobic coverslips and host plants. ΔCspmk1 was completely defective in infectious growth, which may result from failure to suppress host immunity. Furthermore, ΔCspmk1 was impaired in nuclear division and lipid mobilization during appressorium formation, in response to a hydrophobic surface. CsPMK1 was found to interact with CsHOX7, a homeobox transcription factor essential for appressorium formation, via a yeast two-hybridization analysis. Taken together, these findings suggest that CsPMK1 is required for fungal development, stress adaptation, and pathogenicity of C. scovillei.

Protein Kinase Signaling Pathways in Plant-Colletotrichum Interaction

Anthracnose is a fungal disease caused by members of Colletotrichum that affect a wide range of crop plants. Strategies to improve crop resistance are needed to reduce the yield losses; and one strategy is to manipulate protein kinases that catalyze reversible phosphorylation of proteins regulating both plant immune responses and fungal pathogenesis. Hence, in this review, we present a summary of the current knowledge of protein kinase signaling pathways in plant-Colletotrichum interaction as well as the relation to a more general understanding of protein kinases that contribute to plant immunity and pathogen virulence. We highlight the potential of combining genomic resources and phosphoproteomics research to unravel the key molecular components of plant-Colletotrichum interactions. Understanding the molecular interactions between plants and Colletotrichum would not only facilitate molecular breeding of resistant cultivars but also help the development of novel strategies for controlling the anthracnose disease.

Deletion of all three MAP kinase genes results in severe defects in stress responses and pathogenesis in Fusarium graminearum

Mitogen-activated protein kinase (MAPK) cascades are activated by external stimuli and convert signals to cellular changes. Individual MAPKs have been characterized in a number of plant pathogenic fungi for their roles in pathogenesis and responses to biotic or abiotic stresses. However, mutants deleted of all the MAPK genes have not been reported in filamentous fungi. To determine the MAPK-less effects in a fungal pathogen, in this study we generated and characterized mutants deleted of all three MAPK genes in the wheat scab fungus Fusarium graminearum. The Gpmk1 mgv1 Fghog1 triple mutants had severe growth defects and was non-pathogenic. It was defective in infection cushion formation and DON production. Conidiation was reduced in the triple mutant, which often produced elongated conidia with more septa than the wild-type conidia. The triple mutant was blocked in sexual reproduction due to the loss of female fertility. Lack of any MAPKs resulted in an increased sensitivity to various abiotic stress including cell wall, osmotic, oxidative stresses, and phytoalexins, which are likely related to the defects of the triple mutant in environmental adaptation and plant infection. The triple mutant also had increased sensitivity to the biocontrol bacterium Bacillus velezensis and fungus Clonostachys rosea. In co-incubation assays with B. velezensis, the Gpmk1 mgv1 Fghog1 mutant had more severe growth limitation than the wild type and was defective in conidium germination and germ tube growth. In confrontation assays, the triple mutant was defective in defending against mycoparasitic activities of C. rosea and the latter could grow over the mutant but not wild-type F. graminearum. RNA-seq and metabolomics analyses showed that the MAPK triple mutant was altered in the expression of many ATP-binding cassette (ABC) and major facilitator superfamily (MFS) transporter genes and the accumulation of metabolites related to arachidonic acid, linoleic acid, and alpha-linolenic acid metabolisms. Overall, as the first study on mutants deleted of all three MAPKs in fungal pathogens, our results showed that although MAPKs are not essential for growth and asexual reproduction, the Gpmk1 mgv1 Fghog1 triple mutant was blocked in plant infection and sexual reproductions. It also had severe defects in responses to various abiotic stresses and bacterial- or fungal-fungal interactions.

The CfMK1 Gene Regulates Reproduction, Appressorium Formation, and Pathogenesis in a Pear Anthracnose-Causing Fungus

Colletotrichum fructicola, the causal agent of pear anthracnose, causes significant annual economic losses. Mitogen-activated protein kinase (MAPK) cascades are highly conserved signal transduction pathways that play a crucial role in mediating cellular responses to environmental and host signals in plant pathogenic fungi. In this study, we identified an ortholog of the FUS3/KSS1-related MAPK gene, CfMK1, and characterized its function in C. fructicola. The Cfmk1 deletion mutants exhibited poorly developed aerial hyphae, autolysis, no conidial mass or perithecia on solid plates. However, the conidiation of the Cfmk1 mutant in PDB liquid medium was normal compared with that of the wild type (WT). Conidia of the Cfmk1 mutant exhibited a reduced germination rate on glass slides or plant surfaces. The Cfmk1 deletion mutants were unable to form appressoria and lost the capacity to penetrate plant epidermal cells. The ability of the Cfmk1 mutants to infect pear leaves and fruit was severely reduced. Moreover, RNA sequencing (RNA-seq) analysis of the WT and Cfmk1 mutant was performed, and the results revealed 1886 upregulated and 1554 downregulated differentially expressed genes (DEGs) in the mutant. The DEGs were significantly enriched in cell wall and pathogenesis terms, which was consistent with the defects of the Cfmk1 mutant in cell wall integrity and plant infection. Overall, our data demonstrate that CfMK1 plays critical roles in the regulation of aerial hyphal growth, asexual and sexual reproduction, autolysis, appressorium formation, and pathogenicity.

A Lignocellulolytic Colletotrichum sp. OH with Broad-Spectrum Tolerance to Lignocellulosic Pretreatment Compounds and Derivatives and the Efficiency to Produce Hydrogen Peroxide and 5-Hydroxymethylfurfural Tolerant Cellulases

Fungal endophytes are an emerging source of novel traits and biomolecules suitable for lignocellulosic biomass treatment. This work documents the toxicity tolerance of Colletotrichum sp. OH toward various lignocellulosic pretreatment-derived inhibitors. The effects of aldehydes (vanillin, p-hydroxybenzaldehyde, furfural, 5-hydroxymethylfurfural; HMF), acids (gallic, formic, levulinic, and p-hydroxybenzoic acid), phenolics (hydroquinone, p-coumaric acid), and two pretreatment chemicals (hydrogen peroxide and ionic liquid), on the mycelium growth, biomass accumulation, and lignocellulolytic enzyme activities, were tested. The reported Colletotrichum sp. OH was naturally tolerant to high concentrations of single inhibitors like HMF (IC50; 17.5 mM), levulinic acid (IC50; 29.7 mM), hydroquinone (IC50; 10.76 mM), and H2O2 (IC50; 50 mM). The lignocellulolytic enzymes displayed a wide range of single and mixed inhibitor tolerance profiles. The enzymes β-glucosidase and endoglucanase showed H2O2- and HMF-dependent activity enhancements. The enzyme β-glucosidase activity was 34% higher in 75 mM and retained 20% activity in 125 mM H2O2. Further, β-glucosidase activity increased to 24 and 32% in the presence of 17.76 and 8.8 mM HMF. This research suggests that the Colletotrichum sp. OH, or its enzymes, can be used to pretreat plant biomass, hydrolyze it, and remove inhibitory by-products.

Analysis of melanin biosynthesis in the plant pathogenic fungus Colletotrichum gloeosporioides

Melanin is recognized as a dark pigment that can protect fungi from the harm of environmental stresses. To investigate what roles of melanin played in the pathogenicity and development of Colletotrichum gloeosporioides, a causal agent of poplar anthracnose, genes encoding a transcription factor CgCmr1 and a polyketide synthase CgPks1 were isolated as the ortholog of Magnaporthe oryzae Pig1 and Pks1 respectively. Deletion of CgCmr1 or CgPks1 resulted in melanin-deficient fungal colony. The ΔCgPks1 mutant showed no melanin accumulation in appressoria, and lack of CgCmr1 also resulted in the delayed and decreased melanization of appressoria. In addition, the turgor pressure of the appressorium was lower in ΔCgPks1 and ΔCgCmr1 than in the wild-type (WT). However, DHN melanin was not a vital factor for virulence in C. gloeosporioides. Moreover, deletion of CgCmr1 and CgPks1 resulted in the hypersensitivity to hydrogen peroxide (H₂O₂) oxidative stress but not to other abiotic stresses. Collectively, these results suggest that CgCmr1 and CgPks1 play an important role in DHN melanin biosynthesis, and melanin was not an essential factor in penetration and pathogenicity in C. gloeosporioides. The data presented in this study will facilitate future evaluations of the melanin biosynthetic pathway and development in filamentous fungi.

CcPmk1 is a regulator of pathogenicity in Cytospora chrysosperma and can be used as a potential target for disease control

Fus3/Kss1, also known as Pmk1 in several pathogenic fungi, is a component of the mitogen-activated protein kinase (MAPK) signalling pathway that functions as a regulator in fungal development, stress response, mating, and pathogenicity. Cytospora chrysosperma, a notorious woody plant-pathogenic fungus, causes canker disease in many species, and its Pmk1 homolog, CcPmk1, is required for fungal development and pathogenicity. However, the global regulation network of CcPmk1 is still unclear. In this study, we compared transcriptional analysis between a CcPmk1 deletion mutant and the wild type during the simulated infection process. A subset of transcription factor genes and putative effector genes were significantly down-regulated in the CcPmk1 deletion mutant, which might be important for fungal pathogenicity. Additionally, many tandem genes were found to be regulated by CcPmk1. Eleven out of 68 core secondary metabolism biosynthesis genes and several gene clusters were significantly down-regulated in the CcPmk1 deletion mutant. GO annotation of down-regulated genes showed that the ribosome biosynthesis-related processes were over-represented in the CcPmk1 deletion mutant. Comparison of the CcPmk1-regulated genes with the Pmk1-regulated genes from Magnaporthe oryzae revealed only a few overlapping regulated genes in both CcPmk1 and Pmk1, while the enrichment GO terms in the ribosome biosynthesis-related processes were also found. Subsequently, we calculated that in vitro feeding artificial small interference RNAs of CcPmk1 could silence the target gene, resulting in inhibited fungal growth. Furthermore, silencing of BcPmk1 in Botrytis cinerea with conserved CcPmk1 and BcPmk1 fragments could significantly compromise fungal virulence using the virus-induced gene silencing system in Nicotiana benthamiana. These results suggest that CcPmk1 functions as a regulator of pathogenicity and can potentially be designed as a target for broad-spectrum disease control, but unintended effects on nonpathogenic fungi need to be avoided.

Silencing of the Slt2-Type MAP Kinase Bmp3 in Botrytis cinerea by Application of Exogenous dsRNA Affects Fungal Growth and Virulence on Lactuca sativa

Botrytis cinerea can attack over 500 genera of vascular plants and is considered the second phytopathogen in the 'top ten' for its economic importance. Traditional fungicides can be ineffective and with increasing fungicide resistance, new sustainable technologies are required. Lately, RNA interference-based fungicides are emerging for their potential uses in crop protection. Therefore, we assessed the potential of this innovative approach targeting the MAP kinase Bmp3 in B. cinerea, a gene involved in saprophytic growth, response to low osmolarity, conidiation, surface sensing, host penetration and lesion formation. After performing a prediction analysis of small interfering RNAs, a 427 nucleotides long dsRNA was selected as construct. We tested the effect of topical applications of dsRNA construct both in vitro by a fungal growth assay in microtiter plates and in vivo on detached lettuce leaves artificially inoculated. In both cases, topical applications of dsRNA led to gene knockdown with a delay in conidial germination, an evident growth retardation and a strong reduction of necrotic lesions on leaves. These results correlated with a strongly reduced expression of Bmp3 gene. In accordance to these findings, the Bmp3 gene could be a promising target for the development of an RNAi-based fungicide against B. cinerea.

CoGRIM19 is required for invasive hyphal growth of Colletotrichum orbiculare inside epidermal cells of cucumber cotyledons

Colletotrichum orbiculare, an anthracnose disease fungus of cucurbit plants, extends penetration hyphae inside the epidermal cells of host plants. Unlike vegetative hyphae formed on a nutrient rich medium, this pathogen initially develops biotrophic penetration hyphae, which acquire nutrient resources from living host cells and secret effector proteins to suppress host defense responses. Subsequently, the nature of penetration hyphae changes from biotrophy to necrotrophy in response to the interaction with a host plant. Hence, controlling the extension of penetration hyphae is crucial for C. orbiculare infection. Here, we identified CoGRIM19 encoding Nadh-ubiquinone oxidoreductase subunit as a pathogenicity gene. Pathogenicity assays showed that the cogrim19 mutant caused no visible symptoms on cucumber cotyledons. Microscopic observations revealed that the cogrim19 mutant developed an appressorium and penetration hyphae under artificial conditions such as on coverslips or cellulose membranes, but the penetration hyphae of the mutant were retarded in the cucumber cotyledons. Microscopic observations of biotrophy-specific expression fluorescent signals revealed that the biotrophic stage was maintained in the retarded penetration hyphae of the cogrim19 mutant as the penetration of the wild type. In addition to cytological observations, pathogenicity assays using wounded leaves showed that the cogrim19 mutant had an attenuated pathogenesis. Taking our results together, CoGRIM19 is required for invasive hyphal growth inside the epidermal cells of cucumber cotyledons in C. orbiculare.

AaPKAc Regulates Differentiation of Infection Structures Induced by Physicochemical Signals From Pear Fruit Cuticular Wax, Secondary Metabolism, and Pathogenicity of Alternaria alternata

Alternaria alternata, the casual agent of black rot of pear fruit, can sense and respond to the physicochemical cues from the host surface and form infection structures during infection. To evaluate the role of cyclic AMP-dependent protein kinase (cAMP-PKA) signaling in surface sensing of A. alternata, we isolated and functionally characterized the cyclic adenosine monophosphate-dependent protein kinase A catalytic subunit gene (AaPKAc). Gene expression results showed that AaPKAc was strongly expressed during the early stages of appressorium formation on hydrophobic surfaces. Knockout mutants ΔAaPKAc were generated by replacing the target genes via homologous recombination events. We found that intracellular cAMP content increased but PKA content decreased in ΔAaPKAc mutant strain. Appressorium formation and infection hyphae were reduced in the ΔAaPKAc mutant strain, and the ability of the ΔAaPKAc mutant strain to recognize and respond to high hydrophobicity surfaces and different surface waxes was lower than in the wild type (WT) strain. In comparison with the WT strain, the appressorium formation rate of the ΔAaPKAc mutant strain on high hydrophobicity and fruit wax extract surface was reduced by 31.6 and 49.3% 4 h after incubation, respectively. In addition, AaPKAc is required for the hypha growth, biomass, pathogenicity, and toxin production of A. alternata. However, AaPKAc negatively regulated conidia formation, melanin production, and osmotic stress resistance. Collectively, AaPKAc is required for pre-penetration, developmental, physiological, and pathological processes in A. alternata.

The role of vegetative cell fusions in the development and asexual reproduction of the wheat fungal pathogen Zymoseptoria tritici

BACKGROUND

The ability of fungal cells to undergo cell-to-cell communication and anastomosis, the process of vegetative hyphal fusion, allows them to maximize their overall fitness. Previous studies in a number of fungal species have identified the requirement of several signaling pathways for anastomosis, including the so far best characterized soft (So) gene, and the MAPK pathway components MAK-1 and MAK-2 of Neurospora crassa. Despite the observations of hyphal fusions' involvement in pathogenicity and host adhesion, the connection between cell fusion and fungal lifestyles is still unclear. Here, we address the role of anastomosis in fungal development and asexual reproduction in Zymoseptoria tritici, the most important fungal pathogen of wheat in Europe.

RESULTS

We show that Z. tritici undergoes self-fusion between distinct cellular structures, and its mechanism is dependent on the initial cell density. Contrary to other fungi, cell fusion in Z. tritici only resulted in cytoplasmic mixing but not in multinucleated cell formation. The deletion of the So orthologous ZtSof1 disrupted cell-to-cell communication affecting both hyphal and germling fusion. We show that Z. tritici mutants for MAPK-encoding ZtSlt2 (orthologous to MAK-1) and ZtFus3 (orthologous to MAK-2) genes also failed to undergo anastomosis, demonstrating the functional conservation of this signaling mechanism across species. Additionally, the ΔZtSof1 mutant was severely impaired in melanization, suggesting that the So gene function is related to melanization. Finally, we demonstrated that anastomosis is dispensable for pathogenicity, but essential for the pycnidium development, and its absence abolishes the asexual reproduction of Z. tritici.

CONCLUSIONS

We demonstrate the role for ZtSof1, ZtSlt2, and ZtFus3 in cell fusions of Z. tritici. Cell fusions are essential for different aspects of the Z. tritici biology, and the ZtSof1 gene is a potential target to control septoria tritici blotch (STB) disease.

Cell Wall Biogenesis Protein Phosphatase CrSsd1 Is Required for Conidiation, Cell Wall Integrity, and Mycoparasitism in Clonostachys rosea

Cell wall biogenesis protein phosphatases play important roles in various cellular processes in fungi. However, their functions in the widely distributed mycoparasitic fungus Clonostachys rosea remain unclear, as do their potential for controlling plant fungal diseases. Herein, the function of cell wall biogenesis protein phosphatase CrSsd1 in C. rosea 67-1 was investigated using gene disruption and complementation approaches. The gene-deficient mutant ΔCrSsd1 exhibited much lower conidiation, hyphal growth, mycoparasitic ability, and biocontrol efficacy than the wild-type (WT) strain, and it was more sensitive to sorbitol and Congo red. The results indicate that CrSsd1 is involved in fungal conidiation, osmotic stress adaptation, cell wall integrity, and mycoparasitism in C. rosea.

Lifestyle Characteristics and Gene Expression Analysis of Colletotrichum camelliae Isolated from Tea Plant [Camellia sinensis (L.) O. Kuntze] Based on Transcriptome

Colletotrichum camelliae is one of the most serious pathogens causing anthracnose in tea plants, but the interactive relationship between C. camelliae and tea plants has not been fully elucidated. This study investigated the gene expression changes in five different growth stages of C. camelliae based on transcriptome analysis to explain the lifestyle characteristics during the infection. On the basis of gene ontology (GO) enrichment analyses of differentially expressed genes (DEGs) in comparisons of germ tube (GT)/conidium (Con), appressoria (App)/Con, and cellophane infectious hyphae (CIH)/Con groups, the cellular process in the biological process category and intracellular, intracellular part, cell, and cell part in the cellular component category were significantly enriched. Hydrolase activity, catalytic activity, and molecular_function in the molecular function category were particularly enriched in the infection leaves (IL)/Con group. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that the DEGs were enriched in the genetic information processing pathway (ribosome) at the GT stage and the metabolism pathway (metabolic pathways and biosynthesis of secondary metabolism) in the rest of the stages. Interestingly, the genes associated with melanin biosynthesis and carbohydrate-active enzymes (CAZys), which are vital for penetration and cell wall degradation, were significantly upregulated at the App, CIH and IL stages. Subcellular localization results further showed that the selected non-annotated secreted proteins based on transcriptome data were majorly located in the cytoplasm and nucleus, predicted as new candidate effectors. The results of this study may establish a foundation and provide innovative ideas for subsequent research on C. camelliae.

ChCDC25 Regulates Infection-Related Morphogenesis and Pathogenicity of the Crucifer Anthracnose Fungus Colletotrichum higginsianum

The fungal pathogen, Colletotrichum higginsianum, causes a disease called anthracnose on various cruciferous plants. Here, we characterized a Saccharomyces cerevisiae CDC25 ortholog in C. higginsianum, named ChCDC25 (CH063_04363). The ChCDC25 deletion mutants were defective in mycelial growth, conidiation, conidial germination, appressorial formation, and invasive hyphal growth on Arabidopsis leaves, resulting in loss of virulence. Furthermore, deletion of ChCDC25 led to increased sensitivity to cell wall stress and resulted in resistance to osmotic stress. Exogenous cyclic adenosine monophosphate (cAMP) and IBMX treatments were able to induce appressorial formation in the ChCDC25 mutants, but abnormal germ tubes were still formed. The results implied that ChCDC25 is involved in pathogenicity by regulation of cAMP signaling pathways in C. higginsianum. More importantly, we found that ChCDC25 may interact with Ras2 and affects Ras2 protein abundance in C. higginsianum. Taken together, ChCDC25 regulates infection-related morphogenesis and pathogenicity of C. higginsianum. This is the first report to reveal functions of a CDC25 ortholog in a hemibiotrophic phytopathogen.

The cyclase-associated protein ChCAP is important for regulation of hyphal growth, appressorial development, penetration, pathogenicity, conidiation, intracellular cAMP level, and stress tolerance in Colletotrichum higginsianum

Colletotrichum higginsianum causes anthracnose disease in a wide range of cruciferous crops and has been used as a model system to study plant-pathogen interactions and pathogenicity of hemibiotrophic plant pathogens. Conidiation, hyphae growth, appressorial development and appressorial penetration are significant steps during the infection process of C. higginsianum. However, the mechanisms of these important steps during infection remain incompletely understood. To further investigate the mechanisms of the plant-C. higginsianum interactions during infection progress, we characterized Cyclase-Associated Protein (ChCAP) gene. Deletion of the ChCAP gene resulted in reduction in conidiation and hyphal growth rate. The pathogenicity of ΔChCAP mutants was significantly reduced with much smaller lesion on the infected leaves compared to that of wild type strain with typically water-soaked and dark necrotic lesions on Arabidopsis leaves. Further study demonstrated that the appressorial formation rate, turgor pressure, penetration ability and switch from biotrophic to necrotrophic phases decreased obviously in ΔChCAP mutants, indicating that the attenuated pathogenicity of ΔChCAP mutants was due to these defective phenotypes. In addition, the ΔChCAP mutants sectored on PDA with abnormal, dark color, vesicle-like colony morphology and hyphae tip. Moreover, the ΔChCAP mutants had a reduced intracellular cAMP levels and exogenous cAMP can partially rescue the defects of ΔChCAP mutants in appressorial formation and penetration rate, but not in colony morphology, conidial shape and virulence, indicating that ChCAP is a key component in cAMP signaling pathway and likely play other roles in biology of C. higginsianum. In summary, our findings support the role of ChCAP in regulating conidiation, intracellular cAMP level, hyphal growth, appressorial formation, penetration ability and pathogenicity of this hemibiotrophic fungus.

The MAP Kinase CfPMK1 Is a Key Regulator of Pathogenesis, Development, and Stress Tolerance of Colletotrichum fructicola

The Ascomycetes fungus Colletotrichum fructicola causes severe diseases on a wide range of crops, fruits, and vegetables. Its pathogenic mechanisms, however, remain poorly understood. Mitogen-activated protein kinases (MAPKs) are conserved regulators of fungal development and pathogenesis. In this study, a Fus3/Kss1-related MAPK from C. fructicola was functionally characterized via gene deletion. On potato dextrose agar (PDA) and oatmeal agar media, the CfPMK1 gene deletion mutants (ΔCfPMK1) were slightly reduced in radial growth rate, severely limited in aerial hyphal differentiation and hyphal melanization, and formed deformed perithecia that were smaller in size and more compactly organized relative to wild type. When artificially inoculated on plants, conidia of these mutants failed to differentiate appressoria or penetrate cuticle, and their pathogenicity defect could not be rescued by wounding plant tissue prior to inoculation. On PDA, ΔCfPMK1 mutants were hypersensitive to osmotic stresses, but were more tolerant to membrane and cell wall stresses. Genetic complementation rescued all phenotypic changes associated with CfPMK1 gene deletion. Based on GFP fusion expression, CfPMK1 protein accumulation was detected at all life stages, and the accumulation level was higher in nascent appressoria relative to conidia. Overall, this study identified CfPMK1 as a key regulator of appressorium and sexual development, pathogenesis, and stress tolerance in C. fructicola.

Pleiotropic Roles of ChSat4 in Asexual Development, Cell Wall Integrity Maintenance, and Pathogenicity in Colletotrichum higginsianum

Potassium has an important role to play in multiple cellular processes. In Saccharomyces cerevisiae, the serine/threonine (S/T) kinase Sat4/Hal4 is required for potassium accumulation, and thus, regulates the resistance to sodium salts and helps in the stabilization of other plasma membrane transporters. However, the functions of Sat4 in filamentous phytopathogenic fungi are largely unknown. In this study, ChSat4, the yeast Sat4p homolog in Colletotrichum higginsianum, has been identified. Target deletion of ChSAT4 resulted in defects in mycelial growth and sporulation. Intracellular K⁺ accumulation was significantly decreased in the ChSAT4 deletion mutant. Additionally, the ΔChsat4 mutant showed defects in cell wall integrity, hyperoxide stress response, and pathogenicity. Localization pattern analysis indicated ChSat4 was localized in the cytoplasm. Furthermore, ChSat4 showed high functional conservation with the homolog FgSat4 in Fusarium graminearum. Taken together, our data indicated that ChSat4 was important for intracellular K⁺ accumulation and infection morphogenesis in C. higginsianum.

Colletotrichum higginsianum as a Model for Understanding Host⁻Pathogen Interactions: A Review

Colletotrichum higginsianum is a hemibiotrophic ascomycetous fungus that causes economically important anthracnose diseases on numerous monocot and dicot crops worldwide. As a model pathosystem, the Colletotrichum⁻Arabidopsis interaction has the significant advantage that both organisms can be manipulated genetically. The goal of this review is to provide an overview of the system and to point out recent significant studies that update our understanding of the pathogenesis of C. higginsianum and resistance mechanisms of Arabidopsis against this hemibiotrophic fungus. The genome sequence of C. higginsianum has provided insights into how genome structure and pathogen genetic variability has been shaped by transposable elements, and allows systematic approaches to longstanding areas of investigation, including infection structure differentiation and fungal⁻plant interactions. The Arabidopsis-Colletotrichum pathosystem provides an integrated system, with extensive information on the host plant and availability of genomes for both partners, to illustrate many of the important concepts governing fungal⁻plant interactions, and to serve as an excellent starting point for broad perspectives into issues in plant pathology.

Silencing of the Mitogen-Activated Protein Kinases (MAPK) Fus3 and Slt2 in Pseudocercospora fijiensis Reduces Growth and Virulence on Host Plants

Pseudocercospora fijiensis, causal agent of the black Sigatoka disease (BSD) of Musa spp., has spread globally since its discovery in Fiji 1963 to all the banana and plantain growing areas across the globe. It is becoming the most damaging and economically important disease of this crop. The identification and characterization of genes that regulate infection processes and pathogenicity in P. fijiensis will provide important knowledge for the development of disease-resistant cultivars. In many fungal plant pathogens, the Fus3 and Slt2 are reported to be essential for pathogenicity. Fus3 regulates filamentous-invasion pathways including the formation of infection structures, sporulation, virulence, and invasive and filamentous growth, whereas Slt2 is involved in the cell-wall integrity pathway, virulence, invasive growth, and colonization in host tissues. Here, we used RNAi-mediated gene silencing to investigate the role of the Slt2 and Fus3 homologs in P. fijiensis in pathogen invasiveness, growth and pathogenicity. The PfSlt2 and PfFus3 silenced P. fijiensis transformants showed significantly lower gene expression and reduced virulence, invasive growth, and lower biomass in infected leaf tissues of East African Highland Banana (EAHB). This study suggests that Slt2 and Fus3 MAPK signaling pathways play important roles in plant infection and pathogenic growth of fungal pathogens. The silencing of these vital fungal genes through host-induced gene silencing (HIG) could be an alternative strategy for developing transgenic banana and plantain resistant to BSD.

The early response during the interaction of fungal phytopathogen and host plant

Plants can be infected by a variety of pathogens, most of which can cause severe economic losses. The plants resist the invasion of pathogens via the innate or acquired immune system for surviving biotic stress. The associations between plants and pathogens are sophisticated beyond imaging and the interactions between them can occur at a very early stage after their touching each other. A number of researchers in the past decade have shown that many biochemical events appeared even as early as 5 min after their touching for plant disease resistance response. The early molecular interactions of plants and pathogens are likely to involve protein phosphorylation, ion fluxes, reactive oxygen species (ROS) and other signalling transduction. Here, we reviewed the recent progress in the study for molecular interaction response of fungal pathogens and host plant at the early infection stage, which included many economically important crop fungal pathogens such as cereal rust fungi, tomato Cladosporium fulvum, rice blast and so on. By dissecting the earlier infection stage of the diseases, the avirulent/virulent genes of pathogen or resistance genes of plant could be defined more clearly and accurately, which would undoubtedly facilitate fungal pathogenesis study and resistant crop breeding.

The Mitogen-Activated Protein Kinase CgMK1 Governs Appressorium Formation, Melanin Synthesis, and Plant Infection of Colletotrichum gloeosporioides

The fungus Colletotrichum gloeosporiodes infects plant hosts with a specialized cell called an appressorium, which is melanized and required for plant cell wall penetration. Here, we show that the mitogen-activated protein kinase CgMK1 governs appressorium formation and virulence in the poplar anthracnose fungus C. gloeosporioides. Deletion of CgMK1 impairs aerial hyphal growth and biomass accumulation, and CgMK1 is responsible for the expression of melanin biosynthesis-associated genes. CgMK1 deletion mutants are unable to form appressorium and lose the capacity to colonize either wounded or unwounded poplar leaves, leading to loss of virulence. We demonstrate that the exogenous application of cAMP fails to restore defective appressorium formation in the CgMK1 deletion mutants, suggesting that CgMK1 may function downstream or independent of a cAMP-dependent signal for appressorium formation. Moreover, CgMK1 mutants were sensitive to high osmosis, indicating that CgMK1 plays an important role in stress response. We conclude that CgMK1 plays a vital role in regulating appressorium formation, melanin biosynthesis, and virulence in C. gloeosporiodes.

A mitogen-activated protein kinase gene (VmPmk1) regulates virulence and cell wall degrading enzyme expression in Valsa mali

Mitogen-activated protein kinases (MAPKs) play critical roles in the regulation of different developmental processes and hydrolytic enzyme production in many fungal plant pathogens. In this study, an FUS3/KSS1-related MAPK gene, VmPmk1, was identified and characterized in Valsa mali, which causes a highly destructive canker disease on apple. VmPmk1 deletion mutant showed a significant reduction in growth rate in vitro, and could not produce pycnidium, indicating that the MAPK gene is important for growth and asexual development. Also, VmPmk1 played a significant role in response to oxidative stress and in the maintenance of cell wall integrity. More importantly, when deletion mutant was inoculated onto detached apple leaves and twigs, an obvious decrease in lesion size was observed. Furthermore, expression of many cell wall degrading enzyme (CWDE) genes declined in the VmPmk1 deletion mutant during infection. VmPmk1 deletion mutant also showed a significant reduction in activities of CWDEs in both induced media and infection process. Finally, the determination of immunogold labeling of pectin demonstrated that the capacity of degradation pectin was attenuated due to the deletion of VmPmk1. These results indicated that VmPmk1 plays important roles in growth, asexual development, response to oxidative stress, and maintenance of cell wall integrity. More importantly, VmPmk1 is involved in pathogenicity of V. mali mainly by regulating CWDE genes expression.

The cAMP-PKA Signaling Pathway Regulates Pathogenicity, Hyphal Growth, Appressorial Formation, Conidiation, and Stress Tolerance in Colletotrichum higginsianum

Colletotrichum higginsianum is an economically important pathogen that causes anthracnose disease in a wide range of cruciferous crops. Understanding the mechanisms of the cruciferous plant–C. higginsianum interactions will be important in facilitating efficient control of anthracnose diseases. The cAMP-PKA signaling pathway plays important roles in diverse physiological processes of multiple pathogens. C. higginsianum contains two genes, ChPKA1 and ChPKA2, that encode the catalytic subunits of cyclic AMP (cAMP)-dependent protein kinase A (PKA). To analyze the role of cAMP signaling pathway in pathogenicity and development in C. higginsianum, we characterized ChPKA1 and ChPKA2 genes, and adenylate cyclase (ChAC) gene. The ChPKA1 and ChAC deletion mutants were unable to cause disease and significantly reduced in hyphal growth, tolerance to cell wall inhibitors, conidiation, and appressorial formation with abnormal germ tubes, but they had an increased tolerance to elevated temperatures and exogenous H₂O₂. In contrast, the ChPKA2 mutant had no detectable alteration of phenotypes, suggesting that ChPKA1 contributes mainly to PKA activities in C. higginsianum. Moreover, we failed to generate ΔChPKA1ChPKA2 double mutant, indicating that deletion of both PKA catalytic subunits is lethal in C. higginsianum and the two catalytic subunits possibly have overlapping functions. These results indicated that ChPKA1 is the major PKA catalytic subunit in cAMP-PKA signaling pathway and plays significant roles in hyphal growth, pathogenicity, appressorial formation, conidiation, and stress tolerance in C. higginsianum.