Kelch repeat protein Clakel2p and calcium signaling control appressorium development in Colletotrichum lagenarium

Diversity and Function of Appressoria

Endophytic, saprobic, and pathogenic fungi have evolved elaborate strategies to obtain nutrients from plants. Among the diverse plant-fungi interactions, the most crucial event is the attachment and penetration of the plant surface. Appressoria, specialized infection structures, have been evolved to facilitate this purpose. In this review, we describe the diversity of these appressoria and classify them into two main groups: single-celled appressoria (proto-appressoria, hyaline appressoria, melanized (dark) appressoria) and compound appressoria. The ultrastructure of appressoria, their initiation, their formation, and their function in fungi are discussed. We reviewed the molecular mechanisms regulating the formation and function of appressoria, their strategies to evade host defenses, and the related genomics and transcriptomics. The current review provides a foundation for comprehensive studies regarding their evolution and diversity in different fungal groups.

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.

Deciphering the Infectious Process of Colletotrichum lupini in Lupin through Transcriptomic and Proteomic Analysis

The fungal phytopathogen Colletotrichum lupini is responsible for lupin anthracnose, resulting in significant yield losses worldwide. The molecular mechanisms underlying this infectious process are yet to be elucidated. This study proposes to evaluate C. lupini gene expression and protein synthesis during lupin infection, using, respectively, an RNAseq-based transcriptomic approach and a mass spectrometry-based proteomic approach. Patterns of differentially-expressed genes in planta were evaluated from 24 to 84 hours post-inoculation, and compared to in vitro cultures. A total of 897 differentially-expressed genes were identified from C. lupini during interaction with white lupin, of which 520 genes were predicted to have a putative function, including carbohydrate active enzyme, effector, protease or transporter-encoding genes, commonly described as pathogenicity factors for other Colletotrichum species during plant infection, and 377 hypothetical proteins. Simultaneously, a total of 304 proteins produced during the interaction were identified and quantified by mass spectrometry. Taken together, the results highlight that the dynamics of symptoms, gene expression and protein synthesis shared similarities to those of hemibiotrophic pathogens. In addition, a few genes with unknown or poorly-described functions were found to be specifically associated with the early or late stages of infection, suggesting that they may be of importance for pathogenicity. This study, conducted for the first time on a species belonging to the Colletotrichum acutatum species complex, presents an opportunity to deepen functional analyses of the genes involved in the pathogenicity of Colletotrichum spp. during the onset of plant infection.

An efficient gene disruption method for the woody plant pathogen Botryosphaeria dothidea

Background

Botryosphaeria dothidea causes apple white rot and infects many tree plants. Genome data for B. dothidea are available and many pathogenesis-related genes have been predicted. However, a gene manipulation method is needed to study the pathogenic mechanism of B. dothidea.

Results

We established a gene disruption (GD) method based on gene homologous recombination (GHR) for B. dothidea using polyethylene glycol-mediated protoplast transformation. The results showed that a GHR cassette gave much higher GD efficiency than a GHR plasmid. A high GD efficiency (1.3 ± 0.14 per 10⁶ protopasts) and low frequency of random insertions were achieved with a DNA cassette quantity of 15 μg per 10⁶ protoplasts. Moreover, we successfully disrupted genes in two strains. Bdo_05381-disrupted transformants produced less melanin, whereas the Bdo_02540-disrupted transformant showed a slower growth rate and a stronger resistance to Congo red.

Conclusion

The established GD method is efficient and convenient and has potential for studying gene functions and the pathogenic mechanisms of B. dothidea and other coenocytic fungi.

Colletotrichum orbiculare MTF4 Is a Key Transcription Factor Downstream of MOR Essential for Plant Signal-Dependent Appressorium Development and Pathogenesis

The cucumber anthracnose fungus Colletotrichum orbiculare forms a specialized infection structure, called an appressorium. Appressorium differentiation relies on fungal perception of physical and biochemical signals at the plant surface. Our previous report showed that the morphogenesis-related NDR (nuclear Dbf2-related) kinase pathway (MOR) is crucial for translating plant-derived signals for appressorium development. Here, we focused on identifying transcriptional regulators downstream of MOR that are involved in plant signal sensing and transduction for appressorium development. Based on whole-genome transcript profiling, we identified a Zn(II)₂Cys₆ transcription factor, CoMTF4, as a potential downstream factor of MOR. CoMTF4 was expressed in planta rather than in vitro under the control of the NDR kinase CoCbk1. Phenotypes of comtf4 mutants, strains with constitutively active CoCbk1 and strains with constitutive overexpression of CoMTF4 suggested that CoMtf4 acts downstream of MOR. Furthermore, nuclear localization of CoMtf4 was dependent on the MOR and responsive to plant-derived signals that lead to appressorium morphogenesis. Thus, we conclude that CoMtf4 is a transcription factor downstream of MOR that is essential for appressorium morphogenesis and pathogenesis and is regulated in response to plant-derived signals. This study provides insights into fungal sensing of plant signals and subsequent responses critical for appressorium formation.

UmTea1, a Kelch and BAR domain-containing protein, acts at the cell cortex to regulate cell morphogenesis in the dimorphic fungus Ustilago maydis

The spatial organization of a cell is crucial for distribution of cell components and for cell morphogenesis in all organisms. Ustilago maydis, a basidiomycete fungus, has a yeast-like and a filamentous form. The former buds once per cell cycle at one of the cell poles, and can use the same site repeatedly or choose a new site at the same pole or opposite pole. The filamentous form consists of a long apical cell with short septate basal compartments lacking cytoplasm. It grows at the apex and can reverse growth forming a new growth zone at the basal end. We are interested in understanding how these different morphologies are generated. Here we present identification and characterization of U. maydis Tea1, a homologue of the fission yeast cell end marker Tea1. We demonstrate that UmTea1, a Kelch domain protein, interacts with itself and is an important determinant of the site of polarized growth: tea1 mutants bud simultaneously from both cell poles and form bifurcate buds. UmTea1 also regulates septum positioning, cell wall deposition, cell and neck width, coordination of nuclear division and cell separation, and localization of sterol-rich membrane domains. Some of these functions are shared with UmTea4, another cell end marker. We show that Tea1::GFP localizes to sites of polarized or potential polarized growth and to the septation site in the yeast-like form. Additionally, localization of Tea1::GFP as rings along the filament suggests that the filament undergoes septation. We hypothesize that Tea1 may act as a scaffold for the assembly of proteins that determine the site of polarized growth.

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

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

The morphogenesis-related NDR kinase pathway of Colletotrichum orbiculare is required for translating plant surface signals into infection-related morphogenesis and pathogenesis

Plant infection by pathogenic fungi involves the differentiation of appressoria, specialized infection structures, initiated by fungal sensing and responding to plant surface signals. How plant fungal pathogens control infection-related morphogenesis in response to plant-derived signals has been unclear. Here we showed that the morphogenesis-related NDR kinase pathway (MOR) of the cucumber anthracnose fungus Colletotrichum orbiculare is crucial for appressorium development following perception of plant-derived signals. By screening of random insertional mutants, we identified that the MOR element CoPag1 (Perish-in-the-absence-of-GYP1) is a key component of the plant-derived signaling pathway involved in appressorium morphogenesis. Constitutive activation of the NDR kinase CoCbk1 (Cell-wall-biosynthesis-kinase-1) complemented copag1 defects. Furthermore, copag1 deletion impaired CoCbk1 phosphorylation, suggesting that CoPag1 functions via CoCbk1 activation. Searching for the plant signals that contribute to appressorium induction via MOR, we found that the cutin monomer n-octadecanal, degraded from the host cuticle by conidial esterases, functions as a signal molecule for appressorium development. Genome-wide transcriptional profiling during appressorium development revealed that MOR is responsible for the expression of a subset of the plant-signal-induced genes with potential roles in pathogenicity. Thus, MOR of C. orbiculare has crucial roles in regulating appressorium development and pathogenesis by communicating with plant-derived signals.

ChMob2 binds to ChCbk1 and promotes virulence and conidiation of the fungal pathogen Colletotrichum higginsianum

Background

Mob family proteins are conserved between animals, plants and fungi and are essential for the activation of NDR kinases that control crucial cellular processes like cytokinesis, proliferation and morphology.

Results

We identified a hypomorphic allele of ChMOB2 in a random insertional mutant (vir-88) of the hemibiotrophic ascomycete fungus Colletotrichum higginsianum. The mutant is impaired in conidiation, host penetration and virulence on Arabidopsis thaliana. ChMob2 binds to and co-localizes with the NDR/LATS kinase homolog ChCbk1. Mutants in the two potential ChCbk1 downstream targets ChSSD1 and ChACE2 show defects in pathogenicity. The genome of C. higginsianum encodes two more Mob proteins. While we could not detect any effect on pathogenicity in ΔChmob3 mutants, ChMob1 is involved in conidiation, septae formation and virulence.

Conclusion

This study shows that ChMob2 binds to the conserved NDR/LATS Kinase ChCbk1 and plays an important role in pathogenicity of Colletotrichum higginsianum on Arabidopsis thaliana.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-017-0932-7) contains supplementary material, which is available to authorized users.

Friends or foes? Emerging insights from fungal interactions with plants

Fungi interact with plants in various ways, with each interaction giving rise to different alterations in both partners. While fungal pathogens have detrimental effects on plant physiology, mutualistic fungi augment host defence responses to pathogens and/or improve plant nutrient uptake. Tropic growth towards plant roots or stomata, mediated by chemical and topographical signals, has been described for several fungi, with evidence of species-specific signals and sensing mechanisms. Fungal partners secrete bioactive molecules such as small peptide effectors, enzymes and secondary metabolites which facilitate colonization and contribute to both symbiotic and pathogenic relationships. There has been tremendous advancement in fungal molecular biology, omics sciences and microscopy in recent years, opening up new possibilities for the identification of key molecular mechanisms in plant-fungal interactions, the power of which is often borne out in their combination. Our fragmentary knowledge on the interactions between plants and fungi must be made whole to understand the potential of fungi in preventing plant diseases, improving plant productivity and understanding ecosystem stability. Here, we review innovative methods and the associated new insights into plant-fungal interactions.

Colletotrichum orbiculare FAM1 Encodes a Novel Woronin Body-Associated Pex22 Peroxin Required for Appressorium-Mediated Plant Infection

The cucumber anthracnose fungus Colletotrichum orbiculare forms specialized cells called appressoria for host penetration. We identified a gene, FAM1, encoding a novel peroxin protein that is essential for peroxisome biogenesis and that associates with Woronin bodies (WBs), dense-core vesicles found only in filamentous ascomycete fungi which function to maintain cellular integrity. The fam1 disrupted mutants were unable to grow on medium containing oleic acids as the sole carbon source and were nonpathogenic, being defective in both appressorium melanization and host penetration. Fluorescent proteins carrying peroxisomal targeting signals (PTSs) were not imported into the peroxisomes of fam1 mutants, suggesting that FAM1 is a novel peroxisomal biogenesis gene (peroxin). FAM1 did not show significant homology to any Saccharomyces cerevisiae peroxins but resembled conserved filamentous ascomycete-specific Pex22-like proteins which contain a predicted Pex4-binding site and are potentially involved in recycling PTS receptors from peroxisomes to the cytosol. C. orbiculare FAM1 complemented the peroxisomal matrix protein import defect of the S. cerevisiae pex22 mutant. Confocal microscopy of Fam1-GFP (green fluorescent protein) fusion proteins and immunoelectron microscopy with anti-Fam1 antibodies showed that Fam1 localized to nascent WBs budding from peroxisomes and mature WBs. Association of Fam1 with WBs was confirmed by colocalization with WB matrix protein CoHex1 (C. orbiculare Hex1) and WB membrane protein CoWsc (C. orbiculare Wsc) and by subcellular fractionation and Western blotting with antibodies to Fam1 and CoHex1. In WB-deficient cohex1 mutants, Fam1 was redirected to the peroxisome membrane. Our results show that Fam1 is a WB-associated peroxin required for pathogenesis and raise the possibility that localized receptor recycling occurs in WBs.

IMPORTANCE

Colletotrichum orbiculare is a fungus causing damaging disease on Cucurbitaceae plants. In this paper, we characterize a novel peroxisome biogenesis gene from this pathogen called FAM1. Although no genes with significant homology are present in Saccharomyces cerevisiae, FAM1 contains a predicted Pex4-binding site typical of Pex22 proteins, which function in the recycling of PTS receptors from peroxisomes to the cytosol. We show that FAM1 complements the defect in peroxisomal matrix protein import of S. cerevisiae pex22 mutants and that fam1 mutants are completely defective in peroxisome function, fatty acid metabolism, and pathogenicity. Remarkably, we found that this novel peroxin is specifically localized on the bounding membrane of Woronin bodies, which are small peroxisome-derived organelles unique to filamentous ascomycete fungi that function in septal pore plugging. Our finding suggests that these fungi have coopted the Woronin body for localized receptor recycling during matrix protein import.

Colletotrichum orbiculare Regulates Cell Cycle G1/S Progression via a Two-Component GAP and a GTPase to Establish Plant Infection

Morphogenesis in filamentous fungi depends on appropriate cell cycle progression. Here, we report that cells of the cucumber anthracnose fungus Colletotrichum orbiculare regulate G1/S progression via a two-component GAP, consisting of Budding-uninhibited-by-benomyl-2 (Bub2) and Byr-four-alike-1 (Bfa1) as well as its GTPase Termination-of-M-phase-1 (Tem1) to establish successful infection. In a random insertional mutagenesis screen of infection-related morphogenesis, we isolated a homolog of Saccharomyces cerevisiae, BUB2, which encodes a two-component Rab GAP protein that forms a GAP complex with Bfa1p and negatively regulates mitotic exit. Interestingly, disruption of either Co BUB2 or Co BFA1 resulted in earlier onset of nuclear division and decreased the time of phase progression from G1 to S during appressorium development. S. cerevisiae GTPase Tem1p is the downstream target of the Bub2p/Bfa1p GAP complex. Introducing the dominant-negative form of Co Tem1 into Co bub2Δ or Co bfa1Δ complemented the defect in G1/S progression, indicating that Co Bub2/Co Bfa1 regulates G1/S progression via Co Tem1. Based on a pathogenicity assay, we found that Co bub2Δ and Co bfa1Δ reduced pathogenesis by attenuating infection-related morphogenesis and enhancing the plant defense response. Thus, during appressorium development, C. orbiculare Bub2/Bfa1 regulates G1/S progression via Co Tem1, and this regulation is essential to establish plant infection.

A Genetic Screen for Pathogenicity Genes in the Hemibiotrophic Fungus Colletotrichum higginsianum Identifies the Plasma Membrane Proton Pump Pma2 Required for Host Penetration

We used insertional mutagenesis by Agrobacterium tumefaciens mediated transformation (ATMT) to isolate pathogenicity mutants of Colletotrichum higginsianum. From a collection of 7200 insertion mutants we isolated 75 mutants with reduced symptoms. 19 of these were affected in host penetration, while 17 were affected in later stages of infection, like switching to necrotrophic growth. For 16 mutants the location of T-DNA insertions could be identified by PCR. A potential plasma membrane H⁺-ATPase Pma2 was targeted in five independent insertion mutants. We genetically inactivated the Ku80 component of the non-homologous end-joining pathway in C. higginsianum to establish an efficient gene knockout protocol. Chpma2 deletion mutants generated by homologous recombination in the ΔChku80 background form fully melanized appressoria but entirely fail to penetrate the host tissue and are non-pathogenic. The ChPMA2 gene is induced upon appressoria formation and infection of A. thaliana. Pma2 activity is not important for vegetative growth of saprophytically growing mycelium, since the mutant shows no growth penalty under these conditions. Colletotrichum higginsianum codes for a closely related gene (ChPMA1), which is highly expressed under most growth conditions. ChPMA1 is more similar to the homologous yeast genes for plasma membrane pumps. We propose that expression of a specific proton pump early during infection may be common to many appressoria forming fungal pathogens as we found ChPMA2 orthologs in several plant pathogenic fungi.

The cell end marker Tea4 regulates morphogenesis and pathogenicity in the basidiomycete fungus Ustilago maydis

Positional cues localized to distinct cell domains are critical for the generation of cell polarity and cell morphogenesis. These cues lead to assembly of protein complexes that organize the cytoskeleton resulting in delivery of vesicles to sites of polarized growth. Tea4, an SH3 domain protein, was first identified in fission yeast, and is a critical determinant of the axis of polarized growth, a role conserved among ascomycete fungi. Ustilago maydis is a badiomycete fungus that exhibits a yeast-like form that is nonpathogenic and a filamentous form that is pathogenic on maize and teozintle. We are interested in understanding how positional cues contribute to generation and maintenance of these two forms, and their role in pathogenicity. We identified a homologue of fission yeast tea4 in a genetic screen for mutants with altered colony and cell morphology and present here analysis of Tea4 for the first time in a basidiomycete fungus. We demonstrate that Tea4 is an important positional marker for polarized growth and septum location in both forms. We uncover roles for Tea4 in maintenance of cell and neck width, cell separation, and cell wall deposition in the yeast-like form, and in growth rate, formation of retraction septa, growth reversal, and inhibition of budding in the filamentous form. We show that Tea4::GFP localizes to sites of polarized or potential polarized growth in both forms, as observed in ascomycete fungi. We demonstrate an essential role of Tea4 in pathogencity in the absence of cell fusion. Basidiomycete and ascomycete Tea4 homologues share SH3 and Glc7 domains. Tea4 in basidiomycetes has additional domains, which has led us to hypothesize that Tea4 has novel functions in this group of fungi.

Agrobacterium tumefaciens-mediated transformation of Valsa mali: an efficient tool for random insertion mutagenesis

Valsa mali is a causal agent of apple and pear trees canker disease, which is a destructive disease that causes serious economic losses in eastern Asia, especially in China. The lack of an efficient transformation system for Valsa mali retards its investigation, which poses difficulties to control the disease. In this research, a transformation system for this pathogen was established for the first time using A. tumefaciens-mediated transformation (ATMT), with the optimal transformation conditions as follows: 10(6)/mL conidia suspension, cocultivation temperature 22°C, cocultivation time 72 hours, and 200  μ M acetosyringone (AS) in the inductive medium. The average transformation efficiency was 1015.00 ± 37.35 transformants per 10(6) recipient conidia. Thirty transformants were randomly selected for further confirmation and the results showed the presence of T-DNA in all hygromycin B resistant transformants and also revealed random and single gene integration with genetic stability. Compared with wild-type strain, those transformants exhibited various differences in morphology, conidia production, and conidia germination ability. In addition, pathogenicity assays revealed that 14 transformants had mitigated pathogenicity, while one had enhanced infection ability. The results suggest that ATMT of V. mali is a useful tool to gain novel insight into this economically important pathogen at molecular levels.

A yeast STE11 homologue CoMEKK1 is essential for pathogenesis-related morphogenesis in Colletotrichum orbiculare

Several signal transduction pathways, including mitogen-activated protein kinase (MAPK) pathways, are involved in appressorium development in Colletotrichum orbiculare, the causal agent of cucumber anthracnose disease. In this study, CoMEKK1, a yeast MAPK kinases (MAPKK) kinase STE11 homolog, was identified as a disrupted gene in an Agrobacterium tumefaciens-mediated transformation mutant. The phenotype of comekk1 disruptant was similar to that of cmk1, a Saccharomyces cerevisiae Fus3/Kss1 MAPK homolog mutant. Moreover, comekk1 and cmk1 mutants were sensitive to high osmotic and salinity stresses, indicating that Comekk1p/Cmk1p signal transduction is involved in stress tolerance. The transformants of the wild type and the comekk1 mutant expressing a constitutively active form of the CoMEKK1 showed slower hyphal growth and abnormal appressorium formation, whereas those of the cmk1 disruptant did not. A Cmk1p-green fluorescent protein (GFP) intracellular localization experiment indicated that nuclear localization of the Cmk1p-GFP fusion protein induced by salt stress was diminished in comekk1 mutants. These results indicate that Comekk1p functions upstream of Cmk1p.

MoTea4-mediated polarized growth is essential for proper asexual development and pathogenesis in Magnaporthe oryzae

Polarized growth is essential for cellular development and function and requires coordinated organization of the cytoskeletal elements. Tea4, an important polarity determinant, regulates localized F-actin assembly and bipolar growth in fission yeast and directional mycelial growth in Aspergillus. Here, we characterize Tea4 in the rice blast fungus Magnaporthe oryzae (MoTea4). Similar to its orthologs, MoTea4-green fluorescent protein (MoTea4-GFP) showed punctate distribution confined to growth zones, particularly in the mycelial tips, aerial hyphae, conidiophores, conidia, and infection structures (appressoria) in Magnaporthe. MoTea4 was dispensable for vegetative growth in Magnaporthe. However, loss of MoTea4 led to a zigzag morphology in the aerial hyphae and a huge reduction in conidiation. The majority of the tea4Delta conidia were two celled, as opposed to the tricellular conidia in the wild type. Structure-function analysis indicated that the SH3 and coiled-coil domains of MoTea4 are necessary for proper conidiation in Magnaporthe. The tea4Delta conidia failed to produce proper appressoria and consequently failed to infect the host plants. The tea4Delta conidia and germ tubes showed disorganized F-actin structures with significantly reduced numbers of cortical actin patches. Compared to the wild-type conidia, the tea4Delta conidia showed aberrant germination, poor cytoplasmic streaming, and persistent accumulation of lipid droplets, likely due to the impaired F-actin cytoskeleton. Latrunculin A treatment of germinating wild-type conidia showed that an intact F-actin cytoskeleton is indeed essential for appressorial development in Magnaporthe. We show that MoTea4 plays an important role in organizing the F-actin cytoskeleton and is essentially required for polarized growth and morphogenesis during asexual and pathogenic development in Magnaporthe.

A Kelch repeat protein, Cokel1p, associates with microtubules and is involved in appressorium development in Colletotrichum orbiculare

Kelch repeat proteins are conserved in diverse organisms and some are known to mediate fundamental cellular functions. We isolated the gene CoKEL1, encoding a novel kelch repeat protein, from Colletotrichum orbiculare. Analysis of a cokel1 mutant indicated that CoKEL1 is involved in proper appressorium development and cell wall synthesis. Appressoria produced by cokel1 disruption mutants showed irregular shape and impairment of turgor generation and the mutant appressoria rarely penetrated to form infection hyphae in host epidermal cells. Accordingly, cokel1 mutants had reduced pathogenicity on host leaves compared with the wild type. Furthermore, the cokel1 mutant was more sensitive to cell-wall-degrading enzymes and showed altered labeling with the cell wall stain Calcofluor white. Cokel1p was localized on cortical and spindle microtubules in vegetative hyphae. These results suggest that Cokel1p is a microtubule-associated protein involved in infection-related morphogenesis and pathogenicity. This is the first report that a kelch repeat protein is required for the pathogenicity of a fungal plant pathogen.