New genera and species with chloridium-like morphotype in the Chaetosphaeriales and Vermiculariopsiellales

In this study, we investigated the morphological and genetic variability of selected species belonging to the genus Chloridium sensu lato, some also referred to as chloridium-like asexual morphs and other undescribed morphologically similar fungi. These species do not conform to the revised generic concept and thus necessitate a re-evaluation in terms of taxonomy and phylogeny. The family Chaetosphaeriaceae (Chaetosphaeriales) encompasses a wide range of asexual morphotypes, and among them, the simplest form is represented by Chloridium sect. Chloridium. The morphological simplicity of the Chloridium morphotype has historically led to the amalgamation of numerous unrelated species, thereby creating a heterogeneous genus. By conducting phylogenetic reconstruction of four DNA loci and examining a set of 71 strains, including all available ex-type and other non-type strains as well as holotypes and other herbarium material, we were able to gain new insights into the relationships between these taxa. Phylogenetic analyses revealed that the studied species are distantly related to Chloridium sensu stricto and can be grouped into two orders in the Sordariomycetes. Within the Chaetosphaeriales, they formed nine well-separated genera in four clades, such as Cacumisporium, Caliciastrum gen. nov., Caligospora gen. nov., Capillisphaeria gen. nov., Curvichaeta, Fusichloridium, Geniculoseta gen. nov., Papillospora gen. nov., and Spicatispora gen. nov. We also established Chloridiopsiella gen. nov. and Chloridiopsis gen. nov. in Vermiculariopsiellales. Four new species and eight new combinations are proposed in these genera. Our study provides a clearer understanding of the genus Chloridium, its relationship to other morphologically similar fungi, and a new taxonomic treatment and molecular phylogeny to facilitate their accurate identification and classification in future research. Taxonomic novelties: New genera: Caliciastrum Réblová, Caligospora Réblová, Capillisphaeria Réblová, Chloridiopsiella Réblová, Chloridiopsis Réblová, Geniculoseta Réblová, Papillospora Réblová, Spicatispora Réblová; New species: Caliciastrum bicolor Réblová, Caligospora pannosa Réblová, Chloridiopsis syzygii Réblová, Gongromerizella silvana Réblová; New combinations: Caligospora dilabens (Réblová & W. Gams) Réblová, Capillisphaeria crustacea (Sacc.) Réblová, Chloridiopsiella preussii (W. Gams & Hol.-Jech.) Réblová, Chloridiopsis constrictospora (Crous et al.) Réblová, Geniculoseta preussii (W. Gams & Hol.-Jech.) Réblová, Papillospora hebetiseta (Réblová & W. Gams) Réblová, Spicatispora carpatica (Hol.-Jech. & Révay) Réblová, Spicatispora fennica (P. Karst.) Réblová; Epitypifications (basionyms): Chaetosphaeria dilabens Réblová & W. Gams, Chloridium cylindrosporum W. Gams & Hol.-Jech. Citation: Réblová M, Nekvindová J (2023). New genera and species with chloridium-like morphotype in the Chaetosphaeriales and Vermiculariopsiellales. Studies in Mycology 106: 199-258. doi: 10.3114/sim.2023.106.04.

MoMih1 is indispensable for asexual development, cell wall integrity, and pathogenicity of Magnaporthe oryzae

Asexual spore serves as essential inoculum of rice blast during the disease cycle, and differentiation of young conidium from conidiophore is intimately regulated by cell cycle. Mih1 encodes a dual-specificity phosphatase that involved in the G2/M transition of the mitotic cell cycle by regulating the Cdk1 activity in eukaryotes. Till now, the roles of Mih1 homologue, however, remain unclear in Magnaporthe oryzae. We here functionally characterized the Mih1 homologue MoMih1 in M. oryzae. MoMih1 is localized to both the cytoplasm and nucleus and can physically interact with the CDK protein MoCdc28 in vivo. Loss of MoMih1 led to delayed nucleus division and a high level of Tyr15 phosphorylation of MoCdc28. The MoMih1 mutants showed retarded mycelial growth with a defective polar growth, less fungal biomass, and shorter distance between diaphragms, compared with the KU80. Asexual reproduction altered in MoMih1 mutants, with both abnormal conidial morphogenesis and decreased conidiation. The MoMih1 mutants severely attenuated the virulence to host plants due to the impaired ability of penetration and biotrophic growth. The incapability of scavenging of host-derived reactive oxygen species, which was possibly ascribed to the severely decreased extracellular enzymes activities, were partially associated with deficiency of pathogenicity. Besides, the MoMih1 mutants displayed also improper localization of retromer protein MoVps26 and polarisome component MoSpa2, and defects of cell wall integrity (CWI), melanin pigmentation, chitin synthesis, and hydrophobicity. In conclusion, our results demonstrate that MoMih1 plays pleiotropic roles during fungal development and plant infection of M. oryzae.

Aspartate Transaminase AST2 Involved in Sporulation and Necrotrophic Pathogenesis in the Hemibiotrophs Magnaporthe oryzae and Colletotrichum graminicola

Aspartate family includes five additional amino acids other than aspartate, among which most except aspartate have been reported for their action in pathogenesis by amino acid biosynthesis. However, how aspartate, the initial substrate of this family metabolic pathway, is involved in pathogenesis remains unknown. Here, we focused on aspartate transaminase (AST) that catalyzes transamination reaction between glutamate-aspartate in Magnaporthe oryzae. Three MoAST genes were bioinformatically analyzed, of which MoAST2 was uniquely upregulated when invasive hyphae switched to necrotrophic pathogenesis. MoAST2 deletion (ΔMoast2) caused a drastic reduction in conidiogenesis and appressorium formation. Particularly, ΔMoast2 was observed to be proliferated at the biotrophic phase but inhibited at the necrotrophic stage, and with invisible symptoms detected, suggesting a critical role in necrotrophic phase. Glutamate family restored the ΔMoast2 defects but aspartate family did not, inferring that transamination occurs from aspartate to glutamine. MoAST2 is cytosolic and possessed H₂O₂ stress tolerance. In parallel, Colletotrichum graminicola AST2, CgAST2 was proven to be a player in necrotrophic anthracnose development. Therefore, conserved AST2 is qualified to be a drug target for disease control.

Proteomic and Phosphoryproteomic Investigations Reveal that Autophagy-Related Protein 1, a Protein Kinase for Autophagy Initiation, Synchronously Deploys Phosphoregulation on the Ubiquitin-Like Conjugation System in the Mycopathogen Beauveria bassiana

Autophagy is a conserved intracellular degradation mechanism in eukaryotes and is initiated by the protein kinase autophagy-related protein 1 (Atg1). However, except for the autophosphorylation activity of Atg1, the target proteins phosphorylated by Atg1 are largely unknown in filamentous fungi. In Beauveria bassiana (a filamentous insect-pathogenic fungus), Atg1 is indispensable for autophagy and is associated with fungal development. Comparative omics-based analyses revealed that B. bassiana Atg1 (BbAtg1) has key influence on the proteome and phosphoproteome during conidiogenesis. In terms of its physiological functions, the BbAtg1-mediated phosphoproteome is primarily associated with metabolism, signal transduction, cell cycle, and autophagy. At the proteomic level, BbAtg1 mainly regulates genes involved in protein synthesis, protein fate, and protein with binding function. Furthermore, integrative analyses of phosphoproteomic and proteomic data led to the identification of several potential targets regulated by BbAtg1 phosphorylation activity. Notably, we demonstrated that BbAtg1 phosphorylated BbAtg3, an essential component of the ubiquitin-like conjugation system in autophagic progress. Our findings indicate that in addition to being a critical component of the autophagy initiation, Atg1 orchestrates autophagosome elongation via its phosphorylation activity. The data from our study will facilitate future studies on the noncanonical targets of Atg1 and help decipher the Atg1-mediated phosphorylation networks.

IMPORTANCE Autophagy-related protein 1 (Atg1) is a serine/threonine protein kinase for autophagy initiation. In contrast to the unicellular yeast, the target proteins phosphorylated by Atg1 are largely unknown in filamentous fungi. In this study, the entomopathogenic fungus Beauveria bassiana was used as a representative of filamentous fungi due to its importance in the applied and fundamental research. We revealed that Atg1 mediates the comprehensive proteome and phosphoproteome, which differ from those revealed in yeast. Further investigation revealed that Atg1 directly phosphorylates the E2-like enzyme Atg3 of the ubiquitin-like conjugation system (ULCS), and the phosphorylation of Atg3 is indispensable for ULCS functionality. Interestingly, the phosphorylation site of Atg3 is conserved among a set of insect- and plant-pathogenic fungi but not in human-pathogenic fungi. This study reveals new regulatory mechanisms of autophagy and provides new insights into the evolutionary diversity of the Atg1 kinase signaling pathways among different pathogenic fungi.

Optimization of granular formulations of Metarhizium humberi microsclerotia with humectants

Granular microsclerotial formulations of entomopathogenic fungi deserve attention because of their post-application, in situ production of new conidia that enhance and prolong mycoinsecticidal efficacy against a target pest insect. Because high ambient moisture is a crucial condition to induce fungal development and conidiogenesis on granules, we tested the impacts of the additions of three humectants-glycerin, propylene glycol, and polyethylene glycol 400-on water absorption by pellets incorporating microsclerotia of Metarhizium humberi IP 46 with microcrystalline cellulose or vermiculite carriers, and on the production of infective conidia of IP 46 microsclerotia in ambient humidities suboptimal for routine conidiogenesis. Glycerin facilitated greater and faster absorption of water than the other humectants. Microcrystalline cellulose absorbed low quantities of water without any added humectant whereas vermiculite did not. IP 46 did not grow or sporulate on pellets prepared with or without glycerin at 86% relative humidity (RH) or on control pellets without glycerin at 91% RH; conidial production on pellets prepared with vermiculite or microcrystalline cellulose and 10% glycerin reached 1.1 × 10⁵  conidia/mg and 1 × 10⁵  conidia/mg, respectively, after 20 days of exposure at 91% RH. Hence, these results strongly support glycerin as a suitable humectant for granular microsclerotial formulations of this fungus.

Phylogeny, Global Biogeography and Pleomorphism of Zanclospora

Zanclospora (Chaetosphaeriaceae) is a neglected, phialidic dematiaceous hyphomycete with striking phenotypic heterogeneity among its species. Little is known about its global biogeography due to its extreme scarcity and lack of records verified by molecular data. Phylogenetic analyses of six nuclear loci, supported by phenotypic data, revealed Zanclospora as highly polyphyletic, with species distributed among three distantly related lineages in Sordariomycetes. Zanclospora is a pleomorphic genus with multiple anamorphic stages, of which phaeostalagmus-like and stanjehughesia-like are newly discovered. The associated teleomorphs were previously classified in Chaetosphaeria. The generic concept is emended, and 17 species are accepted, 12 of which have been verified with DNA sequence data. Zanclospora thrives on decaying plant matter, but it also occurs in soil or as root endophytes. Its global diversity is inferred from metabarcoding data and published records based on field observations. Phylogenies of the environmental ITS1 and ITS2 sequences derived from soil, dead wood and root samples revealed seven and 15 phylotypes. The field records verified by DNA data indicate two main diversity centres in Australasia and Caribbean/Central America. In addition, environmental ITS data have shown that Southeast Asia represents a third hotspot of Zanclospora diversity. Our data confirm that Zanclospora is a rare genus.

The brlA Gene Deletion Reveals That Patulin Biosynthesis Is Not Related to Conidiation in Penicillium expansum

Dissemination and survival of ascomycetes is through asexual spores. The brlA gene encodes a C2H2-type zinc-finger transcription factor, which is essential for asexual development. Penicillium expansum causes blue mold disease and is the main source of patulin, a mycotoxin that contaminates apple-based food. A P. expansum PeΔbrlA deficient strain was generated by homologous recombination. In vivo, suppression of brlA completely blocked the development of conidiophores that takes place after the formation of coremia/synnemata, a required step for the perforation of the apple epicarp. Metabolome analysis displayed that patulin production was enhanced by brlA suppression, explaining a higher in vivo aggressiveness compared to the wild type (WT) strain. No patulin was detected in the synnemata, suggesting that patulin biosynthesis stopped when the fungus exited the apple. In vitro transcriptome analysis of PeΔbrlA unveiled an up-regulated biosynthetic gene cluster (PEXP_073960-PEXP_074060) that shares high similarity with the chaetoglobosin gene cluster of Chaetomium globosum. Metabolome analysis of PeΔbrlA confirmed these observations by unveiling a greater diversity of chaetoglobosin derivatives. We observed that chaetoglobosins A and C were found only in the synnemata, located outside of the apple, whereas other chaetoglobosins were detected in apple flesh, suggesting a spatial-temporal organization of the chaetoglobosin biosynthesis pathway.

FgHtf1 Regulates Global Gene Expression towards Aerial Mycelium and Conidiophore Formation in the Cereal Fungal Pathogen Fusarium graminearum

The homeobox gene family of transcription factors (HTF) controls many developmental pathways and physiological processes in eukaryotes. We previously showed that a conserved HTF in the plant-pathogenic fungus Fusarium graminearum, Htf1 (FgHtf1), regulates conidium morphology in that organism. This study investigated the mechanism of FgHtf1-mediated regulation and identified putative FgHtf1 target genes by a chromatin immunoprecipitation assay combined with parallel DNA sequencing (ChIP-seq) and RNA sequencing. A total of 186 potential binding peaks, including 142 genes directly regulated by FgHtf1, were identified. Subsequent motif prediction analysis identified two DNA-binding motifs, TAAT and CTTGT. Among the FgHtf1 target genes were FgHTF1 itself and several important conidiation-related genes (e.g., FgCON7), the chitin synthase pathway genes, and the aurofusarin biosynthetic pathway genes. In addition, FgHtf1 may regulate the cAMP-protein kinase A (PKA)-Msn2/4 and Ca²⁺-calcineurin-Crz1 pathways. Taken together, these results suggest that, in addition to autoregulation, FgHtf1 also controls global gene expression and promotes a shift to aerial growth and conidiation in F. graminearum by activation of FgCON7 or other conidiation-related genes.IMPORTANCE The homeobox gene family of transcription factors is known to be involved in the development and conidiation of filamentous fungi. However, the regulatory mechanisms and downstream targets of homeobox genes remain unclear. FgHtf1 is a homeobox transcription factor that is required for phialide development and conidiogenesis in the plant pathogen F. graminearum In this study, we identified FgHtf1-controlled target genes and binding motifs. We found that, besides autoregulation, FgHtf1 also controls global gene expression and promotes conidiation in F. graminearum by activation of genes necessary for aerial growth, FgCON7, and other conidiation-related genes.

A Novel Partitivirus in the Hypovirulent Isolate QT5-19 of the Plant Pathogenic Fungus Botrytis cinerea

A pink isolate (QT5-19) of Botrytis cinerea was compared with three gray isolates of B. cinerea for growth and morphogenesis on potato dextrose agar (PDA), and for pathogenicity on tobacco. A double-stranded (ds) RNA mycovirus infecting QT5-19 was identified based on its genome feature and morphology of the virus particles. The results showed that QT5-19 grew rapidly and established flourishing colonies as the gray isolates did. However, it is different from the gray isolates, as it failed to produce conidia and sclerotia asthe gray isolates did. QT5-19 hardly infected tobacco, whereas the gray isolates aggressively infected tobacco. Two dsRNAs were detected in QT5-19, dsRNA 1 and dsRNA 2, were deduced to encode two polypepetides with homology to viral RNA-dependent RNA polymerase (RdRp) and coat protein (CP), respectively. Phylogenetic analysis of the amino acid sequences of RdRp and CP indicated that the two dsRNAs represent the genome of a novel partitivirus in the genus Alphapartitivirus, designated here as Botrytis cinerea partitivirus 2 (BcPV2). BcPV2 in QT5-19 was successfully transmitted to the three gray isolates through hyphal contact. The resulting BcPV2-infected derivatives showed rapid growth on PDA with defects in conidiogenesis and sclerogenesis, and hypovirulence on tobacco. This study suggests that BcPV2 is closely associated with hypovirulence of B. cinerea.

The Atypical Guanylate Kinase MoGuk2 Plays Important Roles in Asexual/Sexual Development, Conidial Septation, and Pathogenicity in the Rice Blast Fungus

Guanylate kinases (GKs), which convert guanosine monophosphate into guanosine diphosphate (GDP), are important for growth and mannose outer chain elongation of cell wall N-linked glycoproteins in yeast. Here, we identified the ortholog of Saccharomyces cerevisiae GK Guk1, named MoGuk1 and a novel family of fungal GKs MoGuk2 in the rice blast fungus Magnaporthe oryzae. MoGuk1 contains 242 aa with an C-terminal GuKc domain that very similar to yeast Guk1. MoGuk2 contains 810 amino acids with a C-terminal GuKc domain and an additional N-terminal efThoc1 domain. Expression of either MoGuk1 or MoGuk2 in heterozygote yeast guk1 mutant could increase its GDP level. To investigate the biological role of MoGuk1 and MoGuk2 in M. oryzae, the gene replacement vectors were constructed. We obtained the ΔMoguk2 but not ΔMoguk1 mutant by screening over 1,000 transformants, indicating MoGuk1 might be essential for M. oryzae. The ΔMoguk2 mutant showed weak reductions in vegetative growth, conidial germination, appressorial formation, and appressorial turgor, and showed significant reductions in sporulation and pathogenicity. Moreover, the ΔMoguk2 mutant failed to produce perithecia and was sensitive to neomycin and a mixture of neomycin-tunicamycin. Exogenous GDP and ATP partially rescued the defects in conidial germination, appressorial formation, and infectious growth of the mutant. Further analysis revealed that intracellular GDP and GTP level was decreased, and GMP level was increased in the mutant, suggesting that MoGuk2 exhibits enzymatic activity. Structural analysis proved that the efThoc1, GuKc, and P-loop domains are essential for the full function of MoGuk2. Taken together, our data suggest that the guanylate kinase MoGuk2 is involved in the de novo GTP biosynthesis pathway and is important for infection-related morphogenesis in the rice blast fungus.

MoYcp4 is required for growth, conidiogenesis and pathogenicity in Magnaporthe oryzae

The transcription factor MoAP1 has been shown previously to be required for pathogenicity in Magnaporthe oryzae via mediation of the oxidative stress response. In the serial analysis gene expression database, it was found that expression of MoYcp4, a homologue of the Saccharomyces cerevisiae flavodoxin-like protein ScYcp4, was affected by MoAP1. Transcriptional analysis demonstrated that MoYCP4 was significantly up-regulated during conidiation, appressorium formation and infection. The growth rate of a ΔMoycp4 mutant was reduced slightly, but conidial production was increased significantly (more than 10-fold), compared with the wild-type strain. Although the rate of appressorium formation was unaffected, the appressorial turgor was abnormal and the ability to infect rice and barley was reduced, resulting in decreased pathogenicity. In summary, MoYcp4, a target of MoAP1, is involved in the growth, conidiogenesis and pathogenicity of M. oryzae. Our studies provide a comprehensive analysis of flavodoxin-like proteins and will aid in the study of pathogen-related molecular mechanisms.

A Gin4-Like Protein Kinase GIL1 Involvement in Hyphal Growth, Asexual Development, and Pathogenesis in Fusarium graminearum

Fusarium graminearum is the main causal agent of Fusarium head blight (FHB) on wheat and barley. In a previous study, a GIN4-like protein kinase gene, GIL1, was found to be important for plant infection and sexual reproduction. In this study we further characterized the functions of GIL1 kinase in different developmental processes. The Δgil1 mutants were reduced in growth, conidiation, and virulence, and formed whitish and compact colonies. Although phialide formation was rarely observed in the mutants, deletion of GIL1 resulted in increased hyphal branching and increased tolerance to cell wall and cell membrane stresses. The Δgil1 mutants produced straight, elongated conidia lacking of distinct foot cells and being delayed in germination. Compared with the wild type, some compartments in the vegetative hyphae of Δgil1 mutants had longer septal distances and increased number of nuclei, suggesting GIL1 is related to cytokinesis and septation. Localization of the GIL1-GFP fusion proteins to the septum and hyphal branching and fusion sites further supported its roles in septation and branching. Overall, our results indicate that GIL1 plays a role in vegetative growth and plant infection in F. graminearum, and is involved in septation and hyphal branching.

CCR4-Not Complex Subunit Not2 Plays Critical Roles in Vegetative Growth, Conidiation and Virulence in Watermelon Fusarium Wilt Pathogen Fusarium oxysporum f. sp. niveum

CCR4-Not complex is a multifunctional regulator that plays important roles in multiple cellular processes in eukaryotes. In the present study, the biological function of FonNot2, a core subunit of the CCR4-Not complex, was explored in Fusarium oxysporum f. sp. niveum (Fon), the causal agent of watermelon wilt disease. FonNot2 was expressed at higher levels in conidia and germinating conidia and during infection in Fon-inoculated watermelon roots than in mycelia. Targeted disruption of FonNot2 resulted in retarded vegetative growth, reduced conidia production, abnormal conidial morphology, and reduced virulence on watermelon. Scanning electron microscopy observation of infection behaviors and qRT-PCR analysis of in planta fungal growth revealed that the ΔFonNot2 mutant was defective in the ability to penetrate watermelon roots and showed reduced fungal biomass in root and stem of the inoculated plants. Phenotypic and biochemical analyses indicated that the ΔFonNot2 mutant displayed hypersensitivity to cell wall perturbing agents (e.g., Congo Red and Calcofluor White) and oxidative stress (e.g., H₂O₂ and paraquat), decreased fusaric acid content, and reduced reactive oxygen species (ROS) production during spore germination. Our data demonstrate that FonNot2 plays critical roles in regulating vegetable growth, conidiogenesis and conidia morphology, and virulence on watermelon via modulating cell wall integrity, oxidative stress response, ROS production and FA biosynthesis through the regulation of transcription of genes involved in multiple pathways.

Skp1, a component of E3 ubiquitin ligase, is necessary for growth, sporulation, development and pathogenicity in rice blast fungus (Magnaporthe oryzae)

Ubiqitination is an important process in eukaryotic cells involving E3 ubiquitin ligase, which co-ordinates with cell cycle proteins and controls various cell functions. Skp1 (S-phase kinase-associated protein 1) is a core component of the SCF (Skp1-Cullin 1-F-box) E3 ubiquitin ligase complex necessary for protein degradation by the 26S proteasomal pathway. The rice blast fungus Magnaporthe oryzae has a single MoSKP1(MGG_04978) required for viability. Skp1 has multiple functions; however, its roles in growth, sporulation and appressorial development are not understood. MoSKP1 complements Skp1 function in the fission yeast temperature-sensitive mutant skp1 A7, restoring the normal length of yeast cells at restrictive temperature. The MoSkp1 protein in M. oryzae is present in spores and germ tubes, and is abundantly expressed in appressoria. Various RNA interference (RNAi) and antisense transformants of MoSKP1 in B157 show reduced sporulation, defective spore morphology, lesser septation and diffuse nuclei. Further, they show elongated germ tubes and are unable to form appressoria. Transformants arrested in G1/S stage during initial spore germination show a similar phenotype to wild-type spores treated with hydroxyurea (HU). Reduced MoSkp1 transcript and protein levels in knockdown transformants result in atypical germ tube development. MoSkp1 interacts with the putative F-box protein (MGG_06351) revealing the ability to form protein complexes. Our investigation of the role of MoSKP1 suggests that a decrease in MoSkp1 manifests in decreased total protein ubiquitination and, consequently, defective cell cycle and appressorial development. Thus, MoSKP1 plays important roles in growth, sporulation, appressorial development and pathogenicity of M. oryzae.

The syntaxin protein (MoSyn8) mediates intracellular trafficking to regulate conidiogenesis and pathogenicity of rice blast fungus

Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) mediate cellular membrane fusion and intracellular vesicle trafficking in eukaryotic cells, and are critical in the growth and development of pathogenic fungi such as Magnaporthe oryzae which causes rice blast. Rice blast is thought to involve distinct SNARE-mediated transport and secretion of fungal effector proteins into the host to modulate rice immunity. We have previously characterized two SNARE proteins, secretory protein (MoSec22) and vesicle-associated membrane protein (MoVam7), as being important in cellular transport and pathogenicity. Here, we show that syntaxin 8 (MoSyn8), a Qc-SNARE protein homolog, also plays important roles in growth, conidiation, and pathogenicity. The MoSYN8 deletion mutant (∆Mosyn8) mutant exhibits defects in endocytosis and F-actin organization, appressorium turgor pressure generation, and host penetration. In addition, the ∆Mosyn8 mutant cannot elaborate biotrophic invasion of the susceptible rice host, or secrete avirulence factors Avr-Pia (corresponding to the rice resistance gene Pia) and Avrpiz-t (the cognate Avr gene for the resistance gene Piz-t) proteins. Our study of MoSyn8 advances our understanding of SNARE proteins in effector secretion which underlies the normal physiology and pathogenicity of M. oryzae, and it sheds new light on the mechanism of the blight disease caused by M. oryzae.

MoTup1 is required for growth, conidiogenesis and pathogenicity of Magnaporthe oryzae

The general transcriptional repressor Tup1 proteins play important regulatory roles in the growth and development of fungi. In this report, we characterized MoTup1, a protein homologous to Tup1 of Saccharomyces cerevisiae, from M. oryzae. Disruption of MoTUP1 resulted in severe mycelial growth reduction and a defect in conidiogenesis. We found that MoTup1 is required for the maintenance of cell wall integrity by regulating the expression of the genes involved in cell wall biosynthesis. Pathogenicity assays indicated that the ΔMotup1 mutants lost the ability to invade both rice and barley hosts. Moreover, observation of rice epidermis penetration showed that the hyphal tips of the mutants could still form appressorium-like structures, but were unable to invade host cells. Taken together, our results demonstrate that M. oryzae MoTup1 is an important regulatory factor in fungal growth, development and pathogenesis on hosts.