The Colletotrichum gloeosporioides RhoB regulates cAMP and stress response pathways and is required for pathogenesis

Transcription Factor CgSte12 Regulates Pathogenicity by Affecting Appressorium Structural Development in the Anthracnose-Causing Fungus Colletotrichum gloeosporioides

Colletotrichum gloeosporioides is the causal agent of poplar anthracnose, which induces major economic losses and adversely affects the ecosystem services of poplar forests. The appressorium serves as a penetration structure for many pathogenic fungi, including C. gloeosporioides. The production of mucilage and the formation of penetration pegs are critically important for the appressorium-mediated penetration of host tissues. We previously found that CgPmk1 is a key protein involved in appressorium formation, penetration, and pathogenicity. Although CgSte12, which is a transcription factor that functions downstream of CgPmk1, regulates the formation of penetration pegs, its role in C. gloeosporioides appressorium development and pathogenicity has not been elucidated. Here, we developed C. gloeosporioides CgSTE12 mutants and characterized the molecular and cellular functions of CgSTE12. The results showed that mycelial growth and morphology were not affected in the CgSTE12 knockout mutants, which produced normal melanized appressoria. However, these mutants had less mucilage secreted around the appressoria, impaired appressorial cone formation, and the inability to form penetration pores and pegs, which ultimately led to a significant loss of pathogenicity. Our comparative transcriptome analysis revealed that CgSte12 controls the expression of genes involved in appressorium development and function, including genes encoding cutinases, NADPH oxidase, spermine biosynthesis-related proteins, ceramide biosynthesis-related proteins, fatty acid metabolism-related proteins, and glycerophospholipid metabolism-related proteins. Overall, our findings indicate that CgSte12 is a critical regulator of appressorium development and affects C. gloeosporioides pathogenicity by modulating the structural integrity of appressoria.

Recombinant human granulocyte colony stimulating factor (rhG-CSF) participates in the progression of implantation via the hsa_circ_0001550-miRNA-mRNA interaction network

Inadequate endometrial receptivity is a key factor affecting the successful implantation of embryos. Recombinant human granulocyte colony stimulating factor (rhG-CSF) can increase endometrial thickness and improve the outcomes of assisted reproductive technologies (ARTs). In this preliminary study, the function and possible molecular mechanisms of recombinant human granulocyte colony stimulating factor (rhG-CSF) which affects endometrial receptivity and implantation in human Embryonic Stem Cells (hESCs) were investigated. The cell viability of endometrial stromal cells treated with rhG-CSF 0.5 ng/ml for 24 h was significantly increased. Moreover, the expression of hsa_circ_0001550 was downregulated in endometrial stromal cells treated with rhG-CSF. Furthermore, the hsa_circ_0001550-miRNA-mRNA network was constructed and the downstream target genes (including 4 miRNAs and 117 mRNAs) of hsa_circ_0001550 were mainly involved in the cAMP and calcium signalling pathways, which play important roles in regulating endometrial receptivity and embryo implantation. We conclude that rhG-CSF participates in the regulation of embryo implantation by regulating the hsa_circ_0001550-miRNA-mRNA interaction network.

SsCox17, a copper chaperone, is required for pathogenic process and oxidative stress tolerance of Sclerotinia sclerotiorum

Stem rot, caused by Sclerotinia sclerotiorum has emerged as one of the major fungal pathogens of oilseed Brassica across the world. The pathogenic development is exquisitely dependent on reactive oxygen species (ROS) modulation. Cox17 is a crucial factor that shuttles copper ions from the cytosol to the mitochondria for the cytochrome c oxidase (CCO) assembly. Currently, no data is available regarding the impact of Cox17 in fungal pathogenesis. The present research was carried out to functionally characterize the role of Cox17 in S. sclerotiorum pathogenesis. SsCox17 transcripts showed high expression levels during inoculation on rapeseed. Intramitochondrial copper content and CCO activity were decreased in SsCox17 gene-silenced strains. The SsCox17 gene expression was up-regulated in the hyphae under oxidative stress and a deficiency response to oxidative stress was detected in SsCox17 gene-silenced strains. Compared to the S. sclerotiorum wild-type strain, there was a concomitant reduction in the virulence of SsCox17 gene-silenced strains. The SsCox17 overexpression strain was further found to increase copper content, CCO activity, tolerance to oxidative stress and virulence. We also observed a certain correlation of appressoria formation and SsCox17. These results provide evidence that SsCox17 is positively associated with fungal virulence and oxidative detoxification.

Involvement of Protein Kinase CgSat4 in Potassium Uptake, Cation Tolerance, and Full Virulence in Colletotrichum gloeosporioides

The ascomycete Colletotrichum gloeosporioides is a causal agent of anthracnose on crops and trees and causes enormous economic losses in the world. Protein kinases have been implicated in the regulation of growth and development, and responses to extracellular stimuli. However, the mechanism of the protein kinases regulating phytopathogenic fungal-specific processes is largely unclear. In the study, a serine/threonine CgSat4 was identified in C. gloeosporioides. The CgSat4 was localized in the cytoplasm. Targeted gene deletion showed that CgSat4 was essential for vegetative growth, sporulation, and full virulence. CgSat4 is involved in K⁺ uptake by regulating the localization and expression of the potassium transporter CgTrk1. CgSat4 is required for the cation stress resistance by altering the phosphorylation of CgHog1. Our study provides insights into potassium acquisition and the pathogenesis of C. gloeosporioides.

Protein Phosphatase CgPpz1 Regulates Potassium Uptake, Stress Responses, and Plant Infection in Colletotrichum gloeosporioides

Protein phosphatases play important roles in the regulation of various cellular processes in eukaryotes. The ascomycete Colletotrichum gloeosporioides is a causal agent of anthracnose disease on some important crops and trees. In this study, CgPPZ1, a protein phosphate gene and a homolog of yeast PPZ1, was identified in C. gloeosporioides. Targeted gene deletion showed that CgPpz1 was important for vegetative growth and asexual development, conidial germination, and plant infection. Cytological examinations revealed that CgPpz1 was localized to the cytoplasm. The ΔCgppz1 mutant was hypersensitive to osmotic stresses, cell wall stressors, and oxidative stressors. Taken together, our results indicated that CgPpz1 plays an important role in the fungal development and virulence of C. gloeosporioides and the multiple stress responses generated.

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.

Carbamoyl Phosphate Synthase Subunit CgCPS1 Is Necessary for Virulence and to Regulate Stress Tolerance in Colletotrichum gloeosporioides

Glomerella leaf spot (GLS) is a severe infectious disease of apple whose infective area is growing gradually and thus poses a huge economic threat to the world. Different species of Colletotrichum including Colletotrichum gloeosporioides are responsible for GLS. For efficient GLS control, it is important to understand the mechanism by which the cruciferous crops and C. gloeosporioides interact. Arginine is among one of the several types of amino acids, which plays crucial role in biochemical and physiological functions of fungi. The arginine biosynthesis pathway involved in virulence among plant pathogenic fungi is poorly understood. In this study, CgCPS1 gene encoding carbamoyl phosphate synthase involved in arginine biosynthesis has been identified and inactivated experimentally. To assess the effects of CgCPS1, we knocked out CgCPS1 in C. gloeosporioides and evaluated its effects on virulence and stress tolerance. The results showed that deletion of CgCPS1 resulted in loss of pathogenicity. The Δcgcps1 mutants showed slow growth rate, defects in appressorium formation and failed to develop lesions on apple leaves and fruits leading to loss of virulence while complementation strain (CgCPS1-C) fully restored its pathogenicity. Furthermore, mutant strains showed extreme sensitivity to high osmotic stress displaying that CgCPS1 plays a vital role in stress response. These findings suggest that CgCPS1 is major factor that mediates pathogenicity in C. gloeosporioides by encoding carbamoyl phosphate that is involved in arginine biosynthesis and conferring virulence in C. gloeosporioides.

CgEnd3 Regulates Endocytosis, Appressorium Formation, and Virulence in the Poplar Anthracnose Fungus Colletotrichum gloeosporioides

The hemibiotrophic ascomycete fungus Colletotrichum gloeosporioides is the causal agent of anthracnose on numerous plants, and it causes considerable economic losses worldwide. Endocytosis is an essential cellular process in eukaryotic cells, but its roles in C. gloeosporioides remain unknown. In our study, we identified an endocytosis-related protein, CgEnd3, and knocked it out via polyethylene glycol (PEG)-mediated protoplast transformation. The lack of CgEnd3 resulted in severe defects in endocytosis. C. gloeosporioides infects its host through a specialized structure called appressorium, and ΔCgEnd3 showed deficient appressorium formation, melanization, turgor pressure accumulation, penetration ability of appressorium, cellophane membrane penetration, and pathogenicity. CgEnd3 also affected oxidant adaptation and the expression of core effectors during the early stage of infection. CgEnd3 contains one EF hand domain and four calcium ion-binding sites, and it is involved in calcium signaling. A lack of CgEnd3 changed the responses to cell-wall integrity agents and fungicide fludioxonil. However, CgEnd3 regulated appressorium formation and endocytosis in a calcium signaling-independent manner. Taken together, these results demonstrate that CgEnd3 plays pleiotropic roles in endocytosis, calcium signaling, cell-wall integrity, appressorium formation, penetration, and pathogenicity in C. gloeosporioides, and it suggests that CgEnd3 or endocytosis-related genes function as promising antifungal targets.

Calcineurin-Responsive Transcription Factor CgCrzA Is Required for Cell Wall Integrity and Infection-Related Morphogenesis in Colletotrichum gloeosporioides

The ascomycete fungus Colletotrichum gloeosporioides infects a wide range of plant hosts and causes enormous economic losses in the world. The transcription factors (TFs) play an important role in development and pathogenicity of many organisms. In this study, we found that the C₂H₂ TF CgCrzA is localized in both cytoplasm and nucleus under standard condition, and it translocated from cytoplasm to nucleus in a calcineurin-dependent manner. Moreover, the ΔCgCrzA was hypersensitive to cell wall perturbing agents and showed severe cell wall integrity defects. Deletion of the CgCRZA inhibited the development of invasive structures and lost pathogenicity to plant hosts. Our results suggested that calcineurin-responsive TF CgCrzA was not only involved in regulating cell wall integrity, but also in morphogenesis and virulence in C. gloeosporioides.

A Small GTPase RHO2 Plays an Important Role in Pre-infection Development in the Rice Blast Pathogen Magnaporthe oryzae

The rice blast pathogen Magnaporthe oryzae is a global threat to rice production. Here we characterized RHO2 gene (MGG_02457) that belongs to the Rho GTPase family, using a deletion mutant. This mutant ΔMorho2 exhibited no defects in conidiation and germination but developed only 6% of appressoria in response to a hydrophobic surface when compared to the wild-type progenitor. This result indicates that MoRHO2 plays a role in appressorium development. Furthermore, exogenous cAMP treatment on the mutant led to appressoria that exhibited abnormal morphology on both hydrophobic and hydrophilic surfaces. These outcomes suggested the involvement of MoRHO2 in cAMP-mediated appressorium development. ΔMorho2 mutation also delayed the development of appressorium-like structures (ALS) at hyphal tips on hydrophobic surface, which were also abnormally shaped. These results suggested that MoRHO2 is involved in morphological development of appressoria and ALS from conidia and hyphae, respectively. As expected, ΔMorho2 mutant was defective in plant penetration, but was still able to cause lesions, albeit at a reduced rate on wounded plants. These results implied that MoRHO2 plays a role in M. oryzae virulence as well.

The MAPKKK CgMck1 Is Required for Cell Wall Integrity, Appressorium Development, and Pathogenicity in Colletotrichum gloeosporioides

Mitogen-activated protein kinase (MAPK) signaling pathway plays key roles in sensing extracellular signals and transmitting them from the cell membrane to the nucleus in response to various environmental stimuli. A MAPKKK protein CgMck1 in Colletotrichum gloeosporioides was characterized. Phenotypic analyses of the ∆Cgmck1 mutant showed that the CgMck1 was required for vegetative growth, fruiting body development, and sporulation. Additionally, the CgMCK1 deletion mutant showed significant defects in cell wall integrity, and responses to osmotic stresses. The mutant abolished the ability to develop appressorium, and lost pathogenicity to host plants. The ∆Cgmck1 mutant also exhibited a higher sensitivity to antifungal bacterium agent Bacillus velezensis. The deletion mutants of downstream MAPK cascades components CgMkk1 and CgMps1 showed similar defects to the ∆Cgmck1 mutant. In conclusion, CgMck1 is involved in the regulation of vegetative growth, asexual development, cell wall integrity, stresses resistance, and infection morphogenesis in C. gloeosporioides.

A Cdc42 homolog in Colletotrichum gloeosporioides regulates morphological development and is required for ROS-mediated plant infection

The Rho GTPase Cdc42 is conserved in fungi and plays a key role in regulating polarity establishment, morphogenesis and differentiation. In this study, we identified an ortholog of Cdc42, CgCdc42, and functionally characterized it to determine the role of Cdc42 in the development and pathogenicity of Colletotrichum gloeosporioides, a causal agent of poplar anthracnose. Targeted deletion of CgCdc42 resulted in reduced vegetative growth and dramatic morphological defects, including the formation of elongated conidia and abnormally shaped appressoria. Moreover, CgCdc42 deletion mutants were less virulent on poplar leaves than were wild type. Appressoria formed by ΔCgCdc42 mutants were morphologically abnormal and present in lower numbers on poplar leaves than were those formed by wild type. However, an ROS scavenging assay indicated that the ΔCgCdc42 mutants maintained wild type pathogenicity in the absence of ROS despite having fewer appressoria than wild type, suggesting that the ΔCgCdc42 mutants were deficient in their tolerance of ROS. Additionally, we also found that the distribution of ROS was different after the deletion of CgCdc42, the ΔCgCdc42 mutants were hypersensitive to H₂O₂, and transcriptional analysis revealed that CgCdc42 is involved in the regulation of ROS-related genes. Furthermore, loss of CgCdc42 caused defects in cell wall integrity and an uneven distribution of chitin. These data collectively suggest that CgCdc42 plays an important role in the regulation of vegetative growth, morphological development, cell wall integrity and ROS-mediated plant infection in C. gloeosporioides.

Detection of changes in mould cell wall stress-related gene expression by a novel reverse transcription real-time PCR method

The cell wall integrity (CWI) pathway is activated in response to cell wall stresses due to different food-related environments. Rho1 is one of the main regulators within such pathway. The objective of this work was to design an easy-to-use RT-qPCR technique for the evaluation of the Rho1 gene expression useful to measure responses to the presence of cell wall stressors such as the antifungal protein PgAFP. Two primer pairs were designed from published conserved regions. Their specificity initially was determined by in silico analysis for several fungal species. After optimising the qPCR, the primer pair Rho1-F1/R2 was selected due to the lowest Cq values obtained and its specificity. The qPCR method showed efficiencies between 97.5% and 100.5%. Applicability of the designed qPCR method was evaluated in the presence of the stressor PgAFP. The PgAFP-resistant Penicillium polonicum and the PgAFP-sensitive Aspergillus flavus showed Rho1 gene over- and under- expression, respectively, indicating that the CWI pathway is activated in the former species but not activated in the latter one in response to the stress caused by PgAFP. This novel qPCR methodology able to detect changes in CWI-related gene expression in filamentous fungi will be useful in future studies to evaluate physiological mould responses to different food environmental challenges.

Functional analysis of a regulator of G-protein signaling CgRGS1 in the rubber tree anthracnose fungus Colletotrichum gloeosporioides

Colletotrichum gloeosporioides is the causal agent of rubber anthracnose, which is also one of the important biological factors threatening the development of natural rubber industry in the world. Regulators of G-protein signaling (RGS) are key negative regulators of G-proteins, which play important roles in growth, development and pathogenic processes of plant pathogens. In this study, a RGS gene CgRGS1 was functionally characterized in C. gloeosporioides. Compared to the wild type, the CgRGS1 deletion mutant had slow vegetative growth, reduced conidia with multi-end germination, low appressorium formation rate, high resistance to oxidative stress and SDS. Moreover, the mutant was sensitive to osmotic pressure and showed decreased virulence. In conclusion, CgRGS1 is involved in regulation of vegetative growth, conidiation, germination, appressorium formation, oxidative stress, osmotic pressure response and pathogenicity in C. gloeosporioides.

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.

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.