Verticillium dahliae CFEM proteins manipulate host immunity and differentially contribute to virulence

A Novel CFEM Effector in Fusarium verticillioides Required for Virulence Involved in Plant Immunity Suppression and Fungal Cell Wall Integrity

Common in Fungal Extracellular Membrane (CFEM) effectors, a unique class of fungal-specific proteins, play critical roles in host-pathogen interactions. While CFEM proteins have been extensively characterized in phytopathogens, their presence and functions in Fusarium verticillioides remained unexplored. Here, we systematically identified 19 CFEM-containing proteins in F. verticillioides, among which FvCFEM12 exhibited secretory activity and plant infection-induced expression. Functional characterization revealed that FvCFEM12 suppressed Bax- and INF1-triggered cell death in Nicotiana benthamiana leaves. Furthermore, heterologous expression of FvCFEM12 in maize leaves using P. syringae strain D36E can compromise immune responses against bacterial pathogens. Deletion of FvCFEM12 impaired fungal virulence, altered hyphal morphology, and reduced cell wall stress tolerance. Interestingly, FvCFEM12 physically interacted with the maize wall-associated receptor kinase ZmWAK17ET, and targeted silencing of ZmWAK17 in maize enhanced susceptibility to F. verticillioides. Our findings revealed that FvCFEM12 is a dual-function effector that suppresses plant immunity and maintains fungal cell wall integrity, thereby orchestrating fungal pathogenicity at the host-pathogen interface.

Effect of CFEM proteins on pathogenicity, patulin accumulation and host immunity of postharvest apple pathogens Penicillium expansum

Penicillium expansum is a significant post-harvest pathogenic fungi on most pome fruits. Common fungal extracellular membrane (CFEM) proteins, as effectors, contribute to virulence and manipulate host immunity. However, the CFEM proteins in P. expansum have not been identified and functionally studied. In this study, we screened two P. expansum CFEM proteins, PeCFEM5 and PeCFEM8, whose expression was highly up-regulated during postharvest apple infection. Growth and pathogenicity of P. expansum were characterized by knockout and complementary of PeCFEM5 and PeCFEM8. Deletion of PeCFEM5 and PeCFEM8 resulted in changes in spore development and increased resistance to cell wall integrity stress. The lesion spots on apple and pear fruit inoculated with P. expansum gradually expanded and deepened in color. The ΔPeCFEM5 and ΔPeCFEM8 strains reduced lesion diameter on apple fruit by 47 % and 29 %, respectively, compared with the WT strains. Detection of patulin accumulation by high-performance liquid chromatography (HPLC) revealed that deletion of PeCFEM5 or PeCFEM8 suppressed patulin content in medium and apples, and patulin biosynthesis-related genes were down-regulated. The PeCFEM5 and PeCFEM8 were also confirmed as effector proteins capable of suppressing the cell death triggered by BAX and the expression of plant defense genes in Nicotiana benthamiana. Phytohormone ELISA assays showed that jasmonic acid levels were reduced, but salicylic acid levels were increased by transient expression of PeCFEM5 or PeCFEM8 in the host plant. These results indicate that PeCFEM5 and PeCFEM8 effectors are crucial for pathogenicity, patulin biogenesis, and modulating host plant immunity.

Screening and transcriptomic analysis of anti-Sporothrix globosa targeting AbaA

Introduction

Sporotrichosis is a fungal disease caused by a complex of Sporothrix schenckii, leading to chronic infections of the epidermis and subcutaneous tissue in both humans and animals.

Methods

Through virtual screening targeting the key gene abaA to screen out the small-molecule drugs to treat Sporotrichosis. To further validate the antifungal activity of small-molecule drugs, growth curves, minimum bactericidal concentration (MBC), and minimum inhibitory concentration (MIC) for Sporothrix globosa (S. globosa) and Sporothrix schenckii (S. schenckii) were measured. In addition, we have done animal experiments to explore the function of the drugs. At the same time, qRT-PCR and transcriptome were used to verify the important role of abaA gene in Sporothrix.

Results

Azelastine and Mefloquine effectively inhibit S. globosa and S. schenckii. MBC, and MIC for S. globosa and S. schenckii confirmed that both Azelastine and Mefloquine inhibited the growth of S. globosa and S. schenckii. Additionally, animal experiments demonstrated that Azelastine and Mefloquine reduced skin lesions in mice; post-treatment observations revealed improvements in inflammatory infiltration and granuloma formation. Through transcriptome analysis and qRT-PCR for validation, our findings demonstrate that the abaA gene plays a crucial role in regulating the attachment of the Sporothrix cell wall to the host matrix and in melanin regulation. Notably, when the abaA gene was inhibited, there was a marked increase in the expression of repair genes. These results emphasize the significance of the abaA gene in the biology of Sporothrix.

Discussion

Two small-molecule drugs exhibit the ability to inhibit Sporothrix and treat sporotrichosis both in vitro and in murine models, suggesting their potential for development as therapeutic agents for sporotrichosis. And qRT-PCR and transcriptome results underscore the significance of the abaA gene in Sporothrix. Our results lay the foundation for the search for new treatments for other mycosis.

Salivary effector DcE1 suppresses plant defense and facilitates the successful feeding of Asian citrus psyllid, Diaphorina citri

BACKGROUND

Piercing-sucking insects secrete diverse repertoires of effectors into their hosts to weaken host defenses and promote infestation. The Asian citrus psyllid, Diaphorina citri Kuwayama, is the most destructive insect pest in citrus orchards because of its role as a vector for the huanglongbing pathogen, Candidatus Liberibacter asiaticus (CLas). However, specific effector proteins and their functions in D. citri remain unclear.

RESULTS

We demonstrate that DcE1, a salivary protein gene from D. citri, is predominantly expressed in the salivary gland tissues and is delivered into host plants during feeding. Transient expression in tobacco leaves revealed that DcE1 was subcellularly localized in the cytoplasm and plasma membrane, where it inhibited BAX- and INF1-induced cell death, suppressed callose deposition, and activated the salicylic acid pathway by upregulating the expression of endo-β-1,3-glucanase NtBGL2 and regulatory protein NtNPR1. Further, DcE1 knockdown by double-stranded RNA (dsRNA) injection decreased the survival rates of D. citri and interrupted D. citri phloem-feeding on host plants.

CONCLUSION

These results indicate that DcE1 is a novel effector that promotes plant susceptibility and enables D. citri feeding. These findings enhance our understanding of D. citri-plant interactions and offer a potential new target gene for the development of citrus protection strategies. © 2024 Society of Chemical Industry.

A powdery mildew core effector protein targets the host endosome tethering complexes HOPS and CORVET in barley

Powdery mildew fungi are serious pathogens affecting many plant species. Their genomes encode extensive repertoires of secreted effector proteins that suppress host immunity. Here, we revised and analyzed the candidate secreted effector protein (CSEP) effectome of the powdery mildew fungus, Blumeria hordei (Bh). We identified seven putative effectors that are broadly conserved in powdery mildew species, suggesting that they are core effectors of these phytopathogens. We showed that one of these effectors, CSEP0214, interacts with the barley (Hordeum vulgare) vacuolar protein-sorting 18 (VPS18) protein, a shared component of the class C core vacuole/endosome tethering (CORVET) and homotypic fusion and protein-sorting (HOPS) endosomal tethering complexes that mediate fusion of early endosomes and multivesicular bodies, respectively, with the central vacuole. Overexpression of CSEP0214 and knockdown of either VPS18, HOPS-specific VPS41, or CORVET-specific VPS8 blocked the vacuolar pathway and the accumulation of the fluorescent vacuolar marker protein (SP)-RFP-AFVY in the endoplasmic reticulum. Moreover, CSEP0214 inhibited the interaction between VPS18 and VPS16, which are both shared components of CORVET as well as HOPS. Additionally, introducing CSEP0214 into barley leaf cells blocked the hypersensitive cell death response associated with resistance gene-mediated immunity, indicating that endomembrane trafficking is required for this process. CSEP0214 expression also prevented callose deposition in cell wall appositions at attack sites and encasements of fungal infection structures. Our results indicate that the powdery mildew core effector CSEP0214 is an essential suppressor of plant immunity.

The virulence contribution of the CFEM family genes of Beauveria bassiana is closely influenced by the external iron environment

The common in fungal extracellular membrane (CFEM) domain proteins represent characteristic fungal extracellular membrane proteins. The entomopathogenic fungus Beauveria bassiana contains 12 CFEM domain proteins involved in the generation of iron hunger response. However, many BbCFEM genes that infect insects do not promote fungal virulence. In this study, we systematically assessed the role of the BbCFEM family in fungal virulence under moderate iron concentrations and severe iron starvation (0.4 mM BPS) induced by body wall infection and injection infection. The results showed that the BbCFEM family members have different functions based on virulence, which is directly affected by external iron levels. Quantitative real-time reverse-transcription polymerase chain reaction preliminarily demonstrated that deletion of BbCFEM family genes significantly increased the expression levels of other family members. The increased expression levels compensated for the gene damage induced by the deletion of BbMFEM genes. In addition, the results showed that the BbCFEM gene participates in the initiation of fungal responses to cell wall stress and oxidative stress. These findings reveal the evolutionary strategies employed by pathogenic fungi to adapt to the environment and population reproduction. This study expands our understanding of the mechanism of this gene family of entomopathogenic fungi in infecting pests.

IMPORTANCE

The common in fungal extracellular membrane (CFEM) domain is a fungal extracellular membrane protein that can trap heme, which assists in fungal infection and colonization. Beauveria bassiana is an entomopathogenic fungus that is widely used to control pests. We systematically assessed the contribution of the BbCFEM family to B. bassiana's virulence under severe iron starvation and B. bassiana's growth and stress resistance under moderate iron levels. We found that the BbCFEM family members have different functions based on virulence with severe iron starvation, which also plays an important role in fungal responses to cell wall stress and oxidative stress. This study provides new insights into the genetic families of entomopathogenic fungi and the mechanisms by which they infect pests.

Fusarium sacchari CFEM Proteins Suppress Host Immunity and Differentially Contribute to Virulence

The pathogen Fusarium sacchari is responsible for the devastating pokkah boeng disease, which causes significant economic losses in sugarcane production. However, the mechanisms by which it affects plant immunity remain largely unknown. Common in Fungal Extracellular Membrane (CFEM) domain proteins have been implicated in fungal growth, infection processes, and pathogenicity. In this study, we identified three FsCFEM proteins (Fs08184, Fs10706, and Fs13617) that mediate the broad-spectrum suppression of the immune responses induced by typical effectors. A further analysis demonstrated that Fs08184, Fs10706, and Fs13617 suppressed host immunity through two potential iron-binding sites conserved in CFEM family members, characterized by Asp and Phe residues in Fs08184, Fs10706, and Fs13617. Additionally, the Asp and Phe residues within the iron-chelating site were necessary for the iron acquisition of F. sacchari and contributed to creating low-free-iron conditions at the interface of plant and pathogen interactions. It appeared that F. sacchari might employ Asp-Phe-type CFEM members to influence host iron homeostasis to suppress host immunity and to facilitate its successful colonization.

Re-localization of a repeat-containing fungal effector by apoplastic protein Chitinase-like 1 blocks its toxicity

A fungal effector that is toxic to plant cells was identified in Verticillium dahliae. The effector contains a non-canonical Common in several Fungal Extracellular Membrane proteins (CFEM) domain, a tandem repeat region consisting of four 14-amino acid repeats rich in proline, and a C-terminal region, thus is designated V. dahliae tetrapeptide repeat protein (VdTRP). The membrane targeting of VdTRP is vital for its cell toxicity. CFEM mediates the membrane targeting and the tandem repeat region exerts the toxic function upon cell membrane. The chitinase-like 1 (CTL1), an essential apoplastic protein of cotton, can redirect VdTRP from cell membrane to apoplast. Transgenic cotton overexpressing CTL1 greatly enhances cotton resistance to V. dahliae without affecting cotton growth and development, implicating its potential application in breeding cotton with high wilt resistance. Our data demonstrates that genetic manipulation of effector target constitutes potential strategy for improving crop resistance to fungal pathogens.

Global characterization of GH11 family xylanases genes in Neostagonosporella sichuanensis and functional analysis of Nsxyn1 and Nsxyn2

Rhombic-spot disease, caused mainly by Neostagonosporella sichuanensis, significantly impacts the yield and quality of fishscale bamboo (Phyllostachys heteroclada). Xylanases are essential for pathogenic fungi infection, yet their specific functions in the physiology and pathogenicity of N. sichuanensis remain unclear. Here, we characterized three xylanase proteins with glycosyl hydrolase 11 domains from the N. sichuanensis SICAUCC 16-0001 genome and examined the function of Nsxyn1 and Nsxyn2. Purified Nsxyn1 and Nsxyn2 proteins displayed specific xylanase activity in vitro and induced cell death in Nicotiana benthamiana, independent of their enzymatic function. Both proteins possessed signal peptides and were confirmed as secreted proteins using a yeast secretion system. Subcellular localization revealed that Nsxyn1 and Nsxyn2 localized in both the cytoplasm and nucleus and can trigger cell death in N. benthamiana through Agrobacterium tumefaciens-mediated transient transformation. qRT-PCR results showed notable upregulation of Nsxyn1 and Nsxyn2 during infection, with Nsxyn1 exhibiting an 80-fold increase at 15 days post-inoculation. Deletion of Nsxyn1 and Nsxyn2 in N. sichuanensis impaired xylan degradation, adaptation to osmotic and oxidative stress, and pathogenic full virulence. Deletion of Nsxyn1 notably slowed fungal growth and reduced spore production, whereas only a reduction in microconidial production was observed in Nsxyn2 mutants. Complementation of Nsxyn1 and Nsxyn2 only partially restored these phenotypic defects in the ∆Nsxyn1 and ∆Nsxyn2 mutants. These findings suggest that Nsxyn1 and Nsxyn2 contribute to N. sichuanensis virulence and induced plant defense responses, providing new insights into the function of xylanases in the interaction between fishscale bamboo and N. sichuanensis.

CAP superfamily proteins (VdPRYs) manipulate plant immunity and contribute to the virulence of Verticillium dahliae

CAP (cysteine-rich secretory proteins, antigen5, pathogenesis-related proteins) superfamily proteins are widely distributed, can be subdivided into 11 subfamilies, and form a unique branch in fungi, named PRY proteins. Verticillium dahliae is a soil-borne fungal pathogen of vascular plants that causes plant Verticillium wilt. However, the roles of CAP superfamily proteins in this fungus is unclear. Here, four CAP superfamily members with a conserved domain were identified in V. dahliae: VdPRY1, VdPRY2, VdPRY3, and VdPRY4. VdPRY1 and VdPRY3 were found to be key in suppressing plant immune responses. Moreover, these four members are highly expressed during early infection of cotton by V. dahliae. Deleting VdPRY1, VdPRY2, or VdPRY3 reduced the fungus's ability to cause disease, but VdPRY4 deletion did not affect virulence. Deletion of any of four members did not impact fungal growth or carbon source use. Yeast two-hybrid experiments suggest that these proteins may function through interactions with each other. This investigation has, for the initial time, elucidated the pivotal roles of V. dahliae CAP superfamily proteins in inhibiting plant immunity and exerting virulence during interaction with the host plant.

Dual Transcriptome Analysis Reveals the Changes in Gene Expression in Both Cotton and Verticillium dahliae During the Infection Process

Cotton is often threatened by Verticillium wilt caused by V. dahliae. Understanding the molecular mechanism of V. dahlia-cotton interaction is important for the prevention of this disease. To analyze the transcriptome profiles in V. dahliae and cotton simultaneously, the strongly pathogenic strain Vd592 was inoculated into cotton, and the infected cotton roots at 36 h and 3 d post infection were subjected to dual RNA-seq analysis. For the V. dahliae, transcriptomic analysis identified 317 differentially expressed genes (DEGs) encoding classical secreted proteins, which were up-regulated at least at one time point during infection. The 317 DEGs included 126 carbohydrate-active enzyme (CAZyme) and 108 small cysteine-rich protein genes. A pectinesterase gene (VDAG_01782) belonging to CAZyme, designated as VdPE1, was selected for functional validation. VdPE1 silencing by HIGS (host-induced gene silencing) resulted in reduced disease symptoms and the increased resistance of cotton to V. dahliae. For the cotton, transcriptomic analysis found that many DEGs involved in well-known disease resistance pathways (flavonoid biosynthesis, plant hormone signaling, and plant-pathogen interaction) as well as PTI (pattern-triggered immunity) and ETI (effector-triggered immunity) processes were significantly down-regulated in infected cotton roots. The dual RNA-seq data thus potentially connected the genes encoding secreted proteins to the pathogenicity of V. dahliae, and the genes were involved in some disease resistance pathways and PTI and ETI processes for the susceptibility of cotton to V. dahliae. These findings are helpful in the further characterization of candidate genes and breeding resistant cotton varieties via genetic engineering.

An iron-binding protein of entomopathogenic fungus suppresses the proliferation of host symbiotic bacteria

BACKGROUND

Entomopathogenic fungal infection-induced dysbiosis of host microbiota offers a window into understanding the complex interactions between pathogenic fungi and host symbionts. Such insights are critical for enhancing the efficacy of mycoinsecticides. However, the utilization of these interactions in pest control remains largely unexplored.

RESULTS

Here, we found that infection by the host-specialist fungus Metarhizium acridum alters the composition of the symbiotic microbiota and increases the dominance of some bacterial symbionts in locusts. Meanwhile, M. acridum also effectively limits the overgrowth of the predominant bacteria. Comparative transcriptomic screening revealed that the fungus upregulates the production of MaCFEM1, an iron-binding protein, in the presence of bacteria. This protein sequesters iron, thereby limiting its availability. Functionally, overexpression of MaCFEM1 in the fungus induces iron deprivation, which significantly suppresses bacterial growth. Conversely, MaCFEM1 knockout relieves the restriction on bacterial iron availability, resulting in iron reallocation. Upon ΔMaCFEM1 infection, some host bacterial symbionts proliferate uncontrollably, turning into opportunistic pathogens and significantly accelerating host death.

CONCLUSIONS

This study elucidates the critical role of pathogenic fungal-dominated iron allocation in mediating the shift of host microbes from symbiosis to pathogenicity. It also highlights a unique biocontrol strategy that jointly exploits pathogenic fungi and bacterial symbionts to increase host mortality. Video Abstract.

The new CFEM protein CgCsa required for Fe3+ homeostasis regulates the growth, development, and pathogenicity of Colletotrichum gloeosporioides

Secreted common fungal extracellular membrane (CFEM) domain proteins have been implicated in multiple biological functions in fungi. However, it is still largely unknown whether the ferric iron (Fe3+), as an important trace element, was involved with the biological function of CFEM proteins. In this study, a new CFEM protein CgCsa, with high expression levels at the early inoculation stage on peppers by Colletotrichum gloeosporioides was investigated. Deletion of the targeted gene CgCsa revealed multiple biological roles in hyphal growth restriction, highly reduced conidial yield, delayed conidial germination, abnormal appressorium with elongated bud tubes, and significantly reduced virulence of C. gloeosporioides. Moreover, in CgCsa mutants, the expression levels of four cell wall synthesis-related genes were downregulated, and cell membrane permeability and electrical conductivity were increased. Compared to the wild-type, the CgCsa mutants downregulated expressions of iron transport-related genes, in addition, its three-dimensional structure was capable binding with iron. Increase in the Fe3+ concentration in the culture medium partially recovered the functions of ΔCgCsa mutant. This is probably the first report to show the association between CgCsa and iron homeostasis in C. gloeosporioides. The results suggest an alternative pathway for controlling plant fungal diseases by deplete their trace elements.

VdP5CDH is involved in melanin formation, stress resistance and play a regulatory role in virulence of Verticillium dahliae

Introduction

Verticillium dahliae, a soil-borne fungal pathogen, can cause cotton Verticillium wilt. In this study, VdP5CDH, the member of the ALDH_F4-17 family of carboxylate dehydrogenases, was identified in the genome of V. dahliae and investigated function in regulating virulence by generating gene deletion mutants and complementary mutants.

Methods

Homologous recombination method was used to construct mutants, transcriptome sequencing revealed gene-related metabolic pathways, and disease degree of cotton was observed through pathogen infection experiments.

Results

The conidial surface of VdP5CDH deletion strains was dented and shriveled, and the number of conidial spores increased. Compared with the wild-type (WT), the mycelial diameter of deletion mutants increased by 10.59%-11.16%, the mycelial growth showed irregular branching patterns, and misaligned arrangement. Although capable of penetrating cellophane, deletion mutants were unable to produce melanin. VdP5CDH was mainly associated with glucose metabolism, nitrogen metabolism, ABC transporter activity as well as various amino acid metabolic processes. After gene knockout, raffinose and pectin were used as the main carbon sources to promote the growth of strains and the growth rate of deletion strains in the medium containing raffinose was higher than that of WT. Consequently, the deletion mutant strains decreased utilization efficiency with which they utilized various nitrogen sources. The deletion mutants maintain responsiveness to osmotic stress and oxidative stress stimuli. Additionally, compared to WT strains, the deletion mutant strains exhibited differences in culture temperature tolerance, UV exposure response, and fungicide sensitivity. After cotton was infected with deletion strains conidial suspension, its disease index increased dramatically, while it gradually decreased after spraying with 2 mM glutamate in batches. With the increase of spraying times, the effect was more significant, and the disease index decreased by 18.95%-19.66% at 26 dpi.

Discussion

These results indicated that VdP5CDH regulates the pathogenicity of fungi and controls mycelia growth, melanin formation, conidia morphology, abiotic stress resistance, and the expression of infecting structure-related genes.

Deleting an xylosidase-encoding gene VdxyL3 increases growth and pathogenicity of Verticillium dahlia

Introduction

Verticillium dahliae causes a devastating Verticillium wilt disease on hundreds of plant species worldwide, including cotton. Understanding the interaction mechanism between V. dahliae and its hosts is the prerequisite for developing effective strategies for disease prevention.

Methods

Here, based on the previous observation of an xylosidase-encoding gene (VdxyL3) in V. dahliae being obviously up-regulated after sensing root exudates from a cotton variety susceptible to this pathogen, we investigated the function of VdxyL3 in the growth and pathogenesis of V. dahliae by generating its deletion-mutant strains (ΔVdxyL3).

Results

Deleting VdxyL3 led to increased colony expansion rate, conidial production, mycelial growth, carbon and nitrogen utilization capacities, and enhanced stress tolerance and pathogenicity of V. dahliae. VdxyL3 is a secretory protein; however, VdxyL3 failed to induce cell death in N. benthamiana based on transient expression experiment. Transcriptomic analysis identified 1300 genes differentially expressed (DEGs) between wild-type (Vd952) and ΔVdxyL3 during infection, including 348 DEGs encoding secretory proteins, among which contained 122 classical secreted proteins and 226 non-classical secreted proteins. It was notable that of the 122 classical secretory proteins, 50 were carbohydrate-active enzymes (CAZymes) and 58 were small cysteine rich proteins (SCRPs), which were required for the pathogenicity of V. dahliae.

Conclusion

The RNA-seq data thus potentially connected the genes encoding these proteins to the pathogenesis of V. dahliae. This study provides an experimental basis for further studies on the interaction between V. dahliae and cotton and the pathogenic mechanism of the fungus.

Systematic identification and functional characterization of the CFEM proteins in fishscale bamboo rhombic-spot pathogen Neostagonosporella sichuanensis

Fungal effectors play a crucial role in the interaction between pathogenic fungi and their hosts. These interactions directly influence the invasion and spread of pathogens, and the development of diseases. Common in fungal extracellular membrane (CFEM) effectors are closely associated with the pathogenicity, cell wall stability, and pathogenic processes of pathogenic fungi. The aim of this study was to investigate the role of CFEM proteins in Neostagonosporella sichuanensis in pathogen-host interactions. We retrieved 19 proteins containing CFEM structural domains from the genome of N. sichuanensis. By systematic analysis, five NsCFEM proteins had signal peptides but lacked transmembrane structural domains, and thus were considered as potential effectors. Among them, NsCFEM1 and NsCFEM2 were successfully cloned and their functions were further investigated. The validation results show that NsCFEM1 was localized in the cell membrane and nucleus, whereas NsCFEM2 was exclusively observed in the cell membrane. Both were identified as secreted proteins. Additionally, NsCFEM1 inhibited Bax-induced programmed cell death in Nicotiana benthamiana, whereas NsCFEM2 did not induce or inhibit this response. NsCFEM1 was implicated as a virulence factor that contributes to fungal growth, development, stress response, and pathogenicity. NsCFEM2 was implicated in maintenance of cell wall stability. This study lays a foundation for elucidating the role of CFEM proteins in the pathogen of fishscale bamboo rhombic-spot caused by N. sichuanensis. In particular, the functional studies of NsCFEM1 and NsCFEM2 revealed their potential roles in the interaction between N. sichuanensis and the host Phyllostachys heteroclada.

CgCFEM1 Is Required for the Full Virulence of Colletotrichum gloeosporioides

Colletotrichum gloeosporioides is widely distributed and causes anthracnose on many crops, resulting in serious economic losses. Common fungal extracellular membrane (CFEM) domain proteins have been implicated in virulence and their interaction with the host plant, but their roles in C. gloeosporioides are still unknown. In this study, a CFEM-containing protein of C. gloeosporioides was identified and named as CgCFEM1. The expression levels of CgCFEM1 were found to be markedly higher in appressoria, and this elevated expression was particularly pronounced during the initial stages of infection in the rubber tree. Absence of CgCFEM1 resulted in impaired pathogenicity, accompanied by notable perturbations in spore morphogenesis, conidiation, appressorium development and primary invasion. During the process of appressorium development, the absence of CgCFEM1 enhanced the mitotic activity in both conidia and germ tubes, as well as compromised conidia autophagy. Rapamycin was found to basically restore the appressorium formation, and the activity of target of rapamycin (TOR) kinase was significantly induced in the CgCFEM1 knockout mutant (∆CgCFEM1). Furthermore, CgCFEM1 was proved to suppress chitin-triggered reactive oxygen species (ROS) accumulation and change the expression patterns of defense-related genes. Collectively, we identified a fungal effector CgCFEM1 that contributed to pathogenicity by regulating TOR-mediated conidia and appressorium morphogenesis of C. gloeosporioides and inhibiting the defense responses of the rubber tree.

SreC-dependent adaption to host iron environments regulates the transition of trophic stages and developmental processes of Curvularia lunata

Plant pathogens are challenged by host-derived iron starvation or excess during infection, but the mechanism of plant pathogens rapidly adapting to the dynamic host iron environments to assimilate iron for invasion and colonization remains largely unexplored. Here, we found that the GATA transcription factor SreC in Curvularia lunata is required for virulence and adaption to the host iron excess environment. SreC directly binds to the ATGWGATAW element in an iron-dependent manner to regulate the switch between different iron assimilation pathways, conferring adaption to host iron environments in different trophic stages of C. lunata. SreC also regulates the transition of trophic stages and developmental processes in C. lunata. SreC-dependent adaption to host iron environments is essential to the infectious growth and survival of C. lunata. We also demonstrate that CgSreA (a SreC orthologue) plays a similar role in Colletotrichum graminicola. We conclude that Sre mediates adaption to the host iron environment during infection, and the function is conserved in hemibiotrophic fungi.

Fungal Cell Wall-Associated Effectors: Sensing, Integration, Suppression, and Protection

The cell wall (CW) of plant-interacting fungi, as the direct interface with host plants, plays a crucial role in fungal development. A number of secreted proteins are directly associated with the fungal CW, either through covalent or non-covalent interactions, and serve a range of important functions. In the context of plant-fungal interactions many are important for fungal development in the host environment and may therefore be considered fungal CW-associated effectors (CWAEs). Key CWAE functions include integrating chemical/physical signals to direct hyphal growth, interfering with plant immunity, and providing protection against plant defenses. In recent years, a diverse range of mechanisms have been reported that underpin their roles, with some CWAEs harboring conserved motifs or functional domains, while others are reported to have novel features. As such, the current understanding regarding fungal CWAEs is systematically presented here from the perspective of their biological functions in plant-fungal interactions. An overview of the fungal CW architecture and the mechanisms by which proteins are secreted, modified, and incorporated into the CW is first presented to provide context for their biological roles. Some CWAE functions are reported across a broad range of pathosystems or symbiotic/mutualistic associations. Prominent are the chitin interacting-effectors that facilitate fungal CW modification, protection, or suppression of host immune responses. However, several alternative functions are now reported and are presented and discussed. CWAEs can play diverse roles, some possibly unique to fungal lineages and others conserved across a broad range of plant-interacting fungi. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Multifunctionality of AsCFEM6 and AsCFEM12 effectors from the potato early blight pathogen Alternaria solani

Plant pathogens secrete fungal-specific common in several fungal extracellular membrane (CFEM) effectors to manipulate host immunity and contribute to their virulence. Little is known about effectors and their functions in Alternaria solani, the necrotrophic fungal pathogen causing potato early blight. To identify candidate CFEM effector genes, we mined A. solani genome databases. This led to the identification of 12 genes encoding CFEM proteins (termed AsCFEM1-AsCFEM12) and 6 of them were confirmed to be putative secreted effectors. In planta expression revealed that AsCFEM6 and AsCFEM12 have elicitor function that triggers plant defense response including cell death in different botanical families. Targeted gene disruption of AsCFEM6 and AsCFEM12 resulted in a change in spore development, significant reduction of virulence on potato and eggplant susceptible cultivars, increased resistance to fungicide stress, variation in iron acquisition and utilization, and the involvement in 1,8-dihydroxynaphthalene (DHN) melanin biosynthesis pathway. Using maximum likelihood method, we found that positive selection likely caused the polymorphism within AsCFEM6 and AsCFEM12 homologs in different Alternaria spp. Site-directed mutagenesis analysis indicated that positive selection sites within their CFEM domains are required for cell death induction in Nicotiana benthamiana and are critical for response to abiotic stress in yeast. These results demonstrate that AsCFEM effectors possess additional functions beyond their roles in host plant immune response and pathogen virulence.

The elicitor VP2 from Verticillium dahliae triggers defence response in cotton

Verticillium dahliae is a widespread and destructive soilborne vascular pathogenic fungus that causes serious diseases in dicot plants. Here, comparative transcriptome analysis showed that the number of genes upregulated in defoliating pathotype V991 was significantly higher than in the non-defoliating pathotype 1cd3-2 during the early response of cotton. Combined with analysis of the secretome during the V991-cotton interaction, an elicitor VP2 was identified, which was highly upregulated at the early stage of V991 invasion, but was barely expressed during the 1cd3-2-cotton interaction. Full-length VP2 could induce cell death in several plant species, and which was dependent on NbBAK1 but not on NbSOBIR1 in N. benthamiana. Knock-out of VP2 attenuated the pathogenicity of V991. Furthermore, overexpression of VP2 in cotton enhanced resistance to V. dahliae without causing abnormal plant growth and development. Several genes involved in JA, SA and lignin synthesis were significantly upregulated in VP2-overexpressing cotton. The contents of JA, SA, and lignin were also significantly higher than in the wild-type control. In summary, the identified elicitor VP2, recognized by the receptor in the plant membrane, triggers the cotton immune response and enhances disease resistance.

The Botrytis cinerea transglycosylase BcCrh4 is a cell death-inducing protein with cell death-promoting and -suppressing domains

Botrytis cinerea is a necrotrophic fungal plant pathogen that causes grey mould and rot diseases in many crops. Here, we show that the B. cinerea BcCrh4 transglycosylase is secreted during plant infection and induces plant cell death and pattern-triggered immunity (PTI), fulfilling the characteristics of a cell death-inducing protein (CDIP). The CDIP activity of BcCrh4 is independent of the transglycosylase enzymatic activity, it takes place in the apoplast and does not involve the receptor-like kinases BAK1 and SOBIR1. During saprophytic growth, BcCrh4 is localized in the endoplasmic reticulum and in vacuoles, but during plant infection, it accumulates in infection cushions (ICs) and is then secreted to the apoplast. Two domains within the BcCrh4 protein determine the CDIP activities: a 20aa domain at the N' end activates intense cell death and PTI, while a stretch of 52aa in the middle of the protein induces a weaker response and suppresses the activity of the 20aa N' domain. Deletion of bccrh4 affected fungal development and IC formation in particular, resulting in reduced virulence. Collectively, our findings demonstrate that BcCrh4 is required for fungal development and pathogenicity, and hint at a dual mechanism that balances the virulence activity of this, and potentially other CDIPs.

Small secreted effector protein from Fusarium sacchari suppresses host immune response by inhibiting ScPi21-induced cell death

Fusarium sacchari is one of the primary pathogens causing pokkah boeng disease, which impairs the yield and quality of sugarcane around the world. Understanding the molecular mechanisms of the F. sacchari effectors that regulate plant immunity is of great importance for the development of novel strategies for the persistent control of pokkah boeng disease. In a previous study, Fs00367 was identified to inhibit BAX-induced cell death. In this study, Fs00367nsp (without signal peptide) was found to suppress BAX-induced cell death, reactive oxygen species bursts and callose accumulation. The amino acid region 113-142 of Fs00367nsp is the functional region. Gene mutagenesis indicated that Fs00367 is important for the full virulence of F. sacchari. A yeast two-hybrid assay revealed an interaction between Fs00367nsp and sugarcane ScPi21 in yeast that was further confirmed using bimolecular fluorescence complementation, pull-down assay and co-immunoprecipitation. ScPi21 can induce plant immunity, but this effect could be blunted by Fs00367nsp. These results suggest that Fs00367 is a core pathogenicity factor that suppresses plant immunity through inhibiting ScPi21-induced cell death. The findings of this study provide new insights into the molecular mechanisms of effectors in regulating plant immunity.

Identification of common fungal extracellular membrane (CFEM) proteins in Fusarium sacchari that inhibit plant immunity and contribute to virulence

IMPORTANCE

Common fungal extracellular membrane (CFEM) domain-containing protein has long been considered an essential effector, playing a crucial role in the interaction of pathogens and plant. Strategies aimed at understanding the pathogenicity mechanism of F. sacchari are eagerly anticipated to ultimately end the spread of pokkah boeng disease. Twenty FsCFEM proteins in the genome of F. sacchari have been identified, and four FsCFEM effector proteins have been found to suppress BCL2-associated X protein-triggered programmed cell death in N. benthamiana. These four effector proteins have the ability to enter plant cells and inhibit plant immunity. Furthermore, the expression of these four FsCFEM effector proteins significantly increases during the infection stage, with the three of them playing an essential role in achieving full virulence. These study findings provide a direction toward further exploration of the immune response in sugarcane. By applying these discoveries, we can potentially control the spread of disease through techniques such as host-induced gene silencing.

The Verticillium dahliae Small Cysteine-Rich Protein VdSCP23 Manipulates Host Immunity

Verticillium wilt caused by Verticillium dahliae is a notorious soil-borne fungal disease and seriously threatens the yield of economic crops worldwide. During host infection, V. dahliae secretes many effectors that manipulate host immunity, among which small cysteine-rich proteins (SCPs) play an important role. However, the exact roles of many SCPs from V. dahliae are unknown and varied. In this study, we show that the small cysteine-rich protein VdSCP23 inhibits cell necrosis in Nicotiana benthamiana leaves, as well as the reactive oxygen species (ROS) burst, electrolyte leakage and the expression of defense-related genes. VdSCP23 is mainly localized in the plant cell plasma membrane and nucleus, but its inhibition of immune responses was independent of its nuclear localization. Site-directed mutagenesis and peptide truncation showed that the inhibition function of VdSCP23 was independent of cysteine residues but was dependent on the N-glycosylation sites and the integrity of VdSCP23 protein structure. Deletion of VdSCP23 did not affect the growth and development of mycelia or conidial production in V. dahliae. Unexpectedly, VdSCP23 deletion strains still maintained their virulence for N. benthamiana, Gossypium hirsutum and Arabidopsis thaliana seedlings. This study demonstrates an important role for VdSCP23 in the inhibition of plant immune responses; however, it is not required for normal growth or virulence in V. dahliae.

Dual Transcriptomics Reveals Interspecific Interactions between the Mycoparasite Calcarisporium cordycipiticola and Its Host Cordyceps militaris

Calcarisporium cordycipiticola is a mycoparasite of the edible fungus Cordyceps militaris, and mycoparasitism causes devastating diseases of mushrooms. In this study, dual-transcriptomic analysis was performed to reveal interspecific interactions between the mycoparasite C. cordycipiticola and its host C. militaris. At 4 and 8 days postinfection (dpi), 2,959 and 2,077 differentially expressed genes (DEGs) of C. cordycipiticola and 914 and 1,548 DEGs of C. militaris were identified compared with the mycelial stage, respectively, indicating that C. cordycipiticola responded more quickly than C. militaris. Lectins of the pathogen may play a role in the recognition of fungal prey. Both Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses showed that primary metabolism was vigorous for the pathogen to colonize the host and that the pathogen's attack substantially altered C. militaris' primary metabolism. C. cordycipiticola upregulated some carbohydrate-active enzyme (CAZyme) genes, including CBM18, GH18, GH16, and GH76, for degrading the host cell wall and defending against host immunity. C. militaris produced excessive reactive oxygen species (ROS) to respond to the infection. The GO term "heme binding" was the only shared term enriched at both stages at 4 and 8 dpi, indicating that iron was important for both the pathogen and the host. The uptake of iron by pathogens through multiple pathways promoted colonization and removed high ROS levels produced by the host. The transcription levels of Cmhsp78, Cmhsp70, and Cmhyd1 in C. militaris responded quickly, and these genes have potential as candidates for the breeding of resistant varieties. This study provides clues for understanding the interactions between a mycoparasite and its mushroom host and will be helpful for the breeding of resistant varieties and disease prevention and control for this edible fungus. IMPORTANCE White mildew disease caused by Calcarisporium cordycipiticola is devastating for the fruiting body cultivation of Cordyceps militaris, a popular and highly valued edible fungus. Here, the pathogenic mechanisms of C. cordycipiticola, the responses of C. militaris to the infection, and the interaction of these two phylogenetically close species were revealed by time course dual-transcriptome profiles. In general, the host C. militaris responds more slowly than the pathogen C. cordycipiticola. For the first time, we found that iron was important for both the mycoparasite and the host. C. cordycipiticola takes up iron by multiple pathways to promote colonization and remove high ROS levels produced by the host. The rapidly responding genes Cmhsp70, Cmhsp78, and Cmhyd1 in C. militaris may have the potential as candidate genes for the breeding of resistant varieties. This study expands our understanding of the mycoparasitic interactions of two species from sister families and will be helpful for the breeding of and disease prevention and control in mushrooms.

VdGAL4 Modulates Microsclerotium Formation, Conidial Morphology, and Germination To Promote Virulence in Verticillium dahliae

Verticillium dahliae Kleb is a typical soilborne pathogen that can cause vascular wilt disease on more than 400 plants. Functional analysis of genes related to the growth and virulence is crucial to revealing the molecular mechanism of the pathogenicity of V. dahliae. Glycosidase hydrolases can hydrolyze the glycosidic bond, and some can cause host plant immune response to V. dahliae. Here, we reported a functional validation of VdGAL4 as an α-galactosidase that belongs to glycoside hydrolase family 27. VdGAL4 could cause plant cell death, and its signal peptide plays an important role in cellular immune response. VdGAL4-triggered cell death depends on BAK1 and SOBIR1 in Nicotiana benthamiana. In V. dahliae, the function of VdGAL4 in mycelial growth, conidia, microsclerotium, and pathogenicity was studied by constructing VdGAL4 deletion and complementation mutants. Results showed that the deletion of VdGAL4 reduced the conidial yield and conidial germination rate of V. dahliae and changed the microscopic morphology of conidia; the mycelia were arranged more disorderly and were unable to produce microsclerotium. The VdGAL4 deletion mutants exhibited reduced utilization of different carbon sources, such as raffinose and sucrose. The VdGAL4 deletion mutants were also more sensitive to abiotic stress agents of SDS, sorbitol, low-temperature stress of 16°C, and high-temperature stress of 45°C. In addition, the VdGAL4 deletion mutants lost the ability to penetrate cellophane and its mycelium were disorderly arranged. Remarkably, VdGAL4 deletion mutants exhibited reduced pathogenicity of V. dahliae. These results showed that VdGAL4 played a critical role in the pathogenicity of V. dahliae by regulating mycelial growth, conidial morphology, and the formation of microsclerotium. IMPORTANCE This study showed that α-galactosidase VdGAL4 of V. dahliae could activate plant immune response and plays an important role in conidial morphology and yield, formation of microsclerotia, and mycelial penetration. VdGAL4 deletion mutants significantly reduced the pathogenicity of V. dahliae. These findings deepened the understanding of pathogenic virulence factors and how the mechanism of pathogenic fungi infected the host, which may help to seek new strategies for effective control of plant diseases caused by pathogenic fungi.

Getting to the root of a club - Understanding developmental manipulation by the clubroot pathogen

Plasmodiophora brassicae Wor., the clubroot pathogen, is the perfect example of an "atypical" plant pathogen. This soil-borne protist and obligate biotrophic parasite infects the roots of cruciferous crops, inducing galls or clubs that lead to wilting, loss of productivity, and plant death. Unlike many other agriculturally relevant pathosystems, research into the molecular mechanisms that underlie clubroot disease and Plasmodiophora-host interactions is limited. After release of the first P. brassicae genome sequence and subsequent availability of transcriptomic data, the clubroot research community have implicated the involvement of phytohormones during the clubroot pathogen's manipulation of host development. Herein we review the main events leading to the formation of root galls and describe how modulation of select phytohormones may be key to modulating development of the plant host to the benefit of the pathogen. Effector-host interactions are at the base of different strategies employed by pathogens to hijack plant cellular processes. This is how we suspect the clubroot pathogen hijacks host plant metabolism and development to induce nutrient-sink roots galls, emphasizing a need to deepen our understanding of this master manipulator.

Sensing of a spore surface protein by a Drosophila chemosensory protein induces behavioral defense against fungal parasitic infections

In addition to innate immunity in a physiological context, insects have evolved behavioral defenses against parasite attacks. Here, we report that Drosophila can sense the CFEM (common in fungal extracellular membrane) protein Mcdc9, which acts as a negative virulence factor of the entomopathogenic fungus Metarhizium robertsii. The individual deletions of 18 CFEM genes in Metarhizium followed by fly infection identified three null mutants that could kill the flies more quickly than the wild-type strain, among which Mcdc9 can coat fungal spores and interact with the fly chemosensory protein CheA75a. The deletion of Mcdc9 in the fungus or the knockdown of CheA75a in flies had a similar effect, in which a greater number of fungal spores were left on flies than on the respective controls after topical infection. Thus, similar to the accelerated death of the wild-type flies treated with ΔMcdc9, the CheA75a^RNAi flies succumbed more quickly than the control insects topically challenged with the wild-type strain. The CheA75a gene is highly transcribed in fly legs and wings, and positive electrophysiological responses were evidenced in tarsal sensilla after stimulation with the Mcdc9 protein. The results imply that this CFEM protein could be sensed as a contact elicitor inducing the hygienic behavior of flies against fungal parasitic infection, which reveals a previously unsuspected mechanism of fungus-insect interactions.

Interactions between Verticillium dahliae and cotton: pathogenic mechanism and cotton resistance mechanism to Verticillium wilt

Cotton is widely grown in many countries around the world due to the huge economic value of the total natural fiber. Verticillium wilt, caused by the soil-borne pathogen Verticillium dahliae, is the most devastating disease that led to extensive yield losses and fiber quality reduction in cotton crops. Developing resistant cotton varieties through genetic engineering is an effective, economical, and durable strategy to control Verticillium wilt. However, there are few resistance gene resources in the currently planted cotton varieties, which has brought great challenges and difficulties for breeding through genetic engineering. Further revealing the molecular mechanism between V. dahliae and cotton interaction is crucial to discovering genes related to disease resistance. In this review, we elaborated on the pathogenic mechanism of V. dahliae and the resistance mechanism of cotton to Verticillium wilt. V. dahliae has evolved complex mechanisms to achieve pathogenicity in cotton, mainly including five aspects: (1) germination and growth of microsclerotia; (2) infection and successful colonization; (3) adaptation to the nutrient-deficient environment and competition of nutrients; (4) suppression and manipulation of cotton immune responses; (5) rapid reproduction and secretion of toxins. Cotton has evolved multiple physiological and biochemical responses to cope with V. dahliae infection, including modification of tissue structures, accumulation of antifungal substances, homeostasis of reactive oxygen species (ROS), induction of Ca²⁺ signaling, the mitogen-activated protein kinase (MAPK) cascades, hormone signaling, and PAMPs/effectors-triggered immune response (PTI/ETI). This review will provide an important reference for the breeding of new cotton germplasm resistant to Verticillium wilt through genetic engineering.

Fungal CFEM effectors negatively regulate a maize wall-associated kinase by interacting with its alternatively spliced variant to dampen resistance

The fungus Fusarium graminearum causes a devastating disease Gibberella stalk rot of maize. Our knowledge of molecular interactions between F. graminearum effectors and maize immunity factors is lacking. Here, we show that a group of cysteine-rich common in fungal extracellular membrane (CFEM) domain proteins of F. graminearum are required for full virulence in maize stalk infection and that they interact with two secreted maize proteins, ZmLRR5 and ZmWAK17ET. ZmWAK17ET is an alternative splicing isoform of a wall-associated kinase ZmWAK17. Both ZmLRR5 and ZmWAK17ET interact with the extracellular domain of ZmWAK17. Transgenic maize overexpressing ZmWAK17 shows increased resistance to F. graminearum, while ZmWAK17 mutants exhibit enhanced susceptibility to F. graminearum. Transient expression of ZmWAK17 in Nicotiana benthamiana triggers hypersensitive cell death, whereas co-expression of CFEMs with ZmWAK17ET or ZmLRR5 suppresses the ZmWAK17-triggered cell death. Our results show that ZmWAK17 mediates stalk rot resistance and that F. graminearum delivers apoplastic CFEMs to compromise ZmWAK17-mediated resistance.

Systematic identification and functional characterization of the CFEM proteins in poplar fungus Marssonina brunnea

Proteins containing Common in Fungal Extracellular Membrane (CFEM) domains uniquely exist in fungi and play significant roles in their whole life history. In this study, a total of 11 MbCFEM proteins were identified from Marssonina brunnea f. sp. multigermtubi (MULT), a hemibiotrophic pathogenic fungus on poplars that causes severe leaf diseases. Phylogenic analysis showed that the 11 proteins (MbCFEM1-11) were divided into three clades based on the trans-membrane domain and the CFEM domain. Sequence alignment and WebLogo analysis of CFEM domains verified the amino acids conservatism therein. All of them possess eight cysteines except MbCFEM4 and MbCFEM11, which lack two cysteines each. Six MbCFEM proteins with a signal peptide and without trans-membrane domain were considered as candidate effectors for further functional analysis. Three-dimensional (3D) models of their CFEM domains presented a helical-basket structure homologous to the crucial virulence factor Csa2 of Candida albicans. Afterward, four (MbCFEM1, 6, 8, and 9) out of six candidate effectors were successfully cloned and a yeast signal sequence trap (YSST) assay confirmed their secretion activity. Pathogen challenge assays demonstrated that the transient expression of four candidate MbCFEM effectors in Nicotiana benthamiana promoted Fusarium proliferatum infection, respectively. In an N. benthamiana heterogeneous expression system, MbCFEM1, MbCFEM6, and MbCFEM9 appeared to suppress both BAX/INF1-triggered PCD, whereas MbCFEM8 could only defeat BAX-triggered PCD. Additionally, subcellular localization analysis indicated that the four candidate MbCFEM effectors accumulate in the cell membrane, nucleus, chloroplast, and cytosolic bodies. These results demonstrate that MbCFEM1, MbCFEM6, MbCFEM8, and MbCFEM9 are effectors of M. brunnea and provide valuable targets for further dissection of the molecular mechanisms underlying the poplar-M. brunnea interaction.

WideEffHunter: An Algorithm to Predict Canonical and Non-Canonical Effectors in Fungi and Oomycetes

Newer effectorome prediction algorithms are considering effectors that may not comply with the canonical characteristics of small, secreted, cysteine-rich proteins. The use of effector-related motifs and domains is an emerging strategy for effector identification, but its use has been limited to individual species, whether oomycete or fungal, and certain domains and motifs have only been associated with one or the other. The use of these strategies is important for the identification of novel, non-canonical effectors (NCEs) which we have found to constitute approximately 90% of the effectoromes. We produced an algorithm in Bash called WideEffHunter that is founded on integrating three key characteristics: the presence of effector motifs, effector domains and homology to validated existing effectors. Interestingly, we found similar numbers of effectors with motifs and domains within two different taxonomic kingdoms: fungi and oomycetes, indicating that with respect to their effector content, the two organisms may be more similar than previously believed. WideEffHunter can identify the entire effectorome (non-canonical and canonical effectors) of oomycetes and fungi whether pathogenic or non-pathogenic, unifying effector prediction in these two kingdoms as well as the two different lifestyles. The elucidation of complete effectoromes is a crucial step towards advancing effectoromics and disease management in agriculture.

Leveraging genomics to understand the broader role of fungal small secreted proteins in niche colonization and nutrition

The last few years have seen significant advances in the breadth of fungi for which we have genomic resources and our understanding of the biological mechanisms evolved to enable fungi to interact with their environment and other organisms. One field of research that has seen a paradigm shift in our understanding concerns the role of fungal small secreted proteins (SSPs) classified as effectors. Classically thought to be a class of proteins utilized by pathogenic microbes to manipulate host physiology in support of colonization, comparative genomic studies have demonstrated that mutualistic fungi and fungi not associated with a living host (i.e., saprotrophic fungi) also encode inducible effector and candidate effector gene sequences. In this review, we discuss the latest advances in understanding how fungi utilize these secreted proteins to colonize a particular niche and affect nutrition and nutrient cycles. Recent studies show that candidate effector SSPs in fungi may have just as significant a role in modulating hyphosphere microbiomes and in orchestrating fungal growth as they do in supporting colonization of a living host. We conclude with suggestions on how comparative genomics may direct future studies seeking to characterize and differentiate effector from other more generalized functions of these enigmatic secreted proteins across all fungal lifestyles.

Bioinformatics Analysis and Functional Characterization of the CFEM Proteins of Metarhizium anisopliae

The entomopathogen Metarhizium anisopliae is a facultative rhizosphere or endophytic fungus available for managing pests and improving plant growth. The CFEM (common in fungal extracellular membrane) proteins form a unique group in fungi but are rarely reported in entomopathogens. In this study, we cloned and identified 13 CFEM genes from M. anisopliae (MaCFEMs). Sequence alignment and WebLogo analysis showed that eight cysteines were the most conserved amino acids in their CFEM domain. Phylogenic analysis suggested that these 13 proteins could be divided into 4 clades based on the presence of the transmembrane region and the position of CFEM domain in the whole sequence. Six MaCFEM proteins with a signal peptide and without a transmembrane domain were considered candidate effector proteins. According to Phyre2 analysis, the MaCFEM88 and MaCFEM85 have the most homologous to Csa2 in Candida albicans. Subcellular localization analysis revealed that five effectors were located in the plasma membrane, while MaCFEM88 may locate in both plasma membrane and nucleus in the treated Nicotiana benthamiana. Expression pattern analysis showed that MaCFEM81, 85, 88, and 89 expression level was significantly higher in the sporulation stage compared to other growth stages. Furthermore, the yeast secretion assay showed that six candidate effectors were able to secrete out of the cell. All of the MaCFEMs couldn’t affect INF1-induced programmed cell death (PCD), but MaCFEM85 and 88 could trigger a slight hypersensitive response both when applied separately or in combination with INF1 in N. benthamiana leaves. These findings showed that six MaCFEM potential effectors with various structures and subcellular localizations in host cells might be used to illustrate the roles of MaCFEM proteins during M. anisopliae-plant interactions.