The C 2 H 2 transcription factor VdMsn2 controls hyphal growth, microsclerotia formation, and virulence of Verticillium dahliae

The candidate transcription factors PnAtfA, PnCrz1, and PnVf19 contribute to fungal morphogenesis, abiotic stress tolerance, and pathogenicity in the wheat pathogen Parastagonospora nodorum

The necrotrophic fungus Parastagonospora nodorum, the causal agent of wheat glume blotch, is responsible for substantial economic losses in many wheat-growing regions. Despite the high number of transcription factor (TF)-encoding genes in the genome of P. nodorum, very little is known about their regulatory functions. Here, we assessed the role of three TFs in the regulation of P. nodorum virulence on wheat. We identified encoded in the genome of P. nodorum PnAtfA, PnCrz1, and PnVf19, homologous candidate TFs to Schizosaccharomyces pombe Atf1, Saccharomyces cerevisiae CRZ1, and S. cerevisiae Msn2, respectively. Targeted gene replacement of each gene led to reduced mycelial vegetative growth and loss of pathogenicity on wheat. Deletion of PnAtfA resulted in phenotype alteration with ΔPnCrz1 deletion mutants displayed abnormal colony morphology characterized by dense hyphal branching and loss of aerial hyphae development, showing that both PnAtfA and PnCrz1 regulate fungal morphogenesis. Additionally, deletion of PnAtfA and PnVf19 genes abolished pycnidiospore production whereas ΔPnCrz1 produced fewer pycnidiospores compared to the wild type. Furthermore, ΔPnCrz1 and ΔPnVf19 deletion mutants demonstrated increased sensitivity to hydrogen peroxide showing their involvement in oxidative stress response. The ΔPnVf19 deletion mutants exhibited increased sensitivity to sodium chloride, suggesting that PnVf19 is essential for osmotic tolerance response. Taken together, these findings suggest that the selected candidate TFs play a key role in the fungal morphogenesis, sporulation, oxidative and osmotic stress tolerance response, and full virulence in P. nodorum.

The 24-kDa subunit of mitochondrial complex I regulates growth, microsclerotia development, stress tolerance, and virulence in Verticillium dahliae

BACKGROUND

The complete mitochondrial respiratory chain is a precondition for maintaining cellular energy supply, development, and metabolic balance. Due to the evolutionary differentiation of complexes and the semi-autonomy of mitochondria, respiratory chain subunits have become critical targets for crop improvement and fungal control. In fungi, mitochondrial complex I mediates growth and metabolism. However, the role of this complex in the pathogenesis of phytopathogenic fungi is largely unknown.

RESULTS

In this study, we identified the NADH: ubiquinone oxidoreductase 24-kDa subunit (VdNuo1) of complex in vascular wilt pathogen, Verticillium dahliae, and examined its functional conservation in phytopathogenic fungi. Based on the treatments with respiratory chain inhibitors, the mitochondria-localized VdNuo1 was confirmed to regulate mitochondrial morphogenesis and homeostasis. VdNuo1 was induced during the different developmental stages in V. dahliae, including hyphal growth, conidiation, and melanized microsclerotia development. The VdNuo1 mutants displayed variable sensitivity to stress factors and decreased pathogenicity in multiple hosts, indicating that VdNuo1 is necessary in stress tolerance and full virulence. Comparative transcriptome analysis demonstrated that VdNuo1 mediates global transcriptional effects, including oxidation and reduction processes, fatty acid, sugar, and energy metabolism. These defects are partly attributed to impairments of mitochondrial morphological integrity, complex assembly, and related functions. Its homologue (CgNuo1) functions in the vegetative growth, melanin biosynthesis, and pathogenicity of Colletotrichum gloeosporioides; however, CgNuo1 does not restore the VdNuo1 mutant to normal phenotypes.

CONCLUSIONS

Our results revealed that VdNuo1 plays important roles in growth, metabolism, microsclerotia development, stress tolerance, and virulence of V. dahliae, sharing novel insight into the function of complex I and a potential fungicide target for pathogenic fungi.

Genome Sequencing and Comparative Genomic Analysis of Attenuated Strain Gibellulopsis nigrescens GnVn.1 Causing Mild Wilt in Sunflower

Gibellulopsis nigrescens, previously classified in the Verticillium genus until 2007, is an attenuated pathogen known to provide cross-protection against Verticillium wilt in various crops. To investigate the potential mechanisms underlying its reduced virulence, we conducted genome sequencing, annotation, and a comparative genome analysis of G. nigrescens GnVn.1 (GnVn.1), an attenuated strain isolated from sunflower. The genome sequencing and annotation results revealed that the GnVn.1 genome consists of 22 contigs, with a total size of 31.79 Mb. We predicted 10,876 genes, resulting in a gene density of 342 genes per Mb. The pathogenicity gene prediction results indicated 1733 high-confidence pathogenicity factors (HCPFs), 895 carbohydrate-active enzymes (CAZys), and 359 effectors. Moreover, we predicted 40 secondary metabolite clusters (SMCs). The comparative genome analysis indicated that GnVn.1 contains more CAZys, SMCs, predicted effectors, and HCPF genes than Verticillium dahliae (VdLs.17) and Verticillium alfalfae (VaMas.102). The core-pan analysis results showed that GnVn.1 had more specific HCPFs, effectors, CAZys, and secreted protein (SP) genes, and lost many critical pathogenic genes compared to VdLs.17 and VaMs.102. Our results indicate that the GnVn.1 genome harbors more pathogenicity-related genes than the VdLs.17 and VaMs.102 genomes. These abundant genes may play critical roles in regulating virulence. The loss of critical pathogenic genes causes weak virulence and confers biocontrol strategies to GnVn.1.

Transcription factors containing both C2H2 and homeobox domains play different roles in Verticillium dahliae

Verticillium dahliae causes Verticillium wilt in more than 200 plant species worldwide. As a soilborne fungus, it forms melanized microsclerotia and colonizes the xylem of host plants. Our previous study revealed a subfamily of C2H2-homeobox transcription factors in V. dahliae, but their biological roles remain unknown. In this study, we systematically characterized the functions of seven C2H2-homeobox transcription factors in V. dahliae. Deletion of VdChtf3 and VdChtf6 significantly decreased the production of melanized microsclerotia, and knockout of VdChtf1 and VdChtf4 enhanced virulence. Loss of VdChtf2 and VdChtf6 increased conidium production, whereas loss of VdChtf5 and VdChtf7 did not affect growth, conidiation, microsclerotial formation, or virulence. Further research showed that VdChtf3 activated the expression of genes encoding pectic enzymes to participate in microsclerotial formation. In addition, VdChtf4 reduced the expression of VdSOD1 to disturb the scavenging of superoxide radicals but induced the expression of genes related to cell wall synthesis to maintain cell wall integrity. These findings highlight the diverse roles of different members of the C2H2-homeobox gene family in V. dahliae.

IMPORTANCE

Verticillium dahliae is a soilborne fungus that causes plant wilt and can infect a variety of economic crops and woody trees. The molecular basis of microsclerotial formation and infection by this fungus remains to be further studied. In this study, we analyzed the functions of seven C2H2-homobox transcription factors. Notably, VdChtf3 and VdChtf4 exhibited the most severe defects, affecting phenotypes associated with critical developmental stages in the V. dahliae disease cycle. Our results indicate that VdChtf3 is a potential specific regulator of microsclerotial formation, modulating the expression of pectinase-encoding genes. This finding could contribute to a better understanding of microsclerotial development in V. dahliae. Moreover, VdChtf4 was associated with cell wall integrity, reactive oxygen species (ROS) stress resistance, and increased virulence. These discoveries shed light on the biological significance of C2H2-homeobox transcription factors in V. dahliae's adaptation to the environment and infection of host plants.

The Kelch Repeat Protein VdKeR1 Is Essential for Development, Ergosterol Metabolism, and Virulence in Verticillium dahliae

Verticillium dahliae is a soil-borne fungal pathogen that can cause severe vascular wilt in many plant species. Kelch repeat proteins are essential for fungal growth, resistance, and virulence. However, the function of the Kelch repeat protein family in V. dahliae is unclear. In this study, a Kelch repeat domain-containing protein DK185_4252 (VdLs.17 VDAG_08647) included in the conserved VdPKS9 gene cluster was identified and named VdKeR1. Phylogenetic analysis demonstrated a high degree of evolutionary conservation of VdKeR1 and its homologs among fungi. The experimental results showed that the absence of VdKeR1 impaired vegetative growth, microsclerotia development, and pathogenicity of V. dahliae. Osmotic and cell wall stress analyses suggested that VdKeR1-deleted mutants were more tolerant to NaCl, sorbitol, CR, and CFW, while more sensitive to H2O2 and SDS. In addition, analyses of the relative expression level of sqe and the content of squalene and ergosterol showed that VdKeR1 mediates the synthesis of squalene and ergosterol by positively regulating the activity of squalene epoxidase. In conclusion, these results indicated that VdKeR1 was involved in the growth, stress resistance, pathogenicity, and ergosterol metabolism of V. dahliae. Investigating VdKeR1 provided theoretical and experimental foundations for subsequent control of Verticillium wilt.

Zinc finger transcription factor ZFP1 is associated with growth, conidiation, osmoregulation, and virulence in the Polygonatum kingianum pathogen Fusarium oxysporum

Rhizome rot is a destructive soil-borne disease of Polygonatum kingianum and adversely affects the yield and sustenance of the plant. Understanding how the causal fungus Fusarium oxysporum infects P. kingianum may suggest effective control measures against rhizome rot. In germinating conidia of infectious F. oxysporum, expression of the zinc finger transcription factor gene Zfp1, consisting of two C2H2 motifs, was up-regulated. To characterize the critical role of ZFP1, we generated independent deletion mutants (zfp1) and complemented one mutant with a transgenic copy of ZFP1 (zfp1 tZFP1). Mycelial growth and conidial production of zfp1 were slower than those of wild type (ZFP1) and zfp1 tZFP1. Additionally, a reduced inhibition of growth suggested zfp1 was less sensitive to conditions promoting cell wall and osmotic stresses than ZFP1 and zfp1 tZFP1. Furthermore pathogenicity tests suggested a critical role for growth of zfp1 in infected leaves and rhizomes of P. kingianum. Thus ZFP1 is important for mycelial growth, conidiation, osmoregulation, and pathogenicity in P. kingianum.

Two zinc finger proteins, VdZFP1 and VdZFP2, interact with VdCmr1 to promote melanized microsclerotia development and stress tolerance in Verticillium dahliae

BACKGROUND

Melanin plays important roles in morphological development, survival, host-pathogen interactions and in the virulence of phytopathogenic fungi. In Verticillum dahliae, increases in melanin are recognized as markers of maturation of microsclerotia which ensures the long-term survival and stress tolerance, while decreases in melanin are correlated with increased hyphal growth in the host. The conserved upstream components of the VdCmr1-regulated pathway controlling melanin production in V. dahliae have been extensively identified, but the direct activators of this pathway are still unclear.

RESULTS

We identified two genes encoding conserved C2H2-type zinc finger proteins VdZFP1 and VdZFP2 adjacent to VdPKS9, a gene encoding a negative regulator of both melanin biosynthesis and microsclerotia formation in V. dahliae. Both VdZFP1 and VdZFP2 were induced during microsclerotia development and were involved in melanin deposition. Their localization changed from cytoplasmic to nuclear in response to osmotic pressure. VdZFP1 and VdZFP2 act as modulators of microsclerotia melanization in V. dahliae, as confirmed by melanin biosynthesis inhibition and supplementation with the melanin pathway intermediate scytalone in albino strains. The results indicate that VdZFP1 and VdZFP2 participate in melanin biosynthesis by positively regulating VdCmr1. Based on the results obtained with yeast one- and two-hybrid (Y1H and Y2H) and bimolecular fluorescence complementation (BiFC) systems, we determined the melanin biosynthesis relies on the direct interactions among VdZFP1, VdZFP2 and VdCmr1, and these interactions occur on the cell walls of microsclerotia. Additionally, VdZFP1 and/or VdZFP2 mutants displayed increased sensitivity to stress factors rather than alterations in pathogenicity, reflecting the importance of melanin in stress tolerance of V. dahliae.

CONCLUSIONS

Our results revealed that VdZFP1 and VdZFP2 positively regulate VdCmr1 to promote melanin deposition during microsclerotia development, providing novel insight into the regulation of melanin biosynthesis in V. dahliae.

Verticillium longisporum phospholipase VlsPLA2 is a virulence factor that targets host nuclei and modulates plant immunity

Phospholipase A2 (PLA2 ) is a lipolytic enzyme that hydrolyses phospholipids in the cell membrane. In the present study, we investigated the role of secreted PLA2 (VlsPLA2 ) in Verticillium longisporum, a fungal phytopathogen that mostly infects plants belonging to the Brassicaceae family, causing severe annual yield loss worldwide. Expression of the VlsPLA2 gene, which encodes active PLA2 , is highly induced during the interaction of the fungus with the host plant Brassica napus. Heterologous expression of VlsPLA2 in Nicotiana benthamiana resulted in increased synthesis of certain phospholipids compared to plants in which enzymatically inactive PLA2 was expressed (VlsPLA2 ΔCD ). Moreover, VlsPLA2 suppresses the hypersensitive response triggered by the Cf4/Avr4 complex, thereby suppressing the chitin-induced reactive oxygen species burst. VlsPLA2 -overexpressing V. longisporum strains showed increased virulence in Arabidopsis plants, and transcriptomic analysis of this fungal strain revealed that the induction of the gene contributed to increased virulence. VlsPLA2 was initially localized to the host nucleus and then translocated to the chloroplasts at later time points. In addition, VlsPLA2 bound to the vesicle-associated membrane protein A (VAMPA) and was transported to the nuclear membrane. In the nucleus, VlsPLA2 caused major alterations in the expression levels of genes encoding transcription factors and subtilisin-like proteases, which play a role in plant immunity. In conclusion, our study showed that VlsPLA2 acts as a virulence factor, possibly by hydrolysing host nuclear envelope phospholipids, which, through a signal transduction cascade, may suppress basal plant immune responses.

VdTps2 Modulates Plant Colonization and Symptom Development in Verticillium dahliae

The trehalose biosynthesis pathway is a potential target for antifungal drugs development. Trehalose phosphate synthase (TPS) and phosphatase are widely conserved components of trehalose biosynthesis in fungi. However, the role of trehalose biosynthesis in the vascular plant-pathogenic fungus Verticillium dahliae remains unclear. Here, we investigated the functions of the TPS complex, including VdTps1, VdTps2, and VdTps3 in V. dahliae. Unlike VdTps2, deletion of VdTps1 or VdTps3 did not alter any phenotypes compared with the wild-type strain. In contrast, the ΔVdTps2 strain showed severely depressed radial growth due to the abnormal swelling of the hyphal tips. Further, deletion of VdTps2 increased microsclerotia formation, melanin biosynthesis, and resistance to cell-wall perturbation and high-temperature stress. Virulence assays and quantification of fungal biomass revealed that deletion of VdTps2 delayed disease symptom development, as evident by the reduced virulence and decreased biomass of the ΔVdTps2 strain in plant stem tissue following inoculation. Additionally, increases in penetration peg formation observed in the ΔVdTps2 strain in the presence of H2O2 suggested that VdTps2 suppresses initial colonization. Our results also revealed the role of VdTps2 as a regulator of autophagy. Together, these results indicate that VdTps2 contributes to plant colonization and disease development. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

The Frq-Frh Complex Light-Dependently Delays Sfl1-Induced Microsclerotia Formation in Verticillium dahliae

The vascular plant pathogenic fungus Verticillium dahliae has to adapt to environmental changes outside and inside its host. V. dahliae harbors homologs of Neurospora crassa clock genes. The molecular functions and interactions of Frequency (Frq) and Frq-interacting RNA helicase (Frh) in controlling conidia or microsclerotia development were investigated in V. dahliae JR2. Fungal mutant strains carrying clock gene deletions, an FRH point mutation, or GFP gene fusions were analyzed on transcript, protein, and phenotypic levels as well as in pathogenicity assays on tomato plants. Our results support that the Frq-Frh complex is formed and that it promotes conidiation, but also that it suppresses and therefore delays V. dahliae microsclerotia formation in response to light. We investigated a possible link between the negative element Frq and positive regulator Suppressor of flocculation 1 (Sfl1) in microsclerotia formation to elucidate the regulatory molecular mechanism. Both Frq and Sfl1 are mainly present during the onset of microsclerotia formation with decreasing protein levels during further development. Induction of microsclerotia formation requires Sfl1 and can be delayed at early time points in the light through the Frq-Frh complex. Gaining further molecular knowledge on V. dahliae development will improve control of fungal growth and Verticillium wilt disease.

The AwHog1 Transcription Factor Influences the Osmotic Stress Response, Mycelium Growth, OTA Production, and Pathogenicity in Aspergillus westerdijkiae fc-1

Aspergillus westerdijkiae, known as the major ochratoxin A (OTA) producer, usually occurs on agricultural crops, fruits, and dry-cured meats. Microorganisms produce OTA to adapt to the high osmotic pressure environment that is generated during food processing and storage. To investigate the relationship between OTA biosynthesis and the high osmolarity glycerol (HOG) pathway, the transcription factor AwHog1 gene in A. westerdijkiae was functionally characterised by means of a loss-of-function mutant. Our findings demonstrated that the growth and OTA production of a mutant lacking AwHog1 decreased significantly and was more sensitive to high osmotic media. The ΔAwHog1 mutant displayed a lower growth rate and a 73.16% reduction in OTA production in the wheat medium compared to the wild type. After three days of culture, the growth rate of the ΔAwHog1 mutant in medium with 60 g/L NaCl and 150 g/L glucose was slowed down 19.57% and 13.21%, respectively. Additionally, the expression of OTA biosynthesis genes was significantly reduced by the deletion of the AwHog1 gene. The infection ability of the ΔAwHog1 mutant was decreased, and the scab diameter of the pear was 6% smaller than that of the wild type. These data revealed that transcription factor AwHog1 plays a key role in the osmotic response, growth, OTA production, and pathogenicity in A. westerdijkiae.

The C2H2-type zinc-finger regulator AoKap5 is required for the growth and kojic acid synthesis in Aspergillus oryzae

Aspergillus oryzae is an important filamentous fungus widely used for the industrial production of fermented foods and secondary metabolites. The clarifying of the mechanism of the growth and secondary metabolites in A. oryzae is important for its industrial production and utilization. Here, the C2H2-type zinc-finger protein AoKap5 was characterized to be involved in the growth and kojic acid production in A. oryzae. The Aokap5-disrupted mutants were constructed by the CRISPR/Cas9 system, which displayed increased colony growth but decreased conidial formation. Deletion of Aokap5 enhanced the tolerance to cell-wall and oxidative but not osmotic stress. The transcriptional activation assay revealed that AoKap5 itself didn't have transcriptional activation activity. Disruption of Aokap5 resulted in the reduced production of kojic acid, coupled with the reduced expression of the kojic acid synthesis genes kojA and kojT. Meanwhile, overexpression of kojT could rescue the decreased production of kojic acid in Aokap5-deletion strain, indicating that Aokap5 serves upstream of kojT. Furthermore, the yeast one-hybrid assay demonstrated that AoKap5 could directly bind to the kojT promoter. These findings suggest that AoKap5 regulates kojic acid production through binding to the kojT promoter. This study provides an insight into the role of zinc finger protein in the growth and kojic acid biosynthesis of A. oryzae.

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.

The transcription factor Ste12-like increases the mycelial abiotic stress tolerance and regulates the fruiting body development of Flammulina filiformis

Introduction

Flammulina filiformis is one of the most commercially important edible fungi worldwide, with its nutritional value and medicinal properties. It becomes a good model species to study the tolerance of abiotic stress during mycelia growth in edible mushroom cultivation. Transcription factor Ste12 has been reported to be involved in the regulation of stress tolerance and sexual reproduction in fungi.

Methods

In this study, identification and phylogenetic analysis of ste12-like was performed by bioinformatics methods. Four ste12-like overexpression transformants of F. filiformis were constructed by Agrobacterium tumefaciens-mediated transformation.

Results and Discussion

Phylogenetic analysis showed that Ste12-like contained conserved amino acid sequences. All the overexpression transformants were more tolerant to salt stress, cold stress and oxidative stress than wild-type strains. In the fruiting experiment, the number of fruiting bodies of overexpression transformants increased compared with wild-type strains, but the growth rate of stipes slowed down. It suggested that gene ste12-like was involved in the regulation of abiotic stress tolerance and fruiting body development in F. filiformis.

Transcription Factor VdCf2 Regulates Growth, Pathogenicity, and the Expression of a Putative Secondary Metabolism Gene Cluster in Verticillium dahliae

Transcription factors (TFs) bind to the promoters of target genes to regulate gene expression in response to different stimuli. The functions and regulatory mechanisms of transcription factors (TFs) in Verticillium dahliae are, however, still largely unclear. This study showed that a C2H2-type zinc finger TF, VdCf2 (V. dahliae chorion transcription factor 2), plays key roles in V. dahliae growth, melanin production, and virulence. Transcriptome sequencing analysis showed that VdCf2 was involved in the regulation of expression of genes encoding secreted proteins, pathogen-host interaction (PHI) homologs, TFs, and G protein-coupled receptors (GPCRs). Furthermore, VdCf2 positively regulated the expression of VdPevD1 (VDAG_02735), a previously reported virulence factor. VdCf2 thus regulates the expression of several pathogenicity-related genes that also contribute to virulence in V. dahliae. VdCf2 also inhibited the transcription of the Vd276-280 gene cluster and interacted with two members encoding proteins (VDAG_07276 and VDAG_07278) in the gene cluster. IMPORTANCE Verticillium dahliae is an important soilborne phytopathogen which can ruinously attack numerous host plants and cause significant economic losses. Transcription factors (TFs) were reported to be involved in various biological processes, such as hyphal growth and virulence of pathogenic fungi. However, the functions and regulatory mechanisms of TFs in V. dahliae remain largely unclear. In this study, we identified a new transcription factor, VdCf2 (V. dahliae chorion transcription factor 2), based on previous transcriptome data, which participates in growth, melanin production, and virulence of V. dahliae. We provide evidence that VdCf2 regulates the expression of the pathogenicity-related gene VdPevD1 (VDAG_02735) and Vd276-280 gene cluster. VdCf2 also interacts with VDAG_07276 and VDAG_07278 in this gene cluster based on a yeast two-hybrid and bimolecular fluorescence complementation assay. These results revealed the regulatory mechanisms of a pivotal pathogenicity-related transcription factor, VdCf2 in V. dahliae.

A polyketide synthase from Verticillium dahliae modulates melanin biosynthesis and hyphal growth to promote virulence

Background

During the disease cycle, plant pathogenic fungi exhibit a morphological transition between hyphal growth (the phase of active infection) and the production of long-term survival structures that remain dormant during “overwintering.” Verticillium dahliae is a major plant pathogen that produces heavily melanized microsclerotia (MS) that survive in the soil for 14 or more years. These MS are multicellular structures produced during the necrotrophic phase of the disease cycle. Polyketide synthases (PKSs) are responsible for catalyzing production of many secondary metabolites including melanin. While MS contribute to long-term survival, hyphal growth is key for infection and virulence, but the signaling mechanisms by which the pathogen maintains hyphal growth are unclear.

Results

We analyzed the VdPKSs that contain at least one conserved domain potentially involved in secondary metabolism (SM), and screened the effect of VdPKS deletions in the virulent strain AT13. Among the five VdPKSs whose deletion affected virulence on cotton, we found that VdPKS9 acted epistatically to the VdPKS1-associated melanin pathway to promote hyphal growth. The decreased hyphal growth in VdPKS9 mutants was accompanied by the up-regulation of melanin biosynthesis and MS formation. Overexpression of VdPKS9 transformed melanized hyphal-type (MH-type) into the albinistic hyaline hyphal-type (AH-type), and VdPKS9 was upregulated in the AH-type population, which also exhibited higher virulence than the MH-type.

Conclusions

We show that VdPKS9 is a powerful negative regulator of both melanin biosynthesis and MS formation in V. dahliae. These findings provide insight into the mechanism of how plant pathogens promote their virulence by the maintenance of vegetative hyphal growth during infection and colonization of plant hosts, and may provide novel targets for the control of melanin-producing filamentous fungi.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01330-2.

Identification of VdASP F2-interacting protein as a regulator of microsclerotial formation in Verticillium dahliae

Verticillium dahliae, a notorious phytopathogenic fungus, causes vascular wilt diseases in many plant species. The melanized microsclerotia enable V. dahliae to survive for years in soil and are crucial for its disease cycle. In a previous study, we characterized the secretory protein VdASP F2 from V. dahliae and found that VdASP F2 deletion significantly affected the formation of microsclerotia under adverse environmental conditions. In this study, we clarified that VdASP F2 is localized to the cell wall. However, the underlying mechanism of VdASP F2 in microsclerotial formation remains unclear. Transmembrane ion channel protein VdTRP was identified as a candidate protein that interacts with VdASP F2 using pull‐down assays followed by liquid chromatography‐tandem mass spectrometry (LC‐MS/MS) analysis, and interaction of VdASP F2 and VdTRP was confirmed by bimolecular fluorescence complementary and coimmunoprecipitation assays. The deletion mutant was analysed to reveal that VdTRP is required for microsclerotial production, but it is not essential for stress resistance, carbon utilization and pathogenicity of V. dahliae. RNA‐seq revealed some differentially expressed genes related to melanin synthesis and microsclerotial formation were significantly downregulated in the VdTRP deletion mutants. Taken together, these results indicate that VdASP F2 regulates the formation of melanized microsclerotia by interacting with VdTRP.

The bZip Transcription Factor VdMRTF1 is a Negative Regulator of Melanin Biosynthesis and Virulence in Verticillium dahliae

The ascomycete fungus Verticillium dahliae infects over 400 plant species and causes serious losses of economically important crops, such as cotton and tomato, and also of woody plants, such as smoke tree, maple, and olive. Melanized long-term survival structures known as microsclerotia play crucial roles in the disease cycle of V. dahliae, enabling this soilborne fungus to survive for years in the soil in the absence of a host. Previously, we identified VdMRTF1 (microsclerotia-related transcription factor) encoding a bZip transcription factor which is downregulated during microsclerotial development in V. dahliae. In the present study, we showed that VdMRTF1 negatively controls melanin production and virulence by genetic, biological, and transcriptomic analyses. The mutant strain lacking VdMRTF1 (ΔVdMRTF1) exhibited increased melanin biosynthesis and the defect also promoted microsclerotial development and sensitivity to Ca²⁺. In comparison with the wild-type strain, the ΔVdMRTF1 strain showed a significant enhancement in virulence and displayed an increased capacity to eliminate reactive oxygen species in planta. Furthermore, analyses of transcriptomic profiles between the ΔVdMRTF1 and wild-type strains indicated that VdMRTF1 regulates the differential expression of genes associated with melanin biosynthesis, tyrosine metabolism, hydrogen peroxide catabolic processes, and oxidoreductase activity in V. dahliae. Taken together, these data show that VdMRTF1 is a negative transcriptional regulator of melanin biosynthesis, microsclerotia formation, and virulence in V. dahliae.

IMPORTANCE Verticillium wilt is difficult to manage because the pathogen colonizes the plant xylem tissue and produces melanized microsclerotia which survive for more than 10 years in soil without a host. The molecular mechanisms underlying microsclerotia formation are of great importance to control the disease. Here, we provide evidence that a bZip transcription factor, VdMRTF1, plays important roles in melanin biosynthesis, microsclerotial development, resistance to elevated Ca²⁺ levels, and fungal virulence of V. dahliae. The findings extend and deepen our understanding of the complexities of melanin biosynthesis, microsclerotia formation, and virulence that are regulated by bZip transcription factors in V. dahliae.

Genome-wide identification and expression analyses of C2H2 zinc finger transcription factors in Pleurotus ostreatus

The C2H2-type zinc finger proteins (C2H2-ZFPs) regulate various developmental processes and abiotic stress responses in eukaryotes. Yet, a comprehensive analysis of these transcription factors which could be used to find candidate genes related to the control the development and abiotic stress tolerance has not been performed in Pleurotus ostreatus. To fill this knowledge gap, 18 C2H2-ZFs were identified in the P. ostreatus genome. Phylogenetic analysis indicated that these proteins have dissimilar amino acid sequences. In addition, these proteins had variable protein characteristics, gene intron-exon structures, and motif compositions. The expression patterns of PoC2H2-ZFs in mycelia, primordia, and young and mature fruiting bodies were investigated using qRT-PCR. The expression of some PoC2H2-ZFs is regulated by auxin and cytokinin. Moreover, members of PoC2H2-ZFs expression levels are changed dramatically under heat and cold stress, suggesting that these genes may participate in abiotic stress responses. These findings could be used to study the role of P. ostreatus-derived C2H2-ZFs in development and stress tolerance.

The signaling pathways involved in metabolic regulation and stress responses of the yeast-like fungi Aureobasidium spp

Aureobasidium spp. can use a wide range of substrates and are widely distributed in different environments, suggesting that they can sense and response to various extracellular signals and be adapted to different environments. It is true that their pullulan, lipid and liamocin biosynthesis and cell growth are regulated by the cAMP-PKA signaling pathway; Polymalate (PMA) and pullulan biosynthesis is controlled by the Ca²⁺ and TORC1 signaling pathways; the HOG1 signaling pathway determines high osmotic tolerance and high pullulan and liamocin biosynthesis; the Snf1/Mig1 pathway controls glucose repression on pullulan and liamocin biosynthesis; DHN-melanin biosynthesis and stress resistance are regulated by the CWI signaling pathway and TORC1 signaling pathway. In addition, the HSF1 pathway may control cell growth of some novel strains of A. melanogenum at 37 °C. However, the detailed molecular mechanisms of high temperature growth and thermotolerance of some novel strains of A. melanogenum and glucose derepression in A. melanogenum TN3-1 are still unclear.

Transcription Factor MaMsn2 Regulates Conidiation Pattern Shift under the Control of MaH1 through Homeobox Domain in Metarhizium acridum

The growth pattern of filamentous fungi can switch between hyphal radial polar growth and non-polar yeast-like cell growth depending on the environmental conditions. Asexual conidiation after radial polar growth is called normal conidiation (NC), while yeast-like cell growth is called microcycle conidiation (MC). Previous research found that the disruption of MaH1 in Metarhizium acridum led to a conidiation shift from NC to MC. However, the regulation mechanism is not clear. Here, we found MaMsn2, an Msn2 homologous gene in M. acridum, was greatly downregulated when MaH1 was disrupted (ΔMaH1). Loss of MaMsn2 also caused a conidiation shift from NC to MC on a nutrient-rich medium. Yeast one-hybrid (Y1H) and electrophoretic mobility shift assay (EMSA) showed that MaH1 could bind to the promoter region of the MaMsn2 gene. Disrupting the interaction between MaH1 and the promoter region of MaMsn2 significantly downregulated the transcription level of MaMsn2, and the overexpression of MaMsn2 in ΔMaH1 could restore NC from MC of ΔMaH1. Our findings demonstrated that MaMsn2 played a role in maintaining the NC pattern directly under the control of MaH1, which revealed the molecular mechanisms that regulated the conidiation pattern shift in filamentous fungi for the first time.

HD-ZIP Gene Family: Potential Roles in Improving Plant Growth and Regulating Stress-Responsive Mechanisms in Plants

Exploring the molecular foundation of the gene-regulatory systems underlying agronomic parameters or/and plant responses to both abiotic and biotic stresses is crucial for crop improvement. Thus, transcription factors, which alone or in combination directly regulated the targeted gene expression levels, are appropriate players for enlightening agronomic parameters through genetic engineering. In this regard, homeodomain leucine zipper (HD-ZIP) genes family concerned with enlightening plant growth and tolerance to environmental stresses are considered key players for crop improvement. This gene family containing HD and LZ domain belongs to the homeobox superfamily. It is further classified into four subfamilies, namely HD-ZIP I, HD-ZIP II, HD-ZIP III, and HD-ZIP IV. The first HD domain-containing gene was discovered in maize cells almost three decades ago. Since then, with advanced technologies, these genes were functionally characterized for their distinct roles in overall plant growth and development under adverse environmental conditions. This review summarized the different functions of HD-ZIP genes in plant growth and physiological-related activities from germination to fruit development. Additionally, the HD-ZIP genes also respond to various abiotic and biotic environmental stimuli by regulating defense response of plants. This review, therefore, highlighted the various significant aspects of this important gene family based on the recent findings. The practical application of HD-ZIP biomolecules in developing bioengineered plants will not only mitigate the negative effects of environmental stresses but also increase the overall production of crop plants.

Transcription factor control of virulence in phytopathogenic fungi

Plant-pathogenic fungi are a significant threat to economic and food security worldwide. Novel protection strategies are required and therefore it is critical we understand the mechanisms by which these pathogens cause disease. Virulence factors and pathogenicity genes have been identified, but in many cases their roles remain elusive. It is becoming increasingly clear that gene regulation is vital to enable plant infection and transcription factors play an essential role. Efforts to determine their regulatory functions in plant-pathogenic fungi have expanded since the annotation of fungal genomes revealed the ubiquity of transcription factors from a broad range of families. This review establishes the significance of transcription factors as regulatory elements in plant-pathogenic fungi and provides a systematic overview of those that have been functionally characterized. Detailed analysis is provided on regulators from well-characterized families controlling various aspects of fungal metabolism, development, stress tolerance, and the production of virulence factors such as effectors and secondary metabolites. This covers conserved transcription factors with either specialized or nonspecialized roles, as well as recently identified regulators targeting key virulence pathways. Fundamental knowledge of transcription factor regulation in plant-pathogenic fungi provides avenues to identify novel virulence factors and improve our understanding of the regulatory networks linked to pathogen evolution, while transcription factors can themselves be specifically targeted for disease control. Areas requiring further insight regarding the molecular mechanisms and/or specific classes of transcription factors are identified, and direction for future investigation is presented.

Elaborated regulation of griseofulvin biosynthesis in Penicillium griseofulvum and its role on conidiation and virulence

Penicilium griseofulvum, the causal agent of apple blue mold, is able to produce in vitro and on apple a broad spectrum of secondary metabolites (SM), including patulin, roquefortine C and griseofulvin. Among them, griseofulvin is known for its antifungal and antiproliferative activity, and has received interest in many sectors, from medicine to agriculture. The biosynthesis of SM is finely regulated by filamentous fungi and can involve global regulators and pathway specific regulators, which are usually encoded by genes present in the same gene cluster as the backbone gene and tailoring enzymes. In the griseofulvin gene cluster, two putative transcription factors were previously identified, encoded by genes gsfR1 and gsfR2, and their role has been investigated in the present work. Analysis of P. griseofulvum knockout mutants lacking either gene suggest that gsfR2 forms part of a different pathway and gsfR1 exhibits many spectra of action, acting as regulator of griseofulvin and patulin biosynthesis and influencing conidia production and virulence on apple. The analysis of gsfR1 promoter revealed that the regulation of griseofulvin biosynthesis is also controlled by global regulators in response to many environmental stimuli, such as carbon and nitrogen. The influence of carbon and nitrogen on griseofulvin production was further investigated and verified, revealing a complex network of response and confirming the central role of gsfR1 in many processes in P. griseofulvum.

Pullulan biosynthesis in yeast-like fungal cells is regulated by the transcriptional activator Msn2 and cAMP-PKA signaling pathway

Pullulan is an important polysaccharide. Although its synthetic pathway in Aureobasidium melanogenum has been elucidated, the mechanism underlying its biosynthesis as regulated by signaling pathway and transcriptional regulator is still unknown. In this study, it was found that the expression of the UGP1 gene encoding UDPG-pyrophosphorylase (Ugp1) and other genes which were involved in pullulan biosynthesis was controlled by the transcriptional activator Msn2 in the nuclei of yeast-like fungal cells. The Ugp1 was a rate-limiting enzyme for pullulan biosynthesis. In addition, the activity and subcellular localization of the Msn2 were regulated only by the cAMP-PKA signaling pathway. When the cAMP-PKA activity was low, the Msn2 was localized in the nuclei, the UGP1 gene was highly expressed, and pullulan was actively synthesized. By contrast, when the cAMP-PKA activity was high, the Msn2 was localized in the cytoplasm and the UGP1 gene expression was disabled so that pullulan was stopped, but lipid biosynthesis was actively enhanced. This study was the first to report that pullulan and lipid biosynthesis in yeast-like fungal cells were regulated by the Msn2 and cAMP-PKA signaling pathway. Elucidating the regulation mechanisms was important to understand their functions and enhance pullulan and lipid biosynthesis.

Ubiquitin E3 Ligase AaBre1 Responsible for H2B Monoubiquitination Is Involved in Hyphal Growth, Conidiation and Pathogenicity in Alternaria alternata

Ubiquitination is one of several post-transcriptional modifications of histone 2B (H2B) which affect the chromatin structure and, hence, influence gene transcription. This study focuses on Alternaria alternata, a fungal pathogen responsible for leaf spot in many plant species. The experiments show that the product of AaBRE1, a gene which encodes H2B monoubiquitination E3 ligase, regulates hyphal growth, conidial formation and pathogenicity. Knockout of AaBRE1 by the homologous recombination strategy leads to the loss of H2B monoubiquitination (H2Bub1), as well as a remarkable decrease in the enrichment of trimethylated lysine 4 on histone 3 (H3K4me3). RNA sequencing assays elucidated that the transcription of genes encoding certain C2H2 zinc-finger family transcription factors, cell wall-degrading enzymes and chitin-binding proteins was suppressed in the AaBRE1 knockout cells. GO enrichment analysis showed that these proteins encoded by the set of genes differentially transcribed between the deletion mutant and wild type were enriched in the functional categories “macramolecular complex”, “cellular metabolic process”, etc. A major conclusion was that the AaBRE1 product, through its effect on histone 2B monoubiquitination and histone 3 lysine 4 trimethylation, makes an important contribution to the fungus’s hyphal growth, conidial formation and pathogenicity.

Analysis of cell wall synthesis and metabolism during early germination of Blumeria graminis f. sp. hordei conidial cells induced in vitro

As an obligate biotroph, Blumeria graminis f. sp. hordei (Bgh) cannot be grown in an axenic culture, and instead must be cultivated on its host species, Hordeum vulgare (barley). In this study an in vitro system utilizing n-hexacosanal, a constituent of the barley cuticle and known inducer of Bgh germination, was used to cultivate Bgh and differentiate conidia up to the appressorial germ tube stage for analysis. Transcriptomic and proteomic profiling of the appressorial germ tube stage revealed that there was a significant shift towards energy and protein production during the pre-penetrative phase of development, with an up-regulation of enzymes associated with cellular respiration and protein synthesis, modification and transport. Glycosidic linkage analysis of the cell wall polysaccharides demonstrated that during appressorial development an increase in 1,3- and 1,4-linked glucosyl residues and xylosyl residues was detected along with a significant decrease in galactosyl residues. The use of this in vitro cultivation method demonstrates that it is possible to analyse the pre-penetrative processes of Bgh development in the absence of a plant host.

Two Verticillium dahliae MAPKKKs, VdSsk2 and VdSte11, Have Distinct Roles in Pathogenicity, Microsclerotial Formation, and Stress Adaptation

These data provide insights into the distinctive functions of VdSsk2 and VdSte11 in pathogenicity, stress adaptation, and microsclerotial formation in V. dahliae.

Verticillium dahliae causes destructive vascular wilt diseases on more than 200 plant species, including economically important crops and ornamental trees worldwide. The melanized microsclerotia enable the fungus to survive for years in soil and are crucial for its disease cycle. Previously, we found that the VdPbs2-VdHog1 (V. dahliae Pbs2-V. dahliae Hog1) module plays key roles in microsclerotial formation, stress responses, and virulence in V. dahliae. In this study, two mitogen-activated protein kinase kinase kinases (MAPKKKs) homologous to Ssk2p and Ste11p, which activate the Pbs2p-Hog1p module by phosphorylation in budding yeast, were identified in the genome of V. dahliae. Both ΔVdSsk2 (V. dahliaeSsk2) and ΔVdSte11 strains showed severe defects in microsclerotial formation and melanin biosynthesis, but the relative importance of these two genes in microsclerotial development was different. Deletion of VdSsk2, but not VdSte11, affected responses to osmotic stress, fungicidal response, and cell wall stressors. The ΔVdSsk2 strain exhibited a significant reduction in virulence, while the ΔVdSte11 strain was nonpathogenic due to failure to penetrate and form hyphopodia. Phosphorylation assays demonstrated that VdSsk2, but not VdSte11, can phosphorylate VdHog1 in V. dahliae. Moreover, VdCrz1, encoding a calcineurin-responsive zinc finger transcription factor and a key regulator of calcium signaling in fungi, was misregulated in the ΔVdSsk2, ΔVdPbs2, and ΔVdHog1 mutants.

IMPORTANCE These data provide insights into the distinctive functions of VdSsk2 and VdSte11 in pathogenicity, stress adaptation, and microsclerotial formation in V. dahliae.

The α-1,6-mannosyltransferase VdOCH1 plays a major role in microsclerotium formation and virulence in the soil-borne pathogen Verticillium dahliae

Sunflower yellow wilt is a widespread and destructive disease caused by the soil-borne pathogen Verticillium dahliae (V. dahliae). To better understand the pathogenesis mechanism of V. dahliae in sunflower, T-DNA insertion library was generated via Agrobacterium tumefaciens mediated transformation system (ATMT). Eight hundred positive transformants were obtained. Transformants varied in colony morphology, growth rate, conidia production and pathogenicity in sunflower compared to the wild type strain. A mutant, named VdGn3-L2, was chosen for further analysis based on its deprivation on microsclerotia formation. The flanking sequence of T-DNA insertion site of VdGn3-L2 was identified via hiTAIL-PCR, and the interrupted gene encoded an initiation-specific α-1, 6-mannosyltransferase, named as VdOCH1. The deletion mutant ΔVdOCH1 was impaired in certain characteristics such as fungal growth, conidia production, and microsclerotia formation. Also, ΔVdOCH1 mutants were more sensitive to the cell wall perturbing reagents, such as SDS and Congo red, lost their penetration ability through cellophane membrane, and exhibited dramatically decreased pathogenicity to sunflower. The impaired phenotypes could be restored to the wild type level by complementation of the deletion mutant with full-length VdOCH1 gene. In conclusion, VdOCH1, encoded α-1,6-mannosyltransferase, manipulating the biological characteristics, microsclerotia formation and pathogenic ability of V. dahliae in sunflower.

Genomewide Transcriptome Profiles Reveal How Bacillus subtilis Lipopeptides Inhibit Microsclerotia Formation in Verticillium dahliae

Verticillium dahliae is a soilborne fungus and the primary causal agent of vascular wilt diseases worldwide. The fungus produces melanized microsclerotia that are crucially important for the survival and spread of V. dahliae. There are no fungicides available that are both effective and environmentally friendly to suppress the fungus. Previously, Bacillus subtilis C232 was isolated from soil and was demonstrated to suppress microsclerotia formation in V. dahliae. In this study, liquid chromatography coupled with mass spectrometry revealed that the antifungal substance is actually a mixture of lipopeptides. Exposure of V. dahliae to these lipopeptides resulted in hyphal swelling, cell lysis, and downregulation of melanin-related genes. RNA sequencing analyses of the lipopeptide-suppressed transcriptome during microsclerotial development revealed that 5,974 genes (2,131 upregulated and 3,843 downregulated) were differentially expressed versus nonsuppressive conditions. Furthermore, gene ontology enrichment analyses revealed that genes involved in response to stress, cellular metabolic processes, and translation were significantly enriched. Additionally, the lipopeptides inhibited expression of genes associated with secondary metabolism, protein catabolism, and the high-osmolarity glycerol response signaling pathway. Together, these findings provide evidence for the mechanism by which B. subtilis lipopeptides suppress microsclerotia formation. The transcriptomic insight garnered here may facilitate the development of biological agents to combat Verticillium wilt.

Involvement of a Response Regulator VdSsk1 in Stress Response, Melanin Biosynthesis and Full Virulence in Verticillium dahliae

Verticillium dahliae causes vascular wilt disease on over 200 plant species worldwide. This fungus forms melanized microsclerotia which help it to survive under adverse conditions and these structures are vital to the disease spread. Here, we identified and characterized a V. dahliae homolog to of the Saccharomyces cerevisiae Ssk1, a response regulator of the two-component system. Herein, we demonstrated that the VdSsk1 deletion strains were more sensitive to various stresses, including oxidative stress conferred by H₂O₂ and sodium nitroprusside dihydrate, while the mutants confered higher resistance to fungicides such as fludioxonil and iprodione. Furthermore, disruption of VdSsk1 resulted in significant downregulation of melanin biosynthesis-related genes but did not affect microsclerotial development. Phosphorylation of VdHog1 was not detected in the VdSsk1 deletion strains under the treatment of sorbitol, indicating that phosphorylation of VdHog1 is dependent on VdSsk1. Finally, we demonstrated that VdSsk1 is required for full virulence. Taken together, this study suggests that VdSsk1 modulates stress response, melanin biosynthesis and virulence of V. dahliae.

Comparative transcriptome analysis reveals regulatory networks and key genes of microsclerotia formation in the cotton vascular wilt pathogen

Verticillium dahliae is a soil-borne, hemibiotrophic phytopathogenic fungus that causes Verticillium wilt in a broad range of economic crops. The microsclerotia (MS), which act as the main host inoculum, can survive long-term in soil resulting in uncontrollable disease. In order to clarify the mechanism of MS formation, we sequenced the whole genome-wide expression profile of V. dahliae strain V991. Compared with M1 (no MS formation), during the process of MS formation and maturation, 1354, 1571, and 1521 unique tags were significantly regulated in M2, M3, and M4 library, respectively. During MS formation, melanin synthesis-related genes were preferentially upregulated. The process is more likely to regulated by transcription factors (TFs) including C₂H₂, Zn₂Cys₆, bZIP, and fungal-specific TF domain-containing proteins; additionally, G-protein coupled receptors, Ca²⁺, small GTPases, and cAMP were involved in signalling transduction. Protein kinase-encoding (VDAG_06474) and synthase-encoding (VDAG_05314) genes were demonstrated to negatively and positively influence MS production, respectively. The gene expression dynamics revealed during MS formation provide comprehensive theoretical knowledge to further understanding of the metabolism and regulation of MS development in V. dahliae, potentially providing targets to control Verticillium wilt through interfering MS formation.

A transcription factor, MrMsn2, in the dimorphic fungus Metarhizium rileyi is essential for dimorphism transition, aggravated pigmentation, conidiation and microsclerotia formation

Microsclerotia (MS) are pseudoparenchymatous aggregations of hyphae of fungi that can be induced in liquid culture for biocontrol applications. Previously, we determined that the high-osmolarity glycerol (HOG) signalling pathway was involved in regulating MS development in the dimorphic insect pathogen Metarhizium rileyi. To further investigate the mechanisms by which the signalling pathway is regulated, we characterized the transcriptional factor MrMsn2, a homologue of the yeast C2 H2 transcriptional factor Msn2, which is predicted to function downstream of the HOG pathway in M. rileyi. Compared with wild-type and complemented strains, disruption of MrMsn2 increased the yeast-to-hypha transition rate, enhanced conidiation capacity and aggravated pigmentation in M. rileyi. The ▵MrMsn2 mutants were sensitive to stress, produced morphologically abnormal clones and had significantly reduced MS formation and decreased virulence levels. Digital expression profiling revealed that genes involved in antioxidation, pigment biosynthesis and ion transport and storage were regulated by MrMsn2 during conidia and MS development. Taken together, our findings confirm that MrMsn2 controlled the yeast-to-hypha transition, conidia and MS formation, and virulence.

Fungal microsclerotia development: essential prerequisites, influencing factors, and molecular mechanism

Microsclerotia (MS) consist of an outer layer of pigment parenchyma cells and an inner layer of colorless medulla cells. In nature, MS are formed as overwintering and spreading structures in phytopathogenic fungi. For biological applications, MS can be induced in artificial liquid medium. To understand the complicated structure of MS and molecular mechanism of MS development in entomopathogenic and phytopathogenic fungi, data from different studies can be integrated. In this review, the essential prerequisites, environmental cues, and internal stimulating factors for MS development are explored. Emerging knowledges about the association between transcriptional regulatory circuits and signaling pathways involved in MS development in entomopathogenic and phytopathogenic fungi is also highlighted.