VdThit, a Thiamine Transport Protein, Is Required for Pathogenicity of the Vascular Pathogen Verticillium dahliae

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.

Protein Kinase C Is Involved in Vegetative Development, Stress Response and Pathogenicity in Verticillium dahliae

Potato Verticillium wilt, caused by Verticillium dahliae, is a serious soil-borne vascular disease, which restricts the sustainable development of the potato industry, and the pathogenic mechanism of the fungus is complex. Therefore, it is of great significance to explore the important pathogenic factors of V. dahliae to expand the understanding of its pathology. Protein kinase C (PKC) gene is located in the Ca2+ signaling pathway, which is highly conserved in filamentous fungi and involved in the regulation of a variety of biological processes. In the current study, the PKC gene in V. dahliae (VdPKC) was characterized, and its effects on the fungal pathogenicity and tolerance to fungicide stress were further studied. The results showed that the VdPKC positively regulated the growth and development, conidial germination, and production of V. dahliae, which was necessary for the fungus to achieve pathogenicity. It also affected the formation of melanin and microsclerotia and changed the adaptability of V. dahliae to different environmental stresses. In addition, VdPKC altered the tolerance of V. dahliae to different fungicides, which may be a potential target for polyoxin. Therefore, our results strongly suggest that VdPKC gene is necessary for the vegetative growth, stress response, and pathogenicity of V. dahliae.

Verticillium dahliae Asp1 regulates the transition from vegetative growth to asexual reproduction by modulating microtubule dynamic organization

Verticillium dahliae is a devastating pathogenic fungus that causes severe vascular wilts in more than 400 dicotyledonous plants. The conidiation of V. dahliae in plant vascular tissues is the key strategy for its adaptation to the nutrient-poor environment and is required for its pathogenicity. However, it remains unclear about the regulatory mechanism of conidium production of V. dahliae in vascular tissues. Here, we found that VdAsp1, encoding an inositol polyphosphate kinase, is indispensable for the pathogenicity of V. dahliae. Loss of VdAsp1 function does not affect the invasion of the host, but it impairs the colonization and proliferation in vascular tissues. The ΔVdAsp1 mutant shows defective initiation of conidiophore formation and reduced expression of genes associated with the central developmental pathway. By live-cell imaging, we observed that some of ΔVdAsp1 mutant hyphae are swollen, and microtubule arrangements at the apical region of these hyphae are disorganized. These results indicate that VdAsp1 regulates the transition from vegetative growth to asexual reproduction by modulating microtubule dynamic organization, which is essential for V. dahliae to colonize and proliferate in vascular tissues. These findings provided a potential new direction in the control of vascular wilt pathogen by targeting conidium production in vascular tissues.

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.

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 CfMcm1 Regulates Pathogenicity, Conidium Germination, and Sexual Development in Colletotrichum fructicola

Glomerella leaf spot (GLS), caused by Colletotrichum fructicola, is a severe disease worldwide on apple, causing defoliation, leaf and fruit spot, and substantial yield loss. However, little is known about its molecular mechanisms of pathogenesis. Previous transcriptome analysis revealed that a transcription factor, CfMcm1, was induced during leaf infection. In the present work, expression pattern analysis verified that the CfMcm1 gene was strongly expressed in conidia and early infection. Phenotypic analysis revealed that the gene deletion mutant ΔCfMcm1 lost pathogenicity to apple leaves by inhibiting conidial germination and appressorium formation. In addition to appressorium-mediated pathogenicity, ΔCfMcm1 colonization and hyphal extension in wounded apple fruit was also reduced, and conidial germination mode and conidial color were altered. ΔCfMcm1 displayed impairment of cell wall integrity and response to stress caused by oxidation, osmosis, and an acid environment. Furthermore, the deletion mutant produced fewer and smaller perithecia and no ascospores. In contrast, melanin deposition in mycelia of ΔCfMcm1 was strengthened. Further comparative transcriptome and quantitative PCR analysis revealed that CfMcm1 modulated expression of genes related to conidial development (CfERG5A, CfERG5B, CfHik5, and CfAbaA), appressorium formation (CfCBP1 and CfCHS7), pectin degradation (CfPelA and CfPelB), sexual development (CfMYB, CfFork, CfHMG, and CfMAT1-2-1), and melanin biosynthesis (CfCmr1, CfPKS1, CfT4HR1, CfTHR1, and CfSCD1). Our results demonstrated that CfMcm1 is a pivotal regulator possessing multiple functions in pathogenicity, asexual and sexual reproduction, and melanin biosynthesis.

Using a Relative Quantitative Proteomic Method to Identify Differentially Abundant Proteins in Brucella melitensis Biovar 3 and Brucella melitensis M5-90

Brucellosis, caused by Brucella spp., is one of the most widespread bacterial zoonoses worldwide. Vaccination is still considered the best way to control brucellosis. An investigation into the differential proteome expression patterns of wild and vaccine strains may help researchers and clinicians differentiate between the strains to diagnose and better understand the mechanism(s) underlying differences in virulence. In the present study, a mass spectrometry-based, label-free relative quantitative proteomics approach was used to investigate the proteins expressed by the wild strain, B. melitensis biovar 3 and compare it with those expressed by B. melitensis M5-90. The higher level of virulence for B. melitensis biovar 3 compared to B. melitensis M5-90 was validated in vitro and in vivo. A total of 2133 proteins, encompassing 68% of the theoretical proteome, were identified and quantified by proteomic analysis, resulting in broad coverage of the B. melitensis proteome. A total of 147 proteins were identified as differentially expressed (DE) between these two strains. In addition, 9 proteins and 30 proteins were identified as unique to B. melitensis M5-90 and B. melitensis biovar 3, respectively. Pathway analysis revealed that the majority of the DE proteins were involved in iron uptake, quorum sensing, pyrimidine metabolism, glycine betaine biosynthetic and metabolic processes, thiamine-containing compound metabolism and ABC transporters. The expression of BtpA and VjbR proteins (two well-known virulence factors) in B. melitensis biovar 3 was 8-fold and 2-fold higher than in B. melitensis M5-90. In summary, our results identified many unique proteins that could be selected as candidate markers for differentiating vaccinated animals from animals with wild-type infections. BtpA and VjbR proteins might be responsible for the residual virulence of B. melitensis M5-90, while ABC transporters and thiamine metabolism associated proteins may be newly identified Brucella virulence factors. All of the identified DE proteins provide valuable information for the development of vaccines and the discovery of novel therapeutic targets.

The Involvement of Thiamine Uptake in the Virulence of Edwardsiella piscicida

Edwardsiella piscicida is a pathogenic bacterium, which can infect a number of fish species and cause a disease termed edwardsiellosis, threatening global fish farming with high prevalence and mortality. Thiamine (Vitamin B1), functioning in the form of thiamine pyrophosphate (TPP), is essential for almost all organisms. Bacteria acquire TPP by biosynthesis or by transportation of exogenous thiamine. TPP availability has been associated with bacterial pathogenicity, but the underlying mechanisms remain to be discovered. The role of thiamine in the pathogenicity of E. piscicida is unknown. In this study, we characterized a thiamine transporter (TT) operon in E. piscicida. The deletion of the TT operon resulted in an intracellular TPP lacking situation, which led to attenuated overall pathogenicity, impaired abilities associated with motility and host cell adhesion, as well as decreased expression of certain flagellar and adhesion genes. Moreover, TPP starvation led to intracellular c-di-GMP reduction, and introducing into the TPP-suppressed mutant strain an exogenous diguanylate cyclase for c-di-GMP synthesis restored the virulence loss. Taken together, this work reveals the involvement of thiamine uptake in the virulence regulation of E. piscicida, with c-di-GMP implicated in the process. These finding could be employed to explore potential drug targets against E. piscicida.

Verticillium dahliae VdTHI20, Involved in Pyrimidine Biosynthesis, Is Required for DNA Repair Functions and Pathogenicity

Verticillium dahliae (V. dahliae) infects roots and colonizes the vascular vessels of host plants, significantly reducing the economic yield of cotton and other crops. In this study, the protein VdTHI20, which is involved in the thiamine biosynthesis pathway, was characterized by knocking out the corresponding VdTHI20 gene in V. dahliae via Agrobacterium tumefaciens-mediated transformation (ATMT). The deletion of VdTHI20 resulted in several phenotypic defects in vegetative growth and conidiation and in impaired virulence in tobacco seedlings. We show that VdTHI20 increases the tolerance of V. dahliae to UV damage. The impaired vegetative growth of ΔVdTHI20 mutant strains was restored by complementation with a functional copy of the VdTHI20 gene or by supplementation with additional thiamine. Furthermore, the root infection and colonization of the ΔVdTHI20 mutant strains were suppressed, as indicated by green fluorescent protein (GFP)-labelling under microscope observation. When the RNAi constructs of VdTHI20 were used to transform Nicotiana benthamiana, the transgenic lines expressing dsVdTHI20 showed elevated resistance to V. dahliae. Together, these results suggest that VdTHI20 plays a significant role in the pathogenicity of V. dahliae. In addition, the pathogenesis-related gene VdTHI20 exhibits potential for controlling V. dahliae in important crops.

Transcriptomic analysis of gene expression of Verticillium dahliae upon treatment of the cotton root exudates

Background

Cotton Verticillium wilt is one of the most devastating diseases for cotton production in the world. Although this diseases have been widely studied at the molecular level from pathogens, the molecular basis of V. dahliae interacted with cotton has not been well examined.

Results

In this study, RNA-seq analysis was carried out on V. dahliae samples cultured by different root exudates from three cotton cultivars (a susceptible upland cotton cultivar, a tolerant upland cotton cultivar and a resistant island cotton cultivar) and water for 0 h, 6 h, 12 h, 24 h and 48 h. Statistical analysis of differentially expressed genes revealed that V. dahliae responded to all kinds of root exudates but more strongly to susceptible cultivar than to tolerant and resistant cultivars. Go analysis indicated that ‘hydrolase activity, hydrolyzing O-glycosyl compounds’ related genes were highly enriched in V. dahliae cultured by root exudates from susceptible cotton at early stage of interaction, suggesting genes related to this term were closely related to the pathogenicity of V. dahliae. Additionally, ‘transmembrane transport’, ‘coenzyme binding’, ‘NADP binding’, ‘cofactor binding’, ‘oxidoreductase activity’, ‘flavin adenine dinucleotide binding’, ‘extracellular region’ were commonly enriched in V. dahliae cultured by all kinds of root exudates at early stage of interaction (6 h and 12 h), suggesting that genes related to these terms were required for the initial steps of the roots infections.

Conclusions

Based on the GO analysis results, the early stage of interaction (6 h and 12 h) were considered as the critical stage of V. dahliae-cotton interaction. Comparative transcriptomic analysis detected that 31 candidate genes response to root exudates from cotton cultivars with different level of V. dahliae resistance, 68 response to only susceptible cotton cultivar, and 26 genes required for development of V. dahliae. Collectively, these expression data have advanced our understanding of key molecular events in the V. dahliae interacted with cotton, and provided a framework for further functional studies of candidate genes to develop better control strategies for the cotton wilt disease.

VdOGDH is involved in energy metabolism and required for virulence of Verticillium dahliae

Verticillium dahliae, a soil-borne fungus, can invade plant vascular tissue and cause Verticillium wilt. The enzyme α-oxoglutarate dehydrogenase (OGDH), catalyzing the oxidation of α-oxoglutarate in the tricarboxylic acid cycle (TCA), is vital for energy metabolism in the fungi. Here, we identified the OGDH gene in V. dahliae (VdOGDH, VDAG_10018) and investigated its function in virulence by generating gene deletion mutants (ΔVdOGDH) and complementary mutants (ΔVdOGDH-C). When the ΔVdOGDH mutants were supplemented with different carbon sources, vegetative growth on Czapek Dox medium was significantly impaired, suggesting that VdOGDH is crucial for vegetative growth and carbon utilization. Conidia of the ΔVdOGDH mutants were atypically rounded or spherical, and hyphae were irregularly branched and lacked typical whorled branches. Mutants ΔVdOGDH-1 and ΔVdOGDH-2 were highly sensitive to H₂O₂ in the medium plates and had higher intracellular ROS levels. ΔVdOGDH mutants also had elevated expression of oxidative response-related genes, indicating that VdOGDH is involved in response to oxidative stress. In addition, the disruption of VdOGDH caused a significant increase in the expression of energy metabolism-related genes VdICL, VdICDH, VdMDH, and VdPDH and melanin-related genes Vayg1, VdSCD, VdLAC, VT4HR, and VaflM in the ΔVdOGDH mutants; thus, VdOGDH is also important for energy metabolism and melanin accumulation. Cotton plants inoculated with ΔVdOGDH mutants exhibited mild leaf chlorosis and the disease index was lower compared with wild type and ΔVdOGDH-C strains. These results together show that VdOGDH involved in energy metabolism of V. dahliae, is also essential for full virulence by regulating multiple fungal developmental factors.

Physiological and molecular mechanism of defense in cotton against Verticillium dahliae

Cotton, a natural fiber producing crop of huge importance for textile industry, has been reckoned as the backbone in the economy of many developing countries. Verticillium wilt caused by Verticillium dahliae reflected as the most devastating disease of cotton crop in several parts of the world. Average losses due to attack of this disease are tremendous every year. There is urgent need to develop strategies for effective control of this disease. In the last decade, progress has been made to understand the interaction between cotton-V. dahliae and several growth and pathogenicity related genes were identified. Still, most of the molecular components and mechanisms of cotton defense against Verticillium wilt are poorly understood. However, from existing knowledge, it is perceived that cotton defense mechanism primarily depends on the pre-formed defense structures including thick cuticle, synthesis of phenolic compounds and delaying or hindering the expansion of the invader through advanced measures such as reinforcement of cell wall structure, accumulation of reactive oxygen species (ROS), release of phytoalexins, the hypersensitive response and the development of broad spectrum resistance named as, systemic acquired resistance (SAR). Investigation of these defense tactics provide valuable information about the improvement of cotton breeding strategies for the development of durable, cost effective, and broad spectrum resistant varieties. Consequently, this management approach will help to reduce the use of fungicides and also minimize other environmental hazards. In the present paper, we summarized the V. dahliae virulence mechanism and comprehensively discussed the cotton molecular mechanisms of defense such as physiological, biochemical responses with the addition of signaling pathways that are implicated towards attaining resistance against Verticillium wilt.

VdPLP, A Patatin-Like Phospholipase in Verticillium dahliae, Is Involved in Cell Wall Integrity and Required for Pathogenicity

The soil-borne ascomycete fungus Verticillium dahliae causes vascular wilt disease and can seriously diminish the yield and quality of important crops. Functional analysis of growth- and pathogenicity-related genes is essential for revealing the pathogenic molecular mechanism of V. dahliae. Phospholipase is an important virulence factor in fungi that hydrolyzes phospholipids into fatty acid and other lipophilic substances and is involved in hyphal development. Thus far, only a few V. dahliae phospholipases have been identified, and their involvement in V. dahliae development and pathogenicity remains unknown. In this study, the function of the patatin-like phospholipase gene in V. dahliae (VdPLP, VDAG_00942) is characterized by generating gene knockout and complementary mutants. Vegetative growth and conidiation of VdPLP deletion mutants (ΔVdPLP) were significantly reduced compared with wild type and complementary strains, but more microsclerotia formed. The ΔVdPLP mutants were very sensitive to the cell-wall-perturbing agents: calcofluor white (CFW) and Congo red (CR). The transcriptional level of genes related to the cell wall integrity (CWI) pathway and chitin synthesis were downregulated, suggesting that VdPLP has a pivotal role in the CWI pathway and chitin synthesis in V. dahliae. ΔVdPLP strains were distinctly impaired in in their virulence and ability to colonize Nicotiana benthamiana roots. Our results demonstrate that VdPLP regulates hyphal growth and conidial production and is involved in stabilizing the cell wall, thus mediating the pathogenicity of V. dahliae.

FreB is involved in the ferric metabolism and multiple pathogenicity-related traits of Verticillium dahliae

Ferric reductases are integral membrane proteins involved in the reduction of environmental ferric iron into the biologically available ferrous iron. In the most overwhelming phytopathogenic fungus, Verticillium dahliae, these ferric reductase are not studied in details. In this study we explored the role of FreB gene (VDAG_06616) in the ferric reduction and virulence of V. dahliae by generating the knockout mutants (ΔFreB) and complementary strains (ΔFreB-C) using protoplast transformation. When cultured on media supplemented with FeSO₄, FeCl₃ and no iron, ΔFreB exhibited significantly reduced growth and spore production especially on media with no iron. Transmembrane ferric reductase activity of ΔFreB was decreased up to 50% than wild type strains (Vd-wt). The activity was fully restored in ΔFreB-C. Meanwhile, the expression levels of other related genes (Frect-4, Frect-5, Frect-6 and Met) were obviously increased in ΔFreB. Compared with the Vd-wt and ΔFreB-C, ΔFreB-1 and ΔFreB-2 were impaired in colony diameter and spore number on different carbon sources (starch, sucrose, galactose and xylose). ΔFreB-1 and ΔFreB-2 were also highly sensitive to oxidative stress as revealed by the plate diffusion assay when 100 µM H₂O₂ was applied to the fungal culture. When Nicotiana benthamiana plants were inoculated, ΔFreB exhibited less disease symptoms than Vd-wt and ΔFreB-C. In conclusion, the present findings not only indicate that FreB mediates the ferric metabolism and is required for the full virulence in V. dahliae, but would also accelerate future investigation to uncover the pathogenic mechanism of this fungus.