The chitin synthase FgChs2 and other FgChss co-regulate vegetative development and virulence in F. graminearum

Fgk3, a Glycogen Synthase Kinase, Regulates Chitin Synthesis through the Carbon Catabolite Repressor FgCreA in Fusarium graminearum

The glycogen synthase kinase-3 (GSK3) orthologs are well-conserved in eukaryotic organisms. However, their functions remain poorly characterized in filamentous fungi. In our previous study, we unveiled the function of Fgk3, the GSK3 ortholog, in glycogen metabolism in Fusarium graminearum, the causal agent of Fusarium head blight. Interestingly, the fgk3 mutant was unstable and tended to produce fast-growing suppressors, including secondary suppressors. Using whole-genome sequencing, we identified suppressor mutations in FgCHS5, FgFKS1, FgCREA, FgSSN6, FgRGR1, and FgPP2A in nine primary and four secondary suppressors. Subsequently, we validated that deletion of FgCHS5 or FgCREAΔH253 mutation partially suppressed the defects of fgk3 in vegetative growth and cell wall integrity, suggesting that Fgk3 may regulate the chitin synthesis through FgCreA-mediated transcriptional regulation in F. graminearum. Accordingly, the FGK3 deletion led to hyphal swelling with abnormal chitin deposition, and deletion of FGK3 or FgCREA caused the upregulation of the expression of chitin synthases FgCHS5 and FgCHS6. The interaction between Fgk3 and FgCreA was verified by Yeast two-hybrid and Co-Immunoprecipitation assays. More importantly, we verified that the nuclear localization and protein stability of FgCreA relies on the Fgk3 kinase, while the H253 deletion facilitated the re-localization of FgCreA to the nucleus in the fgk3 mutant background, potentially contributing to the suppression of the fgk3 mutant's defects. Intriguingly, the ΔH253 mutation of FgCreA, identified in suppressor mutant S3, is adjacent to a conserved phosphorylation site, S254, suggesting that this mutation may inhibit the S254 phosphorylation and promote the nuclear localization of FgCreA. Collectively, our findings indicate that the glycogen synthase kinase Fgk3 regulates the chitin synthesis through the carbon catabolite repressor FgCreA in F. graminearum.

The Non-Histone Protein FgNhp6 Is Involved in the Regulation of the Development, DON Biosynthesis, and Virulence of Fusarium graminearum

Fusarium graminearum is the primary causative agent of Fusarium head blight (FHB), a devastating disease affecting cereals globally. The high-mobility group (HMG) of non-histone proteins constitutes vital architectural elements within chromatin, playing diverse roles in various biological processes in eukaryotic cells. Nonetheless, the specific functions of HMG proteins in F. graminearum have yet to be elucidated. Here, we identified 10 HMG proteins in F. graminearum and extensively characterized the biological roles of one HMGB protein, FgNhp6. We constructed the FgNhp6 deletion mutant and its complementary strains. With these strains, we confirmed the nuclear localization of FgNhp6 and discovered that the absence of FgNhp6 led to reduced radial growth accompanied by severe pigmentation defects, a significant reduction in conidial production, and a failure to produce perithecia. The ∆FgNhp6 mutant exhibited a markedly reduced pathogenicity on wheat coleoptiles and spikes, coupled with a significant increase in deoxynivalenol production. An RNA sequencing (RNA-seq) analysis indicated that FgNhp6 deletion influenced a wide array of metabolic pathways, particularly affecting several secondary metabolic pathways, such as sterol biosynthesis and aurofusarin biosynthesis. The findings of this study highlight the essential role of FgNhp6 in the regulation of the asexual and sexual reproduction, deoxynivalenol (DON) production, and pathogenicity of F. graminearum.

Venturicidin A Is a Potential Fungicide for Controlling Fusarium Head Blight by Affecting Deoxynivalenol Biosynthesis, Toxisome Formation, and Mitochondrial Structure

Fusarium graminearum, which causes Fusarium head blight (FHB) in cereals, is one of the most devastating fungal diseases by causing great yield losses and mycotoxin contamination. A major bioactive ingredient, venturicidin A (VentA), was isolated from Streptomyces pratensis S10 mycelial extract with an activity-guided approach. No report is available on antifungal activity of VentA against F. graminearum and effects on deoxynivalenol (DON) biosynthesis. Here, VentA showed a high antagonistic activity toward F. graminearum with an EC50 value of 3.69 μg/mL. As observed by scanning electron microscopy, after exposure to VentA, F. graminearum conidia and mycelia appeared abnormal. Different dyes staining revealed that VentA increased cell membrane permeability. In growth chamber and field trials, VentA effectively reduced disease severity of FHB. Moreover, VentA inhibited DON biosynthesis by reducing pyruvic acid, acetyl-CoA production, and accumulation of reactive oxygen species (ROS) and then inhibiting trichothecene (TRI) genes expression and toxisome formation. These results suggest that VentA is a potential fungicide for controlling FHB.

Cell Wall Integrity Mediated by CfCHS1 Is Important for Growth, Stress Responses and Pathogenicity in Colletotrichum fructicola

Camellia oleifera, a woody plant that produces edible oil, is indigenous to China. The devastating disease of anthracnose inflicts significant financial losses on Ca. oleifera. The primary causative agent of anthracnose on Ca. oleifera is Colletotrichum fructicola. Chitin, a pivotal constituent of fungal cell walls, assumes a critical function in their proliferation and maturation. To study the biological functions of chitin synthase 1(Chs1) in C. fructicola, the CfCHS1 gene knockout mutants, ∆Cfchs1-1 and ∆Cfchs1-2, and their complementary strain, ∆Cfchs1/CfCHS1, of C. fructicola were generated. Our results showed that the colony diameters of wild-type and complement-strain ∆Cfchs1/CfCHS1, mutant ∆Cfchs1-1 and ∆Cfchs1-2 cultured on the CM and MM medium were 5.2, 5.0, 2.2 and 2.4 cm and 4.0, 4.0, 2.1 and 2.6 cm, respectively, which were significantly smaller for the mutant than for the wild type and complement strain; the inhibition rates on the CM medium supplemented with H₂O₂, DTT, SDS and CR were 87.0% and 88.5%, 29.6% and 27.1%, 88.0% and 89.4%, and 41.7% and 28.7%, respectively, for the mutant strains, ∆Cfchs1-1 and ∆Cfchs1-2, which were significantly higher than those for the other two strains; the rate of hyphal tips with CFW fluorescence in ∆Cfchs1-1 and ∆Cfchs1-2 was 13.3% and 15.0%, which was significantly lower than those for the other two strains; the mutant strains, ∆Cfchs1-1 and ∆Cfchs1-2, lost the ability to produce conidia; the mutant strains showed weaker pathogenicity on wounded and unwounded Ca. oleifera leaves than the wild type and complement strain. The findings of this study suggest that CfChs1 plays a crucial role in the growth and development, stress responses, and pathogenicity of C. fructicola. Thus, this gene could be a potential target for developing novel fungicide.

Streptomyces pratensis S10 Controls Fusarium Head Blight by Suppressing Different Stages of the Life Cycle and ATP Production

Fusarium head blight (FHB) of wheat, predominately caused by Fusarium graminearum, is an economically important plant disease worldwide. With increased fungicide resistance, controlling this filamentous fungal disease has become an enormous challenge. Biocontrol agents alone or integrated with other methods could better manage FHB. Streptomyces pratensis S10 has strong antagonistic activity against FHB as reported in our previous study. We now have investigated S10 controls of FHB in more detail by combining microscope observations, biological assays, and transcriptome profiling. S10 culture filtrates (SCF) significantly inhibited essential stages of the life cycle of F. graminearum in the laboratory and under simulated natural conditions. SCF at different concentrations inhibited conidiation of F. graminearum with an inhibition of 57.49 to 83.83% in the medium and 64.04 to 85.89% in plants. Different concentrations of SCF reduced conidia germination by 47.33 to 67.67%. Two percent (vol/vol) SCF suppressed perithecia formation of F. graminearum by 84 and 81% in the laboratory and under simulated natural conditions, respectively. The S10 also reduced the pathogenicity and penetration ability of F. graminearum by suppressing ATP production. Collectively, these findings indicate that S. pratensis S10 should be explored further for efficacy at controlling FHB.

Transcriptomic Profiling of Fusarium pseudograminearum in Response to Carbendazim, Pyraclostrobin, Tebuconazole, and Phenamacril

Fusarium pseudograminearum has been identified as a significant pathogen. It causes Fusarium crown rot (FCR), which occurs in several major wheat-producing areas in China. Chemical control is the primary measure with which to control this disease. In this study, transcriptome sequencing (RNA-Seq) was used to determine the different mechanisms of action of four frequently used fungicides including carbendazim, pyraclostrobin, tebuconazole, and phenamacril on F. pseudograminearum. In brief, 381, 1896, 842, and 814 differentially expressed genes (DEGs) were identified under the carbendazim, pyraclostrobin, tebuconazole, and phenamacril treatments, respectively. After the joint analysis, 67 common DEGs were obtained, and further functional analysis showed that the ABC transported pathway was significantly enriched. Moreover, FPSE_04130 (FER6) and FPSE_11895 (MDR1), two important ABC multidrug transporter genes whose expression levels simultaneously increased, were mined under the different treatments, which unambiguously demonstrated the common effects. In addition, Mfuzz clustering analysis and WGCNA analysis revealed that the core DEGs are involved in several critical pathways in each of the four treatment groups. Taken together, these genes may play a crucial function in the mechanisms of F. pseudograminearum's response to the fungicides stress.

Palmitoyl Transferase FonPAT2-Catalyzed Palmitoylation of the FonAP-2 Complex Is Essential for Growth, Development, Stress Response, and Virulence in Fusarium oxysporum f. sp. niveum

Protein palmitoylation, one of posttranslational modifications, is catalyzed by a group of palmitoyl transferases (PATs) and plays critical roles in the regulation of protein functions. However, little is known about the function and mechanism of PATs in plant pathogenic fungi. The present study reports the function and molecular mechanism of FonPATs in Fusarium oxysporum f. sp. niveum (Fon), the causal agent of watermelon Fusarium wilt. The Fon genome contains six FonPAT genes with distinct functions in vegetative growth, conidiation and conidial morphology, and stress response. FonPAT1, FonPAT2, and FonPAT4 have PAT activity and are required for Fon virulence on watermelon mainly through regulating in planta fungal growth within host plants. Comparative proteomics analysis identified a set of proteins that were palmitoylated by FonPAT2, and some of them are previously reported pathogenicity-related proteins in fungi. The FonAP-2 complex core subunits FonAP-2α, FonAP-2β, and FonAP-2μ were palmitoylated by FonPAT2 in vivo. FonPAT2-catalyzed palmitoylation contributed to the stability and interaction ability of the core subunits to ensure the formation of the FonAP-2 complex, which is essential for vegetative growth, asexual reproduction, cell wall integrity, and virulence in Fon. These findings demonstrate that FonPAT1, FonPAT2, and FonPAT4 play important roles in Fon virulence and that FonPAT2-catalyzed palmitoylation of the FonAP-2 complex is critical to Fon virulence, providing novel insights into the importance of protein palmitoylation in the virulence of plant fungal pathogens. IMPORTANCE Fusarium oxysporum f. sp. niveum (Fon), the causal agent of watermelon Fusarium wilt, is one of the most serious threats for the sustainable development of the watermelon industry worldwide. However, little is known about the underlying molecular mechanism of pathogenicity in Fon. Here, we found that the palmitoyl transferase (FonPAT) genes play distinct and diverse roles in basic biological processes and stress response and demonstrated that FonPAT1, FonPAT2, and FonPAT4 have PAT activity and are required for virulence in Fon. We also found that FonPAT2 palmitoylates the core subunits of the FonAP-2 complex to maintain the stability and the formation of the FonAP-2 complex, which is essential for basic biological processes, stress response, and virulence in Fon. Our study provides new insights into the understanding of the molecular mechanism involved in Fon virulence and will be helpful in the development of novel strategies for disease management.

Protein kinase A participates in hyphal and appressorial development by targeting Efg1-mediated transcription of a Rab GTPase in Setosphaeria turcica

The cyclic adenosine monophosphate (cAMP) signalling pathway plays an important role in the regulation of the development and pathogenicity of filamentous fungi. cAMP-dependent protein kinase A (PKA) is the conserved element downstream of cAMP, and its diverse mechanisms in multiple filamentous fungi are not well known yet. In the present study, gene knockout mutants of two catalytic subunits of PKA (PKA-C) in Setosphaeria turcica were created to illustrate the regulatory mechanisms of PKA-Cs on the development and pathogenicity of S. turcica. As a result, StPkaC2 was proved to be the main contributor of PKA activity in S. turcica. In addition, it was found that both StPkaC1 and StPkaC2 were necessary for conidiation and invasive growth, while only StPkaC2 played a negative role in the regulation of filamentous growth. We reveal that only StPkaC2 could interact with the transcription factor StEfg1, and it inhibited the transcription of StRAB1, a Rab GTPase homologue coding gene in S. turcica, whereas StPkaC1 could specifically interact with a transcriptional regulator StFlo8, which could rescue the transcriptional inhibition of StEfg1 on StRAB1. We also demonstrated that StRAB1 could positively influence the biosynthesis of chitin in hyphae, thus changing the filamentous growth. Our findings clarify that StPkaC2 participates in chitin biosynthesis to modulate mycelium development by targeting the Efg1-mediated transcription of StRAB1, while StFlo8, interacting with StPkaC1, acts as a negative regulator during this process.

Genomic footprints related with adaptation and fumonisins production in Fusarium proliferatum

Fusarium proliferatum is the principal etiological agent of rice spikelet rot disease (RSRD) in China, causing yield losses and fumonisins contamination in rice. The intraspecific variability and evolution pattern of the pathogen is poorly understood. Here, we performed whole-genome resequencing of 67 F. proliferatum strains collected from major rice-growing regions in China. Population structure indicated that eastern population of F. proliferatum located in Yangtze River with the high genetic diversity and recombinant mode that was predicted as the putative center of origin. Southern population and northeast population were likely been introduced into local populations through gene flow, and genetic differentiation between them might be shaped by rice-driven domestication. A total of 121 distinct genomic loci implicated 85 candidate genes were suggestively associated with variation of fumonisin B1 (FB1) production by genome-wide association study (GWAS). We subsequently tested the function of five candidate genes (gabap, chsD, palA, hxk1, and isw2) mapped in our association study by FB1 quantification of deletion strains, and mutants showed the impact on FB1 production as compared to the wide-type strain. Together, this is the first study to provide insights into the evolution and adaptation in natural populations of F. proliferatum on rice, as well as the complex genetic architecture for fumonisins biosynthesis.

Quantitative multiplexed proteomics analysis reveals reshaping of the lysine 2-hydroxyisobutyrylome in Fusarium graminearum by tebuconazole

Backgrounds

Lysine 2-hydroxyisobutyrylation (Khib) is a newly discovered posttranslational modification (PTM) and has been identified in several prokaryotic and eukaryotic organisms. Fusarium graminearum, a major pathogen of Fusarium head blight (FHB) in cereal crops, can cause considerable yield loss and produce various mycotoxins that threaten human health. The application of chemical fungicides such as tebuconazole (TEC) remains the major method to control this pathogen. However, the distribution of Khib in F. graminearum and whether Khib is remodified in response to fungicide stress remain unknown.

Results

Here, we carried out a proteome-wide analysis of Khib in F. graminearum, identifying the reshaping of the lysine 2-hydroxyisobutyrylome by tebuconazole, using the most recently developed high-resolution LC–MS/MS technique in combination with high-specific affinity enrichment. Specifically, 3501 Khib sites on 1049 proteins were identified, and 1083 Khib sites on 556 modified proteins normalized to the total protein content were changed significantly after TEC treatment. Bioinformatics analysis showed that Khib proteins are involved in a wide range of biological processes and may be involved in virulence and deoxynivalenol (DON) production, as well as sterol biosynthesis, in F. graminearum.

Conclusions

Here, we provided a wealth of resources for further study of the roles of Khib in the fungicide resistance of F. graminearum. The results enhanced our understanding of this PTM in filamentous ascomycete fungi and provided insight into the remodification of Khib sites during azole fungicide challenge in F. graminearum.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08372-4.

Genome-Wide Identification of bZIP Transcription Factor Genes and Functional Analyses of Two Members in Cytospora chrysosperma

The basic leucine zipper (bZIP) transcription factor (TF) family, one of the largest and the most diverse TF families, is widely distributed across the eukaryotes. It has been described that the bZIP TFs play diverse roles in development, nutrient utilization, and various stress responses in fungi. However, little is known of the bZIP members in Cytospora chrysosperma, a notorious plant pathogenic fungus, which causes canker disease on over 80 woody plant species. In this study, 26 bZIP genes were systematically identified in the genome of C. chrysosperma, and two of them (named CcbZIP05 and CcbZIP23) significantly down-regulated in CcPmk1 deletion mutant (a pathogenicity-related mitogen-activated protein kinase) were selected for further analysis. Deletion of CcbZIP05 or CcbZIP23 displayed a dramatic reduction in fungal growth but showed increased hypha branching and resistance to cell wall inhibitors and abiotic stresses. The CcbZIP05 deletion mutants but not CcbZIP23 deletion mutants were more sensitive to the hydrogen peroxide compared to the wild-type and complemented strains. Additionally, the CcbZIP23 deletion mutants produced few pycnidia but more pigment. Remarkably, both CcbZIP05 and CcbZIP23 deletion mutants were significantly reduced in fungal virulence. Further analysis showed that CcbZIP05 and CcbZIP23 could regulate the expression of putative effector genes and chitin synthesis-related genes. Taken together, our results suggest that CcbZIP05 and CcbZIP23 play important roles in fungal growth, abiotic stresses response, and pathogenicity, which will provide comprehensive information on the CcbZIP genes and lay the foundation for further research on the bZIP members in C. chrysosperma.

Antifungal activity of volatile compounds generated by endophytic fungi Sarocladium brachiariae HND5 against Fusarium oxysporum f. sp. cubense

The soil-born filamentous fungal pathogen Fusarium oxysporum f. sp. cubense (FOC), which causes vascular wilt disease in banana plants, is one of the most economically important Fusarium species. Biocontrol using endophytic microorganisms is among the most effective methods for controlling banana Fusarium wilt. In this study, volatile organic compounds (VOCs) showed strong antifungal activity against FOC. Seventeen compounds were identified from the VOCs produced by endophytic fungi Sarocladium brachiariae HND5, and three (2-methoxy-4-vinylphenol, 3,4-dimethoxystyrol and caryophyllene) showed antifungal activity against FOC with 50% effective concentrations of 36, 60 and 2900 μL/L headspace, respectively. Transmission electron microscopy (TEM) and double fluorescence staining revealed that 2-methoxy-4-vinylphenol and 3,4-dimethoxystyrol damaged the plasma membranes, resulting in cell death. 3,4-dimethoxystyrol also could induce expression of chitin synthases genes and altered the cell walls of FOC hyphae. Dichloro-dihydro-fluorescein diacetate staining indicated the caryophyllene induced accumulation of reactive oxygen species (ROS) in FOC hyphae. FOC secondary metabolism also responded to active VOC challenge by producing less fusaric acid and expressions of genes related to fusaric acid production were interrupted at sublethal concentrations. These findings indicate the potential of S. brachiariae HND5 as a biocontrol agent against FOC and the antifungal VOCs as fumigants.

Application of Double-Strand RNAs Targeting Chitin Synthase, Glucan Synthase, and Protein Kinase Reduces Fusarium graminearum Spreading in Wheat

Controlling the devastating fungal pathogen Fusarium graminearum (Fg) is a challenge due to inadequate resistance in nature. Here, we report on the identification of RNAi molecules and their applications for controlling Fg in wheat through silencing chitin synthase 7 (Chs7), glucan synthase (Gls) and protein kinase C (Pkc). From transgenic Fg strains four RNAi constructs from Chs7 (Chs7RNAi−1, −2, −3, and −4), three RNAi constructs from Gls (GlsRNAi−2, −3, and −6), and one RNAi construct from Pkc (PkcRNAi−5) were identified that displayed effective silencing effects on mycelium growth in medium and pathogenicity in wheat spikes. Transcript levels of Chs7, Gls and Pkc were markedly reduced in those strains. Double-strand RNAs (dsRNAs) of three selected RNAi constructs (Chs7RNAi-4, GlsRNAi-6 and PkcRNA-5) strongly inhibited mycelium growth in vitro. Spray of those dsRNAs on detached wheat leaves significantly reduced lesion sizes; the independent dsRNAs showed comparable effects on lesions with combination of two or three dsRNAs. Expression of three targets Chs7, Gls, and Pkc was substantially down-regulated in Fg-infected wheat leaves. Further application of dsRNAs on wheat spikes in greenhouse significantly reduced infected spikelets. The identified RNAi constructs may be directly used for spray-induced gene silencing and stable expression in plants to control Fusarium pathogens in agriculture.

Secreted in Xylem Genes: Drivers of Host Adaptation in Fusarium oxysporum

Fusarium oxysporum (Fo) is a notorious pathogen that significantly contributes to yield losses in crops of high economic status. It is responsible for vascular wilt characterized by the browning of conductive tissue, wilting, and plant death. Individual strains of Fo are host specific (formae speciales), and approximately, 150 forms have been documented so far. The pathogen secretes small effector proteins in the xylem, termed as Secreted in Xylem (Six), that contribute to its virulence. Most of these proteins contain cysteine residues in even numbers. These proteins are encoded by SIX genes that reside on mobile pathogenicity chromosomes. So far, 14 proteins have been reported. However, formae speciales vary in SIX protein profile and their respective gene sequence. Thus, SIX genes have been employed as ideal markers for pathogen identification. Acquisition of SIX-encoding mobile pathogenicity chromosomes by non-pathogenic lines, through horizontal transfer, results in the evolution of new virulent lines. Recently, some SIX genes present on these pathogenicity chromosomes have been shown to be involved in defining variation in host specificity among formae speciales. Along these lines, the review entails the variability (formae speciales, races, and vegetative compatibility groups) and evolutionary relationships among members of F. oxysporum species complex (FOSC). It provides updated information on the diversity, structure, regulation, and (a)virulence functions of SIX genes. The improved understanding of roles of SIX in variability and virulence of Fo has significant implication in establishment of molecular framework and techniques for disease management. Finally, the review identifies the gaps in current knowledge and provides insights into potential research landscapes that can be explored to strengthen the understanding of functions of SIX genes.

Soil microbiota influences clubroot disease by modulating Plasmodiophora brassicae and Brassica napus transcriptomes

The contribution of surrounding plant microbiota to disease development has led to the 'pathobiome' concept, which represents the interaction between the pathogen, the host plant and the associated biotic microbial community, resulting or not in plant disease. The aim herein is to understand how the soil microbial environment may influence the functions of a pathogen and its pathogenesis, and the molecular response of the plant to the infection, with a dual-RNAseq transcriptomics approach. We address this question using Brassica napus and Plasmodiophora brassicae, the pathogen responsible for clubroot. A time-course experiment was conducted to study interactions between P. brassicae, two B. napus genotypes and three soils harbouring high, medium or low microbiota diversities and levels of richness. The soil microbial diversity levels had an impact on disease development (symptom levels and pathogen quantity). The P. brassicae and B. napus transcriptional patterns were modulated by these microbial diversities, these modulations being dependent on the host genotype plant and the kinetic time. The functional analysis of gene expressions allowed the identification of pathogen and plant host functions potentially involved in the change of plant disease level, such as pathogenicity-related genes (NUDIX effector) in P. brassicae and plant defence-related genes (glucosinolate metabolism) in B. napus.

Cell Wall Biogenesis Protein Phosphatase CrSsd1 Is Required for Conidiation, Cell Wall Integrity, and Mycoparasitism in Clonostachys rosea

Cell wall biogenesis protein phosphatases play important roles in various cellular processes in fungi. However, their functions in the widely distributed mycoparasitic fungus Clonostachys rosea remain unclear, as do their potential for controlling plant fungal diseases. Herein, the function of cell wall biogenesis protein phosphatase CrSsd1 in C. rosea 67-1 was investigated using gene disruption and complementation approaches. The gene-deficient mutant ΔCrSsd1 exhibited much lower conidiation, hyphal growth, mycoparasitic ability, and biocontrol efficacy than the wild-type (WT) strain, and it was more sensitive to sorbitol and Congo red. The results indicate that CrSsd1 is involved in fungal conidiation, osmotic stress adaptation, cell wall integrity, and mycoparasitism in C. rosea.

The Myosin Motor Domain-Containing Chitin Synthases Are Involved in Cell Wall Integrity and Sensitivity to Antifungal Proteins in Penicillium digitatum

Penicillium digitatum is the main postharvest pathogen of citrus fruit and is responsible for important economic losses in spite of the massive use of fungicides. The fungal cell wall (CW) and its specific component chitin are potential targets for the development of new antifungal molecules. Among these are the antifungal peptides and proteins that specifically interact with fungal CW. Chitin is synthesized by a complex family of chitin synthases (Chs), classified into up to eight classes within three divisions. Previously, we obtained and characterized a mutant of P. digitatum in the class VII gene (ΔchsVII), which contains a short myosin motor-like domain (MMD). In this report, we extend our previous studies to the characterization of mutants in chsII and in the gene coding for the other MMD-Chs (chsV), and study the role of chitin synthases in the sensitivity of P. digitatum to the self-antifungal protein AfpB, and to AfpA obtained from P. expansum. The ΔchsII mutant showed no significant phenotypic and virulence differences with the wild type strain, except in the production and morphology of the conidia. In contrast, mutants in chsV showed a more dramatic phenotype than the previous ΔchsVII, with reduced growth and conidial production, increased chitin content, changes in mycelial morphology and a decrease in virulence to citrus fruit. Mutants in chsVII were specifically more tolerant than the wild type to nikkomycin Z, an antifungal inhibitor of chitin biosynthesis. Treatment of P. digitatum with its own antifungal protein AfpB resulted in an overall reduction in the expression of the chitin synthase genes. The mutants corresponding to MMD chitin synthases exhibited differential sensitivity to the antifungal proteins AfpA and AfpB, ΔchsVII being more susceptible than its parental strain and ΔchsV being slightly more tolerant despite its reduced growth in liquid broth. Taking these results together, we conclude that the MMD-containing chitin synthases affect cell wall integrity and sensitivity to antifungal proteins in P. digitatum.

Fusarium oxysporum f. sp. lycopersici causal agent of vascular wilt disease of tomato: Biology to diversity- A review

Tomato (Lycopersicon esculentum) is one of the widely grown vegetables worldwide. Fusarium oxysporum f. sp. lycopersici (FOL) is the significant contributory pathogen of tomato vascular wilt. The initial symptoms of the disease appear in the lower leaves gradually, trail by wilting of the plants. It has been reported that FOL penetrates the tomato plant, colonizing and leaving the vascular tissue dark brown, and this discoloration extends to the apex, leading to the plants wilting, collapsing and dying. Therefore, it has been widely accepted that wilting caused by this fungus is the result of a combination of various physiological activities, including the accumulation of fungal mycelia in and around xylem, mycotoxin production, inactivation of host defense, and the production of tyloses; however, wilting symptoms are variable. Therefore, the selection of molecular markers may be a more effective means of screening tomato races. Several studies on the detection of FOL have been carried out and have suggested the potency of the technique for diagnosing FOL. This review focuses on biology and variability of FOL, understanding and presenting a holistic picture of the vascular wilt disease of tomato in relation to disease model, biology, virulence. We conclude that genomic and proteomic approachesare greater tools for identification of informative candidates involved in pathogenicity, which can be considered as one of the approaches in managing the disease.