Phenylpyrrole fungicides act on triosephosphate isomerase to induce methylglyoxal stress and alter hybrid histidine kinase activity

Metatranscriptomic response of deep ocean microbial populations to infusions of oil and/or synthetic chemical dispersant

Oil spills are a frequent perturbation to the marine environment that has rapid and significant impacts on the local microbiome. Previous studies have shown that exposure to synthetic dispersant alone did not enhance heterotrophic microbial activity or oxidation rates of specific hydrocarbon components but increased the abundance of some taxa (e.g., Colwellia). In contrast, exposure to oil, but not dispersants, increased the abundance of other taxa (e.g., Marinobacter) and stimulated hydrocarbon oxidation rates. Here, we advance these findings by interpreting metatranscriptomic data from this experiment to explore how and why specific components of the microbial community responded to distinct organic carbon exposure regimes. Dispersant alone was selected for a unique community and for dominant organisms that reflected treatment- and time-dependent responses. Dispersant amendment also led to diverging functional profiles among the different treatments. Similarly, oil alone was selected for a community that was distinct from treatments amended with dispersants. The presence of oil and dispersants with added nutrients led to substantial differences in microbial responses, likely suggesting increased fitness driven by the presence of additional inorganic nutrients. The oil-only additions led to a marked increase in the expression of phages, prophages, transposable elements, and plasmids (PPTEPs), suggesting that aspects of microbial community response to oil are driven by the "mobilome," potentially through viral-associated regulation of metabolic pathways in ciliates and flagellates that would otherwise throttle the microbial community through grazing.IMPORTANCEMicrocosm experiments simulated the April 2010 Deepwater Horizon oil spill by applying oil and synthetic dispersants (Corexit EC9500A and EC9527A) to deep ocean water samples. The exposure regime revealed severe negative alterations in the treatments' heterotrophic microbial activity and hydrocarbon oxidation rates. We expanded these findings by exploring metatranscriptomic signatures of the microbial communities during the chemical amendments in the microcosm experiments. Here we report how dominant organisms were uniquely associated with treatment- and time-dependent trajectories during the exposure regimes; nutrient availability was a significant factor in driving changes in metatranscriptomic responses. Remarkable signals associated with PPTEPs showed the potential role of mobilome and viral-associated survival responses. These insights underscore the time-dependent environmental perturbations of fragile marine environments under oil and anthropogenic stress.

A Conservative Mutant Version of the Mrr1 Transcription Factor Correlates with Reduced Sensitivity to Fludioxonil in Botrytis cinerea

Fludioxonil is a highly effective phenylpyrrole fungicide for controlling Botrytis cinerea. Although the field efficacy of fludioxonil remains high, Botrytis cinerea isolates with reduced sensitivity have been reported globally. The molecular target of fludioxonil still remains unknown; however, a mechanism of reduced sensitivity to fludioxonil underlies the overexpression of the ATP binding cassette (ABC) transporter AtrB in a dependent pathway of the Mrr1 transcription factor. Fludioxonil is a key player in controlling B. cinerea infection in table grapes in Chile. However, some isolates with a reduced sensitivity to fludioxonil were detected. This study observed endogenous atrB overexpression in Chilean isolates with reduced sensitivity to fludioxonil (n = 22) compared to the sensitive isolates (n = 10). All isolates increased the expression of atrB in a growth medium supplemented with fludioxonil (0.05 μg/mL). However, sensitive isolates showed lower atrB expression than those with reduced fludioxonil sensitivity. Remarkably, a mutant version of the transcription factor Mrr1 carrying 21 amino acid modifications was identified in all isolates with reduced sensitivity to fludioxonil. These changes alter the protein's transcription factor domain and the C-terminal portion of the protein but not the Zn (2)-C6 fungal-type DNA-binding domain. These results suggest a direct relationship between the conserved and divergent mutant version of mrr1 and sensitivity to fludioxonil. This study provides a new target for developing molecular diagnostic strategies to monitor B. cinerea's sensitivity to fludioxonil in the field.

An array of signal-specific MoYpd1 isoforms determines full virulence in the pathogenic fungus Magnaporthe oryzae

Magnaporthe oryzae is placed first on a list of the world's top ten plant pathogens with the highest scientific and economic importance. The locus MGG_07173 occurs only once in the genome of M. oryzae and encodes the phosphotransfer protein MoYpd1p, which plays an important role in the high osmolarity glycerol (HOG) signaling pathway for osmoregulation. Originating from this locus, at least three MoYPD1 isoforms are produced in a signal-specific manner. The transcript levels of these MoYPD1-isoforms were individually affected by external stress. Salt (KCI) stress raised MoYPD1_T0 abundance, whereas osmotic stress by sorbitol elevates MoYPD1_T1 levels. In line with this, signal-specific nuclear translocation of green fluorescent protein-fused MoYpd1p isoforms in response to stress was observed. Mutant strains that produce only one of the MoYpd1p isoforms are less virulent, suggesting a combination thereof is required to invade the host successfully. In summary, we demonstrate signal-specific production of MoYpd1p isoforms that individually increase signal diversity and orchestrate virulence in M. oryzae.

Residue dynamics of a contact and a systemic fungicide in pollen, nectar, and other plant matrices of courgette (Cucurbita pepo L.)

Pollen and nectar can be contaminated with a range of pesticides, including insecticides, fungicides, and herbicides. Since these matrices are important food sources for pollinators and other beneficial insects, their contamination can represent a key route of exposure. However, limited knowledge exists with respect to pesticide residue levels and their dynamics in these matrices for many crops and active ingredients (AIs). We used controlled glasshouse studies to investigate the residue dynamics of a systemic (cyprodinil) and a contact (fludioxonil) fungicide in the floral matrices and other plant parts of courgette/zucchini (Cucurbita pepo L.). We aimed to better understand the processes behind residue accumulation and decline in pollen and nectar. Each AI was applied to plants, either by spraying whole plants or by targeted spraying onto leaves only. Samples of pollen, nectar, anthers, flowers, and leaves were taken on the day of application and each subsequent morning for up to 13 days and analysed for residues using LC-MS/MS. Significant differences in residue levels and dynamics were found between AIs and floral matrices. The present study allowed for the identification of potential routes by which residues translocate between tissues and to link those to the physicochemical properties of each AI, which may facilitate the prediction of residue levels in pollen and nectar. Residues of the contact AI declined more quickly than those of the systemic AI in pollen and nectar. Our results further suggest that the risk of oral exposure for pollinators may be considerably reduced by using contact AIs during the green bud stage of plants, but application of systemic compounds could still result in a low, but continuous long-term exposure for pollinators with limited decline.

Distinct transcriptional responses to fludioxonil in Aspergillus fumigatus and its ΔtcsC and Δskn7 mutants reveal a crucial role for Skn7 in the cell wall reorganizations triggered by this antifungal

BACKGROUND

Aspergillus fumigatus is a major fungal pathogen that causes severe problems due to its increasing resistance to many therapeutic agents. Fludioxonil is a compound that triggers a lethal activation of the fungal-specific High Osmolarity Glycerol pathway. Its pronounced antifungal activity against A. fumigatus and other pathogenic molds renders this agent an attractive lead substance for the development of new therapeutics. The group III hydride histidine kinase TcsC and its downstream target Skn7 are key elements of the multistep phosphorelay that represents the initial section of the High Osmolarity Glycerol pathway. Loss of tcsC results in resistance to fludioxonil, whereas a Δskn7 mutant is partially, but not completely resistant.

RESULTS

In this study, we compared the fludioxonil-induced transcriptional responses in the ΔtcsC and Δskn7 mutant and their parental A. fumigatus strain. The number of differentially expressed genes correlates well with the susceptibility level of the individual strains. The wild type and, to a lesser extend also the Δskn7 mutant, showed a multi-faceted stress response involving genes linked to ribosomal and peroxisomal function, iron homeostasis and oxidative stress. A marked difference between the sensitive wild type and the largely resistant Δskn7 mutant was evident for many cell wall-related genes and in particular those involved in the biosynthesis of chitin. Biochemical data corroborate this differential gene expression that does not occur in response to hyperosmotic stress.

CONCLUSIONS

Our data reveal that fludioxonil induces a strong and TcsC-dependent stress that affects many aspects of the cellular machinery. The data also demonstrate a link between Skn7 and the cell wall reorganizations that foster the characteristic ballooning and the subsequent lysis of fludioxonil-treated cells.

Polypeptides Targeting Paracoccidioides brasiliensis Drk1

Considering the toxicity of conventional therapeutic approaches and the importance of precise mechanistic targets, it is important to explore signaling pathways implicated in fungal pathobiology. Moreover, treatment of paracoccidioidomycosis, a systemic mycosis caused by a dimorphic fungus, requires prolonged therapeutic regimens. Among the numerous factors underpinning the establishment of Paracoccidioides spp. infection, the capacity to transition from the mycelial to the yeast form is of pivotal importance. The Drk1 protein of Paracoccidioides brasiliensis likely plays a decisive role in this morphological shift and subsequent virulence. We identified peptides with affinity for the PbDrk1 protein using the phage-display method and assessed the effects of these peptides on P. brasiliensis. The peptides were found to inhibit the phase transition of P. brasiliensis. Furthermore, a substantial proportion of these peptides prevented adhesion to pneumocytes. Although these peptides may not possess inherent antifungal properties, they can augment the effects of certain antifungal agents. Notably, the cell wall architecture of P. brasiliensis appears to be modulated by peptide intervention, resulting in a reduced abundance of glycosylated proteins and lipids. These peptides were also evaluated for their efficacy in a Galleria mellonella model and shown to contribute to enhanced larval survival rates. The role of PbDrk1, which is notably absent in mammals, should be further investigated to improve the understanding of its functional role in P. brasiliensis, which may be helpful for designing novel therapeutic modalities.

Overexpression of FgPtp3 Is Involved in Fludioxonil Resistance in Fusarium graminearum by Inhibiting the Phosphorylation of FgHog1

Fusarium graminearum is the main causal agent of Fusarium head blight (FHB), a destructive disease in cereal crops worldwide. Resistance to fludioxonil has been reported in F. graminearum in the field, but its underlying mechanisms remain elusive. In this study, 152 fludioxonil-resistant (FR) mutants of F. graminearum were obtained by selection in vitro. The FR strains exhibited dramatically impaired fitness, but only 7 of the 13 analyzed strains possessed mutations in genes previously reported to underlie fludioxonil resistance. Comparison between the FR-132 strain and its parental strain PH-1 using whole genome sequencing revealed no mutations between them, but transcriptome analysis, after the strains were treated with 0.5 μg/mL fludioxonil, revealed 2778 differently expressed genes (DEGs) mapped to 96 KEGG pathways. Investigation of DEGs in the MAPK pathway showed that overexpression of the tyrosine protein phosphatase FgPtp3, but not FgPtp2, enhanced fludioxonil resistance. Further analysis found that FgPtp3 interacted directly with FgHog1 to regulate the phosphorylation of Hog1, and overexpressed FgPtp3 in PH-1 could significantly suppress the phosphorylation of FgHog1 and hinder signal transmission of the HOG-MAPK pathway. Overall, FgPtp3 plays a significant role in regulating fludioxonil resistance in F. graminearum.

Human Triosephosphate Isomerase Is a Potential Target in Cancer Due to Commonly Occurring Post-Translational Modifications

Cancer involves a series of diseases where cellular growth is not controlled. Cancer is a leading cause of death worldwide, and the burden of cancer incidence and mortality is rapidly growing, mainly in developing countries. Many drugs are currently used, from chemotherapeutic agents to immunotherapy, among others, along with organ transplantation. Treatments can cause severe side effects, including remission and progression of the disease with serious consequences. Increased glycolytic activity is characteristic of cancer cells. Triosephosphate isomerase is essential for net ATP production in the glycolytic pathway. Notably, some post-translational events have been described that occur in human triosephosphate isomerase in which functional and structural alterations are provoked. This is considered a window of opportunity, given the differences that may exist between cancer cells and their counterpart in normal cells concerning the glycolytic enzymes. Here, we provide elements that bring out the potential of triosephosphate isomerase, under post-translational modifications, to be considered an efficacious target for treating cancer.

Sensitivity and resistance risk of Botryosphaeria dothidea causing Chinese hickory trunk canker to fludioxonil

Hickory trunk canker (HTC), primarily caused by Botryosphaeria dothidea, is an aggravating disease that threatens an important regional economic tree species of Chinese hickory and few information is available in the control of this disease. Here, the sensitivity of 93 isolates to fludioxonil and the resistance risk were investigated. All the isolates tested were sensitive to fludioxonil and the EC50 ranged from 0.0028 to 0.0569 μg/mL. The tamed fludioxonil-resistant mutants remained highly resistant to fludioxonil even after 10 consecutive transfers to fludioxonil-free PDA plates. As for fitness penalty, the fludioxonil-resistant mutants demonstrated a reduction in conidia production and virulence as well as increased sensitivity to high osmotic stress. While, variations in mycelial growth and responses to SDS and H2O2 were not detected in all the resistant mutants. In addition, the resistant mutants demonstrated positive cross-resistance to iprodione but not to fungicides of other modes of action. Sequential analysis of BdNik1 showed that premature stop codon occurred in all the resistant mutants despite of point mutation (BD16-22R9 and BD16-22R20) or frameshift mutation (BD16-22R8, BD16-22R11 and BD16-22R18). Our study suggested that fludioxonil exhibited excellent inhibition activity on mycelial growth of B. dothidea in vitro, the resistance risk of B. dothidea to fludioxonil should be low to moderate and fludioxonil would be a nice candidate in controlling HTC caused by B. dothidea.

Induced Expression of CYP51a and HK1 Genes Associated with Penconazole and Fludioxonil Resistance in the Potato Pathogen Fusarium oxysporum

Preventing antifungal resistance development and identifying pathogens with high, medium, and low risk of resistance development to a particular fungicide or fungicide class is crucial in the fight against phytopathogens. We characterized the sensitivity of potato wilt-associated Fusarium oxysporum isolates to fludioxonil and penconazole and assessed the effect of these fungicides on the expression of fungal sterol-14-α-demethylase (CYP51a) and histidine kinase (HK1) genes. Penconazole stunted the growth of F. oxysporum strains at all concentrations used. While all isolates were susceptible to this fungicide, concentrations of up to 1.0 μg/mL were insufficient to cause a 50% inhibition. At low concentrations (0.63 and 1.25 μg/mL), fludioxonil stimulated growth in F. oxysporum. With an increase in the concentration of fludioxonil, only one strain (F. oxysporum S95) exhibited moderate sensitivity to the fungicide. Interaction of F. oxysporum with penconazole and fludioxonil leads to respective elevated expressions of the CYP51a and HK1 genes, which upsurge with increasing concentration of the fungicides. The data obtained indicate that fludioxonil may no longer be suitable for potato protection and its continuous use could only lead to an increased resistance with time.

Comparative Transcriptomic Analysis of MAPK-Mediated Regulation of Pathogenicity, Stress Responses, and Development in Cytospora chrysosperma

Mitogen-activated protein kinase (MAPK) cascades are highly conserved signal transduction pathways that mediate cellular responses to various biotic and abiotic signals in plant-pathogenic fungi. Generally, there are three MAPKs in filamentous pathogenic fungi: Pmk1/Fus3/Kss1, Hog1, and Stl2. Our previous studies have shown that CcPmk1 is a core regulator of fungal pathogenicity in Cytospora chrysosperma, the causal agent of canker disease in a wide range of woody plants. Here, we identified and functionally characterized the other two MAPK genes (CcHog1 and CcSlt2) and then compared the transcriptional differences among these three MAPKs in C. chrysosperma. We found that the MAPKs shared convergent and distinct roles in fungal development, stress responses, and virulence. For example, CcHog1, CcSlt2, and CcPmk1 were all involved in conidiation and response to stresses, including hyperosmotic pressure, cell wall inhibition agents, and H₂O₂, but only CcPmk1 and CcSlt2 were required for hyphal growth and fungal pathogenicity. Transcriptomic analysis showed that numerous hyperosmosis- and cell wall-related genes significantly reduced their expression levels in ΔCcHog1 and ΔCcSlt2, respectively. Interestingly, RNA- and ribosome-related processes were significantly enriched in the upregulated genes of ΔCcSlt2, whereas they were significantly enriched in the downregulated genes of ΔCcPmk1. Moreover, two secondary metabolite gene clusters were significantly downregulated in ΔCcPmk1, ΔCcSlt2, and/or ΔCcHog1. Importantly, some virulence-associated genes were significantly downregulated in ΔCcPmk1 and/or ΔCcSlt2, such as candidate effector genes. Collectively, these results suggest that the similar and distinct phenotypes of each MAPK deletion mutant may result from the transcriptional regulation of a series of common or specific downstream genes, which provides a better understanding of the regulation network of MAPKs in C. chrysosperma.

Phenotypic and Target-Directed Screening Yields New Acaricidal Alternatives for the Control of Ticks

Rhipicephalus microplus, the "common cattle tick", is the most important ectoparasite in livestock worldwide due to the economic and health losses it produces. This tick is a vector for pathogens of several tick-borne diseases. In Latin American countries, damages reach approximately USD 500 million annually due to tick infections, as well as tick-borne diseases. Currently, resistant populations for every chemical group of acaricides have been reported, posing a serious problem for tick control. This study aims to find new alternatives for controlling resistant ticks with compounds derived from small synthetic organic molecules and natural origins. Using BME26 embryonic cells, we performed phenotypic screening of 44 natural extracts from 10 Mexican plants used in traditional medicine, and 33 compounds selected from our chemical collection. We found 10 extracts and 13 compounds that inhibited cell growth by 50% at 50 µg/mL and 100 µM, respectively; the dose-response profile of two of them was characterized, and these compounds were assayed in vitro against different life stages of Rhipicephalus microplus. We also performed a target-directed screening of the activity of triosephosphate isomerase, using 86 compounds selected from our chemical collection. In this collection, we found the most potent and selective inhibitor of tick triosephosphate isomerase reported until now. Two other compounds had a potent acaricidal effect in vitro using adults and larvae when compared with other acaricides such as ivermectin and Amitraz. Those compounds were also selective to the ticks compared with the cytotoxicity in mammalian cells like macrophages or bovine spermatozoids. They also had a good toxicological profile, resulting in promising acaricidal compounds for tick control in cattle raising.

Detection of Venturia inaequalis Isolates with Multiple Resistance in Greece

The excessive use of fungicides against Venturia inaequalis, the causal agent of apple scab, has led to the emergence of resistant populations to multiple fungicides over the years. In Greece, there is no available information on fungicide resistance, despite the fact that control failures have been reported on certain areas. An amount of 418 single-spore isolates were collected from three major apple production areas and tested for their sensitivity to eight commonly used fungicides from unrelated chemical groups. The isolates were tested on malt extract agar media enriched with the discriminatory dose of each fungicide using the point inoculation method. To define the discriminatory dose for assessing the levels of resistance, EC₅₀ values on both spore germination and mycelial growth assays were previously determined. Isolates exhibiting high resistance to trifloxystrobin (92% in total) and difenoconazole (3%); and moderate resistance to cyprodinil (75%), dodine (28%), difenoconazole (36%), boscalid (5%), and fludioxonil (7%) were found for the first time in Greece. A small percentage of the isolates were also found less sensitive to captan (8%) and dithianon (6%). Two isolates showed various levels of resistance to all eight fungicides. Despite the occurrence of strains with multiple resistances to many fungicides, we concluded that this practical resistance in the field arose mainly due to the poor control of apple scab with trifloxystrobin and difenoconazole.

The Transcription Factor CsAtf1 Negatively Regulates the Cytochrome P450 Gene CsCyp51G1 to Increase Fludioxonil Sensitivity in Colletotrichum siamense

Previous studies have shown that the high-osmolarity glycerol mitogen-activated protein kinase (HOG MAPK) signaling pathway and its downstream transcription factor CsAtf1 are involved in the regulation of fludioxonil sensitivity in C. siamense. However, the downstream target genes of CsAtf1 related to the fludioxonil stress response remain unclear. Here, we performed chromatin immunoprecipitation sequencing (ChIP-Seq) and high-throughput RNA-sequencing (RNA-Seq) to identify genome-wide potential CsAtf1 target genes. A total of 3809 significantly differentially expressed genes were predicted to be directly regulated by CsAtf1, including 24 cytochrome oxidase-related genes. Among them, a cytochrome P450-encoding gene, designated CsCyp51G1, was confirmed to be a target gene, and its transcriptional expression was negatively regulated by CsAtf1, as determined using an electrophoretic mobility shift assay (EMSA), a yeast one-hybrid (Y1H) assay, and quantitative real-time PCR (qRT-PCR). Moreover, the overexpression mutant CsCYP51G1 of C. siamense exhibited increased fludioxonil tolerance, and the CsCYP51G1 deletion mutant exhibited decreased fludioxonil resistance, which revealed that CsCyp51G1 is involved in fludioxonil sensitivity regulation in C. siamense. However, the cellular ergosterol content of the mutants was not consistent with the phenotype of fludioxonil sensitivity, which indicated that CsCyp51G1 regulates fludioxonil sensitivity by affecting factors other than the ergosterol level in C. siamense. In conclusion, our data indicate that the transcription factor CsAtf1 negatively regulates the cytochrome P450 gene CsCyp51G1 to increase fludioxonil sensitivity in C. siamense.

Exploring Potential Mechanisms of Fludioxonil Resistance in Fusarium oxysporum f. sp. melonis

Melon Fusarium wilt (MFW), which is caused by Fusarium oxysporum f. sp. melonis (FOM), is a soil-borne disease that commonly impacts melon cultivation worldwide. In the absence of any disease-resistant melon cultivars, the control of MFW relies heavily on the application of chemical fungicides. Fludioxonil, a phenylpyrrole fungicide, has been shown to have broad-spectrum activity against many crop pathogens. Sensitivity analysis experiments suggest that fludioxonil has a strong inhibitory effect on the mycelial growth of FOM isolates. Five fludioxonil-resistant FOM mutants were successfully generated by repeated exposure to fludioxonil under laboratory conditions. Although the mutants exhibited significantly reduced mycelial growth in the presence of the fungicide, there initially appeared to be little fitness cost, with no significant difference (p < 0.05) in the growth rates of the mutants and wild-type isolates. However, further investigation revealed that the sporulation of the fludioxonil-resistant mutants was affected, and mutants exhibited significantly (p < 0.05) reduced growth rates in response to KCl, NaCl, glucose, and mannitol. Meanwhile, molecular analysis of the mutants strongly suggested that the observed fludioxonil resistance was related to changes in the sequence and expression of the FoOs1 gene. In addition, the current study found no evidence of cross-resistance between fludioxonil and any of the other fungicides tested. These results indicate that fludioxonil has great potential as an alternative method of control for FOM in melon crops.

Baseline Sensitivity and Potential Resistance Mechanisms for Fusarium pseudograminearum to Fludioxonil

Fusarium crown rot (FCR), which is caused by Fusarium pseudograminearum, is one of the most important diseases affecting wheat production in the Huanghuai wheat-growing region of China. Although the phenylpyrrole fungicide fludioxonil is known to have a broad-spectrum activity against a wide range of plant pathogens, including F. pseudograminearum, it has not yet been registered for the control of FCR in China, and further research is needed to assess the biological characteristics and molecular mechanisms associated with fludioxonil resistance, and especially the potential for highly resistant isolates to emerge. The current study demonstrated that the baseline fludioxonil sensitivity of 61 F. pseudograminearum isolates collected from the Henan province of China during the summers of 2019 to 2021 conformed to a unimodal distribution with a mean effective concentration for 50% inhibition (EC₅₀) value of 0.021 ± 0.003 μg/ml, which indicated that none of the isolates exhibited natural resistance to fludioxonil. Nevertheless, four fludioxonil-resistant mutants were attained after repeated exposure to fludioxonil under laboratory conditions. All resistant mutants exhibited significantly lower growth rates on potato dextrose agar (PDA) and lower levels of sporulation and pathogenicity in wheat seedlings. In addition, the resistant mutants also exhibited less growth on PDA amended with either 0.5 M mannitol, 0.5 M glucose, 0.5 M MgCl₂, or 0.5 M NaCl, which indicated that they had greater sensitivity to osmotic stress. Molecular analysis of the proposed fludioxonil target protein FpOs1 indicated that the predicted sequences of the resistant mutants contained none of the characteristic amino acid changes previously associated with fludioxonil resistance in other species. Further investigation via quantitative real-time PCR analysis revealed that expression of the FpOs1 gene was significantly altered in the resistant mutants in both the absence and presence of fludioxonil. Meanwhile, plate assays found evidence of cross-resistance between fludioxonil and cyprodinil, as well as with the triazole fungicides tebuconazole and difenoconazole, but not with other commonly used fungicides including prochloraz, fluazinam, and carbendazim. Taken together, these results provide new insights into the mechanism and biological characteristics associated with fludioxonil resistance in F. pseudograminearum and indicate that fludioxonil could provide effective and sustained control of FCR during wheat production.

BEM2, a RHO GTPase Activating Protein That Regulates Morphogenesis in S. cerevisiae, Is a Downstream Effector of Fungicidal Action of Fludioxonil

Fludioxonil belongs to the phenylpyrrole group of fungicides with a broad antifungal spectrum that has been widely used in agricultural practices for the past thirty years. Although fludioxonil is known to exert its fungicidal action through group III hybrid histidine kinases, the downstream effector of its cytotoxicity is poorly understood. In this study, we utilized a S. cerevisiae model to decipher the cytotoxic effect of fludioxonil. Through genome wide transposon mutagenesis, we have identified Bem2, a Rho GTPase activating protein, which is involved in this process. The deletion of BEM2 resulted in fludioxonil resistance. Our results showed that both the GAP and morphogenesis checkpoint activities of Bem2 were important for this. We also provided the genetic evidence that the role of Bem2 in the cell wall integrity (CWI) pathway and cell cycle regulation could contribute to the fludioxonil resistance phenotype.

Cell Wall Integrity and Its Industrial Applications in Filamentous Fungi

Signal transduction pathways regulating cell wall integrity (CWI) in filamentous fungi have been studied taking into account findings in budding yeast, and much knowledge has been accumulated in recent years. Given that the cell wall is essential for viability in fungi, its architecture has been analyzed in relation to virulence, especially in filamentous fungal pathogens of plants and humans. Although research on CWI signaling in individual fungal species has progressed, an integrated understanding of CWI signaling in diverse fungi has not yet been achieved. For example, the variety of sensor proteins and their functional differences among different fungal species have been described, but the understanding of their general and species-specific biological functions is limited. Our long-term research interest is CWI signaling in filamentous fungi. Here, we outline CWI signaling in these fungi, from sensor proteins required for the recognition of environmental changes to the regulation of cell wall polysaccharide synthesis genes. We discuss the similarities and differences between the functions of CWI signaling factors in filamentous fungi and in budding yeast. We also describe the latest findings on industrial applications, including those derived from studies on CWI signaling: the development of antifungal agents and the development of highly productive strains of filamentous fungi with modified cell surface characteristics by controlling cell wall biogenesis.

Sensitivity of Colletotrichum nymphaeae to Six Fungicides and Characterization of Fludioxonil-Resistant Isolates in China

Colletotrichum nymphaeae is the dominant species causing anthracnose disease of peach in China. In this study, 140 isolates of C. nymphaeae were assessed for their sensitivity to six fungicides. It was found that C. nymphaeae was highly resistant to carbendazim, procymidone, and boscalid but sensitive to pyraclostrobin and prochloraz. For fludioxonil, the fungus exhibited differential sensitivities (i.e., approximately 14% of isolates were resistant to fludioxonil and the resistance was stable). Fludioxonil-resistant isolates had a mean EC₅₀ value of 2.2380 µg/ml, whereas the mean EC₅₀ value was 0.0194 µg/ml in fludioxonil-sensitive isolates. The mean EC₅₀ values of C. nymphaeae for pyraclostrobin and prochloraz were 0.0083 µg/ml and 0.002 µg/ml, respectively. No cross-resistance was observed between fungicides from different groups. Mycelial growth rate, control efficacy, and osmotic stress responses were significantly different (P < 0.05) between fludioxonil-sensitive (Flu^S) and -resistant (Flu^R) isolates, but no significant difference was observed (P > 0.05) in virulence and sporulation between Flu^S and Flu^R isolates. No mutation was detected in coding regions of the CnOs-1, Cal, Hk1, Hog1, TPI, and Mrr1 genes. Interestingly, with fludioxonil treatment, the expression of ABC transporter gene atrB was significantly overexpressed in some resistant isolates. However, overexpression of the atrB gene was not detected in one moderately and one highly resistant isolate, indicating that other unknown mechanisms may be involved. Current findings uncovered several effective chemicals and provided the foundation for designing management strategies to practically control peach anthracnose with the most effective demethylation inhibitor fungicides and quinone outside inhibitor fungicides.

The high osmolarity glycerol (HOG) pathway in fungi†

While fungi are widely occupying nature, many species are responsible for devastating mycosis in humans. Such niche diversity explains how quick fungal adaptation is necessary to endow the capacity of withstanding fluctuating environments and to cope with host-imposed conditions. Among all the molecular mechanisms evolved by fungi, the most studied one is the activation of the phosphorelay signalling pathways, of which the high osmolarity glycerol (HOG) pathway constitutes one of the key molecular apparatus underpinning fungal adaptation and virulence. In this review, we summarize the seminal knowledge of the HOG pathway with its more recent developments. We specifically described the HOG-mediated stress adaptation, with a particular focus on osmotic and oxidative stress, and point out some lags in our understanding of its involvement in the virulence of pathogenic species including, the medically important fungi Candida albicans, Cryptococcus neoformans, and Aspergillus fumigatus, compared to the model yeast Saccharomyces cerevisiae. Finally, we also highlighted some possible applications of the HOG pathway modifications to improve the fungal-based production of natural products in the industry.

The Role of Dimorphism Regulating Histidine Kinase (Drk1) in the Pathogenic Fungus Paracoccidioides brasiliensis Cell Wall

Dimorphic fungi of the Paracoccidioides genus are the causative agents of paracoccidioidomycosis (PCM), an endemic disease in Latin America with a high incidence in Brazil. This pathogen presents as infective mycelium at 25 °C in the soil, reverting to its pathogenic form when inhaled by the mammalian host (37 °C). Among these dimorphic fungal species, dimorphism regulating histidine kinase (Drk1) plays an essential role in the morphological transition. These kinases are present in bacteria and fungi but absent in mammalian cells and are important virulence and cellular survival regulators. Hence, the purpose of this study was to investigate the role of PbDrk1 in the cell wall modulation of P. brasiliensis. We observed that PbDrk1 participates in fungal resistance to different cell wall-disturbing agents by reducing viability after treatment with iDrk1. To verify the role of PbDRK1 in cell wall morphogenesis, qPCR results showed that samples previously exposed to iDrk1 presented higher expression levels of several genes related to cell wall modulation. One of them was FKS1, a β-glucan synthase that showed a 3.6-fold increase. Furthermore, confocal microscopy analysis and flow cytometry showed higher β-glucan exposure on the cell surface of P. brasiliensis after incubation with iDrk1. Accordingly, through phagocytosis assays, a significantly higher phagocytic index was observed in yeasts treated with iDrk1 than the control group, demonstrating the role of PbDrk1 in cell wall modulation, which then becomes a relevant target to be investigated. In parallel, the immune response profile showed increased levels of proinflammatory cytokines. Finally, our data strongly suggest that PbDrk1 modulates cell wall component expression, among which we can identify β-glucan. Understanding this signalling pathway may be of great value for identifying targets of antifungal molecular activity since HKs are not present in mammals.

Suspect and non-target screening of contaminants of emerging concern in streams in agricultural watersheds

Surface water runoff is an important source of water contamination affecting nearby rivers and streams. Many rural creeks are documented habitats for important aquatic species and the focus of restoration activities. In this study, we collected creek water samples in watersheds with a range of commercial-to-agricultural land use during rain events, and applied suspect and non-target screening with high-resolution mass spectrometry (HRMS) to characterize the occurrence of contaminants of emerging concern (CECs). In total, 58 CECs were identified, and 36 of them were confirmed and semi-quantified with reference standards. Pesticides were detected in all land use, including urban/commercial areas. Some pesticides were observed at concentrations of >10,000 ng/L demonstrating the strong contamination input during rain events. Five pesticides (azoxystrobin, fludioxonil, 4-hydroxy-chlorothalonil, imidacloprid, 2-methyl-4-chlorophenoxyacetic acid) were prioritized based on their risk quotients. HRMS chemical profiles demonstrated the wide range of chemical exposures in a given stream system and that compounds associated with specific land uses occur across land uses. Temporal trends suggested that some CECs remain present in creek water for months, resulting in chronic exposures across the life stages of aquatic species. These findings highlight the potential for contamination from agricultural runoff and the associated ecological risk to aquatic species. SYNOPSIS: Suspect and non-target screening revealed the chronic occurrence of emerging contaminants in streams in agricultural catchments during rain events.

Functional dissection of individual domains in group III histidine kinase Sshk1p from the phytopathogenic fungus Sclerotinia sclerotiorum

A conserved kinase domain and phosphoryl group receiver domain at the C-terminus and poly-HAMP domains at the N-terminus comprise the structural components of the group III HK which was considered as a potential antifungal target. However, the roles of individual domains in the function of group III HKs have rarely been dissected in fungi. In this study, we dissected the roles of individual domains to better understand the function of Sshk1p, a group III HK from Sclerotinia sclerotiorum. The results suggest that individual domains play different roles in the functionality of Sshk1p and are implicated in the regulation of mycelial growth, sclerotia formation, pathogenicity. And the mutants of each domain in Sshk1 showed significantly increased sensitivity to hyperosmotic stress. However, the mutants of each domain in Sshk1 showed high resistance to fludioxonil and dimethachlon which suggested that all nine domains of Sshk1p were indispensable for susceptibility to fludioxonil and dimethachlon. Moreover, deletion of each individual domain in Sshk1 cancelled intracellular glycerol accumulation and increased SsHog1p phosphorylation level triggered by NaCl and fludioxonil, suggesting that all the domains of Sshk1 were essential for Sshk1-mediated SsHog1p phosphorylation and subsequent polyol accumulation in response to fludioxonil and hyperosmotic stress.

Downregulation of the ypdA Gene Encoding an Intermediate of His-Asp Phosphorelay Signaling in Aspergillus nidulans Induces the Same Cellular Effects as the Phenylpyrrole Fungicide Fludioxonil

Many eukaryotic histidine-to-aspartate (His-Asp) phosphorelay systems consist of three types of signal transducers: a His-kinase (HK), a response regulator (RR), and a histidine-containing phosphotransfer intermediate (HPt). In general, the HPt acts as an intermediate between the HK and the RR and is indispensable for inducing appropriate responses to environmental stresses. In a previous study, we attempted but were unable to obtain deletion mutants of the ypdA gene in order to characterize its function in the filamentous fungus Aspergillus nidulans. In the present study, we constructed the CypdA strain in which ypdA expression is conditionally regulated by the A. nidulans alcA promoter. We constructed CypdA strains with RR gene disruptions (CypdA-sskAΔ, CypdA-srrAΔ, and CypdA-sskAΔsrrAΔ). Suppression of YpdA induced by ypdA downregulation activated the downstream HogA mitogen-activated protein kinase cascade. YpdA suppression caused severe growth defects and abnormal hyphae, with features such as enhanced septation, a decrease in number of nuclei, nuclear fragmentation, and hypertrophy of vacuoles, both regulated in an SskA-dependent manner. Fludioxonil treatment caused the same cellular responses as ypdA suppression. The growth-inhibitory effects of fludioxonil and the lethality caused by ypdA downregulation may be caused by the same or similar mechanisms and to be dependent on both the SskA and SrrA pathways.

Regulation of biotic interactions and responses to abiotic stresses by MAP kinase pathways in plant pathogenic fungi

Like other eukaryotes, fungi use MAP kinase (MAPK) pathways to mediate cellular changes responding to external stimuli. In the past two decades, three well-conserved MAP kinase pathways have been characterized in various plant pathogenic fungi for regulating responses and adaptations to a variety of biotic and abiotic stresses encountered during plant infection or survival in nature. The invasive growth (IG) pathway is homologous to the yeast pheromone response and filamentation pathways. In plant pathogens, the IG pathway often is essential for pathogenesis by regulating infection-related morphogenesis, such as appressorium formation, penetration, and invasive growth. The cell wall integrity (CWI) pathway also is important for plant infection although the infection processes it regulates vary among fungal pathogens. Besides its universal function in cell wall integrity, it often plays a minor role in responses to oxidative and cell wall stresses. Both the IG and CWI pathways are involved in regulating known virulence factors as well as effector genes during plant infection and mediating defenses against mycoviruses, bacteria, and other fungi. In contrast, the high osmolarity growth (HOG) pathway is dispensable for virulence in some fungi although it is essential for plant infection in others. It regulates osmoregulation in hyphae and is dispensable for appressorium turgor generation. The HOG pathway also plays a major role for responding to oxidative, heat, and other environmental stresses and is overstimulated by phenylpyrrole fungicides. Moreover, these three MAPK pathways crosstalk and coordinately regulate responses to various biotic and abiotic stresses. The IG and CWI pathways, particularly the latter, also are involved in responding to abiotic stresses to various degrees in different fungal pathogens, and the HOG pathway also plays a role in interactions with other microbes or fungi. Furthermore, some infection processes or stress responses are co-regulated by MAPK pathways with cAMP or Ca2+/CaM signaling. Overall, functions of individual MAP kinase pathways in pathogenesis and stress responses have been well characterized in a number of fungal pathogens, showing the conserved genetic elements with diverged functions, likely by rewiring transcriptional regulatory networks. In the near future, applications of genomics and proteomics approaches will likely lead to better understanding of crosstalk among the MAPKs and with other signaling pathways as well as roles of MAPKs in defense against other microbes (biotic interactions).

Distinct role of HAMP and HAMP-like linker domains in regulating the activity of Hik1p, a hybrid histidine kinase 3 from Magnaporthe oryzae

Nik1 orthologs or group III hybrid histidine kinases (HHK3) represent a unique cytoplasmic osmosensor that act upstream of HOG/p38 MAPK pathway in fungi. It is an important molecular target for developing new antifungal agents against human pathogens. HHK3 orthologs contain a linear array of alternative HAMP and HAMP-like linker domains (poly-HAMP) in the N-terminal region. HAMP domains are quite common in prokaryotic histidine kinases where it mostly functions as signal transducer mediating conformational changes in the kinase domains. In contrast, poly-HAMP in HHK3 acts as a sensor and signal transducer to regulate histidine kinase activity. However, the mechanistic detail of this is poorly understood. Interestingly, recent studies indicate that the poly-HAMP-mediated regulation of the kinase activity varies among the orthologs. Hik1 is an important HHK3 ortholog from fungus Magnaporthe oryzae. In this paper, we aimed to decipher the role HAMP and HAMP-like linker domains in regulating the activity of Hik1p. We show that Hik1p acts as a bona fide osmosensor and negatively regulates the downstream HOG/p38 MAPK pathway in Saccharomyces cerevisiae. Our data suggest a differential role of the HAMP domains in the functionality of Hik1p. Most interestingly, the deletion of individual domains in poly-HAMP resulted in distinct active forms of Hik1p and thereby indicating that the poly-HAMP domain, instead of acting as on-off switch, regulates the histidine kinase activity by transition through multiple conformational states.

A Radical Reimagining of Fungal Two-Component Regulatory Systems

Bacterial two-component regulatory systems (TCSs) mediate signal transduction by transferring phosphoryl groups between sensor kinase and response regulator proteins, sometimes using intermediary histidine-phosphotransferase (Hpt) domains to form multistep phosphorelays. Because (i) almost all known fungal sensor kinases exhibit a domain architecture characteristic of bacterial TCS phosphorelays, (ii) all known fungal Hpts are stand-alone proteins suited to shuttle between cytoplasm and nucleus, and (iii) the best-characterized fungal TCS is a canonical phosphorelay, it is widely assumed that most or all fungal TCSs function via phosphorelays. However, fungi generally encode more sensor kinases than Hpts or response regulators, leading to a disparity between putative phosphorelay inputs and outputs. The simplest resolution of this paradox is to hypothesize that most fungal sensor kinases do not participate in phosphorelays. Reimagining how fungal TCSs might function leads to multiple testable predictions.

Advances in Understanding Fungicide Resistance in Botrytis cinerea in China

Gray mold, caused by Botrytis cinerea, is a devastating disease that causes significant yield losses in various economically important plants. Fungicide application is one of the main strategies for management of gray mold; however, B. cinerea has developed resistance to various groups of fungicide. In China, benzimidazole-, dicarboximide-, and quinone outside inhibitor-resistant populations of B. cinerea have become dominant. Substitute mutations in fungicide target genes are responsible for resistance in B. cinerea. Based on known resistance mechanisms, molecular methods including loop-mediated isothermal amplification have been developed for rapid detection of resistant isolates of B. cinerea. Because B. cinerea is able to quickly develop resistance to various fungicides, various integrated strategies have been implemented in the last decade, including biological and agricultural practices, to manage fungicide resistance in B. cinerea.

Non-Target Site Mechanisms of Fungicide Resistance in Crop Pathogens: A Review

The rapid emergence of resistance in plant pathogens to the limited number of chemical classes of fungicides challenges sustainability and profitability of crop production worldwide. Understanding mechanisms underlying fungicide resistance facilitates monitoring of resistant populations at large-scale, and can guide and accelerate the development of novel fungicides. A majority of modern fungicides act to disrupt a biochemical function via binding a specific target protein in the pathway. While target-site based mechanisms such as alternation and overexpression of target genes have been commonly found to confer resistance across many fungal species, it is not uncommon to encounter resistant phenotypes without altered or overexpressed target sites. However, such non-target site mechanisms are relatively understudied, due in part to the complexity of the fungal genome network. This type of resistance can oftentimes be transient and noninheritable, further hindering research efforts. In this review, we focused on crop pathogens and summarized reported mechanisms of resistance that are otherwise related to target-sites, including increased activity of efflux pumps, metabolic circumvention, detoxification, standing genetic variations, regulation of stress response pathways, and single nucleotide polymorphisms (SNPs) or mutations. In addition, novel mechanisms of drug resistance recently characterized in human pathogens are reviewed in the context of nontarget-directed resistance.

Carbonyl Stress in Red Blood Cells and Hemoglobin

The paper overviews the peculiarities of carbonyl stress in nucleus-free mammal red blood cells (RBCs). Some functional features of RBCs make them exceptionally susceptible to reactive carbonyl compounds (RCC) from both blood plasma and the intracellular environment. In the first case, these compounds arise from the increased concentrations of glucose or ketone bodies in blood plasma, and in the second-from a misbalance in the glycolysis regulation. RBCs are normally exposed to RCC-methylglyoxal (MG), triglycerides-in blood plasma of diabetes patients. MG modifies lipoproteins and membrane proteins of RBCs and endothelial cells both on its own and with reactive oxygen species (ROS). Together, these phenomena may lead to arterial hypertension, atherosclerosis, hemolytic anemia, vascular occlusion, local ischemia, and hypercoagulation phenotype formation. ROS, reactive nitrogen species (RNS), and RCC might also damage hemoglobin (Hb), the most common protein in the RBC cytoplasm. It was Hb with which non-enzymatic glycation was first shown in living systems under physiological conditions. Glycated HbA1c is used as a very reliable and useful diagnostic marker. Studying the impacts of MG, ROS, and RNS on the physiological state of RBCs and Hb is of undisputed importance for basic and applied science.

Fluorodesulfurization of Thionobenzodioxoles with Silver(I) Fluoride

Difluorobenzodioxole is an important functional group found in both pharmaceuticals and agrochemicals. The late-stage introduction of this functional group is challenged by typical fluorination conditions of HF and strong oxidants. Here, we demonstrate that a range of difluorobenzodioxoles can be prepared from catechols in two steps through conversion into thionobenzodioxoles, followed by desulfurative fluorination with silver(I) fluoride. These mild reaction conditions are compatible with a variety of functional groups and enable access to a range of functionalized difluorobenzodioxoles.

Biological Characteristics and Molecular Mechanisms of Fludioxonil Resistance in Fusarium graminearum in China

Fusarium graminearum is the primary causal agent of Fusarium head blight (FHB) of wheat. The phenylpyrrole fungicide fludioxonil is not currently registered for the management of FHB in China. The current study assessed the fludioxonil sensitivity of a total of 53 F. graminearum isolates collected from the six most important wheat-growing provinces of China during 2018 and 2019. The baseline fludioxonil sensitivity distribution indicated that all of the isolates were sensitive, exhibiting a unimodal cure with a mean effective concentration for 50% inhibition value of 0.13 ± 0.12 μg/ml (standard deviation). Five fludioxonil-resistant mutants were subsequently induced by exposure to fludioxonil under laboratory conditions. Ten successive rounds of subculture in the absence of the selection pressure indicated that the mutation was stably inherited. However, the fludioxonil-resistant mutants were found to have reduced pathogenicity, higher glycerol accumulation, and higher osmotic sensitivity than the parental wild-type isolates, indicating that there was a fitness cost associated with fludioxonil resistance. In addition, the study also found a positive cross resistance between fludioxonil, procymidone, and iprodione, but not with other fungicides such as boscalid, carbendazim, tebuconazole, and fluazinam. Sequence analysis of four candidate target genes (FgOs1, FgOs2, FgOs4, and FgOs5) revealed that the HBXT2R mutant contained two point mutations that resulted in amino acid changes at K223T and K415R in its FgOs1 protein, and one point mutation at residue 520 of its FgOs5 protein that resulted in a premature stop codon. Similarly, the three other mutants contained point mutations that resulted in changes at the K192R, K293R, and K411R residues of the FgOs5 protein but none in the FgOs2 and FgOs4 genes. However, it is important to point out that the FgOs2 and FgOs4 expression of all the fludioxonil-resistant mutants was significantly (P < 0.05) downregulated compared with the sensitive isolates (except for the SQ1-2 isolate). It was also found that one of the resistant mutants did not have changes in any of the sequenced target genes, indicating that an alternative mechanism could also lead to fludioxonil resistance.

Pseudomonas synxantha 2-79 Transformed with Pyrrolnitrin Biosynthesis Genes Has Improved Biocontrol Activity Against Soilborne Pathogens of Wheat and Canola

A four-gene operon (prnABCD) from Pseudomonas protegens Pf-5 encoding the biosynthesis of the antibiotic pyrronitrin was introduced into P. synxantha (formerly P. fluorescens) 2-79, an aggressive root colonizer of both dryland and irrigated wheat roots that naturally produces the antibiotic phenazine-1-carboxylic acid and suppresses both take-all and Rhizoctonia root rot of wheat. Recombinant strains ZHW15 and ZHW25 produced both antibiotics and maintained population sizes in the rhizosphere of wheat that were comparable to those of strain 2-79. The recombinant strains inhibited in vitro the wheat pathogens Rhizoctonia solani anastomosis group 8 (AG-8) and AG-2-1, Gaeumannomyces graminis var. tritici, Sclerotinia sclerotiorum, Fusarium culmorum, and F. pseudograminearum significantly more than did strain 2-79. Both the wild-type and recombinant strains were equally inhibitory of Pythium ultimum. When applied as a seed treatment, the recombinant strains suppressed take-all, Rhizoctonia root rot of wheat, and Rhizoctonia root and stem rot of canola significantly better than did wild-type strain 2-79.

Aging, Alzheimer's Disease and Dysfunctional Glycolysis; Similar Effects of Too Much and Too Little

Aging and much related dysfunction can be delayed by decreased glycolysis, however dysfunctional glycolysis appears to play a causative role in Alzheimer's disease (AD). It is proposed here that this apparent contradiction can be reconciled by suggesting that both over-use and inhibition of the glycolytic enzyme triosephosphate isomerase can limit NADH generation and increase protein glycation. It is also suggested that excessive glycolysis in erythrocytes may provide a source of systemic methylglyoxal and glycated alpha-synuclein, both of which accelerate aging onset and neurodegeneration.

CgHog1 controls the adaptation to both sorbitol and fludioxonil in Colletotrichum gloeosporioides

The HOG (high-osmolarity glycerol) pathway is critical for the appropriate adaptation to adverse conditions. Here, we demonstrated that the deletion of CgHog1 resulted in enhanced sensitivity to osmotic stress and increased resistance to fludioxonil in the poplar anthracnose fungus Colletotrichum gloeosporioides. The accumulation of chitin around hyphal tips was obviously decreased in the ΔCgHog1 strain under sorbitol, whereas it strongly was increased in the response to fludioxonil compared with the wild type. To investigate the underlying mechanism of CgHog1-mediated adaption to osmotic stress and fludioxonil, transcriptomic profiles were performed in both the ΔCgHog1 strain and the wild type under the treatment of sorbitol and fludioxonil, respectively. Under sorbitol, genes associated with glycolysis, lipid metabolism, and accumulation of soluble sugars and amino acids were differentially expressed; under fludioxonil, vesicle trafficking-related genes were highly downregulated in the ΔCgHog1 strain, which was consistent with abnormal vacuoles distribution and morphology of hyphae, indicating that the growth defect caused by fludioxonil may be associated with disruption of endocytosis. Taken together, we elucidated the adaptation mechanisms of how CgHog1 regulates appropriate response to sorbitol and fludioxonil via different metabolism pathways. These findings extend our insights into the HOG pathway in fungi.