FcStuA from Fusarium culmorum controls wheat foot and root rot in a toxin dispensable manner

CFHTF2 Is Needed for Vegetative Growth, Conidial Morphogenesis and the Osmotic Stress Response in the Tea Plant Anthracnose (Colletotrichum fructicola)

Tea is an important cash crop worldwide, and its nutritional value has led to its high economic benefits. Tea anthracnose is a common disease of tea plants that seriously affects food safety and yield and has a far-reaching impact on the sustainable development of the tea industry. In this study, phenotypic analysis and pathogenicity analysis were performed on knockout and complement strains of HTF2-the transcriptional regulator of tea anthracnose homeobox-and the pathogenic mechanism of these strains was explored via RNA-seq. The MoHox1 gene sequence of the rice blast fungus was indexed, and the anthracnose genome was searched for CfHTF2. Evolutionary analysis recently reported the affinity of HTF2 for C. fructicola and C. higginsianum. The loss of CfHTF2 slowed the vegetative growth and spore-producing capacity of C. fructicola and weakened its resistance and pathogenesis to adverse conditions. The transcriptome sequencing of wild-type N425 and CfHTF2 deletion mutants was performed, and a total of 3144 differentially expressed genes (DEGs) were obtained, 1594 of which were upregulated and 1550 of which were downregulated. GO and KEGG enrichment analyses of DEGs mainly focused on signaling pathways such as the biosynthesis of secondary metabolites. In conclusion, this study lays a foundation for further study of the pathogenic mechanism of tea anthracnose and provides a molecular basis for the analysis of the pathogenic molecular mechanism of CfHTF2.

PdStuA Is a Key Transcription Factor Controlling Sporulation, Hydrophobicity, and Stress Tolerance in Penicillium digitatum

Penicillium digitatum has become one of the main pathogens in citrus due to its high spore production and easy spread. In this study, the function of the APSES transcription factor StuA in P. digitatum was characterized, and the results indicated that it was involved in conidium and conidiophore development. No conidiophores were observed in the mycelium of the ∆PdStuA mutant that had grown for two days, while an abnormal conidiophore was found after another two days of incubation, and only small thin phialides as well as a very small number of spores were formed at the top of the hyphae. Moreover, it was observed that the ∆PdStuA mutant showed various defects, such as reduced hydrophobicity and decreased tolerance to cell wall inhibitors and H2O2. Compared to the original P. digitatum, the colony diameter of the ∆PdStuA mutant was not significantly affected, but the growth of aerial hyphae was obviously induced. In in vivo experiments, the spore production of the ∆PdStuA mutant grown on citrus fruit was remarkably decreased; however, there was no significant difference in the lesion diameter between the mutant and original strain. It could be inferred that less spore production might result in reduced spread in citrus, thereby reducing the green mold infection in citrus fruit during storage. This study provided a gene, PdStuA, which played key role in the sporulation of P. digitatum, and the results might provide a reference for the molecular mechanisms of sporulation in P. digitatum.

Investigating the impact of fungicides and mungbean genotypes on the management of pod rot disease caused by Fusarium equiseti and Fusarium chlamydosporum

INTRODUCTION

Mungbean is a vital pulse crop in India that can thrive in dry-land conditions and is grown in three seasons, with the added benefit of being used as green manure due to its ability to fix atmospheric nitrogen. Recently, pod rot disease has emerged as a serious threat to mungbean cultivation in India.

METHODS

In this study, morpho-molecular identification of associated pathogens and the bio-efficacy of systemic and non-systemic fungicides as well as genotype screening was performed during the years 2019 and 2020. The pathogens associated with this disease were confirmed on the basis of morphological and molecular characterization. For the molecular characterization, the translation elongation factor 1-alpha (tef-1) gene sequences were amplified by using primers (EF1 and EF2).

RESULTS

Under in vitro conditions, trifloxystrobin + tebuconazole 75% WG was found to be the most effective against Fusarium equiseti (ED50 2.39 μg ml-1) and Fusarium chlamydosporum (ED50 4.23 μg ml-1) causal agents of pod rot of mungbean. Under field conditions, three applications of trifloxystrobin + tebuconazole 75% WG at 0.07% as a foliar application at fortnightly intervals starting from the last week of July proved to be the most effective against pod rot disease on mungbean cultivars, i.e., ML 2056 and SML 668. To identify the potential resistance sources, 75 interspecific derivative and mutant lines of mungbean were screened for disease reaction to pod rot under natural epiphytotic conditions for the years 2019 and 2020. Genotypic differences were observed for resistance to pod rot disease. The study revealed that among the tested genotypes, ML 2524 exhibited resistance to pod rot disease, with a disease incidence of 15.62% and disease severity of 7.69%. In addition, 41 other genotypes were found to be moderately resistant (MR) to the disease.

CONCLUSION

Altogether, the identified management options will offer an immediate solution to manage this disease under recent outbreak conditions and pave a path for futuristic disease management using identified resistant sources in breeding programs.

Exploration of Novel Scaffolds Targeting Cytochrome b of Pyricularia oryzae

The fulfilment of the European "Farm to Fork" strategy requires a drastic reduction in the use of "at risk" synthetic pesticides; this exposes vulnerable agricultural sectors-among which is the European risiculture-to the lack of efficient means for the management of devastating diseases, thus endangering food security. Therefore, novel scaffolds need to be identified for the synthesis of new and more environmentally friendly fungicides. In the present work, we employed our previously developed 3D model of P. oryzae cytochrome bc1 (cyt bc1) complex to perform a high-throughput virtual screening of two commercially available compound libraries. Three chemotypes were selected, from which a small collection of differently substituted analogues was designed and synthesized. The compounds were tested as inhibitors of the cyt bc1 enzyme function and the mycelium growth of both strobilurin-sensitive (WT) and -resistant (RES) P. oryzae strains. This pipeline has permitted the identification of thirteen compounds active against the RES cyt bc1 and five compounds that inhibited the WT cyt bc1 function while inhibiting the fungal mycelia only minimally. Serendipitously, among the studied compounds we identified a new chemotype that is able to efficiently inhibit the mycelium growth of WT and RES strains by ca. 60%, without inhibiting the cyt bc1 enzymatic function, suggesting a different mechanism of action.

Thermal Shift Assay as a Tool to Evaluate the Release of Breakdown Peptides from Cowpea β-Vignin during Seed Germination

The present work aimed to characterize the molecular relationships between structure and function of the seed storage protein β-vignin, the vicilin storage protein of cowpea (Vigna unguiculata, l. Walp) seeds. The molecular characterization of β-vignin was carried out firstly by assessing its thermal stability, under different conditions of pH and ionic strength, by thermal shift assay (TSA) using SYPRO Orange fluorescent dye. Secondly, its aggregation propensity was evaluated using a combination of chromatographic and electrophoretic techniques. Two forms of β-vignin were considered: the native form purified from mature quiescent seeds, and a stable breakdown intermediate of 27 kDa produced while seeds germinate. TSA is a useful tool for determining and following over time the structural changes that occur to the protein during germination. The main result was the molecular characterization of the 27 kDa intermediate breakdown polypeptide, which, to the best of our knowledge, has never been described before. β-vignin seems to retain its trimeric conformation despite the evident degradation of its polypeptides.

NOXA Is Important for Verticillium dahliae's Penetration Ability and Virulence

NADPH oxidase (Nox) genes are responsible for Reactive Oxygen Species (ROS) production in living organisms such as plants, animals, and fungi, where ROS exert different functions. ROS are critical for sexual development and cellular differentiation in fungi. In previous publications, two genes encoding thioredoxin and NADH-ubiquinone oxidoreductase involved in maintaining ROS balance were shown to be remarkably induced in a highly versus a weakly aggressive Verticillium dahliae isolate. This suggested a role of these genes in the virulence of this pathogen. NoxA (NADPH oxidase A) was identified in the V. dahliae genome. We compared in vitro expression of NoxA in highly and weakly aggressive isolates of V. dahliae after elicitation with extracts from different potato tissues. NoxA expression was induced more in the weakly than highly aggressive isolate in response to leaf and stem extracts. After inoculation of potato detached leaves with these two V. dahliae isolates, NoxA was drastically up-regulated in the highly versus the weakly aggressive isolate. We generated single gene disruption mutants for NoxA genes. noxa mutants had significantly reduced virulence, indicating important roles in V. dahliae pathogenesis on the potato. This is consistent with a significant reduction of cellophane penetration ability of the mutants compared to the wild type. However, the cell wall integrity was not impaired in the noxa mutants when compared with the wild type. The resistance of noxa mutants to oxidative stress were also similar to the wild type. Complementation of noxa mutants with a full length NoxA clones restored penetration and pathogenic ability of the fungus. Our data showed that NoxA is essential for both penetration peg formation and virulence in V. dahliae.

Transcription factor control of virulence in phytopathogenic fungi

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

Nuclear status and leaf tumor formation in the Ustilago maydis-maize pathosystem

Ustilago maydis is a biotrophic fungus causing smut disease in corn. The infectious forms are dikaryotic hyphae. Here we analyze mutants lacking the nlt1 transcription factor and investigate why these mutants are unable to induce leaf tumors. The study involved reverse genetics, complementation, epistasis analysis, microscopy, gene expression analysis by quantitative reverse transcriptase PCR and virulence assays. We show that nlt1 mutants colonize maize leaves efficiently but fail to undergo karyogamy and are attenuated in late proliferation. Nlt1 activates transcription of ros1, a transcription factor controlling karyogamy, and represses see1, an effector previously shown to contribute to leaf tumor induction. In mononuclate solopathogenic strains, nlt1 mutants cause attenuated leaf tumor formation. In actively dividing maize organs, nlt1 mutants undergo karyogamy and induce tumor formation. Sporisorium reilianum, a smut fungus unable to induce leaf tumors, possesses an ortholog of nlt1 that controls the fusion of dikaryotic nuclei late in infection during cob colonization. Our results have established a regulatory connection between nlt1, ros1 and see1 and suggest the existence of two stages contributing to leaf tumor formation, one before nuclear fusion and involving nlt1 and one after karyogamy that is nlt1 independent.

StuA-Regulated Processes in the Dermatophyte Trichophyton rubrum: Transcription Profile, Cell-Cell Adhesion, and Immunomodulation

Fungal infections represent a significant concern worldwide, contributing to human morbidity and mortality. Dermatophyte infections are among the most significant mycoses, and Trichophyton rubrum appears to be the principal causative agent. Thus, an understanding of its pathophysiology is urgently required. Several lines of evidence have demonstrated that the APSES family of transcription factors (Asm1p, Phd1p, Sok2p, Efg1p, and StuA) is an important point of vulnerability in fungal pathogens and a potential therapeutic target. These transcription factors are unique to fungi, contributing to cell differentiation and adaptation to environmental cues and virulence. It has recently been demonstrated that StuA plays a pleiotropic role in dermatophyte pathophysiology. It was suggested that it functions as a mediator of crosstalk between different pathways that ultimately contribute to adaptive responses and fungal-host interactions. The complex regulation of StuA and its interaction pathways are yet to be unveiled. Thus, this study aimed to gain a deeper understanding of StuA-regulated processes in T. rubrum by assessing global gene expression following growth on keratin or glucose sources. The data showed the involvement of StuA in biological processes related to central carbon metabolism and glycerol catabolism, reactive oxygen species metabolism, and cell wall construction. Changes in carbohydrate metabolism may be responsible for the significant alteration in cell wall pattern and consequently in cell-cell interaction and adhesion. Loss of StuA led to impaired biofilm production and promoted proinflammatory cytokine secretion in a human keratinocyte cell line. We also observed the StuA-dependent regulation of catalase genes. Altogether, these data demonstrate the multitude of regulatory targets of StuA with a critical role in central metabolism that may ultimately trigger a cascade of secondary effects with substantial impact on fungal physiology and virulence traits.

Draft genome sequences of two Streptomyces albidoflavus strains DEF1AK and DEF147AK with plant growth-promoting and biocontrol potential

Purpose

Bacteria belonging to the Streptomyces genus can be exploited in environmentally friendly approaches to food safety. Genome information can help to characterize bioactive strains opening the possibility to decipher their mechanisms of action.

Methods

The biocontrol and plant growth-promoting activity of two Streptomyces spp. strains, DEF1AK and DEF147AK, were assessed in vitro and in planta. The genome sequences were determined using the Illumina NextSeq sequencing system and were assembled using EvoCAT (Evogene Clustering and Assembly Toolbox).

Result

Streptomyces spp. DEF1AK and DEF147AK were able to improve seed germination and early plant development of maize, wheat, and tomato and inhibited the mycelium growth of diverse fungal plant pathogens in vitro. The genome sequence analysis identified both strains as S. albidoflavus (99% sequence identity). Both genomes were of 7.1-Mb length with an average GC content of 73.45%. AntiSMASH and MIBiG analyses revealed strain-specific sets of secondary metabolite gene clusters in the two strains as well as differences in the number and type of duplicated genes.

Conclusion

The combination of the biological activity and genomic data is the basis for in-depth studies aimed at the identification of secondary metabolites involved in plant growth-promoting and biocontrol activity of Streptomyces spp. The comparison of unique genomic features of the two strains will help to explain their diverse biocontrol and plant growth-promoting activities and warrant targeted functional genomics approaches to verify their mechanisms of action.

Searching molecular determinants of sensitivity differences towards four demethylase inhibitors in Fusarium graminearum field strains

Demethylase inhibitors (DMIs) also referred to as azoles or triazoles are currently the main fungicides used for controlling Fusarium diseases and associated toxins in cereals. DMIs also represent an important class of fungicides used in the medical domain. The level of sensitivity of a set of F. graminearum strains (n = 23), collected over the period 1994-2010 in Luxembourg, Germany, Canada, USA, Italy and Belgium against three DMIs (cyproconazole, propiconazole, tebuconazole) used in agriculture and one DMI used in medicine (tioconazole) was assessed using a microplate test. Median molar EC₅₀ values varied 113-fold among DMIs and on average 11-fold within DMIs with cyproconazole and tebuconazole being the least and the most effective ones, respectively. The EC₅₀ values of the two DMIs registered for use against Fusarium species on cereals (propiconazole and tebuconazole) were significantly correlated (r = 0.597**), while no evidence for cross-resistance was obtained for other fungicide combinations. Haplotypes for CYP51A and CYP51C were defined based on snps determining amino acid variations in the two genes. EC₅₀ values of strains with the CYP51A haplotype A0 and the CYP51C haplotype D1 varied greatly for the agricultural DMIs tebuconazole, propiconazole and cyproconazole, but not for the medical DMI tioconazole. None of the mutations and snps that were previously reported to be associated with resistance towards propiconazole was unambiguously related with resistance to tioconazole, because the mutations and snps were found in strains with low as well as with high EC₅₀ values. Our results show that (1) DMI sensitivity of F. graminearum mycelium has been largely stable between 1994 and 2010, (2) effects of snps on sensitivity towards one DMI detected in one set of strains cannot be extrapolated to other DMIs and sets of strains and (3) F. graminearum strains responded differently to DMIs used in agriculture and to a representative of a medical DMI with no evidence for cross-resistance.

Selection of an Endophytic Streptomyces sp. Strain DEF09 From Wheat Roots as a Biocontrol Agent Against Fusarium graminearum

Selection of biological control agents (BCA) profits from an integrated study of the tripartite interactions occurring among the BCA, the plant and the pathogen. The environment plays a crucial role in the efficacy of BCA, therefore, the selection process shall utmost mimic naturally occurring conditions. To identify effective biocontrol strains against Fusarium graminearum, the major cause of Fusarium head blight (FHB) in wheat and deoxynivalenol (DON) accumulation in grains, a workflow consisting of in vitro and in vivo assays was set up. Twenty-one Streptomyces strains, 16 of which were endophytes of different plants, were analyzed. In vitro and in vivo tests characterized their plant growth promoting (PGP) traits. Biocontrol activity against F. graminearum was firstly assessed with a dual culture assay. An in vivo germination blotter assay measured Fusarium foot rot and root rot symptoms (FFR-FRR) reduction as well as growth parameters of the plant treated with the Streptomyces strains. A selected subset of Streptomyces spp. strains was then assessed in a growth chamber measuring FFR symptoms and growth parameters of the wheat plant. The approach led to the identification of an effective Streptomyces sp. strain, DEF09, able to inhibit FHB on wheat in controlled conditions by blocking the spread of the pathogen at the infection site. The results were further confirmed in field conditions on both bread and durum wheat, where DEF09 decreased disease severity up to 60%. This work confirms that FRR and FFR pathosystems can be used to identify BCA effective against FHB.

Evaluation of in-vitro methods to select effective streptomycetes against toxigenic fusaria

Biocontrol microorganisms are emerging as an effective alternative to pesticides. Ideally, biocontrol agents (BCAs) for the control of fungal plant pathogens should be selected by an in vitro method that is high-throughput and is predictive of in planta efficacy, possibly considering environmental factors, and the natural diversity of the pathogen. The purpose of our study was (1) to assess the effects of Fusarium strain diversity (N = 5) and culture media (N = 6) on the identification of biological control activity of Streptomyces strains (N = 20) against Fusarium pathogens of wheat in vitro and (2) to verify the ability of our in vitro screening methods to simulate the activity in planta. Our results indicate that culture media, Fusarium strain diversity, and their interactions affect the results of an in vitro selection by dual culture assay. The results obtained on the wheat-based culture media resulted in the highest correlation score (r = 0.5) with the in planta root rot (RR) inhibition, suggesting that this in vitro method was the best predictor of in planta performance of streptomycetes against Fusarium RR of wheat assessed as extension of the necrosis on the root. Contrarily, none of the in vitro plate assays using the media tested could appropriately predict the activity of the streptomycetes against Fusarium foot rot symptoms estimated as the necrosis at the crown level. Considering overall data of correlation, the activity in planta cannot be effectively predicted by dual culture plate studies, therefore improved in vitro methods are needed to better mimic the activity of biocontrol strains in natural conditions. This work contributes to setting up laboratory standards for preliminary screening assays of Streptomyces BCAs against fungal pathogens.

Characterization of the APSES-family transcriptional regulators of Histoplasma capsulatum

The fungal APSES protein family of transcription factors is characterized by a conserved DNA-binding motif facilitating regulation of gene expression in fungal development and other biological processes. However, their functions in the thermally dimorphic fungal pathogen Histoplasma capsulatum are unexplored. Histoplasma capsulatum switches between avirulent hyphae in the environment and virulent yeasts in mammalian hosts. We identified five APSES domain-containing proteins in H. capsulatum homologous to Swi6, Mbp1, Stu1 and Xbp1 proteins and one protein found in related Ascomycetes (APSES-family protein 1; Afp1). Through transcriptional analyses and RNA interference-based functional tests we explored their roles in fungal biology and virulence. Mbp1 serves an essential role and Swi6 contributes to full yeast cell growth. Stu1 is primarily expressed in mycelia and is necessary for aerial hyphae development and conidiation. Xbp1 is the only factor enriched specifically in yeast cells. The APSES proteins do not regulate conversion of conidia into yeast and hyphal morphologies. The APSES-family transcription factors are not individually required for H. capsulatum infection of cultured macrophages or murine infection, nor do any contribute significantly to resistance to cellular stresses including cell wall perturbation, osmotic stress, oxidative stress or antifungal treatment. Further studies of the downstream genes regulated by the individual APSES factors will be helpful in revealing their functional roles in H. capsulatum biology.

Cereal Root Interactions with Soilborne Pathogens—From Trait to Gene and Back

Realizing the yield potential of crop plants in the presence of shifting pathogen populations, soil quality, rainfall, and other agro-environmental variables remains a challenge for growers and breeders worldwide. In this review, we discuss current approaches for combatting the soilborne phytopathogenic nematodes, Pratylenchus and Heterodera of wheat and barley, and Meloidogyne graminicola Golden and Birchfield, 1965 of rice. The necrotrophic fungal pathogens, Rhizoctonia solani Kühn 1858 AG-8 and Fusarium spp. of wheat and barley, also are discussed. These pathogens constitute major causes of yield loss in small-grain cereals of the Pacific Northwest, USA and throughout the world. Current topics include new sources of genetic resistance, molecular leads from whole genome sequencing and genome-wide patterns of hosts, nematode or fungal gene expression during root-pathogen interactions, host-induced gene silencing, and building a molecular toolbox of genes and regulatory sequences for deployment of resistance genes. In conclusion, improvement of wheat, barley, and rice will require multiple approaches.

Development of a Highly Sensitive FcMito qPCR Assay for the Quantification of the Toxigenic Fungal Plant Pathogen Fusarium culmorum

Fusarium culmorum is a ubiquitous, soil-borne fungus (ascomycete) causing foot and root rot and Fusarium head blight on cereals. It is responsible for yield and quality losses as well as grain contamination with mycotoxins, which are a potential health hazard. An extremely sensitive mitochondrial-based qPCR assay (FcMito qPCR) for quantification of F. culmorum was developed in this study. To provide specificity, the FcMito assay was successfully validated against 85 F. culmorum strains and 53 isolates of 30 other fungal species. The assay efficiency and sensitivity were evaluated against different F. culmorum strains with various amounts of pure fungal DNA and in the presence of background wheat DNA. The results demonstrated the high efficiency of the assay (97.2⁻106.0%, R²-values > 0.99). It was also shown that, in the presence of background DNA, 0.01 pg of fungal template could be reliably quantified. The FcMito assay was used to quantify F. culmorum DNA using 108 grain samples with different trichothecene levels. A significant positive correlation was found between fungal DNA quantity and the total trichothecene content. The obtained results showed that the sensitivity of the FcMito assay was much higher than the nuclear-based qPCR assay for F. culmorum.

FcRav2, a gene with a ROGDI domain involved in Fusarium head blight and crown rot on durum wheat caused by Fusarium culmorum

Fusarium culmorum is a soil-borne fungal pathogen which causes foot and root rot and Fusarium head blight on small-grain cereals, in particular wheat and barley. It causes significant yield and quality losses and results in the contamination of kernels with type B trichothecene mycotoxins. Our knowledge of the pathogenicity factors of this fungus is still limited. A transposon tagging approach based on the mimp1/impala double-component system has allowed us to select a mutant altered in multiple metabolic and morphological processes, trichothecene production and virulence. The flanking regions of mimp1 were used to seek homologies in the F. culmorum genome, and revealed that mimp1 had reinserted within the last exon of a gene encoding a hypothetical protein of 318 amino acids which contains a ROGDI-like leucine zipper domain, supposedly playing a protein-protein interaction or regulatory role. By functional complementation and bioinformatic analysis, we characterized the gene as the yeast Rav2 homologue, confirming the high level of divergence in multicellular fungi. Deletion of FcRav2 or its orthologous gene in F. graminearum highlighted its ability to influence a number of functions, including virulence, trichothecene type B biosynthesis, resistance to azoles and resistance to osmotic and oxidative stress. Our results indicate that the FcRav2 protein (and possibly the RAVE complex as a whole) may become a suitable target for new antifungal drug development or the plant-mediated resistance response in filamentous fungi of agricultural interest.

Titania (TiO2) nanoparticles enhance the performance of growth-promoting rhizobacteria

A novel use of nanotitania (TNs) as agents in the nanointerface interaction between plants and colonization of growth promoting rhizobacteria (PGPR) is presented. The effectiveness of PGPRs is related to the effectiveness of the technology used for their formulation. TNs produced by the Captigel patented SolGel approach, characterized by the transmission and scanning electron microscopy were used for formulation of the harsh environment PGPR strains. Changes in the biomass of wheat seedlings and in the density of single and double inoculants with and without TNs were monitored during two weeks of stress induced by drought salt and by the pathogen Fusarium culmorum. We show that double inoculants with TNs can attach stably to plant roots. Regression analysis indicates that there is a positive interaction between seedling biomass and TN-treated second inoculant colonization. We conclude that TN treatment provides an effectual platform for PGPR rational application via design of root microbial community. Our studies illustrate the importance of considering natural soil nanoparticles for PGPR application and thereby may explain the generally observed inconsistent behavior of PGPRs in the field. These new advancements importantly contribute towards solving food security issues in changing climates. The model systems established here provide a basis for new PGPR nanomaterials research.

Natural Phenolic Inhibitors of Trichothecene Biosynthesis by the Wheat Fungal Pathogen Fusarium culmorum: A Computational Insight into the Structure-Activity Relationship

A model of the trichodiene synthase (TRI5) of the wheat fungal pathogen and type-B trichothecene producer Fusarium culmorum was developed based on homology modelling with the crystallized protein of F. sporotrichioides. Eight phenolic molecules, namely ferulic acid 1, apocynin 2, propyl gallate 3, eugenol 4, Me-dehydrozingerone 5, eugenol dimer 6, magnolol 7, and ellagic acid 8, were selected for their ability to inhibit trichothecene production and/or fungal vegetative growth in F. culmorum. The chemical structures of phenols were constructed and partially optimised based on Molecular Mechanics (MM) studies and energy minimisation by Density Functional Theory (DFT). Docking analysis of the phenolic molecules was run on the 3D model of F. culmorum TRI5. Experimental biological activity, molecular descriptors and interacting-structures obtained from computational analysis were compared. Besides the catalytic domain, three privileged sites in the interaction with the inhibitory molecules were identified on the protein surface. The TRI5-ligand interactions highlighted in this study represent a powerful tool to the identification of new Fusarium-targeted molecules with potential as trichothecene inhibitors.

The transcriptional regulators SteA and StuA contribute to keratin degradation and sexual reproduction of the dermatophyte Arthroderma benhamiae

Most superficial fungal infections are caused by dermatophytes, a specialized group of filamentous fungi which exclusively infect keratinized host structures such as hair, skin and nails. Since little is known about the molecular basis of pathogenicity and sexual reproduction in dermatophytes, here we functionally addressed two central transcriptional regulators, SteA and StuA. In the zoophilic species Arthroderma benhamiae a strategy for targeted genetic manipulation was recently established, and moreover, the species is teleomorphic and thus allows performing assays based on mating. By comparative genome analysis homologs of the developmental regulators SteA and StuA were identified in A. benhamiae. Knock-out mutants of the corresponding genes as well as complemented strains were generated and phenotypically characterized. In contrast to A. benhamiae wild type and complemented strains, both mutants failed to produce sexual reproductive structures in mating experiments. Analysis of growth on keratin substrates indicated that loss of steA resulted in the inability of ΔsteA mutants to produce hair perforation organs, but did not affect mycelia formation during growth on hair and nails. By contrast, ΔstuA mutants displayed a severe growth defect on these substrates, but were still able to produce hair perforations. Hence, formation of hair perforation organs and fungal growth on hair per se are differentially regulated processes. Our findings on the major role of SteA and StuA during sexual development and keratin degradation in A. benhamiae provide insights into their role in dermatophytes and further enhance our knowledge of basic biology and pathogenicity of these fungi.

The APSES transcription factor LmStuA is required for sporulation, pathogenic development and effector gene expression in Leptosphaeria maculans

Leptosphaeria maculans causes stem canker of oilseed rape (Brassica napus). The APSES transcription factor StuA is a key developmental regulator of fungi, involved in morphogenesis, conidia production and also more recently described as required for secondary metabolite production and for effector gene expression in phytopathogenic fungi. We investigated the involvement of the orthologue of StuA in L. maculans, LmStuA, in morphogenesis, pathogenicity and effector gene expression. LmStuA is induced during mycelial growth and at 14 days after infection, corresponding to the development of pycnidia on oilseed rape leaves, consistent with the function of StuA described so far. We set up the functional characterization of LmStuA using an RNA interference approach. Silenced LmStuA transformants showed typical phenotypic defects of StuA mutants with altered growth in axenic culture and impaired conidia production and perithecia formation. Silencing of LmStuA abolished the pathogenicity of L. maculans on oilseed rape leaves and also resulted in a drastic decrease in expression of at least three effector genes during in planta infection, suggesting either that LmStuA regulates, directly or indirectly, the expression of several effector genes in L. maculans or that the infection stage in which effectors are expressed is not reached when LmStuA expression is silenced.

Conserved and Distinct Functions of the “Stunted” (StuA)-Homolog Ust1 During Cell Differentiation in the Corn Smut Fungus Ustilago maydis

Ustilago maydis, causal agent of corn smut, can proliferate saprobically in a yeast form but its infectious filamentous form is an obligate parasite. Previously, we showed that Ust1, the first APSES (Asm1p, Phd1p, Sok2p, Efg1p, and StuAp) transcription factor functionally characterized in the phylum Basidiomycota, controlled morphogenesis and virulence in this species. Here, we further analyzed Ust1 function using multiple experimental approaches and determined that i) Ust1 activity was able to partially reverse stuA− conidiophore defects in Aspergillus nidulans; ii) in U. maydis, normal development and virulence were strongly dependent on precise induction or repression of Ust1 activity; iii) consistent with its role as a transcription factor regulating multiple processes, Ust1 accumulated in the nucleus at various stages of the life cycle; iv) however, it was undetectable at specific stages of pathogenic growth, indicating that Ust1 repression is part of normal development in planta; v) StuA response elements upstream of the ust1 open reading frame exhibited affinity for U. maydis DNA-binding proteins; vi) however, loss of regulated ust1 transcription had minor phenotypic effects; and vii) Ust1 was subject to post-translational phosphorylation but is not a target of cAMP signaling. Thus, the broad functional conservation between Ust1 and Ascomycota APSES proteins does not extend to the mechanisms regulating their activity.

The APSES family proteins in fungi: Characterizations, evolution and functions

The APSES protein family belongs to transcriptional factors of the basic helix-loop-helix (bHLH) class, the originally described members (APSES: Asm1p, Phd1p, Sok2p, Efg1p and StuAp) are used to designate this group of proteins, and they have been identified as key regulators of fungal development and other biological processes. APSES proteins share a highly conserved DNA-binding domain (APSES domain) of about 100 amino acids, whose central domain is predicted to form a typical bHLH structure. Besides APSES domain, several APSES proteins also contain additional domains, such as KilA-N and ankyrin repeats. In recent years, an increasing number of APSES proteins have been identified from diverse fungi, and they involve in numerous biological processes, such as sporulation, cellular differentiation, mycelial growth, secondary metabolism and virulence. Most fungi, including Aspergillus fumigatus, Aspergillus nidulans, Candida albicans, Fusarium graminearum, and Neurospora crassa, contain five APSES proteins. However, Cryptococcus neoformans only contains two APSES proteins, and Saccharomyces cerevisiae contains six APSES proteins. The phylogenetic analysis showed the APSES domains from different fungi were grouped into four clades (A, B, C and D), which is consistent with the result of homologous alignment of APSES domains using DNAman. The roles of APSES proteins in clade C have been studied in detail, while little is known about the roles of other APSES proteins in clades A, B and D. In this review, the biochemical properties and functional domains of APSES proteins are predicted and compared, and the phylogenetic relationship among APSES proteins from various fungi are analyzed based on the APSES domains. Moreover, the functions of APSES proteins in different fungi are summarized and discussed.

Deoxynivalenol: a major player in the multifaceted response of Fusarium to its environment

The mycotoxin deoxynivalenol (DON), produced by several Fusarium spp., acts as a virulence factor and is essential for symptom development after initial wheat infection. Accumulating evidence shows that the production of this secondary metabolite can be triggered by diverse environmental and cellular signals, implying that it might have additional roles during the life cycle of the fungus. Here, we review data that position DON in the saprophytic fitness of Fusarium, in defense and in the primary C and N metabolism of the plant and the fungus. We combine the available information in speculative models on the role of DON throughout the interaction with the host, providing working hypotheses that await experimental validation. We also highlight the possible impact of control measures in the field on DON production and summarize the influence of abiotic factors during processing and storage of food and feed matrices. Altogether, we can conclude that DON is a very important compound for Fusarium to cope with a changing environment and to assure its growth, survival, and production of toxic metabolites in diverse situations.