Talaromyces–Insect Relationships

Facing the urgent need to reduce the input of agrochemicals, in recent years, the ecological relationships between plants and their associated microorganisms have been increasingly considered as an essential tool for improving crop production. New findings and data have been accumulated showing that the application of fungi can go beyond the specific role that has been traditionally assigned to the species, employed in integrated pest management as entomopathogens or mycoparasites, and that strains combining both aptitudes can be identified and possibly used as multipurpose biocontrol agents. Mainly considered for their antagonistic relationships with plant pathogenic fungi, species in the genus Talaromyces have been more and more widely reported as insect associates in investigations carried out in various agricultural and non-agricultural contexts. Out of a total of over 170 species currently accepted in this genus, so far, 27 have been found to have an association with insects from 9 orders, with an evident increasing trend. The nature of their mutualistic and antagonistic relationships with insects, and their ability to synthesize bioactive compounds possibly involved in the expression of the latter kind of interactions, are analyzed in this paper with reference to the ecological impact and applicative perspectives in crop protection.

Systemic Identification and Functional Characterization of Common in Fungal Extracellular Membrane Proteins in Lasiodiplodia theobromae

Plant pathogenic fungi deploy secreted proteins into apoplastic space or intracellular lumen to promote successful infections during plant-pathogen interactions. In the present study, fourteen CFEM domain-containing proteins were systemically identified in Lasiodiplodia theobromae and eight of them were functionally characterized. All eight proteins were confirmed to be secreted into extracellular space by a yeast signal peptide trapping system. The transcriptional levels of most CFEM genes, except for LtCFEM2 and LtCFEM6, were significantly elevated during infection. In addition, almost all LtCFEM genes, apart from LtCFEM2, LtCFEM3, and LtCFEM6, were transcriptionally up-regulated at 35°C in contrast to that at 25°C and 30°C. As two elicitors, LtCFEM1 induced local yellowish phenotype and LtCFEM4 triggered cell death in Nicotiana benthamiana leaves. Furthermore, these proteins displayed distinct subcellular localizations when expressed transiently in N. benthamiana. Moreover, two genes, LtCFEM7 and LtCFEM8, were found to be spliced alternatively by RT-PCR and sequencing. Therefore, our data suggest that LtCFEM proteins play important roles in multiple aspects, including pathogenicity and plant immune response, which will enhance our understanding of the sophisticated pathogenic mechanisms of plant opportunistic pathogen L. theobromae.

Regulation of effector gene expression as concerted waves in Leptosphaeria maculans: a two-players game

During infection, plant pathogenic fungi secrete a set of molecules collectively known as effectors, involved in overcoming the host immune system and in disease establishment. Effector genes are concertedly expressed as waves all along plant pathogenic fungi lifecycle. However, little is known about how coordinated expression of effector genes is regulated. Since many effector genes are located in repeat-rich regions, the role of chromatin remodeling in the regulation of effector expression was recently investigated. In Leptosphaeria maculans, causing stem canker of oilseed rape, we established that the repressive histone modification H3K9me3 (trimethylation of Lysine 9 of Histone H3), deposited by the histone methyltransferase KMT1, was involved in the regulation of expression of genes highly expressed during infection, including effectors. Nevertheless, inactivation of KMT1 did not induce expression of these genes at the same level as observed during infection of oilseed rape, suggesting that a second regulator, such as a transcription factor (TF), might be involved. Pf2, a TF belonging to the Zn2Cys6 fungal specific TF family, was described in several Dothideomycete species as essential for pathogenicity and effector gene expression. We identified the orthologue of Pf2 in L. maculans, LmPf2, and investigated the role of LmPf2 together with KMT1, by inactivating and over-expressing LmPf2 in a wild type (WT) strain and a ∆kmt1 mutant. Functional analyses of the corresponding transformants highlighted an essential role of LmPf2 in the establishment of pathogenesis. Transcriptomic analyses during axenic growth showed that LmPf2 is involved in the control of effector gene expression. We observed an enhanced effect of the over-expression of LmPf2 on effector gene expression in a ∆kmt1 background, suggesting an antagonist role between KMT1 and LmPf2.

Transcription factor lineages in plant-pathogenic fungi, connecting diversity with fungal virulence

Plant-pathogenic fungi span diverse taxonomic lineages. Their host-infection strategies are often specialised and require the coordinated regulation of molecular virulence factors. Transcription factors (TFs) are fundamental regulators of gene expression, controlling development and virulence in plant pathogenic fungi. Recent research has established regulatory roles for several taxonomically conserved fungal TFs, but the evolution of specific virulence regulators is not well understood. This study sought to explore the representation of TFs across a taxonomically-diverse range of fungi, with a focus on plant pathogens. A significant trend was observed among the obligate, host-associated pathogens, which possess a reduced overall TF repertoire, alluding to a lack of pressure for maintaining diversity. A novel orthology-based analysis is then presented that refined TF classifications, traditionally based on the nature of the DNA-binding domains. Using this analysis, cases of TF over/underrepresentation across fungal pathogen lineages are systematically highlighted. Specific examples are then explored and discussed that included the TF orthologues of Ste12, Pf2 and EBR1, plus phytotoxic secondary-metabolite cluster regulators, which all presented novel and distinct evolutionary insights. Ultimately, as the examples presented demonstrate, this resource can be interrogated to guide functional studies that seek to characterise virulence-specific regulators and shed light on the factors underpinning plant pathogenicity.

Colloidal Silver Hydrogen Peroxide: New Generation Molecule for Management of Phytopathogens

Plant pathogenic fungi and bacteria are a significant threat to global commercial crop production resulting in increased cost of production, reduced crop establishment and productivity. An effort was made to study the antimicrobial activity of silver hydrogen peroxide (SHP) against selected plant pathogenic fungi and bacteria under in vitro conditions. Higher antibacterial activity of SHP was observed against Xanthomonas axonopodis pv. citri (Xac; 39.67 mm), Xanthomonas citri pv. punicae (Xap; 39.00 mm), and Ralstonia solanacearum (Rs; 36.67 mm) at 500 ppm concentration. SHP was superior to streptocycline (500 ppm) against Xac (25.33 mm) and Xcp (22.67 mm) at 100 ppm. The soil-borne fungi viz., Pythium aphanidermatum and Fusarium solani failed to initiate mycelium growth on PDA at the concentration of 5000 ppm and above. The average size of SHP particles was 462 nm in diameter, and 73.40% of particles had the size of 378 nm, which reflects the particles present in SHP solution in the form of colloids. The effective doses (100–5000 ppm) did not show any phytotoxicity symptoms in plants, while leaf necrosis was noticed at 10,000 ppm after four days of application. SHP (≤5000 ppm) can be used to effectively manage both fungal and bacterial plant pathogens by a single application. Further field studies need to be conducted for validation and commercial use of SHP.

RNA Modification and Its Implication in Plant Pathogenic Fungi

Interaction of a pathogen with its host plant requires both flexibility and rapid shift in gene expression programs in response to environmental cues associated with host cells. Recently, a growing volume of data on the diversity and ubiquity of internal RNA modifications has led to the realization that such modifications are highly dynamic and yet evolutionarily conserved system. This hints at these RNA modifications being an additional regulatory layer for genetic information, culminating in epitranscriptome concept. In plant pathogenic fungi, however, the presence and the biological roles of RNA modifications are largely unknown. Here we delineate types of RNA modifications, and provide examples demonstrating roles of such modifications in biology of filamentous fungi including fungal pathogens. We also discuss the possibility that RNA modification systems in fungal pathogens could be a prospective target for new agrochemicals.

A Selective Medium for the Recovery and Enumeration of Fomitopsis meliae, Causing Lemon Canker and Wood Rot

A selective medium (FMS medium) was developed for the isolation and quantification of Fomitopsis meliae, the causal agent of lemon canker and brown wood rot, from plants, soil, and air. The optimal concentration and combination of fungicides and antibiotics was evaluated to determine the most selective condition for growing F. meliae. The resultant composition of the medium (FMS) per litre (pH 3.5) was: 16 mg thiophanate-methyl, 8 mg dichloran, 5 mg 2-phenylphenol, 100 mg fluopyram, 0.5 mg fludioxonil, 100 mg chloramphenicol, 100 mg streptomycin, 15 g malt extract, 2.5 g mycological peptone, and 15 g agar. The fungus was successfully isolated and enumerated from air, soil and plant tissues using FMS medium. Furthermore, FMS medium almost completely inhibited the growth of other plant pathogenic fungi, soil and air saprophytes. This selectivity was high enough to estimate spore inoculum of F. meliae in an air sample or as a spore trapping device in commercial lemon orchards. FMS medium will be useful for studying epidemiology and management of F. meliae.

Maize AFP1 confers antifungal activity by inhibiting chitin deacetylases from a broad range of fungi

Adapted plant pathogenic fungi deacetylate chitin to chitosan to avoid host perception and disarm the chitin-triggered plant immunity. Whether plants have evolved factors to counteract this fungal evasion mechanism in the plant-pathogen interface remains obscure. Here, we decipher the underlying mechanism of maize cysteine-rich receptor-like secreted proteins (CRRSPs)- AFP1, which exhibits mannose-binding dependent antifungal activity. AFP1 initials the action by binding to specific sites on the surface of yeast-like cells, filaments, and germinated spores of the biotrophic fungi Ustilago maydis. This could result in fungal cell growth and cell budding inhibition, delaying spore germination and subsequently reducing fungal viability in a mannose-binding dependence manner. The antifungal activity of AFP1 is conferred by its interaction with the PMT-dependent mannosylated chitin deacetylases (CDAs) and interfering with the conversion of chitin. Our finding that AFP1 targets CDAs from pathogenic fungi and nonpathogenic budding yeast suggests a potential application of the CRRSP in combating fungal diseases and reducing threats posed by the fungal kingdom.

Cutinases: Characteristics and Insights in Industrial Production

Cutinases (EC 3.1.1.74) are serin esterases that belong to the α/β hydrolases superfamily and present in the Ser-His-Asp catalytic triad. They show characteristics between esterases and lipases. These enzymes hydrolyze esters and triacylglycerols and catalyze esterification and transesterification reactions. Cutinases are synthesize by plant pathogenic fungi, but some bacteria and plants have been found to produce cutinases as well. In nature they facilitate a pathogen’s invasion by hydrolyzing the cuticle that protects plants, but can be also used for saprophytic fungi as a way to nourish themselves. Cutinases can hydrolyze a wide range of substrates like esters, polyesters, triacylglycerols and waxes and that makes this enzyme very attractive for industrial purposes. This work discusses techniques of industrial interest such as immobilization and purification, as well as some of the most important uses of cutinases in industries.

Trends in Nanotechnology and Its Potentialities to Control Plant Pathogenic Fungi: A Review

Approximately 15–18% of crops losses occur as a result of animal pests, while weeds and microbial diseases cause 34 and 16% losses, respectively. Fungal pathogens cause about 70–80% losses in yield. The present strategies for plant disease control depend transcendently on agrochemicals that cause negative effects on the environment and humans. Nanotechnology can help by reducing the negative impact of the fungicides, such as enhancing the solubility of low water-soluble fungicides, increasing the shelf-life, and reducing toxicity, in a sustainable and eco-friendly manner. Despite many advantages of the utilization of nanoparticles, very few nanoparticle-based products have so far been produced in commercial quantities for agricultural purposes. The shortage of commercial uses may be associated with many factors, for example, a lack of pest crop host systems usage and the insufficient number of field trials. In some areas, nanotechnology has been advanced, and the best way to be in touch with the advances in nanotechnology in agriculture is to understand the major aspect of the research and to address the scientific gaps in order to facilitate the development which can provide a rationale of different nanoproducts in commercial quantity. In this review, we, therefore, described the properties and synthesis of nanoparticles, their utilization for plant pathogenic fungal disease control (either in the form of (a) nanoparticles alone, that act as a protectant or (b) in the form of a nanocarrier for different fungicides), nano-formulations of agro-nanofungicides, Zataria multiflora, and ginger essential oils to control plant pathogenic fungi, as well as the biosafety and limitations of the nanoparticles applications.