Mycoparasitic Trichoderma Species Research Articles

Identifying glycoside hydrolase family 18 genes in the mycoparasitic fungal species Clonostachys rosea

Clonostachysrosea is a mycoparasitic fungal species that is an efficient biocontrol agent against many plant diseases. During mycoparasitic interactions, one of the most crucial steps is the hydrolysis of the prey's fungal cell wall, which mainly consists of glucans, glycoproteins and chitin. Chitinases are hydrolytic enzymes responsible for chitin degradation and it is suggested that they play an important role in fungal-fungal interactions. Fungal chitinases belong exclusively to the glycoside hydrolase (GH) family 18.These GH18 proteins are categorized into three distinct phylogenetic groups (A, B and C), subdivided into several subgroups. In this study, we identified 14 GH18 genes in the C. rosea genome, which is remarkably low compared with the high numbers found in mycoparasitic Trichoderma species. Phylogenetic analysis revealed that C. rosea contains eight genes in group A, two genes in group B, two genes in group C, one gene encoding a putative ENGase (endo-β-N-acetylglucosaminidase) and the ech37 gene, which is of bacterial origin. Gene expression analysis showed that only two genes had higher transcription levels during fungal-fungal interactions, while eight out of 14 GH18 genes were triggered by chitin. Furthermore, deletion of the C group chiC2 gene decreased the growth inhibitory activity of C. rosea culture filtrates against Botrytis cinerea and Rhizoctonia solani, although the biocontrol ability of C. rosea against B. cinerea was not affected. In addition, a potential role of the CHIC2 chitinase in the sporulation process was revealed. These results provide new information about the role of GH18 proteins in mycoparasitic interactions.

Insights on the evolution of mycoparasitism from the genome of Clonostachys rosea.

Clonostachys rosea is a mycoparasitic fungus that can control several important plant diseases. Here, we report on the genome sequencing of C. rosea and a comparative genome analysis, in order to resolve the phylogenetic placement of C. rosea and to study the evolution of mycoparasitism as a fungal lifestyle. The genome of C. rosea is estimated to 58.3 Mb, and contains 14,268 predicted genes. A phylogenomic analysis shows that C. rosea clusters as sister taxon to plant pathogenic Fusarium species, with mycoparasitic/saprotrophic Trichoderma species in an ancestral position. A comparative analysis of gene family evolution reveals several distinct differences between the included mycoparasites. Clonostachys rosea contains significantly more ATP-binding cassette (ABC) transporters, polyketide synthases, cytochrome P450 monooxygenases, pectin lyases, glucose-methanol-choline oxidoreductases, and lytic polysaccharide monooxygenases compared with other fungi in the Hypocreales. Interestingly, the increase of ABC transporter gene number in C. rosea is associated with phylogenetic subgroups B (multidrug resistance proteins) and G (pleiotropic drug resistance transporters), whereas an increase in subgroup C (multidrug resistance-associated proteins) is evident in Trichoderma virens. In contrast with mycoparasitic Trichoderma species, C. rosea contains very few chitinases. Expression of six group B and group G ABC transporter genes was induced in C. rosea during exposure to the Fusarium mycotoxin zearalenone, the fungicide Boscalid or metabolites from the biocontrol bacterium Pseudomonas chlororaphis. The data suggest that tolerance toward secondary metabolites is a prominent feature in the biology of C. rosea.

Generation of Trichoderma atroviride mutants with constitutively activated G protein signaling by using geneticin resistance as selection marker

BackgroundSpecies of the fungal genus Trichoderma are important industrial producers of cellulases and hemicellulases, but also widely used as biocontrol agents (BCAs) in agriculture. In the latter function Trichoderma species stimulate plant growth, induce plant defense and directly antagonize plant pathogenic fungi through their mycoparasitic capabilities. The recent release of the genome sequences of four mycoparasitic Trichoderma species now forms the basis for large-scale genetic manipulations of these important BCAs. Thus far, only a limited number of dominant selection markers, including Hygromycin B resistance (hph) and the acetamidase-encoding amdS gene, have been available for transformation of Trichoderma spp. For more extensive functional genomics studies the utilization of additional dominant markers will be essential.ResultsWe established the Escherichia coli neomycin phosphotransferase II-encoding nptII gene as a novel selectable marker for the transformation of Trichoderma atroviride conferring geneticin resistance. The nptII marker cassette was stably integrated into the fungal genome and transformants exhibited unaltered phenotypes compared to the wild-type. Co-transformation of T. atroviride with nptII and a constitutively activated version of the Gα subunit-encoding tga3 gene (tga3Q207L) resulted in a high number of mitotically stable, geneticin-resistant transformants. Further analyses revealed a co-transformation frequency of 68% with 15 transformants having additionally integrated tga3Q207L into their genome. Constitutive activation of the Tga3-mediated signaling pathway resulted in increased vegetative growth and an enhanced ability to antagonize plant pathogenic host fungi.ConclusionThe neomycin phosphotransferase II-encoding nptII gene from Escherichia coli proved to be a valuable tool for conferring geneticin resistance to the filamentous fungus T. atroviride thereby contributing to an enhanced genetic tractability of these important BCAs.

Self versus non-self: fungal cell wall degradation in Trichoderma

Lysis of the prey's cell wall is one of the key steps during mycoparasitism. Genome analysis of two mycoparasitic Trichoderma species, T. atroviride and T. virens, revealed an expanded arsenal of genes encoding enzymes potentially involved in cell wall hydrolysis. Glycoside hydrolase family 18, which contains all fungal chitinases, is the largest family of carbohydrate-active enzymes in mycoparasitic Trichoderma species. However, in addition to their aggressive functions during mycoparasitism, the roles of chitinases and other cell wall degrading enzymes also include remodelling and recycling of the fungus's own cell wall. In this review we discuss current knowledge about fungal cell wall degrading enzymes in Trichoderma and how the fungus distinguishes between self- and non-self fungal cell wall degradation. In the past few years, the chitinolytic enzyme machinery of Trichoderma has been used as a model system to address this question. Gene expression profiles of most investigated chitinases indicate an overlap of functions of the respective enzymes and an involvement in both self- and non-self fungal cell wall degradation. Similar sets of enzymes appear to be involved in mycoparasitism, exogenous chitin decomposition and recycling of the fungus's own cell wall. Thus, we hypothesize that the regulation of self and non-self fungal cell wall degradation is not due to a speciation of individual chitinases. Rather, we hypothesize that it is regulated by substrate accessibility due to cell wall protection in healthy hyphae vs deprotection during mycoparasitic attack, hyphal ageing and autolysis.

The seven-transmembrane receptor Gpr1 governs processes relevant for the antagonistic interaction of Trichoderma atroviride with its host

Mycoparasitic Trichoderma species are applied as biocontrol agents in agriculture to guard plants against fungal diseases. During mycoparasitism, Trichoderma directly interacts with phytopathogenic fungi, preceded by a specific recognition of the host and resulting in its disarming and killing. In various fungal pathogens, including mycoparasites, signalling via heterotrimeric G proteins plays a major role in regulating pathogenicity-related functions. However, the corresponding receptors involved in the recognition of host-derived signals are largely unknown. Functional characterization of Trichoderma atroviride Gpr1 revealed a prominent role of this seven-transmembrane protein of the cAMP-receptor-like family of fungal G-protein-coupled receptors in the antagonistic interaction with the host fungus and governing of mycoparasitism-related processes. Silencing of gpr1 led to an avirulent phenotype accompanied by an inability to attach to host hyphae. Furthermore, gpr1-silenced transformants were unable to respond to the presence of living host fungi with the expression of chitinase- and protease-encoding genes. Addition of exogenous cAMP was able to restore host attachment in gpr1-silenced transformants but could not restore mycoparasitic overgrowth. A search for downstream targets of the signalling pathway(s) involving Gpr1 resulted in the isolation of genes encoding e.g. a member of the cyclin-like superfamily and a small secreted cysteine-rich protein. Although silencing of gpr1 caused defects similar to those of mutants lacking the Tga3 Gα protein, no direct interaction between Gpr1 and Tga3 was observed in a split-ubiquitin two-hybrid assay.

Differential Regulation of Orthologous Chitinase Genes in Mycoparasitic Trichoderma Species

Mycoparasitic Trichoderma species have expanded numbers of fungal subgroup C chitinases that contain multiple carbohydrate binding modules and could thus be important for fungal cell wall degradation during the mycoparasitic attack. In this study, we analyzed the gene regulation of subgroup C chitinases in the mycoparasite Trichoderma virens. In addition to regulation by nutritional stimuli, we found complex expression patterns in different parts of the fungal colony, and also, the mode of cultivation strongly influenced subgroup C chitinase transcript levels. Thus, the regulation of these genes is governed by a combination of colony-internal and -external signals. Our results showed completely different expression profiles of subgroup C chitinase genes in T. virens than in a previous study with T. atroviride, although both fungi are potent mycoparasites. Only a few subgroup C chitinase orthologues were found in T. atroviride and T. virens, and even those showed substantially divergent gene expression patterns. Microscopic analysis revealed morphogenetic differences between T. atroviride and T. virens, which could be connected to differential subgroup C chitinase gene expression. The biological function of fungal subgroup C chitinases therefore might not be as clear-cut as previously anticipated. They could have pleiotropic roles and might be involved in both degradation of exogenous chitinous carbon sources, including other fungal cell walls, and recycling of their own cell walls during hyphal development and colony formation.

The Rhizosphere of Coffea Arabica in Its Native Highland Forests of Ethiopia Provides a Niche for a Distinguished Diversity of Trichoderma

The southwestern highlands forests of Ethiopia are the origin of the coffee plant Coffea arabica. The production of coffee in this area is affected by tracheomycosis caused by a soil-born fungus Gibberella xylarioides. The use of endemic antagonistic strains of mycoparasitic Trichoderma species would be a nature conserving means to combat this disease. We have used molecular methods to reveal that the community of Trichoderma in the rhizosphere of C. arabica in its native forests is highly diverse and includes many putatively endemic species. Among others, the putative new species were particularly efficient to inhibit growth of G. xylarioides.

Hydrophobicity and surface electrostatic charge of conidia of the mycoparasitic Trichoderma species

The present investigation was done to understand the fungal-fungal interactions mechanisms based on level of nonspecific adhesion of a potential fungal mycoparasite (Trichoderma) to their fungal host (Macrophomina phaseolina). The relative cell surface hydrophobicity (CSH) and cell surface electrostatic charge (CSEC) of 29 isolates of Trichoderma species, analyzed by bacterial adhesion to hydrocarbon (BATH), hydrophobic interaction chromatography (HIC), microelectrophoresis and contact angle, revealed a large degree of variability. CSH and CSEC of conidia depended on culture age, pH and temperature. Maximum CSH and CSEC were recorded in 25–28 °C range, and both declined significantly with increasing temperature. Isolate Trichoderma hazianum (Th)-23/98 expressed surface hydrophobicity at 25–28 °C and hydrophilicity at 40 °C. Surface hydrophobicity of the isolate was susceptible to various proteases (trypsin, pepsin, proteinase k and a-chymotrypsin) and inhibitors (SDS, mercaptoethanol and Triton X-100) and a significant reduction in CSH was recorded in hydrophobic conidia. Hydrophilic conidia remained more or less unaffected by such treatments. SDS-PAGE analysis of the hydrophobic and hydrophilic conidia exhibited several protein bands in the 25 to 61 kDa range. However, each protein population contained one protein that was not observed in the other population. For hydrophobic conidia, the unique protein had an apparent molecular mass of 49 kDa, while the unique protein associated with hydrophilic conidia had a molecular mass of 61 kDa. Our findings suggest that CSH and CSEC of mycoparasitic Trichoderma may contribute to non-specific adhesion on to the sclerotial surfaces of Macrophomina phaseolina that may be influenced by growth and environmental conditions.