Functional analysis of a subtilisin-like serine protease gene from biocontrol fungus Trichoderma harzianum

Genome and transcriptome sequencing of Trichoderma harzianum T4, an important biocontrol fungus of Rhizoctonia solani, reveals genes related to mycoparasitism

Trichoderma harzianum is a well-known biological control strain and a mycoparasite of Rhizoctonia solani. To explore the mechanisms of mycoparasitism, the genome and transcriptome of T. harzianum T4 were both assembled and analyzed in this study. The genome of T. harzianum T4 was assembled into 106 scaffolds, sized 41.25 Mb, and annotated with a total of 8118 predicted genes. We analyzed the transcriptome of T. harzianum T4 against R. solani in a dual culture in three culture periods: before contact (BC), during contact (C), and after contact (AC). Transcriptome sequencing identified 1092, 1222, and 2046 differentially expressed genes (DEGs), respectively. These DEGs, which are involved in pathogen recognition and signal transduction, hydrolase, transporters, antibiosis, and defense-related functional genes, are significantly upregulated in the mycoparasitism process. The results of genome and transcriptome analysis indicated that the mycoparasitism process of T. harzianum T4 was very complex. T. harzianum successfully recognizes and invades host cells and kills plant pathogens by regulating various DEGs at different culture periods. The relative expression levels of the 26 upregulated DEGs were confirmed by RT-qPCR to validate the reliability of the transcriptome data. The results provide insight into the molecular mechanisms underlying T. harzianum T4's mycoparasitic processes, and they provide a potential molecular target for the biological control mechanism of T. harzianum T4.

Analysis of the Properties of 44 ABC Transporter Genes from Biocontrol Agent Trichoderma asperellum ACCC30536 and Their Responses to Pathogenic Alternaria alternata Toxin Stress

ATP-binding cassette (ABC) transporters are involved in transporting multiple substrates, such as toxins, and may be important for the survival of Trichoderma when encountering biotic toxins. In this study, genome searching revealed that there are 44 ABC transporters encoded in the genome of Trichoderma asperellum. These ABC transporters were divided into six types based on three-dimensional (3D) structure prediction, of which four, represented by 39 ABCs, are involved in transport and the remaining two, represented by 5 ABCs, are involved in regulating translation. The characteristics of nucleotide-binding domain (NBD) are important in the identification of ABC proteins. Even though the 3D structures of the 79 NBDs in the 44 ABCs are similar, multiple sequence alignment showed they can be divided into three classes. In total, 794 motifs were found in the promoter regions of the 44 ABC genes, of which 541 were cis-regulators related to stress responses. To characterize how their ABCs respond when T. asperellum interact with fungi or plants, T. asperellum was cultivated in either minimal media (MM) control, C-hungry, N-hungry, or poplar medium (PdPap) to simulate normal conditions, competition with pathogens, interaction with pathogens, and interaction with plants, respectively. The results show that 17 of 39 transport ABCs are highly expressed in at least one condition, whereas four of the five translation-regulating ABCs are highly expressed in at least one condition. Of these 21 highly expressed ABCs, 6 were chosen for RT-qPCR expression under the toxin stress of phytopathogen Alternaria alternata, and the results show ABC01, ABC04, ABC05, and ABC31 were highly expressed and may be involved in pathogen interaction and detoxifying toxins from A. alternata.

Insights into the ecological generalist lifestyle of Clonostachys fungi through analysis of their predicted secretomes

Introduction

The fungal secretome comprise diverse proteins that are involved in various aspects of fungal lifestyles, including adaptation to ecological niches and environmental interactions. The aim of this study was to investigate the composition and activity of fungal secretomes in mycoparasitic and beneficial fungal-plant interactions.

Methods

We used six Clonostachys spp. that exhibit saprotrophic, mycotrophic and plant endophytic lifestyles. Genome-wide analyses was performed to investigate the composition, diversity, evolution and gene expression of Clonostachys secretomes in relation to their potential role in mycoparasitic and endophytic lifestyles.

Results and discussion

Our analyses showed that the predicted secretomes of the analyzed species comprised between 7 and 8% of the respective proteomes. Mining of transcriptome data collected during previous studies showed that 18% of the genes encoding predicted secreted proteins were upregulated during the interactions with the mycohosts Fusarium graminearum and Helminthosporium solani. Functional annotation of the predicted secretomes revealed that the most represented protease family was subclass S8A (11-14% of the total), which include members that are shown to be involved in the response to nematodes and mycohosts. Conversely, the most numerous lipases and carbohydrate-active enzyme (CAZyme) groups appeared to be potentially involved in eliciting defense responses in the plants. For example, analysis of gene family evolution identified nine CAZyme orthogroups evolving for gene gains (p ≤ 0.05), predicted to be involved in hemicellulose degradation, potentially producing plant defense-inducing oligomers. Moreover, 8-10% of the secretomes was composed of cysteine-enriched proteins, including hydrophobins, important for root colonization. Effectors were more numerous, comprising 35-37% of the secretomes, where certain members belonged to seven orthogroups evolving for gene gains and were induced during the C. rosea response to F. graminearum or H. solani. Furthermore, the considered Clonostachys spp. possessed high numbers of proteins containing Common in Fungal Extracellular Membranes (CFEM) modules, known for their role in fungal virulence. Overall, this study improves our understanding of Clonostachys spp. adaptation to diverse ecological niches and establishes a basis for future investigation aiming at sustainable biocontrol of plant diseases.

Strain improvement of Trichoderma harzianum for enhanced biocontrol capacity: Strategies and prospects

In the control of plant diseases, biocontrol has the advantages of being efficient and safe for human health and the environment. The filamentous fungus Trichoderma harzianum and its closely related species can inhibit the growth of many phytopathogenic fungi, and have been developed as commercial biocontrol agents for decades. In this review, we summarize studies on T. harzianum species complex from the perspective of strain improvement. To elevate the biocontrol ability, the production of extracellular proteins and compounds with antimicrobial or plant immunity-eliciting activities need to be enhanced. In addition, resistance to various environmental stressors should be strengthened. Engineering the gene regulatory system has the potential to modulate a variety of biological processes related to biocontrol. With the rapidly developing technologies for fungal genetic engineering, T. harzianum strains with increased biocontrol activities are expected to be constructed to promote the sustainable development of agriculture.

The dark septate endophyte Phialocephala sphaeroides suppresses conifer pathogen transcripts and promotes root growth of Norway spruce

Plant-associated microbes including dark septate endophytes (DSEs) of forest trees play diverse functional roles in host fitness including growth promotion and increased defence. However, little is known about the impact on the fungal transcriptome and metabolites during tripartite interaction involving plant host, endophyte and pathogen. To understand the transcriptional regulation of endophyte and pathogen during co-infection, Norway spruce (Picea abies) seedlings were infected with DSE Phialocephala sphaeroides, or conifer root-rot pathogen Heterobasidion parviporum, or both. Phialocephala sphaeroides showed low but stable transcripts abundance (a decrease of 40%) during interaction with Norway spruce and conifer pathogen. By contrast, H. parviporum transcripts were significantly reduced (92%) during co-infection. With RNA sequencing analysis, P. sphaeroides experienced a shift from cell growth to anti-stress and antagonistic responses, while it repressed the ability of H. parviporum to access carbohydrate nutrients by suppressing its carbohydrate/polysaccharide-degrading enzyme machinery. The pathogen on the other hand secreted cysteine peptidase to restrict free growth of P. sphaeroides. The expression of both DSE P. sphaeroides and pathogen H. parviporum genes encoding plant growth promotion products were equally detected in both dual and tripartite interaction systems. This was further supported by the presence of tryptophan-dependent indolic compound in liquid culture of P. sphaeroides. Norway spruce and Arabidopsis seedlings treated with P. sphaeroides culture filtrate exhibited auxin-like phenotypes, such as enhanced root hairs, and primary root elongation at low concentration but shortened primary root at high concentration. The results suggested that the presence of the endophyte had strong repressive or suppressive effect on H. parviporum transcripts encoding genes involved in nutrient acquisition.

Predicted Input of Uncultured Fungal Symbionts to a Lichen Symbiosis from Metagenome-Assembled Genomes

Basidiomycete yeasts have recently been reported as stably associated secondary fungal symbionts of many lichens, but their role in the symbiosis remains unknown. Attempts to sequence their genomes have been hampered both by the inability to culture them and their low abundance in the lichen thallus alongside two dominant eukaryotes (an ascomycete fungus and chlorophyte alga). Using the lichen Alectoria sarmentosa, we selectively dissolved the cortex layer in which secondary fungal symbionts are embedded to enrich yeast cell abundance and sequenced DNA from the resulting slurries as well as bulk lichen thallus. In addition to yielding a near-complete genome of the filamentous ascomycete using both methods, metagenomes from cortex slurries yielded a 36- to 84-fold increase in coverage and near-complete genomes for two basidiomycete species, members of the classes Cystobasidiomycetes and Tremellomycetes. The ascomycete possesses the largest gene repertoire of the three. It is enriched in proteases often associated with pathogenicity and harbors the majority of predicted secondary metabolite clusters. The basidiomycete genomes possess ∼35% fewer predicted genes than the ascomycete and have reduced secretomes even compared with close relatives, while exhibiting signs of nutrient limitation and scavenging. Furthermore, both basidiomycetes are enriched in genes coding for enzymes producing secreted acidic polysaccharides, representing a potential contribution to the shared extracellular matrix. All three fungi retain genes involved in dimorphic switching, despite the ascomycete not being known to possess a yeast stage. The basidiomycete genomes are an important new resource for exploration of lifestyle and function in fungal–fungal interactions in lichen symbioses.

Production of tailor-made enzymes to facilitate lipid extraction from the oleaginous yeast Schwanniomyces occidentalis

Due to the depletion of fossil fuel resources and concern about increasing atmospheric CO₂ levels, the production of microbial oil as source for energy and chemicals is considered as a sustainable alternative. A promising candidate strain for the production of microbial oil is the oleaginous yeast Schwanniomyces occidentalis CBS 2864. To compete with fossil resources, cultivation and processing of S. occidentalis requires improvement. Currently, different cell wall disruption techniques based on mechanical, chemical, physiological, and biological methods are being investigated using a variety of oil producing yeasts and microalgae. Most of these techniques are not suitable for upscaling because they are technically or energetically unfavorable. Therefore, new techniques have to be developed to overcome this challenge. Here, we demonstrate an effective mild enzymatic approach for cell disruption to facilitate lipid extraction from the oleaginous yeast S. occidentalis. Most oil was released by applying 187 mg L⁻¹ tailor-made enzymes from Trichoderma harzianum CBS 146429 against the yeast cell wall of S. occidentalis at pH 5.0 and 40 °C with 4 h of incubation time after applying 1 M NaOH as a pretreatment step.

Comparative evolutionary histories of fungal proteases reveal gene gains in the mycoparasitic and nematode-parasitic fungus Clonostachys rosea

Background

The ascomycete fungus Clonostachys rosea (order Hypocreales) can control several important plant diseases caused by plant pathogenic fungi and nematodes. Subtilisin-like serine proteases are considered to play an important role in pathogenesis in entomopathogenic, mycoparasitic, and nematophagous fungi used for biological control. In this study, we analysed the evolutionary histories of protease gene families, and investigated sequence divergence and regulation of serine protease genes in C. rosea.

Results

Proteases of selected hypocrealean fungal species were classified into families based on the MEROPS peptidase database. The highest number of protease genes (590) was found in Fusarium solani, followed by C. rosea with 576 genes. Analysis of gene family evolution identified non-random changes in gene copy numbers in the five serine protease gene families S1A, S8A, S9X, S12 and S33. Four families, S1A, S8A, S9X, and S33, displayed gene gains in C. rosea. A gene-tree / species-tree reconciliation analysis of the S8A family revealed that the gene copy number increase in C. rosea was primarily associated with the S08.054 (proteinase K) subgroup. In addition, regulatory and predicted structural differences, including twelve sites evolving under positive selection, among eighteen C. rosea S8A serine protease paralog genes were also observed. The C. rosea S8A serine protease gene prs6 was induced during interaction with the plant pathogenic species F. graminearum.

Conclusions

Non-random increases in S8A, S9X and S33 serine protease gene numbers in the mycoparasitic species C. rosea, Trichoderma atroviride and T. virens suggests an involvement in fungal-fungal interactions. Regulatory and predicted structural differences between C. rosea S8A paralogs indicate that functional diversification is driving the observed increase in gene copy numbers. The induction of prs6 expression in C. rosea during confrontation with F. graminearum suggests an involvement of the corresponding protease in fungal-fungal interactions. The results pinpoint the importance of serine proteases for ecological niche adaptation in C. rosea, including a potential role in the mycoparasitic attack on fungal prey.

Electronic supplementary material

The online version of this article (10.1186/s12862-018-1291-1) contains supplementary material, which is available to authorized users.

Functional analysis of eliciting plant response protein Epl1-Tas from Trichoderma asperellum ACCC30536

Eliciting plant response protein (Epl) is a small Trichoderma secreted protein that acts as an elicitor to induce plant defense responses against pathogens. In the present study, the differential expression, promoter analysis, and phylogenetic tree analysis of Epl1-Tas (GenBank JN966996) from T. asperellum ACCC30536 were performed. The results showed Epl1-Tas could play an important role in the interaction between T. asperellum ACCC30536 and woody plant or woody plant pathogen. Furthermore, the effect of the Escherichia coli recombinant protein rEpl1-e and the Pichia pastoris recombinant protein rEpl1-p on Populus davidiana × P. alba var. pyramidalis (PdPap) was studied. In PdPap seedlings, rEpl1-e or rEpl1-p induction altered the expression levels of 11 genes in the salicylic acid (SA, three genes), jasmonic acid (JA, four genes) and auxin (four genes) signal transduction pathways, and five kinds of enzymes activities The induction level of rEpl1-p was significantly higher than that of rEpl1-e, indicating that rEpl1-p could be used for further induction experiment. Under 3 mg/mL rEpl1-p induction, the mean height of the PdPap seedlings increased by 57.65% and the mean lesion area on the PdPap seedlings leaves challenged with Alternaria alternata decreased by 91.22% compared with those of the control. Thus, elicitor Epl1-Tas could induce the woody plant resistance to pathogen.

Biocontrol activity of recombinant aspartic protease from Trichoderma harzianum against pathogenic fungi

The use of cell wall degrading enzymes of Trichoderma is a promising alternative for improving food storage. The aspartic protease P6281 secreted by the fungus Trichoderma harzianum plays an important role in mycoparasitism on phytopathogenic fungi. In this study, recombinant P6281 (rP6281) expressed in Pichia pastoris showed high activity of 321.8 U/mL. Maximum activity was observed at pH 2.5 and 40 °C, and the enzyme was stable in the pH range of 2.5-6.0. rP6281 significantly inhibited spore germination and growth of plant and animal pathogenic fungi such as Botrytis cinerea, Mucor circinelloides, Aspergillus fumigatus, Aspergillus flavus, Rhizoctonia solani, and Candida albicans. Transmission electron microscopy revealed that rP6281 efficiently damages the cell wall of Botrytis cinerea. In addition, the protease significantly inhibited the development of grey mold that causes rotting of apple, orange, and cucumber, indicating that rP6281 may be developed as an effective anti-mold agent for fruit storage.

Subtilisin-like serine protease gene TghSS42 from Trichoderma ghanense ACCC 30153 was successfully expressed in Escherichia coli and recombinant protease rTghSS42 exhibited antifungal ability to five phytopathogens

　The subtilisin-like serine protease gene TghSS42 was cloned from biocontrol agent Trichoderma ghanense ACCC 30153. Its coding region is 1302 bp in length, encoding 433 aa with a predicted protein molecular weight of 42.5 kDa and pI of 5.53. The accession number of cDNA sequence of TghSS42 gene is KJ740359. Furthermore, the transcription of the TghSS42 gene was all up-regulated under nine different treatments by RT-qPCR analysis, and the highest transcription level of TghSS42 approached 177.29-fold at 4 h under induction with 1% (w/v) Alternaria alternata cell walls, indicating that TghSS42 could be induced by the plant or phytopathogen. Furthermore, Escherichia coli recombinant strain BL21-TghSS42 was constructed. The recombinant protease rTghSS42, with an expected molecular weight of approximately 68.5 kDa (containing 26.0 kDa GST tag), has been successfully expressed and purified from BL21-TghSS42. The purified protease rTghSS42 activity reached a peak of 18.7 U/mL at 4 h following 1.0 mM IPTG induction. The optimal enzyme reaction temperature was 40℃ and the optimal pH was 7.0. The recombinant protease rTghSS42 exerted broad-spectrum antifungal ability against Rhizoctonia solani, Fusarium oxysporum, A. alternata, Sclerotinia sclerotiorum and Cytospora chrysosperma. The inhibition rate of mycelial growth varied between 21.2% and 50.0%.

A novel organic solvent- and detergent-stable serine alkaline protease from Trametes cingulata strain CTM10101

A protease-producing fungus was isolated from an alkaline wastewater of chemical industries and identified as Trametes cingulata strain CTM10101 on the basis of the ITS rDNA gene-sequencing. It was observed that the fungus strongly produce extracellular protease grown at 30°C in potato-dextrose-broth (PDB) optimized media (13500U/ml). The pure serine protease isolated by Trametes cingulata (designated SPTC) was purified by ammonium sulfate precipitation-dialysis followed by heat-treatment and UNO S-1 FPLC cation-exchange chromatography. The chemical characterization carried on include phisico-chemical determination and spectroscopie analysis. The MALDI-TOF/MS analysis revealed that the purified enzyme was a monomer with a molecular mass of 31405.16-Da. The enzyme had an NH2-terminal sequence of ALTTQTEAPWALGTVSHKGQAST, thus sharing high homology with those of fungal-proteases. The optimum pH and temperature values of its proteolytic activity were pH 9 and 60°C, respectively, and its half-life times at 60 and 70°C were 9 and 5-h, respectively. It was completely inhibited by PMSF and DFP, which strongly suggested its belonging to the serine protease family. Compared to Flavourzyme(®)500L from Aspergillus oryzae and Thermolysin typeX from Geobacillus stearothermophilus, SPTC displayed higher levels of hydrolysis, substrate specificity, and catalytic efficiency as well as elevated organic solvent tolerance and considerable detergent stability. Finally, SPTC could potentially be used in peptide synthesis and detergent formulations.