Isolation and sequence of an endochitinase-encoding gene from a cDNA library of Trichoderma harzianum

Surface characterization and interfacial activity of chitinase chi18-5 against chitosan in langmuir monolayers

One of the challenges for producing active chitinase formulations relies on the gap between the laboratory tests and the biological scenarios where the enzyme will perform its function. In this work, we have employed different Langmuir monolayer arrays to evaluate the interfacial behavior of a recently purified recombinant chitinase, Chi18-5. We have demonstrated that two conformations exist for the chitinase at pH values close to its pI, showing very distinct structural properties at the air/aqueous interface. Enzyme activity was assessed by implementing different kinetic approaches and using a chitosan-1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) mixed film as organized substrate model membrane. Combining these strategies, we demonstrated that better catalytic efficiencies can be obtained for Chi18-5 at pH 5. Moreover, the chitinase activity at the air/aqueous interface can be tuned by introducing in situ pH modifications over the surrounding milieu. We also studied the changes in the topography at the mesoscale level using Brewster Angle Microscopy (BAM). We found that Chi18-5 segregated onto the chitosan domains of the membrane, showing differences in homogeneity depending on the pH imposed. Alternatively, pure Chi18-5 was tested for immobilization onto a hydrophilic activated solid support using the Langmuir-Blodgett technique. Atomic Force Microscopy (AFM) analyses showed successfully stabilization and preservation of molecular features attributed to the pH at which the enzyme deposition was performed.

Structure-Function Insights into the Fungal Endo-Chitinase Chit33 Depict its Mechanism on Chitinous Material

Chitin is the most widespread amino renewable carbohydrate polymer in nature and the second most abundant polysaccharide. Therefore, chitin and chitinolytic enzymes are becoming more importance for biotechnological applications in food, health and agricultural fields, the design of effective enzymes being a paramount issue. We report the crystal structure of the plant-type endo-chitinase Chit33 from Trichoderma harzianum and its D165A/E167A-Chit33-(NAG)₄ complex, which showed an extended catalytic cleft with six binding subsites lined with many polar interactions. The major trait of Chit33 is the location of the non-conserved Asp117 and Arg274 acting as a clamp, fixing the distorted conformation of the sugar at subsite -1 and the bent shape of the substrate, which occupies the full catalytic groove. Relevant residues were selected for mutagenesis experiments, the variants being biochemically characterized through their hydrolytic activity against colloidal chitin and other polymeric substrates with different molecular weights and deacetylation percentages. The mutant S118Y stands out, showing a superior performance in all the substrates tested, as well as detectable transglycosylation capacity, with this variant providing a promising platform for generation of novel Chit33 variants with adjusted performance by further design of rational mutants'. The putative role of Tyr in binding was extrapolated from molecular dynamics simulation.

Virulence Vs. Immunomodulation: Roles of the Paracoccin Chitinase and Carbohydrate-Binding Sites in Paracoccidioides brasiliensis Infection

Paracoccin (PCN) is a bifunctional protein primarily present in the cell wall of Paracoccidioides brasiliensis, a human pathogenic dimorphic fungus. PCN has one chitinase region and four potential lectin sites and acts as both a fungal virulence factor and an immunomodulator of the host response. The PCN activity on fungal virulence, mediated by the chitinase site, was discovered by infecting mice with yeast overexpressing PCN (PCN-ov). PCN-ov are characterized by increased chitin hydrolysis, a narrow cell wall, and augmented resistance to phagocytes' fungicidal activity. Compared to wild-type (wt) yeast, infection with PCN-ov yeast causes a more severe disease, which is attributed to the increased PCN chitinase activity. In turn, immunomodulation of the host response was demonstrated by injecting, subcutaneously, recombinant PCN in mice infected with wt-P. brasiliensis. Through its carbohydrate binding site, the injected recombinant PCN interacts with Toll-like receptor 2 (TLR2) and Toll-like receptor 4 (TLR4) N-glycans on macrophages, triggers M1 polarization, and stimulates protective Th1 immunity against the fungus. The PCN-treatment of wt yeast-infected mice results in mild paracoccidioidomycosis. Therefore, PCN paradoxically influences the course of murine paracoccidioidomycosis. The disease is severe when caused by yeast that overexpress endogenous PCN, which exerts a robust local chitinase activity, followed by architectural changes of the cell wall and release of low size chito-oligomers. However, the disease is mild when exogenous PCN is injected, which recognizes N-glycans on systemic macrophages resulting in immunomodulation.

Thermophilic Chitinases: Structural, Functional and Engineering Attributes for Industrial Applications

Chitin is the second most widely found natural polymer next to cellulose. Chitinases degrade the insoluble chitin to bioactive chitooligomers and monomers for various industrial applications. Based on their function, these enzymes act as biocontrol agents against pathogenic fungi and invasive pests compared with conventional chemical fungicides and insecticides. They have other functional roles in shellfish waste management, fungal protoplast generation, and Single-Cell Protein production. Among the chitinases, thermophilic and thermostable chitinases are gaining popularity in recent years, as they can withstand high temperatures and maintain the enzyme stability for longer periods. Not all chitinases are thermostable; hence, tailor-made thermophilic chitinases are designed to enhance their thermostability by direct evolution, genetic engineering involving mutagenesis, and proteomics approach. Although research has been done extensively on cloning and expression of thermophilic chitinase genes, there are only few papers discussing on the mechanism of chitin degradation using thermophiles. The current review discusses the sources of thermophilic chitinases, improvement of protein stability by gene manipulation, metagenomics approaches, chitin degradation mechanism in thermophiles, and their prospective applications for industrial, agricultural, and pharmaceutical purposes.

Chitinase from Thermomyces lanuginosus SSBP and its biotechnological applications

Chitinases are ubiquitous class of extracellular enzymes, which have gained attention in the past few years due to their wide biotechnological applications. The effectiveness of conventional insecticides is increasingly compromised by the occurrence of resistance; thus, chitinase offers a potential alternative to the use of chemical fungicides. The thermostable enzymes from thermophilic microorganisms have numerous industrial, medical, environmental and biotechnological applications due to their high stability for temperature and pH. Thermomyces lanuginosus produced a large number of chitinases, of which chitinase I and II are successfully cloned and purified recently. Molecular dynamic simulations revealed that the stability of these enzymes are maintained even at higher temperature. In this review article we have focused on chitinases from different sources, mainly fungal chitinase of T. lanuginosus and its industrial application.

Glycoprotein YKL-40: a novel biomarker of chronic graft-vs-host disease activity and severity?

AIM

To investigate whether increased YKL-40 levels positively correlate with graft-vs-host disease (cGVHD) activity and severity and if YKL-40 could serve as a disease biomarker.

METHODS

This case-control study was conducted at the University Hospital Centre Zagreb from July 2013 to October 2015. 56 patients treated with hematopoietic stem cell transplantation (HSCT) were included: 35 patients with cGVHD and 21 without cGVHD. There was no difference between groups in age, sex, median time from transplant to study enrollment, intensity of conditioning, type of donor, or source of stem cells. Blood samples were collected at study enrollment and YKL-40 levels were measured with ELISA. Disease activity was estimated using Clinician's Impression of Activity and Intensity of Immunosuppression scales and disease severity using Global National Institutes of Health (NIH) score.

RESULTS

YKL-40 levels were significantly higher in cGVHD patients than in controls (P=0.003). The difference remained significant when patients with myelofibrosis were excluded from the analysis (P=0.017). YKL-40 level significantly positively correlated with disease severity (P<0.001; correlation coefficient 0.455), and activity estimated using Clinician's Impression of Activity (P=0.016; correlation coefficient 0.412) but not using Intensity of Immunosuppression (P=0.085; correlation coefficient 0.296).

CONCLUSION

YKL-40 could be considered a biomarker of cGVHD severity and activity. However, validation in a larger group of patients is warranted, as well as longitudinal testing of YKL-40 levels in patients at risk of developing cGVHD.

Tissue-specific and pathogen-inducible expression of a fusion protein containing a Fusarium-specific antibody and a fungal chitinase protects wheat against Fusarium pathogens and mycotoxins

Fusarium head blight (FHB) in wheat and other small grain cereals is a globally devastating disease caused by toxigenic Fusarium pathogens. Controlling FHB is a challenge because germplasm that is naturally resistant against these pathogens is inadequate. Current control measures rely on fungicides. Here, an antibody fusion comprised of the Fusarium spp.-specific recombinant antibody gene CWP2 derived from chicken, and the endochitinase gene Ech42 from the biocontrol fungus Trichoderma atroviride was introduced into the elite wheat cultivar Zhengmai9023 by particle bombardment. Expression of this fusion gene was regulated by the lemma/palea-specific promoter Lem2 derived from barley; its expression was confirmed as lemma/palea-specific in transgenic wheat. Single-floret inoculation of independent transgenic wheat lines of the T3 to T6 generations revealed significant resistance (type II) to fungal spreading, and natural infection assays in the field showed significant resistance (type I) to initial infection. Gas chromatography-mass spectrometry analysis revealed marked reduction of mycotoxins in the grains of the transgenic wheat lines. Progenies of crosses between the transgenic lines and the FHB-susceptible cultivar Huamai13 also showed significantly enhanced FHB resistance. Quantitative real-time PCR analysis revealed that the tissue-specific expression of the antibody fusion was induced by salicylic acid drenching and induced to a greater extent by F. graminearum infection. Histochemical analysis showed substantial restriction of mycelial growth in the lemma tissues of the transgenic plants. Thus, the combined tissue-specific and pathogen-inducible expression of this Fusarium-specific antibody fusion can effectively protect wheat against Fusarium pathogens and reduce mycotoxin content in grain.

Postharvest application of a novel chitinase cloned from Metschnikowia fructicola and overexpressed in Pichia pastoris to control brown rot of peaches

Metschnikowia fructicola strain AP47 is a yeast antagonist against postharvest pathogens of fruits. The yeast was able to produce chitinase enzymes in the presence of pathogen cell wall. A novel chitinase gene MfChi (GenBank accession number HQ113461) was amplified from the genomic DNA of Metschnikowia fructicola AP47. Sequence analysis showed lack of introns, an open reading frame (ORF) of 1098 bp encoding a 365 amino acid protein with a calculated molecular weight of 40.9 kDa and a predicted pI of 5.27. MfChi was highly induced in Metschnikowia fructicola after interaction with Monilinia fructicola cell wall, suggesting a primary role of MfChi chitinase in the antagonistic activity of the yeast. The MfChi gene overexpressed in the heterologous expression system of Pichia pastoris KM71 and the recombinant chitinase showed high endochitinase activity towards 4-Nitrophenyl β-d-N,N',N″-triacetylchitotriose substrate. The antifungal activity of the recombinant chitinase was investigated against Monilinia fructicola and Monilinia laxa in vitro and on peaches. The chitinase significantly controlled the spore germination and the germ tube length of the tested pathogens in PDB medium and the mycelium diameter in PDA. The enzyme, when applied on peaches cv. Redhaven, successfully reduced brown rot severity. This work shows that the chitinase MfChi could be developed as a postharvest treatment with antimicrobial activity for fruit undergoing a short shelf life, and confirms that P. pastoris KM71 is a suitable microorganism for cost-effective large-scale production of recombinant chitinases.

Genetically engineered Thompson Seedless grapevine plants designed for fungal tolerance: selection and characterization of the best performing individuals in a field trial

The fungi Botrytis cinerea and Erysiphe necator are responsible for gray mold and powdery mildew diseases, respectively, which are among the most devastating diseases of grapes. Two endochitinase (ech42 and ech33) genes and one N-acetyl-β-D-hexosaminidase (nag70) gene from biocontrol agents related to Trichoderma spp. were used to develop a set of 103 genetically modified (GM) 'Thompson Seedless' lines (568 plants) that were established in open field in 2004 and evaluated for fungal tolerance starting in 2006. Statistical analyses were carried out considering transgene, explant origin, and plant response to both fungi in the field and in detached leaf assays. The results allowed for the selection of the 19 consistently most tolerant lines through two consecutive years (2007-2008 and 2008-2009 seasons). Plants from these lines were grafted onto the rootstock Harmony and established in the field in 2009 for further characterization. Transgene status was shown in most of these lines by Southern blot, real-time PCR, ELISA, and immunostrips; the most tolerant candidates expressed the ech42-nag70 double gene construct and the ech33 gene from a local Hypocrea virens isolate. B. cinerea growth assays in Petri dishes supplemented with berry juices extracted from the most tolerant individuals of the selected population was inhibited. These results demonstrate that improved fungal tolerance can be attributed to transgene expression and support the iterative molecular and physiological phenotyping in order to define selected individuals from a population of GM grapevines.

Chitinases: An update

Chitin, the second most abundant polysaccharide in nature after cellulose, is found in the exoskeleton of insects, fungi, yeast, and algae, and in the internal structures of other vertebrates. Chitinases are enzymes that degrade chitin. Chitinases contribute to the generation of carbon and nitrogen in the ecosystem. Chitin and chitinolytic enzymes are gaining importance for their biotechnological applications, especially the chitinases exploited in agriculture fields to control pathogens. Chitinases have a use in human health care, especially in human diseases like asthma. Chitinases have wide-ranging applications including the preparation of pharmaceutically important chitooligosaccharides and N-acetyl D glucosamine, preparation of single-cell protein, isolation of protoplasts from fungi and yeast, control of pathogenic fungi, treatment of chitinous waste, mosquito control and morphogenesis, etc. In this review, the various types of chitinases and the chitinases found in different organisms such as bacteria, plants, fungi, and mammals are discussed.

RNA interference of endochitinases in the sugarcane endophyte Trichoderma virens 223 reduces its fitness as a biocontrol agent of pineapple disease

The sugarcane root endophyte Trichoderma virens 223 holds enormous potential as a sustainable alternative to chemical pesticides in the control of sugarcane diseases. Its efficacy as a biocontrol agent is thought to be associated with its production of chitinase enzymes, including N-acetyl-ß-D-glucosaminidases, chitobiosidases and endochitinases. We used targeted gene deletion and RNA-dependent gene silencing strategies to disrupt N-acetyl-ß-D-glucosaminidase and endochitinase activities of the fungus, and to determine their roles in the biocontrol of soil-borne plant pathogens. The loss of N-acetyl-ß-D-glucosaminidase activities was dispensable for biocontrol of the plurivorous damping-off pathogens Rhizoctonia solani and Sclerotinia sclerotiorum, and of the sugarcane pathogen Ceratocystis paradoxa, the causal agent of pineapple disease. Similarly, suppression of endochitinase activities had no effect on R. solani and S. sclerotiorum disease control, but had a pronounced effect on the ability of T. virens 223 to control pineapple disease. Our work demonstrates a critical requirement for T. virens 223 endochitinase activity in the biocontrol of C. paradoxa sugarcane disease, but not for general antagonism of other soil pathogens. This may reflect its lifestyle as a sugarcane root endophyte.

Enhanced Expression of Endochitinase in Trichoderma harzianum with the cbh1 Promoter of Trichoderma reesei

Production of extracellular endochitinase could be increased 5-fold in the mycoparasite fungus Trichoderma harzianum by using the cellulase promoter cbh1 of Trichoderma reesei, whereas the total endochitinase activity increased 10-fold. The cbh1 promoter was not expressed on glucose and sucrose in T. harzianum and was induced by sophorose and on cellulase-inducing medium. The endogenous endochitinase gene was expressed at a low basal level on glucose and sucrose. No specific induction by crab shell chitin or sophorose was observed.

Three endochitinase-encoding genes identified in the biocontrol fungus Clonostachys rosea are differentially expressed

Three endochitinase-encoding genes, cr-ech58, cr-ech42 and cr-ech37 were identified and characterised from the mycoparasitic C. rosea strain IK726. The endochitinase activity was specifically induced in media containing chitin or Fusarium culmorum cell walls as sole carbon sources. RT-PCR analysis showed that the three genes were differentially expressed. The expression of the cr-ech42 and cr-ech37 genes was triggered by F. culmorum cell walls and chitin whereas glucose repressed their expression. In contrast, the expression of cr-ech58 was not triggered by F. culmorum cell walls and chitin, suggesting a different role for this endochitinase. Phylogenetically, the cr-ech42 and cr-ech37 genes showed to be orthologous to endochitinase 42 and 37 kDa encoding genes from other mycoparasitic fungi, while no orthologous gene for the cr-ech58 gene was found. Three genetically modified mutants of C. rosea were made by disruption of the endochitinase genes via Agrobacterium-mediated transformation and their biocontrol activity was evaluated. While in planta bioassays showed no significant difference in biocontrol efficacy between the disruptants and the wildtype, the real time RT-PCR analysis showed that disruption of each endochitinase gene affected the activity of C. rosea during interaction with F. culmorum in liquid cultures.

Cloning and phylogenetic analysis of the chitinase gene from the facultative pathogen Paecilomyces lilacinus

AIMS

To PCR-amplify the full-length genomic-encoding sequence for one chitinase from the facultative fungal pathogen Paecilomyces lilacinus, analyse the DNA and deduced amino acid sequences and compare the amino acid sequence with chitinases reported from mycopathogens, entomopathogens and nematopathogens.

METHODS AND RESULTS

The encoding gene (designated as PLC) was isolated using the degenerate PCR primers and the DNA-Walking method. The gene is 1458 bp in length and contains three putative introns. A number of sequence motifs that might play a role in its regulation and function had also been found. Alignment of the translation product (designated as Plc, molecular mass of 45.783 kDa and pI of 5.65) with homologous sequences from other species showed that Plc belongs to Class V chitinase within the glycosyl hydrolase family 18. The phylogenetic and molecular evolutionary analysis using mega (Molecular Evolutionary Genetics Analysis) indicated that these chitinases from mycopathogens, entomopathogens and nematopathogens, the majority of which belong to glycosyl hydrolase family 18, were clustered into two well-supported subgroups corresponding to ascomycetes fungal and nonfungal chitinases (bacteria, baculoviruses).

CONCLUSIONS

Our study showed that chitinases from mycoparasitic, entomopathogenic and nematophagous fungi are closely related to each other and reaffirmed the hypothesis that baculovirus chitinase is most likely to be of a bacterial origin - acquired by gene transfer. Bacterial and baculoviral chitinases in our study are potential pathogenicity factors; however, we still cannot ascribe any specific function to those chitinases from the fungi.

SIGNIFICANCE AND IMPACT OF THE STUDY

To our knowledge, this is the first report describing the chitinase gene and its translation product from Paecilomyces lilacinus, which constitutes the largest number of formulated biological nematicides reported so far, this is also the first study to analyse and resolve the phylogenetic and molecular evolutionary relationships among the chitinases produced by mycopathogens, entomopathogens and nematopathogens.

Serum YKL-40 levels and chitotriosidase activity as potential biomarkers in primary prostate cancer and benign prostatic hyperplasia

BACKGROUND

YKL-40, also called human cartilage glycoprotein-39 (HC gp-39) and chitotriosidase are homologs of family 18 glycosyl hydrolases secreted by human macrophages. Although high levels of YKL-40 and chitotriosidase are associated with several diseases, the physiological functions of these enzymes are still unclear. YKL-40, a growth factor for connective tissue cells, a migration factor for endothelial and vascular smooth muscle cells, is expressed by several types of solid human carcinoma, including prostate carcinoma.

PURPOSE

The purpose of this study was to compare serum YKL-40 levels and chitotriosidase activity both in benign prostatic hyperplasia and primary prostate cancer.

METHODS

YKL-40 and chitotriosidase were determined in serum samples from 93 patients with primary prostate cancer and 61 patients with benign prostatic hyperplasia. Serum YKL-40 levels were measured by ELISA and chitotriosidase activity was determined by fluorometer. PSA levels were also measured by using an automated system.

RESULTS

Serum YKL-40 levels were significantly higher (P < 0.001) in patients with prostate cancer compared with control group whereas there was no significant difference between BPH and control group. Serum chitotriosidase activities were significantly higher in carcinoma patients with high Gleason score than the control group (P < 0.001). No significant difference was observed in BPH patients (P > 0.05). Both YKL-40 and chitotriosidase were found statistically significant higher in primary prostate cancer and BPH.

CONCLUSION

High serum YKL-40 levels in patients with primary prostate cancer indicate that YKL-40 may have a function in the progression of malignant diseases, whereas no significant elevation was observed in benign prostatic hyperplasia. Meanwhile, high serum chitotriosidase activity was observed only in patients with Gleason high grade, indicating possible macrophage involvement in cancer progression. Further studies are needed to elucidate the biologic role of YKL-40 in cancer aggressiveness and in progression of malignant diseases.

Overexpression of an endochitinase gene (ThEn-42) in Trichoderma atroviride for increased production of antifungal enzymes and enhanced antagonist action against pathogenic fungi

Trichoderma is one of the most promising biocontrol agents against plant fungal diseases. In this study, a transgenic strain of Trichoderma atroviride was characterized. The transgenic strain contains an endochitinase gene (ThEn-42) driven by the cellulase promoter cbh1 of T. reesei for overexpression of ThEn-42. The culture filtrates of the transformant and the parental strain grown in eight different media were evaluated for chitinase and antifungal enzyme production based on activity gels, protein profiles, and antifungal activities. Results demonstrated that chitinases are important components and synergistic interactions play a key role in the antagonistic action of T. atroviride. Moreover, altering medium nutrient concentration and composition led to enhanced production of antifungal enzymes, a potential strategy for mass production. Two of the culture filtrates contained almost pure endochitinase, and could be excellent commercial sources for this enzyme. Several culture filtrates were highly antifungal. Two filtrates were so effective in biocontrol of a fungal pathogen, Penicillium digitatum, that they not only inhibited spore germination but destroyed the spores completely when 20 microl of culture filtrate (corresponding to approximately 104 microg of total protein) was applied in a total volume of 150 microl (approximately 0.7 mg protein ml(-1)).

Analysis of both chitinase and chitosanase produced by Sphingomonas sp. CJ-5

A novel chitinolytic and chitosanolytic bacterium, Sphingomonas sp. CJ-5, has been isolated and characterized. It secretes both chitinase and chitosanase into surrounding medium in response to chitin or chitosan induction. To characterize the enzymes, both chitinase and chitosanase were purified by ammonium sulfate precipitation, Sephadex G-200 gel filtration and DEAE-Sepharose Fast Flow. SDS-PAGE analysis demonstrated molecular masses of chitinase and chitosanase were 230 kDa and 45 kDa respectively. The optimum hydrolysis conditions for chitinase were about pH 7.0 and 36 degrees C, and these for chitosanase were pH 6.5 and 56 degrees C, respectively. Both enzymes were quite stable up to 45 degrees C for one hour at pH 5~8. These results show that CJ-5 may have potential for industrial application particularly in recycling of chitin wastes.

Application of DNA bar codes for screening of industrially important fungi: the haplotype of Trichoderma harzianum sensu stricto indicates superior chitinase formation

Selection of suitable strains for biotechnological purposes is frequently a random process supported by high-throughput methods. Using chitinase production by Hypocrea lixii/Trichoderma harzianum as a model, we tested whether fungal strains with superior enzyme formation may be diagnosed by DNA bar codes. We analyzed sequences of two phylogenetic marker loci, internal transcribed spacer 1 (ITS1) and ITS2 of the rRNA-encoding gene cluster and the large intron of the elongation factor 1-alpha gene, tef1, from 50 isolates of H. lixii/T. harzianum, which were also tested to determine their ability to produce chitinases in solid-state fermentation (SSF). Statistically supported superior chitinase production was obtained for strains carrying one of the observed ITS1 and ITS2 and tef1 alleles corresponding to an allele of T. harzianum type strain CBS 226.95. A tef1-based DNA bar code tool, TrichoCHIT, for rapid identification of these strains was developed. The geographic origin of the strains was irrelevant for chitinase production. The improved chitinase production by strains containing this haplotype was not due to better growth on N-acetyl-beta-D-glucosamine or glucosamine. Isoenzyme electrophoresis showed that neither the isoenzyme profile of N-acetyl-beta-glucosaminidases or the endochitinases nor the intensity of staining of individual chitinase bands correlated with total chitinase in the culture filtrate. The superior chitinase producers did not exhibit similarly increased cellulase formation. Biolog Phenotype MicroArray analysis identified lack of N-acetyl-beta-D-mannosamine utilization as a specific trait of strains with the chitinase-overproducing haplotype. This observation was used to develop a plate screening assay for rapid microbiological identification of the strains. The data illustrate that desired industrial properties may be an attribute of certain populations within a species, and screening procedures should thus include a balanced mixture of all genotypes of a given species.

Expression regulation of the endochitinase-encoding gene sechi44 from the mycoparasite Stachybotrys elegans

The regulation of the gene encoding the extracellular chitinase sechi44 produced by the mycoparasite Stachybotrys elegans was studied using real-time quantitative reverse-transcription polymerase chain reaction. Alteration of sechi44 expression was observed when S. elegans was in interaction with its host, Rhizoctonia solani, and also when the mycoparasite was grown on minimal media amended with different carbon and nitrogen sources. Direct contact with R. solani leading to mycoparasitism significantly up-regulated the expression of sechi44, although the analysis showed that sechi44 was constitutively expressed but at substantially lower levels. In addition, the study of sechi44 over 12 days showed that its expression followed a cyclical pattern with peaks every 2 days, which suggests that this gene has a role not only in mycoparasitism but also in growth. The addition of external carbon sources, such as N-acetylglucosamine, chitin, and R. solani cell wall (simulated mycoparasitism), triggered an increase in the expression of sechi44, which varied with time and carbon source. Among the carbon sources examined, N-acetylglucosamine induced the highest increase in sechi44 transcript levels. The addition of high concentrations of glucose and ammonium triggered a decrease of sechi44 expression, suggesting that sechi44 is subject to glucose and ammonium repression.

Increased insect virulence in Beauveria bassiana strains overexpressing an engineered chitinase

Entomopathogenic fungi are currently being used for the control of several insect pests as alternatives or supplements to chemical insecticides. Improvements in virulence and speed of kill can be achieved by understanding the mechanisms of fungal pathogenesis and genetically modifying targeted genes, thus improving the commercial efficacy of these biocontrol agents. Entomopathogenic fungi, such as Beauveria bassiana, penetrate the insect cuticle utilizing a plethora of hydrolytic enzymes, including chitinases, which are important virulence factors. Two chitinases (Bbchit1 and Bbchit2) have previously been characterized in B. bassiana, neither of which possesses chitin-binding domains. Here we report the construction and characterization of several B. bassiana hybrid chitinases where the chitinase Bbchit1 was fused to chitin-binding domains derived from plant, bacterial, or insect sources. A hybrid chitinase containing the chitin-binding domain (BmChBD) from the silkworm Bombyx mori chitinase fused to Bbchit1 showed the greatest ability to bind to chitin compared to other hybrid chitinases. This hybrid chitinase gene (Bbchit1-BmChBD) was then placed under the control of a fungal constitutive promoter (gpd-Bbchit1-BmChBD) and transformed into B. bassiana. Insect bioassays showed a 23% reduction in time to death in the transformant compared to the wild-type fungus. This transformant also showed greater virulence than another construct (gpd-Bbchit1) with the same constitutive promoter but lacking the chitin-binding domain. We utilized a strategy where genetic components of the host insect can be incorporated into the fungal pathogen in order to increase host cuticle penetration ability.

Molecular cloning, characterization, and expression studies of a novel chitinase gene (ech30) from the mycoparasite Trichoderma atroviride strain P1

We describe the cloning and characterization of a single copy gene from Trichoderma atroviride P1 encoding a novel 30 kDa chitinase, Ech30. Ech30 is a family 18 chitinase showing low sequence similarity to other Trichoderma chitinases. Real-time quantitative RT-PCR studies revealed that expression of the ech30 gene was induced by the presence of Botrytis cinerea in plate confrontation assays, but hardly by chitin in liquid cultures. Studies of Ech30 purified from an Escherichia coli strain overexpressing the ech30 gene devoid of the leader sequence and a predicted intron, showed that the gene encodes an active chitinase, which, as expected for family 18 chitinases, is inhibited by allosamidin.

A screening system for carbon sources enhancing beta-N-acetylglucosaminidase formation in Hypocrea atroviridis (Trichoderma atroviride)

To identify carbon sources that trigger beta-N-acetylglucosaminidase (NAGase) formation in Hypocrea atroviridis (anamorph Trichoderma atroviride), a screening system was designed that consists of a combination of Biolog Phenotype MicroArray plates, which contain 95 different carbon sources, and specific enzyme activity measurements using a chromogenic substrate. The results revealed growth-dependent kinetics of NAGase formation and it was shown that NAGase activities were enhanced on carbon sources sharing certain structural properties, especially on alpha-glucans (e.g. glycogen, dextrin and maltotriose) and oligosaccharides containing galactose. Enzyme activities were assessed in the wild-type and a H. atroviridis Deltanag1 strain to investigate the influence of the two NAGases, Nag1 and Nag2, on total NAGase activity. Reduction of NAGase levels in the Deltanag1 strain in comparison to the wild-type was strongly carbon-source and growth-phase dependent, indicating the distinct physiological roles of the two proteins. The transcript abundance of nag1 and nag2 was increased on carbon sources with elevated NAGase activity, indicating transcriptional regulation of these genes. The screening method for the identification of carbon sources that induce enzymes or a gene of interest, as presented in this paper, can be adapted for other purposes if appropriate enzyme or reporter assays are available.

Review of fungal chitinases

Chitin is the second most abundant organic and renewable source in nature, after cellulose. Chitinases are chitin-degrading enzymes. Chitinases have important biophysiological functions and immense potential applications. In recent years, researches on fungal chitinases have made fast progress, especially in molecular levels. Therefore, the present review will focus on recent advances of fungal chitinases, containing their nomenclature and assays, purification and characterization, molecular cloning and expression, family and structure, regulation, and function and application.

Heterologous expression and site-directed mutagenesis studies of two Trichoderma harzianum chitinases, Chit33 and Chit42, in Escherichia coli

Heterologous expression of two fungal chitinases, Chit33 and Chit42, from Trichoderma harzianum was tested in the different compartments and on the surface of Escherichia coli cells. Our goal was to find a fast and efficient expression system for protein engineering and directed evolution studies of the two fungal enzymes. Cytoplasmic overexpression resulted in both cases in inclusion body formation, where active enzyme could be recovered after refolding. Periplasmic expression of Chit33, and especially of Chit42, proved to be better suited for mutagenesis purposes. Recombinant chitinases from the periplasmic expression system showed activity profiles similar to those of the native proteins. Both chitinases also degraded a RET (resonance energy transfer) based bifunctionalized chitinpentaose substrate in a similar manner as reported for some putative exochitinases in the glycosyl hydrolase family 18, offering a sensitive way to assay their activities. We further demonstrated that Chit42 can also be displayed on E. coli surface and the enzymatic activity can be measured directly from the whole cells using methylumbelliferyl-chitinbioside as a substrate. The periplasmic expression and the surface display of Chit42, both offer a suitable expression system for protein engineering and activity screening in a microtiter plate scale. As a first mutagenesis approach we verified the essential role of the two carboxylic acid residues E172 (putative proton donor) and D170 (putative stabilizer) in the catalytic mechanism of Chit42, and additionally the role of the carboxylic acid E145 (putative proton donor) in the catalytic mechanism of Chit33.

Isolation and characterisation of a partial peptide synthetase gene fromTrichoderma asperellum

Many species of Trichoderma have attracted interest as agents for the biological control of soil borne fungal pathogens of a range of crop plants. Research on the biochemical mechanisms associated with this application has focused on the ability of these fungi to produce enzymes which lyse fungal cell walls, and antifungal antibiotics. An important group of the latter are the non-ribosomal peptides called peptaibols. In this study Trichoderma asperellum, a strain used in biological control in Malaysia, was found to produce the peptaibol, trichotoxin. This type of peptide molecule is synthesised by a peptide synthetase (PES) enzyme template encoded by a peptide synthetase (pes) gene. Using nucleotide sequences amplified from adenylation (A-) domains as probes, to hybridise against a lambda FIXII genomic library from T. asperellum, 25 clones were recovered. These were subsequently identified as representative of four groups based on their encoding properties for specific amino acid incorporation modules in a PES. This was based on analysis of their amino acid sequences which showed up to 86% identity to other PESs including TEX 1.

A complete survey of Trichoderma chitinases reveals three distinct subgroups of family 18 chitinases

Genome-wide analysis of chitinase genes in the Hypocrea jecorina (anamorph: Trichoderma reesei) genome database revealed the presence of 18 ORFs encoding putative chitinases, all of them belonging to glycoside hydrolase family 18. Eleven of these encode yet undescribed chitinases. A systematic nomenclature for the H. jecorina chitinases is proposed, which designates the chitinases corresponding to their glycoside hydrolase family and numbers the isoenzymes according to their pI from Chi18-1 to Chi18-18. Phylogenetic analysis of H. jecorina chitinases, and those from other filamentous fungi, including hypothetical proteins of annotated fungal genome databases, showed that the fungal chitinases can be divided into three groups: groups A and B (corresponding to class V and III chitinases, respectively) also contained the so Trichoderma chitinases identified to date, whereas a novel group C comprises high molecular weight chitinases that have a domain structure similar to Kluyveromyces lactis killer toxins. Five chitinase genes, representing members of groups A-C, were cloned from the mycoparasitic species H. atroviridis (anamorph: T. atroviride). Transcription of chi18-10 (belonging to group C) and chi18-13 (belonging to a novel clade in group B) was triggered upon growth on Rhizoctonia solani cell walls, and during plate confrontation tests with the plant pathogen R. solani. Therefore, group C and the novel clade in group B may contain chitinases of potential relevance for the biocontrol properties of Trichoderma.

Purification, characterization, and gene cloning of 46 kDa chitinase (Chi46) from Trichoderma reesei PC-3-7 and its expression in Escherichia coli

We purified a chitinase (named Chi46), with a molecular mass of 46 kDa estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, from the culture filtrate of Trichoderma reesei PC-3-7 grown on N-acetylglucosamine (GlcNAc). The relative activity of this enzyme reduced when the degrees of acetylation (DA) of chitosan decreased. Furthermore, the enzyme was able to hydrolyze colloidal chitin and ethylene glycol chitin. The gene chi46 was cloned and sequenced. chi46 encodes a protein of 424 amino acid residues containing a 35-amino acid prepro-type secretion signal peptide. The molecular mass of mature Chi46 calculated from deduced amino acid sequence was 42,265 Da. The chi46 transcript was biphasic when the mycelia were grown on GlcNAc, suggesting that the multiple regulatory proteins are involved in the chi46 expression. The chi46 cDNA was expressed in Escherichia coli (ca. 0.23 mg/ml culture). To determine substrate cleavage fashion of Chi46 in more detail, we carried out high-performance liquid chromatography analysis and viscosimetric assay using recombinant Chi46 (rChi46). Chi46 was shown to release mainly (GlcNAc)(2) from colloidal chitin (insoluble chitin) as an exo-type manner and to act on chitosan 7B (DA ca. 30%) and N-acetylchitooligosaccharides (soluble chitins) in an endo-type one.

A comparison of constitutive promoters for expression of transgenes in alfalfa (Medicago sativa)

The activity of constitutive promoters was compared in transgenic alfalfa plants using two marker genes. Three promoters, the 35S promoter from cauliflower mosaic virus (CaMV), the cassava vein mosaic virus (CsVMV) promoter, and the sugarcane bacilliform badnavirus (ScBV) promoter were each fused to the beta-glucuronidase (gusA) gene. The highest GUS enzyme activity was obtained using the CsVMV promoter and all alfalfa cells assayed by in situ staining had high levels of enzyme activity. The 35S promoter was expressed in leaves, roots, and stems at moderate levels, but the promoter was not active in stem pith cells, root cortical cells, or in the symbiotic zones of nodules. The ScBV promoter was active primarily in vascular tissues throughout the plant. In leaves, GUS activity driven by the CsVMV promoter was approximately 24-fold greater than the activity from the 35S promoter and 38-fold greater than the activity from the ScBV promoter. Five promoters, the double 35S promoter, figwort mosaic virus (FMV) promoter, CsVMV promoter, ScBV promoter, and alfalfa small subunit Rubisco (RbcS) promoter were used to control expression of a cDNA from Trichoderma atroviride encoding an endochitinase (ech42). Highest chitinase activity in leaves, roots, and root nodules was obtained in plants containing the CsVMV:ech42 transgene. Plants expressing the endochitinase were challenged with Phoma medicaginis var. medicaginis, the causal agent of spring black stem and leaf spot of alfalfa. Although endochitinase activity in leaves of transgenic plants was 50- to 2650-fold greater than activity in control plants, none of the transgenic plants showed a consistent increase in disease resistance compared to controls. The high constitutive levels of both GUS and endochitinase activity obtained demonstrate that the CsVMV promoter is useful for high-level transgene expression in alfalfa.

Overexpression and characterization of a novel chitinase from Trichoderma atroviride strain P1

We describe the overexpression and characterization of a new 30 kDa family 18 chitinase (Ech30) from Trichoderma atroviride strain P1. Sequence alignments indicate that the active site architecture of Ech30 resembles that of endochitinases such as hevamine from the rubber tree (Hevea brasiliensis). The ech30 gene was overexpressed in Escherichia coli without its signal peptide and with an N-terminal His-tag. The enzyme was produced as inclusion bodies, from which active chitinase could be recovered using a simple refolding procedure. The enzyme displayed an acidic pH-optimum (pH 4.5-5.0), probably due to the presence of a conserved Asn residue near the catalytic glutamate, which is characteristic for acidic family 18 chitinases. Studies with oligomers of N-acetylglucosamine [(GlcNAc)(n)], 4-methylumbelliferyl (4-MU) labelled GlcNAc oligomers and beta-chitin reveal enzymatic properties typical of an endochitinase: 1) low activity towards short substrates (kinetic parameters for the hydrolysis of 4-MU-(GlcNAc)2 were K(m), 149+/-29 microM and k(cat), 0.0048+/-0.0005 s(-1)), and 2) production of relatively large amounts of trimers and tetramers during degradation of beta-chitin. Detailed studies with GlcNAc oligomers indicated that Ech30 has as many as seven subsites for sugar binding. As expected for a family 18 chitinase, catalysis proceeded with retention of the beta-anomeric configuration.

Disruption of the gene encoding the ChiB1 chitinase of Aspergillus fumigatus and characterization of a recombinant gene product

The gene encoding a major, inducible 45 kDa chitinase of Aspergillus fumigatus was cloned and analysis of the deduced amino acid sequence identified a chitinase of the fungal/bacterial class which was designated ChiB1. Recombinant ChiB1, expressed in Pichia pastoris, was shown to function by a retaining mechanism of action. That is, the beta-conformation of the chitin substrate linkage was preserved in the product in a manner typical of family 18 chitinases. Cleavage patterns with the N-acetylglucosamine (GlcNAc) oligosaccharide substrates GlcNAc(4), GlcNAc(5) and GlcNAc(6) indicated that the predominant reaction involved hydrolysis of GlcNAc(2) from the non-reducing end of each substrate. Products of transglycosylation were also identified in each incubation. Following disruption of chiB1 by gene replacement, growth and morphology of disruptants and of the wild-type strain were essentially identical. However, during the autolytic phase of batch cultures the level of chitinase activity in culture filtrate from a disruptant was much lower than the activity from the wild-type. The search for chitinases with morphogenetic roles in filamentous fungi should perhaps focus on chitinases of the fungal/plant class although such an investigation will be complicated by the identification of at least 11 putative active site domains for family 18 chitinases in the A. fumigatus TIGR database (http://www.tigr.org/).

Enhanced enzymatic hydrolysis of langostino shell chitin with mixtures of enzymes from bacterial and fungal sources

A combination of enzyme preparations from Trichoderma atroviride and Serratia marcescens was able to completely degrade high concentrations (100 g/L) of chitin from langostino crab shells to N-acetylglucosamine (78%), glucosamine (2%), and chitobiose (10%). The result was achieved at 32 degrees C in 12 days with no pre-treatment (size reduction or swelling) of the substrate and without removal of the inhibitory end-products from the mixture. Enzymatic degradation of three forms of chitin by Serratia/Trichoderma and Streptomyces/Trichoderma blends was carried out according to a simplex-lattice mixture design. Fitted polynomial models indicated that there was synergy between prokaryotic and fungal enzymes for both hydrolysis of crab chitin and reduction of turbidity of colloidal chitin (primarily endo-type activity). Prokaryotic/fungal enzymes were not synergistic in degrading chitosan. Enzymes from prokaryotic sources had much lower activity against chitosan than enzymes from T. atroviride.

Molecular cloning, characterization, and expression of a cDNA encoding an endochitinase gene from the mycoparasite Stachybotrys elegans

Stachybotrys elegans is a mycoparasite of the soilborne plant pathogenic fungus Rhizoctonia solani. The mycoparasitic activity of S. elegans is correlated with the production of cell wall degrading enzymes such as chitinases. This report details the cloning by RACE-PCR and characterization of a full-length cDNA clone, sechi44, that appears to encode an extracellular endochitinase. An analysis of the sechi44 sequence indicates that this gene contains a 1269-bp ORF and encodes a 423-aa polypeptide. The SECHI44 protein has a calculated molecular weight of 44.1kDa and pI of 5.53. Since the SECHI44 protein also appears to encode a signal peptide, an extracellular location for the corresponding protein is predicted. Comparison of SECHI44 sequence with known sequences of fungal endochitinases revealed that SECHI44 is grouped with endochitinases from other mycoparasites. Real-time quantitative RT-PCR analysis showed an elevated level of expression of sechi44 (21-fold) in chitin-rich (induced) as compared to no-carbon (non-induced) culture conditions. In dual culture, the temporal expression of sechi44 increased after 2 days of contact with R. solani, reaching a 10-fold increase after 9 days, followed by a decrease to basic expression level at 12 days. Interestingly, inhibition of sechi44 expression was observed when S. elegans hyphae were in close proximity with R. solani hyphae.

Interaction of ammonium, glucose, and chitin regulates the expression of cell wall-degrading enzymes in Trichoderma atroviride strain P1

Chitinolytic and glucanolytic fungal cell wall-degrading enzymes have been suggested to be primary determinants of biocontrol by Trichoderma spp. We examined the effects of ammonium, glucose, chitin, and chito-oligomers on transcription of specific genes and secretion of fungal cell wall-degrading enzymes. The genes ech42, nag1, and gluc78 were examined, as were the enzymes they encode (endochitinase CHIT42, N-acetylhexosaminidase CHIT73, and glucan exo-1,3-beta-glucanase GLUC78, respectively). gluc78 could be induced by nitrogen starvation alone, while both ech42 and nag1 required nitrogen starvation and the presence of chitin for induction. Starvation for both ammonium and glucose resulted in very early expression and secretion of all cell wall-degrading enzymes examined. In the presence of low levels of ammonium (10 mM), both chito-oligomers and chitin triggered CHIT42 and CHIT40 (chitobiosidase) production. CHIT73 secretion occurred in the presence of N-acetylglucosamine and chito-oligomers, while chitin was less effective. The presence of different chito-oligomers resulted in secretion of specific N-acetylhexosaminidases, of which CHIT73 is one. Our results indicate that the expression and secretion of cell wall-degrading enzymes is nitrogen repressed, that effects of carbon and nitrogen nutrition are interactive, and that especially for chitinolytic enzymes, the inductive effect of chitin is altered by the level of ammonium or glucose in the medium.

Synergistic activity of endochitinase and exochitinase from Trichoderma atroviride (T. harzianum) against the pathogenic fungus (Venturia inaequalis) in transgenic apple plants

Genes from the biocontrol fungus Trichoderma atroviride encoding the antifungal proteins endochitinase or exochitinase (N-acetyl-beta-D-hexosaminidase) were inserted into 'Marshall McIntosh' apple singly and in combination. The genes were driven by a modified CaMV35S promoter. The resulting plants were screened for resistance to Venturia inaequalis, the causal agent of apple scab, and for effects of enzyme expression on growth. Disease resistance was correlated with the level of expression of either enzyme when expressed alone but exochitinase was less effective than endochitinase. The level of expression of endochitinase was negatively correlated with plant growth while exochitinase had no consistent effect on this character. Plants expressing both enzymes simultaneously were more resistant than plants expressing either single enzyme at the same level; analyses indicated that the two enzymes acted synergistically to reduce disease. Selected lines, especially one expressing low levels of endochitinase activity and moderate levels of exochitinase activity, were highly resistant in growth chamber trials and had negligible reduction in vigor relative to control plants. We believe that this is the first report of resistance in plants induced by expression of an N-acetylhexosaminidase and is the first report of in planta synergy between an exochitinase and an endochitinase.

Subset of hybrid eukaryotic proteins is exported by the type I secretion system of Erwinia chrysanthemi

Erwinia chrysanthemi exports degradative enzymes by using a type I protein secretion system. The proteases secreted by this system lack an N-terminal signal peptide but contain a C-terminal secretion signal. To explore the substrate specificity of this system, we have expressed the E. chrysanthemi transporter system (prtDEF genes) in Escherichia coli and tested the ability of this ABC transporter to export hybrid proteins carrying C-terminal fragments of E. chrysanthemi protease B. The C terminus contains six glycine-rich repeated motifs, followed by two repeats of the sequences DFLV and DIIV. Two types of hybrid proteins were assayed for transport, proteins with the 93-residue-protease-B C terminus containing one glycine-rich repeat and both hydrophobic terminal repeats and proteins with the 181-residue C terminus containing all repeat motifs. Although the shorter C terminus is unable to export the hybrids, the longer C terminus can promote the secretion of hybrid proteins with N termini as large as 424 amino acids, showing that the glycine-rich motifs are required for the efficient secretion of these hybrids. However, the secretion of hybrids occurs only if these proteins do not carry disulfide bonds in their mature structures. These latter results suggest that disulfide bond formation can occur prior to or during the secretion. Disulfide bonds may prevent type I secretion of hybrids. One simple hypothesis to explain these results is that the type I channel is too narrow to permit the export of proteins with secondary structures stabilized by disulfide bonds.

Endochitinase gene-based phylogenetic analysis of Trichoderma

DNA sequences of the single-copy gene coding for the 42 kDa endochitinase enzyme (EC 3.2.1.14) were used for phylogenetic analysis in Trichoderma. A set of 12 primers was developed and the entire gene was sequenced for 16 strains, and nucleotide and deduced amino acid sequences were compared to data from GenBank for additional Trichoderma strains. Analysis of the sequences revealed parsimony informative variation from 2.4 to 43.6% depending on the part of the gene (exons/introns) and the taxonomic level considered. Results are discussed in comparison to previous data from ITS-1 and ITS-2 rDNA sequencing and suggest the 42 kDa endochitinase gene as a potential molecular marker for reconstructing phylogenetic relationships in the genus Trichoderma at species level.

Expression of Endochitinase from Trichoderma harzianum in Transgenic Apple Increases Resistance to Apple Scab and Reduces Vigor

ABSTRACT The goal of this research was to improve scab resistance of apple by transformation with genes encoding chitinolytic enzymes from the bio-control organism Trichoderma harzianum. The endochitinase gene, as cDNA and genomic clones, was transferred into apple cv. Marshall McIntosh by Agrobacterium-transformation. A total of 15 lines were identified as transgenic by NPTII enzyme-linked immunosorbent assay and polymerase chain reaction and confirmed by Southern analysis. Substantial differences in endochitinase activity were detected among different lines by enzymatic assay and western analysis. Eight lines propagated as grafted and own-rooted plants were inoculated with Venturia inaequalis. Six of these transgenic lines expressing endochitinase were more resistant than nontransformed cv. Marshall McIntosh. Disease severity compared with cv. Marshall McIntosh was reduced by 0 to 99.7% (number of lesions), 0 to 90% (percentage of leaf area infected), and 1 to 56% (conidia recovered) in the transgenic lines tested. Endochitinase also had negative effects on the growth of both inoculated and uninoculated plants. There was a significant negative correlation between the level of endochitinase production and both the amount of disease and plant growth.

Synthesis of a Trichoderma chitinase which affects the Sclerotium rolfsii and Rhizoctonia solani cell walls

A Trichoderma sp. isolate, hereafter called T6, produces a 46-kDa endochitinase (CHIT 46) which had been shown to drastically affect in vitro the cell walls of the phytopathogens Sclerotium rolfsii and Rhizoctonia solani. We attempted to gain insight into its properties. The CHIT 46 N-terminal amino acid sequence shares a very high homology with other fungal chitinases. Western blot analysis using polyclonal antibodies anti-CHIT 46 revealed that this enzyme is immunologically distinct from other proteins produced by the same Trichoderma isolate T6, but is immunologically identical with proteins having equivalent molar mass, probably chitinases, produced by other Trichoderma spp. isolates. In addition, the antibodies revealed also that a substantial amount of this enzyme is secreted into the culture medium 2 d after the Trichoderma isolate T6 comes into contact with chitin.

Biological control of agricultural pests by filamentous fungi

Agricultural use of chemical pesticides has polluted the environment and resulted in resistance among the target organisms. The chemical strategies of pest control are dangerous to both the nontarget organisms in natural habitats and human health. Biological control is an attractive less dangerous possibility for controlling plant pathogens.Some methods of biological control are becoming now commercially available against plant parasitic fungi, nematods and insects. Among filamentous fungi many candidates with biocontrol potential can be found. Fungal biocontrol agents are less effective and reliable than the synthetic pesticides therefore their use in the agricultural practice requires genetic improvement.

Expression of two major chitinase genes of Trichoderma atroviride (T. harzianum P1) is triggered by different regulatory signals

Regulation of the expression of the two major chitinase genes, ech42 (encoding the CHIT42 endochitinase) and nag1 (encoding the CHIT73 N-acetyl-beta-D-glucosaminidase), of the chitinolytic system of the mycoparasitic biocontrol fungus Trichoderma atroviride (= Trichoderma harzianum P1) was investigated by using a reporter system based on the Aspergillus niger glucose oxidase. Strains harboring fusions of the ech42 or nag1 5' upstream noncoding sequences with the A. niger goxA gene displayed a glucose oxidase activity pattern that was consistent under various conditions with expression of the native ech42 and nag1 genes, as assayed by Northern analysis. The expression product of goxA in the mutants was completely secreted into the medium, detectable on Western blots, and quantifiable by enzyme-linked immunosorbent assay. nag1 gene expression was triggered during growth on fungal (Botrytis cinerea) cell walls and on the chitin degradation product N-acetylglucosamine. N-Acetylglucosamine, di-N-acetylchitobiose, or tri-N-acetylchitotriose also induced nag1 gene expression when added to mycelia pregrown on different carbon sources. ech42 expression was also observed during growth on fungal cell walls but, in contrast, was not triggered by addition of chitooligomers to pregrown mycelia. Significant ech42 expression was observed after prolonged carbon starvation, independent of the use of glucose or glycerol as a carbon source, suggesting that relief of carbon catabolite repression was not involved in induction during starvation. In addition, ech42 gene transcription was triggered by physiological stress, such as low temperature, high osmotic pressure, or the addition of ethanol. Four copies of a putative stress response element (CCCCT) were found in the ech42 promoter.

Molecular characterization of a novel beta-1,3-exoglucanase related to mycoparasitism of Trichoderma harzianum

Trichoderma harzianum, a soil-borne filamentous fungus, is capable of parasitizing several plant pathogenic fungi. Secretion of lytic enzymes, mainly glucanases and chitinases, is considered the most crucial step of the mycoparasitic process. The lytic enzymes degrade the cell walls of the pathogenic fungi, enabling Trichoderma to utilize both their cell walls and cellular contents for nutrition. We have purified a 110kDa novel extracellular beta-1,3-exoglucanase from T. harzianum, grown with laminarin or in dual cultures with host fungi. The corresponding gene, lam1.3, and its cDNA were isolated and their nucleotide sequences determined. The deduced amino-acid sequence predicted a molecular mass of 110.7kDa of a mature protein excluding a signal peptide. LAM1.3 showed high homology to EXG1, a beta-1,3-exoglucanase of the phytopathogenic fungus Cochliobolus carbonum, and a lower homology to BGN13.1, a beta-1,3-endoglucanase isolated from T. harzianum. However, it contains a unique C-terminal embodying cysteine motifs. The expression of lam1.3 in growth with laminarin, but not with glucose, was found to be a result of differential accumulation of the corresponding mRNA.