The Nag1 N-acetylglucosaminidase of Trichoderma atroviride is essential for chitinase induction by chitin and of major relevance to biocontrol

Bacterial mycophagy: definition and diagnosis of a unique bacterial-fungal interaction

This review analyses the phenomenon of bacterial mycophagy, which we define as a set of phenotypic behaviours that enable bacteria to obtain nutrients from living fungi and thus allow the conversion of fungal into bacterial biomass. We recognize three types of bacterial strategies to derive nutrition from fungi: necrotrophy, extracellular biotrophy and endocellular biotrophy. Each is characterized by a set of uniquely sequential and differently overlapping interactions with the fungal target. We offer a detailed analysis of the nature of these interactions, as well as a comprehensive overview of methodologies for assessing and quantifying their individual contributions to the mycophagy phenotype. Furthermore, we discuss future prospects for the study and exploitation of bacterial mycophagy, including the need for appropriate tools to detect bacterial mycophagy in situ in order to be able to understand, predict and possibly manipulate the way in which mycophagous bacteria affect fungal activity, turnover, and community structure in soils and other ecosystems.

Trichoderma biocontrol: signal transduction pathways involved in host sensing and mycoparasitism

Fungi of the genus Trichoderma are used as biocontrol agents against several plant pathogenic fungi like Rhizoctonia spp., Pythium spp., Botrytis cinerea and Fusarium spp. which cause both soil-borne and leaf- or flower-borne diseases of agricultural plants. Plant disease control by Trichoderma is based on complex interactions between Trichoderma, the plant pathogen and the plant. Until now, two main components of biocontrol have been identified: direct activity of Trichoderma against the plant pathogen by mycoparasitism and induced systemic resistance in plants. As the mycoparasitic interaction is host-specific and not merely a contact response, it is likely that signals from the host fungus are recognised by Trichoderma and provoke transcription of mycoparasitism-related genes. In the last few years examination of signalling pathways underlying Trichoderma biocontrol started and it was shown that heterotrimeric G-proteins and mitogen-activated protein (MAP) kinases affected biocontrol-relevant processes such as the production of hydrolytic enzymes and antifungal metabolites and the formation of infection structures. MAPK signalling was also found to be involved in induction of plant systemic resistance in Trichoderma virens and in the hyperosmotic stress response in Trichoderma harzianum. Analyses of the function of components of the cAMP pathway during Trichoderma biocontrol revealed that mycoparasitism-associated coiling and chitinase production as well as secondary metabolism are affected by the internal cAMP level; in addition, a cross talk between regulation of light responses and the cAMP signalling pathway was found in Trichoderma atroviride.

Signaling via the Trichoderma atroviride mitogen-activated protein kinase Tmk 1 differentially affects mycoparasitism and plant protection

Trichoderma atroviride is a mycoparasite of a number of plant pathogenic fungi thereby employing morphological changes and secretion of cell wall degrading enzymes and antibiotics. The function of the tmk 1 gene encoding a mitogen-activated protein kinase (MAPK) during fungal growth, mycoparasitic interaction, and biocontrol was examined in T. atroviride. Deltatmk 1 mutants exhibited altered radial growth and conidiation, and displayed de-regulated infection structure formation in the absence of a host-derived signal. In confrontation assays, tmk 1 deletion caused reduced mycoparasitic activity although attachment to Rhizoctonia solani and Botrytis cinerea hyphae was comparable to the parental strain. Under chitinase-inducing conditions, nag 1 and ech 42 transcript levels and extracellular chitinase activities were elevated in a Deltatmk 1 mutant, whereas upon direct confrontation with R. solani or B. cinerea a host-specific regulation of ech 42 transcription was found and nag 1 gene transcription was no more inducible over an elevated basal level. Deltatmk 1 mutants exhibited higher antifungal activity caused by low molecular weight substances, which was reflected by an over-production of 6-pentyl-alpha-pyrone and peptaibol antibiotics. In biocontrol assays, a Deltatmk 1 mutant displayed a higher ability to protect bean plants against R. solani.

Collimonas fungivorans, an unpredicted in vitro but efficient in vivo biocontrol agent for the suppression of tomato foot and root rot

Although bacteria from the genus Collimonas have demonstrated in vitro antifungal activity against many different fungi, they appeared inactive against the plant-pathogenic fungus Fusarium oxysporum f.sp. radicis-lycopersici (Forl), the causal agent of tomato foot and root rot (TFRR). Visualization studies using fluorescently labelled organisms showed that bacterial cells attached extensively to the fungal hyphae under nutrient-poor conditions but not in glucose-rich Armstrong medium. Collimonas fungivorans was shown to be as efficient in colonizing tomato root tips as the excellent colonizer Pseudomonas fluorescens strain WCS365. Furthermore, it appeared to colonize the same sites on the root as did the phytopathogenic fungus. Under greenhouse conditions in potting soil, C. fungivorans performed as well in biocontrol of TFRR as the well-established biocontrol strains P. fluorescens WCS365 and Pseudomonas chlororaphis PCL1391. Moreover, under biocontrol conditions, C. fungivorans did not attach to Forl hyphae colonizing plant roots. Based on these observations, we hypothesize that C. fungivorans mainly controls TFRR through a mechanism of competition for nutrients and niches rather than through its reported mycophagous properties, for which attachment of the bacteria to the fungal hyphae is assumed to be important.

The MAP kinase TVK1 regulates conidiation, hydrophobicity and the expression of genes encoding cell wall proteins in the fungus Trichoderma virens

Mitogen-activated protein (MAP) kinases modulate morphological and genetic processes, which determine cell fate. The tvk1 gene encodes a MAP kinase of Trichoderma virens and its deletion promotes an unusual conidiation phenotype in submerged culture. Here, it is reported that the morphology, physiology and expression of genes encoding cell wall proteins from Trichoderma are significantly affected by Tvk1. Morphological changes were evident in the cell walls of aerial conidia produced by a MAPK null mutant when compared to those produced by the wild-type. Unexpectedly, conidia produced in submerged culture by the Deltatvk1 strain were highly hydrophobic, whereas in aerial conidia hydrophobicity was severely reduced. In addition, the Deltatvk1 strain was unable to break the liquid-air interface when the fungus grew in rich medium; however, when it grew in minimal medium the fungus produced large filaments which were much more efficient at breaking the interface than the wild-type. Through cDNA subtractive hybridization between the wild-type and Deltatvk1 grown in submerged culture, five genes encoding hydrophobin-like proteins and two additional genes encoding cell wall proteins were identified. Four hydrophobin-encoding genes (Tv-hfb1, Tv-srh1, tv-cfth1 and Tv-qid3) and a gene encoding a clock-controlled-like protein (Tv-ccg14/TvSm1) were upregulated in Deltatvk1, whereas genes encoding a cell wall protein (tv-qid74) and an additional hydrophobin (tv-hfb3) were absent in the mutant strain. Clear differences in gene expression were shown during conidiation and emergence from the liquid-air interface, suggesting different functions of the corresponding proteins in these two phenomena. The results support a model in which Tvk1 regulates morphology and genes encoding cell wall proteins during development of Trichoderma.

Enhanced biocontrol activity of Trichoderma virens transformants constitutively coexpressing beta-1,3- and beta-1,6-glucanase genes

Evidence for the role of chitinases, proteases and beta-1,3- and beta-1,6-glucanases in mycoparasitism by Trichoderma species has been well documented. Moreover, constitutive over-expression of genes encoding individual cell-wall-degrading enzymes (CWDEs) has been shown to improve the potential of biological agents. In this study, we generated transformants of T. virens in which beta-1,3- and beta-1,6-glucanase genes, TvBgn2 and TvBgn3, respectively, were constitutively coexpressed in the same genetic T. virens Gv29.8 wild-type background. The double over-expression transformants (dOEs) grow and sporulate slower than the wild-type (WT). However, the reduction in growth did not seem to affect their mycoparasitic and biocontrol capabilities, as dOEs displayed much higher levels of total beta-1,3- and beta-1,6-glucanase activity than the WT. This higher enzymatic activity of dOEs positively correlated with observed in vitro inhibition of Pythium ultimum and Rhizoctonia solani mycelia, and with enhanced bioprotection of cotton seedlings against P. ultimum, R. solani and Rhizopus oryzae. Besides effective biocontrol of all pathogens at an original inoculum level, the performance of dOEs was highly enhanced (up to 312% of WT performance) when pathogen pressure was greater (i.e. concentration of inoculum was higher or pathogens applied in combination). These results demonstrate that the strategy of introducing multiple lytic enzyme-encoding genes through transformation of a given biocontrol strain can be successfully used to achieve better biocontrol.

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.

Chitinase production during interaction of Trichoderma aggressivum and Agaricus bisporus

The competitor fungus Trichoderma aggressivum causes green mould disease, a potentially devastating problem of the commercial mushroom Agaricus bisporus. Due to the recent appearance of this problem, very little is known about the mechanisms by which T. aggressivum interacts with and inhibits A. bisporus. A mechanism generally used by Trichoderma species in the antagonism of other fungi is the secretion of cell wall degrading enzymes. In this study, we determined the activities of chitinases produced in dual cultures of these fungi over a 2 week period. Both intracellular and extracellular enzymes were studied. Agaricus bisporus produced N-acetylglucosaminidases with apparent molecular masses of 111, 105, and 96 kDa. Two resistant brown strains produced greater activities of the 96 kDa N-acetylglucosaminidase than susceptible off-white and white strains. This result suggested that this enzyme might have a role in the resistance of commercial brown strains to green mould disease. Trichoderma aggressivum produced three N-acetylglucosaminidases with apparent molecular masses of 131, 125, and 122 kDa, a 40 kDa chitobiosidase, and a 36 kDa endochitinase. The 122 kDa N-acetylglucosaminidase showed the greatest activity and may be an important predictor of antifungal activity.Key words: mushrooms, chitinases, Trichoderma, Agaricus.

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.

Impact of transgenic Bt maize residues on the mycotoxigenic plant pathogen Fusarium graminearum and the biocontrol agent Trichoderma atroviride

Transformation of maize with genes encoding for insecticidal crystal (Cry) proteins from Bacillus thuringiensis (Bt) could have an impact on the saprophytic survival of plant pathogens and their antagonists on crop residues. We assessed potential effects on the mycotoxin deoxynivalenol (DON)-producing wheat and maize pathogen Fusarium graminearum and on the biocontrol agent Trichoderma atroviride. Purified Cry1Ab protein caused no growth inhibition of these fungi on agar plates. Cry1Ab concentrations above levels common in Bt maize tissue stimulated the growth of F. graminearum. The fungi were also grown on gamma-radiation-sterilized leaf tissue of four Bt maize hybrids and their non transgenic isolines collected at maize maturity on a field trial in 2002 and 2003. Both fungi degraded the Cry1Ab protein in Bt maize tissue. Fungal biomass quantification with microsatellite-based polymerase chain reaction (PCR) assays revealed differential fungal growth on leaf tissue of different maize varieties but no consistent difference between corresponding Bt and non-Bt hybrids. Generally, year of maize tissue collection had a greater impact on biomass production than cultivar or Bt transformation. The mycotoxin DON levels observed in maize tissue experiments corresponded with patterns in F. graminearum biomass, indicating that Bt transformation has no impact on DON production. In addition to bioassays, maize leaf tissue was analyzed with a mass spectrometer-based electronic nose, generating fingerprints of volatile organic compounds. Chemical fingerprints of corresponding Bt and non-Bt leaf tissues differed only for those hybrid pairs that caused differential fungal biomass production in the bioassays. Our results suggest that Cry1Ab protein in maize residues has no direct effect on F. graminearum and T. atroviride but some corresponding Bt/non-Bt maize hybrids differ more in composition than Cry protein content alone, which can affect the saprophytic growth of fungi on crop residues.

Overview of Mechanisms and Uses of Trichoderma spp

ABSTRACT Fungi in the genus Trichoderma have been known since at least the 1920s for their ability to act as biocontrol agents against plant pathogens. Until recently, the principal mechanisms for control have been assumed to be those primarily acting upon the pathogens and included mycoparasitism, antibiosis, and competition for resources and space. Recent advances demonstrate that the effects of Trichoderma on plants, including induced systemic or localized resistance, are also very important. These fungi colonize the root epidermis and outer cortical layers and release bioactive molecules that cause walling off of the Trichoderma thallus. At the same time, the transcriptome and the proteome of plants are substantially altered. As a consequence, in addition to induction of pathways for resistance in plants, increased plant growth and nutrient uptake occur. However, at least in maize, the increased growth response is genotype specific, and some maize inbreds respond negatively to some strains. Trichoderma spp. are beginning to be used in reasonably large quantities in plant agriculture, both for disease control and yield increases. The studies of mycoparasitism also have demonstrated that these fungi produce a rich mixture of antifungal enzymes, including chitinases and beta-1,3 glucanases. These enzymes are synergistic with each other, with other antifungal enzymes, and with other materials. The genes encoding the enzymes appear useful for producing transgenic plants resistant to diseases and the enzymes themselves are beneficial for biological control and other processes.

A microsatellite based method for quantification of fungi in decomposing plant material elucidates the role of Fusarium graminearum DON production in the saprophytic competition with Trichoderma atroviride in maize tissue microcosms

Common PCR assays for quantification of fungi in living plants cannot be used to study saprophytic colonization of fungi because plant decomposition releases PCR-inhibiting substances and saprophytes degrade the plant DNA which could serve as internal standard. The microsatellite PCR assays presented here overcome these problems by spiking samples prior to DNA extraction with mycelium of a reference strain. PCR with fluorescent primers co-amplifies microsatellite fragments of different length from target and reference strains. These fragments were separated in a capillary sequencer with fluorescence detection. The target/reference ratio of fluorescence signal was used to calculate target biomass in the sample. Such PCR assays were developed for the mycotoxin deoxynivalenol (DON)-producing wheat and maize pathogen Fusarium graminearum and the biocontrol agent Trichoderma atroviride, using new microsatellite markers. In contrast to real-time PCR assays, the novel PCR assays showed reliable fungal biomass quantification in samples with differentially decomposed plant tissue. The PCR assays were used to quantify the two fungi after competitive colonization of autoclaved maize leaf tissue in microcosms. Using a DON-producing F. graminearum wild-type strain and its nontoxigenic mutant we found no evidence for a role of DON production in F. graminearum defense against T. atroviride. The presence of T. atroviride resulted in a 36% lower wild-type DON production per biomass.

The G protein alpha subunit Tga1 of Trichoderma atroviride is involved in chitinase formation and differential production of antifungal metabolites

Trichoderma mycoparasitism includes recognition, attack, overgrowth and lysis of the host fungus accompanied by morphological changes and secretion of hydrolytic enzymes and antibiotics. Studying the underlying signal transduction pathways, the tga1 gene encoding a Galpha subunit of Trichoderma atroviride P1 was analysed. A Deltatga1 mutant showed continuous sporulation and elevated internal steady-state cAMP levels. tga1 gene deletion resulted in a complete loss of mycoparasitic overgrowth and lysis of Rhizoctonia solani, Botrytis cinerea, and Sclerotinia sclerotiorum during direct confrontation, although infection structure formation was unaffected. The reduced mycoparasitic abilities were reflected by strongly decreased chitinase activities and reduced nag1 and ech42 gene transcription. Furthermore, production of 6-pentyl-alpha-pyrone and of metabolites with sesquiterpene structure was reduced in the Deltatga1 mutant. Regardless of these deficiencies, the mutant displayed an enhanced growth inhibition of the host fungi by over-producing other low molecular weight antifungal metabolites, suggesting opposite roles of Tga1 in regulating the biosynthesis of different antifungal substances in T. atroviride.

Improvement of the fungal biocontrol agent Trichoderma atroviride to enhance both antagonism and induction of plant systemic disease resistance

Biocontrol agents generally do not perform well enough under field conditions to compete with chemical fungicides. We determined whether transgenic strain SJ3-4 of Trichoderma atroviride, which expresses the Aspergillus niger glucose oxidase-encoding gene, goxA, under a homologous chitinase (nag1) promoter had increased capabilities as a fungal biocontrol agent. The transgenic strain differed only slightly from the wild-type in sporulation or the growth rate. goxA expression occurred immediately after contact with the plant pathogen, and the glucose oxidase formed was secreted. SJ3-4 had significantly less N-acetylglucosaminidase and endochitinase activities than its nontransformed parent. Glucose oxidase-containing culture filtrates exhibited threefold-greater inhibition of germination of spores of Botrytis cinerea. The transgenic strain also more quickly overgrew and lysed the plant pathogens Rhizoctonia solani and Pythium ultimum. In planta, SJ3-4 had no detectable improved effect against low inoculum levels of these pathogens. Beans planted in heavily infested soil and treated with conidia of the transgenic Trichoderma strain germinated, but beans treated with wild-type spores did not germinate. SJ3-4 also was more effective in inducing systemic resistance in plants. Beans with SJ3-4 root protection were highly resistant to leaf lesions caused by the foliar pathogen B. cinerea. This work demonstrates that heterologous genes driven by pathogen-inducible promoters can increase the biocontrol and systemic resistance-inducing properties of fungal biocontrol agents, such as Trichoderma spp., and that these microbes can be used as vectors to provide plants with useful molecules (e.g., glucose oxidase) that can increase their resistance to pathogens.

Signal transduction by Tga3, a novel G protein alpha subunit of Trichoderma atroviride

Trichoderma species are used commercially as biocontrol agents against a number of phytopathogenic fungi due to their mycoparasitic characterisitics. The mycoparasitic response is induced when Trichoderma specifically recognizes the presence of the host fungus and transduces the host-derived signals to their respective regulatory targets. We made deletion mutants of the tga3 gene of Trichoderma atroviride, which encodes a novel G protein alpha subunit that belongs to subgroup III of fungal Galpha proteins. Deltatga3 mutants had changes in vegetative growth, conidiation, and conidial germination and reduced intracellular cyclic AMP levels. These mutants were avirulent in direct confrontation assays with Rhizoctonia solani or Botrytis cinerea, and mycoparasitism-related infection structures were not formed. When induced with colloidal chitin or N-acetylglucosamine in liquid culture, the mutants had reduced extracellular chitinase activity even though the chitinase-encoding genes ech42 and nag1 were transcribed at a significantly higher rate than they were in the wild type. Addition of exogenous cyclic AMP did not suppress the altered phenotype or restore mycoparasitic overgrowth, although it did restore the ability to produce the infection structures. Thus, T. atroviride Tga3 has a general role in vegetative growth and can alter mycoparasitism-related characteristics, such as infection structure formation and chitinase gene expression.

Regulation of N-acetyl-beta-D-glucosaminidase produced by Trichoderma harzianum: evidence that cAMP controls its expression

Trichoderma harzianum is a filamentous fungus reported to be a producer of extracellular N-acetyl-beta-D-glucosaminidase (NAGase) when grown in chitin-containing medium. An approximately 64-kDa protein with NAGase activity was purified by gel filtration and ion exchange chromatography. The involvement of cyclic AMP (cAMP) in the synthesis of NAGase from T. harzianum in chitin-containing medium was also investigated. Molecules that increase the intracellular levels of cAMP, including caffeine, aluminium tetrafluoride and dinitrophenol, were used. Western blot analysis showed that NAGase synthesis was repressed by increasing the levels of intracellular cAMP. Using specific nag primers in a reverse transcription-polymerase chain reaction-based approach, NAGase synthesis was shown to be regulated at the level of gene transcription.

Occurrence of N-acetylhexosaminidase-encoding genes in ectomycorrhizal basidiomycetes

•  The genetic potential of ectomycorrhizal fungi to produce N-acetylhexosaminidases was investigated here. N-acetylhexosaminidases are enzymes that cleave monosaccharides from oligomers of N-acetylhexosamines and play an important role in the degradation of chitin. •  Degenerate PCR-primers were designed against genes coding for N-acetylhexosaminidases in basidiomycetes. PCR was performed with DNA templates extracted from sporocarps of 26 ectomycorrhizal fungal species and two saprotrophs. •  PCR-products were obtained from 18 species representing 12 genera distributed throughout the basidiomycete phylogeny. Sequencing confirmed that the products were homologous with N-acetylhexosaminidase genes from plants, animals and other fungi. Some species yielded two PCR-products representing isoenzymes. •  Chitin constitutes a potentially important nitrogen source in soil. Our results demonstrate that a wide range of ectomycorrhizal fungi have the genetic potential to produce N-acetylhexosaminidases, and the expression of this potential would enable them to exploit polymers of amino sugars as a source of nitrogen for themselves and their host plants.

In vivo study of trichoderma-pathogen-plant interactions, using constitutive and inducible green fluorescent protein reporter systems

Plant tissue colonization by Trichoderma atroviride plays a critical role in the reduction of diseases caused by phytopathogenic fungi, but this process has not been thoroughly studied in situ. We monitored in situ interactions between gfp-tagged biocontrol strains of T. atroviride and soilborne plant pathogens that were grown in cocultures and on cucumber seeds by confocal scanning laser microscopy and fluorescence stereomicroscopy. Spores of T. atroviride adhered to Pythium ultimum mycelia in coculture experiments. In mycoparasitic interactions of T. atroviride with P. ultimum or Rhizoctonia solani, the mycoparasitic hyphae grew alongside the pathogen mycelia, and this was followed by coiling and formation of specialized structures similar to hooks, appressoria, and papillae. The morphological changes observed depended on the pathogen tested. Branching of T. atroviride mycelium appeared to be an active response to the presence of the pathogenic host. Mycoparasitism of P. ultimum by T. atroviride occurred on cucumber seed surfaces while the seeds were germinating. The interaction of these fungi on the cucumber seeds was similar to the interaction observed in coculture experiments. Green fluorescent protein expression under the control of host-inducible promoters was also studied. The induction of specific Trichoderma genes was monitored visually in cocultures, on plant surfaces, and in soil in the presence of colloidal chitin or Rhizoctonia by confocal microscopy and fluorescence stereomicroscopy. These tools allowed initiation of the mycoparasitic gene expression cascade to be monitored in vivo.

Trichoderma species — opportunistic, avirulent plant symbionts

Trichoderma spp. are free-living fungi that are common in soil and root ecosystems. Recent discoveries show that they are opportunistic, avirulent plant symbionts, as well as being parasites of other fungi. At least some strains establish robust and long-lasting colonizations of root surfaces and penetrate into the epidermis and a few cells below this level. They produce or release a variety of compounds that induce localized or systemic resistance responses, and this explains their lack of pathogenicity to plants. These root-microorganism associations cause substantial changes to the plant proteome and metabolism. Plants are protected from numerous classes of plant pathogen by responses that are similar to systemic acquired resistance and rhizobacteria-induced systemic resistance. Root colonization by Trichoderma spp. also frequently enhances root growth and development, crop productivity, resistance to abiotic stresses and the uptake and use of nutrients.

Regulation of two homodimer hexosaminidases in the mycoparasitic fungus Trichoderma asperellum by glucosamine

Trichoderma asperellum is a mycoparasitic fungus which is used as a biocontrol agent against plant pathogens. Its hydrolytic enzymes take part in its parasitic interaction, degrading the pathogen cell wall and thereby helping to control disease. One of those enzymes, beta- N-acetyl- d-glucosaminidase (GlcNAcase), degrades chitin, which is a major component of the cell wall of many plant-pathogenic fungi. Two GlcNAcases of T. asperellum T203, designated EXC1Y and EXC2Y, were purified, their genes and their promoters were sequenced, and their regulation was studied. The enzymes share homology (59% identity) but are easily distinguished by PAGE assay. Biochemical characterization, Edman degradation, and mass spectrometry demonstrated that EXC1Y and EXC2Y are both active as homodimers. Both genes are up-regulated by glucosamine (GlcN), in contrast to two endochitinases of this fungus. GlcN induces the secretion of several proteins (including a beta-glucosidase), among which EXC1Y is the most abundant. An exc2y knockout was constructed, to study the regulation of EXC1Y expression and secretion. The fungus has the ability to store a high amount of this enzyme in an active form and secrete it into the medium later.