Cloning and targeted disruption of MLG1, a gene encoding two of three extracellular mixed-linked glucanases of Cochliobolus carbonum

A specific fungal transcription factor controls effector gene expression and orchestrates the establishment of the necrotrophic pathogen lifestyle on wheat

The fungus Parastagonospora nodorum infects wheat through the use of necrotrophic effector (NE) proteins that cause host-specific tissue necrosis. The Zn₂Cys₆ transcription factor PnPf2 positively regulates NE gene expression and is required for virulence on wheat. Little is known about other downstream targets of PnPf2. We compared the transcriptomes of the P. nodorum wildtype and a strain deleted in PnPf2 (pf2-69) during in vitro growth and host infection to further elucidate targets of PnPf2 signalling. Gene ontology enrichment analysis of the differentially expressed (DE) genes revealed that genes associated with plant cell wall degradation and proteolysis were enriched in down-regulated DE gene sets in pf2-69 compared to SN15. In contrast, genes associated with redox control, nutrient and ion transport were up-regulated in the mutant. Further analysis of the DE gene set revealed that PnPf2 positively regulates twelve genes that encode effector-like proteins. Two of these genes encode proteins with homology to previously characterised effectors in other fungal phytopathogens. In addition to modulating effector gene expression, PnPf2 may play a broader role in the establishment of a necrotrophic lifestyle by orchestrating the expression of genes associated with plant cell wall degradation and nutrient assimilation.

Three glycoside hydrolase family 12 enzymes display diversity in substrate specificities and synergistic action between each other

PoCel12A, PoCel12B, and PoCel12C are genes that encode glycoside hydrolase family 12 (GH12) enzymes in Penicillium oxalicum. PoCel12A and PoCel12B are typical GH12 enzymes that belong to fungal subfamilies 12-1 and 12-2, respectively. PoCel12C contains a low-complexity region (LCR) domain, which is not found in PoCel12A or PoCel12B and independent of fungal subfamily 12-1 or 12-2. Recombinant enzymes (named rCel12A, rCel12B and rCel12C) demonstrate existing diversity in the substrate specificities. Although most members in GH family 12 are typical endoglucanases and preferentially hydrolyze β-1,4-glucan (e.g., carboxymethylcellulose), recombinant PoCel12A is a non-typical endo-(1-4)-β-glucanase; it preferentially hydrolyzes mix-linked β-glucan (barley β-glucan, β-1,3-1,4-glucan) and slightly hydrolyzes β-1,4-glucan (carboxymethylcellulose). Recombinant PoCel12B possesses a significantly high activity against xyloglucan. A specific activity of rCel12B toward xyloglucan (239 µmol/min/mg) is the second-highest value known. Recombinant PoCel12C shows low activity toward β-glucan, carboxymethylcellulose, or xyloglucan. All three enzymes can degrade phosphoric acid-swollen cellulose (PASC). However, the hydrolysis products toward PASC by enzymes are different: the main hydrolysis products are cellotriose, cellotetraose, and cellobiose for rCel12A, rCel12B, and rCel12C, correspondingly. A synergistic action toward PASC among rCel12A and rCel12B is observed, thereby suggesting a potential application for preparing enzyme cocktails used in lignocellulose hydrolysis.

Fungal β-1,3-1,4-glucanases: production, proprieties and biotechnological applications

β-1,3-1,4-glucanases (or lichenases; EC 3.2.1.73) comprise one of the main enzymes used in industry during recent decades. These enzymes hydrolyze β-glucans containing β-1,3 and β-1,4 linkages, such as cereal β-glucans and lichenan. The β-1,3-1,4-glucanases are produced by a variety of bacteria, fungi, plants and animals. A large number of microbial β-1,3-1,4-glucanases have potential application in industrial processes, such as feed, food and detergent industries. The present review summarizes the available studies with respect to β-1,3-1,4-glucanases production conditions, enzyme biochemical properties and potential industrial application. © 2018 Society of Chemical Industry.

Improvement of the thermostability and catalytic efficiency of a highly active β-glucanase from Talaromyces leycettanus JCM12802 by optimizing residual charge-charge interactions

BACKGROUND

β-Glucanase is one of the most extensively used biocatalysts in biofuel, food and animal feed industries. However, the poor thermostability and low catalytic efficiency of most reported β-glucanases limit their applications. Currently, two strategies are used to overcome these bottlenecks, i.e., mining for novel enzymes from extremophiles and engineering existing enzymes.

RESULTS

A novel endo-β-1,3-1,4-glucanase of GH16 (Tlglu16A) from the thermophilic fungus Talaromyces leycettanus JCM12802 was produced in Pichia pastoris and characterized. For potential industrial applications, recombinant TlGlu16A exhibits favorable enzymatic properties over most reported glucanases, i.e., remarkable stability over a wide pH range from 1.0 to 10.0 and superior activity on glucan substrates (up to 15,197 U/mg). The only weakness of TlGlu16A is the thermolability at 65 °C and higher. To improve the thermostability, the enzyme thermal stability system was then used to engineer TlGlu16A through optimization of residual charge-charge interactions. Eleven mutants were constructed and compared to the wild-type TlGlu16A. Four mutants, H58D, E134R, D235G and D296K, showed longer half-life time at 80 °C (31, 7, 25, 22 vs. 0.5 min), and two mutants, D235G and D296K, had greater specific activities (158.2 and 122.2 %, respectively) and catalytic efficiencies (k cat/K m, 170 and 114 %, respectively).

CONCLUSIONS

The engineered TlGlu16A has great application potentials from the perspectives of enzyme yield and properties. Its thermostability and activity were apparently improved in the engineered enzymes through charge optimization. This study spans the genetic, functional and structural fields, and provides a combination of gene mining and protein engineering approaches for the systematic improvement of enzyme performance.

High-level production of β-1,3-1,4-glucanase by Rhizomucor miehei under solid-state fermentation and its potential application in the brewing industry

AIMS

To improve the β-1,3-1,4-glucanase production by Rhizomucor miehei under solid-state fermentation (SSF) for industrial application.

METHODS AND RESULTS

The fermentation conditions for β-1,3-1,4-glucanase production by R. miehei CAU432 under SSF were optimized using a 'one-factor-at-a-time' method. Under the optimized fermentation conditions, viz. oatmeal (0·45-0·9 mm) as sole carbon source, 5% (w/w) peptone as sole nitrogen source, initial moisture of 80% (w/w), initial culture pH of 5·0, incubation temperature of 50°C and incubation time of 6 days, the highest β-1,3-1,4-glucanase activity of 20,025 U g(-1) dry substrate was achieved, which represents the highest yield for β-1,3-1,4-glucanase production ever reported. The crude enzyme was extracted and purified to homogeneity with a purification fold of 4·6 and a recovery yield of 9·0%. The addition of the purified β-1,3-1,4-glucanase in mash obviously reduced its filtration time (24·6%) and viscosity (2·61%).

CONCLUSIONS

The optimal fermentation conditions for maximal β-1,3-1,4-glucanase production under SSF was obtained, and the enzyme was suitable for application in the malting process.

SIGNIFICANCE AND IMPACT OF THE STUDY

The high production yield and excellent capability of the enzyme may enable it great potential in industries, especially in brewing industry.

Purification and characterization of a novel alkaline β-1,3-1,4-glucanase (lichenase) from thermophilic fungus Malbranchea cinnamomea

A novel alkaline β-1,3-1,4-glucanase (McLic1) from a thermophilic fungus, Malbranchea cinnamomea, was purified and biochemically characterized. McLic1 was purified to homogeneity with a purification fold of 3.1 and a recovery yield of 3.7 %. The purified enzyme was most active at pH 10.0 and 55 °C, and exhibited a wide range of pH stability (pH 4.0–10.0). McLic1 displayed strict substrate specificity for barley β-glucan, oat β-glucan and lichenan, but did not show activity towards other tested polysaccharides and synthetic p-nitrophenyl derivates, suggesting that it is a specific β-1,3-1,4-glucanase. The K  m values for barley β-glucan, oat β-glucan and lichenan were determined to be 0.69, 1.11 and 0.63 mg mL−1, respectively. Moreover, the enzyme was stable in various non ionic surfactants, oxidizing agents and several commercial detergents. Thus, the alkaline β-1,3-1,4-glucanase may have potential in industrial applications, such as detergent, paper and pulp industries.

Purification and characterization of a novel β-1,3-1,4-glucanase (lichenase) from thermophilic Rhizomucor miehei with high specific activity and its gene sequence

Production, purification, and characterization of a novel β-1,3-1,4-glucanase (lichenase) from thermophilic Rhizomucor miehei CAU432 were investigated. High-level extracellular β-1,3-1,4-glucanase production of 6230 U/mL was obtained when oat flour (3%, w/v) was used as a carbon source at 50 °C. The crude enzyme was purified to homogeneity with a specific activity of 28818 U/mg. The molecular weight of purified enzyme was estimated to be 35.4 kDa and 33.7 kDa by SDS-PAGE and gel filtration, respectively. The optimal pH and temperature of the enzyme were pH 5.5 and 60 °C, respectively. The K(m) values of purified β-1,3-1,4-glucanase for barley β-glucan and lichenan were 2.0 mM and 1.4 mM, respectively. Furthermore, the gene (RmLic16A) encoding the β-1,3-1,4-glucanase was cloned and its deduced amino acid sequence showed the highest identity (50%) to characterized β-1,3-1,4-glucanase from Paecilomyces thermophila. The high-level production and biochemical properties of the enzyme enable its potential industrial applications.

A multi-step chromatographic strategy to purify three fungal endo-β-glucanases

Fungi and fungal enzymes have traditionally occupied a central role in biotechnology. Understanding the biochemical properties of the variety of enzymes produced by these eukaryotes has been an area of research interest for decades and again more recently due to global interest in greener bio-production technologies. Purification of an individual enzyme allows its unique biochemical and functional properties to be determined, can provide key information as to the role of individual biocatalysts within a complex enzyme system, and can inform both protein engineering and enzyme production strategies in the development of novel green technologies based on fungal biocatalysts. Many enzymes of current biotechnological interest are secreted by fungi into the extracellular culture medium. These crude enzyme mixtures are typically complex, multi-component, and generally also contain other non-enzymatic proteins and secondary metabolites. In this chapter, we describe a multi-step chromatographic strategy required to isolate three new endo-β-glucanases (denoted EG V, EG VI, and EG VII) with activity against cereal mixed-linkage β-glucans from the thermophilic fungus Talaromyces emersonii. This work also illustrates the challenges frequently involved in isolating individual extracellular fungal proteins in general.

Identification, characterization, and molecular cloning of a novel hyaluronidase, a member of glycosyl hydrolase family 16, from Penicillium spp

Hyaluronidase (HAase) activity was detected in the culture supernatants of Penicillium purpurogenum and Penicillium funiculosum. The HAase from Penicillium spp. (HAase-P) was a hyaluronate 4-glycanohydrolase, which catalyzed the endolytic hydrolysis of the β-1,4 glycosidic linkage, as do vertebrate HAases. The gene encoding HAase-P was cloned and expressed in Escherichia coli. According to homology analyses of the deduced amino acid sequences, HAase-P is not classified into any of the known HAase groups, but belongs to glycoside hydrolase family 16, which includes endo-β-1,3(4)-glucanase. Regarding the substrate specificities, no chondroitinase and glucanase activities were detected. Judging from homology analyses and enzymatic properties, HAase-P seems to be a new type of HAase.

Reverse genetics for functional genomics of phytopathogenic fungi and oomycetes

Sequencing of over 40 fungal and oomycete genomes has been completed. The next major challenge in modern fungal/oomycete biology is now to translate this plethora of genome sequence information into biological functions. Reverse genetics has emerged as a seminal tool for functional genomics investigations. Techniques utilized for reverse genetics like targeted gene disruption/replacement, gene silencing, insertional mutagenesis, and targeting induced local lesions in genomes will contribute greatly to the understanding of gene function of fungal and oomycete pathogens. This paper provides an overview on high-throughput reverse genetics approaches to decode fungal/oomycete genomes.

Biochemical characterization of a novel thermostable beta-1,3-1,4-glucanase (lichenase) from Paecilomyces thermophila

The purification and characterization of a novel extracellular beta-1,3-1,4-glucanase from the thermophilic fungus Paecilomyces thermophila J18 were studied. The strain produced the maximum level of extracellular beta-glucanase (135.6 U mL(-1)) when grown in a medium containing corncob (5%, w/v) at 50 degrees C for 4 days. The crude enzyme solution was purified by 122.5-fold with an apparent homogeneity and a recovery yield of 8.9%. The purified enzyme showed as a single protein band on SDS-PAGE with a molecular mass of 38.6 kDa. The molecular masses were 34.6 kDa and 31692.9 Da when detected by gel filtration and mass spectrometry, respectively, suggesting that it is a monomeric protein. The enzyme was a glycoprotein with a carbohydrate content of 19.0% (w/w). Its N-terminal sequence of 10 amino acid residues was determined as H2N-A(?)GYVSNIVVN. The purified enzyme was optimally active at pH 7.0 and 70 degrees C. It was stable within pH range 4.0-10.0 and up to 65 degrees C, respectively. Substrate specificity studies revealed that the enzyme is a true beta-1,3-1,4-D-glucanase. The K m values determined for barley beta-D-glucan and lichenan were 2.46 and 1.82 mg mL(-1), respectively. The enzyme hydrolyzed barley beta-D-glucan and lichenan to yield bisaccharide, trisaccharide, and tetrasaccharide as the main products. Circular dichroism studies indicated that the protein contains 28% alpha-helix, 24% beta-sheet, and 48% random coil. Circular dichroism spectroscopy is also used to investigate the thermostability of the purified enzyme. This is the first report on the purification and characterization of a beta-1,3-1,4-glucanase from Paecilomyces sp. These properties make the enzyme highly suitable for industrial applications.

Biochemistry and molecular biology of exocellular fungal beta-(1,3)- and beta-(1,6)-glucanases

Many fungi produce exocellular beta-glucan-degrading enzymes, the beta-glucanases including the noncellulolytic beta-(1,3)- and beta-(1,6)-glucanases, degrading beta-(1,3)- and beta-(1,6)-glucans. An ability to purify several exocellular beta-glucanases attacking the same linkage type from a single fungus is common, although unlike the beta-1,3-glucanases, production of multiple beta-1,6-glucanases is quite rare in fungi. Reasons for this multiplicity remain unclear and the multiple forms may not be genetically different but arise by posttranslational glycosylation or proteolytic degradation of the single enzyme. How their synthesis is regulated, and whether each form is regulated differentially also needs clarifying. Their industrial potential will only be realized when the genes encoding them are cloned and expressed in large quantities. This review considers what is known in molecular terms about their multiplicity of occurrence, regulation of synthesis and phylogenetic diversity. It discusses how this information assists in understanding their functions in the fungi producing them. It deals largely with exocellular beta-glucanases which here refers to those recoverable after the cells are removed, since those associated with fungal cell walls have been reviewed recently by Adams (2004). It also updates the earlier review by Pitson et al. (1993).

Mutational analysis of the glycosylphosphatidylinositol (GPI) anchor pathway demonstrates that GPI-anchored proteins are required for cell wall biogenesis and normal hyphal growth in Neurospora crassa

Using mutational and proteomic approaches, we have demonstrated the importance of the glycosylphosphatidylinositol (GPI) anchor pathway for cell wall synthesis and integrity and for the overall morphology of the filamentous fungus Neurospora crassa. Mutants affected in the gpig-1, gpip-1, gpip-2, gpip-3, and gpit-1 genes, which encode components of the N. crassa GPI anchor biosynthetic pathway, have been characterized. GPI anchor mutants exhibit colonial morphologies, significantly reduced rates of growth, altered hyphal growth patterns, considerable cellular lysis, and an abnormal "cell-within-a-cell" phenotype. The mutants are deficient in the production of GPI-anchored proteins, verifying the requirement of each altered gene for the process of GPI-anchoring. The mutant cell walls are abnormally weak, contain reduced amounts of protein, and have an altered carbohydrate composition. The mutant cell walls lack a number of GPI-anchored proteins, putatively involved in cell wall biogenesis and remodeling. From these studies, we conclude that the GPI anchor pathway is critical for proper cell wall structure and function in N. crassa.

A lichenase-like family 12 endo-(1→4)-β-glucanase from Aspergillus japonicus: study of the substrate specificity and mode of action on β-glucans in comparison with other glycoside hydrolases

Using anion-exchange chromatography on Source 15Q followed by hydrophobic interaction chromatography on Source 15 Isopropyl, a lichenase-like endo-(1-->4)-beta-glucanase (BG, 28kDa, pI4.1) was isolated from a culture filtrate of Aspergillus japonicus. The enzyme was highly active against barley beta-glucan and lichenan (263 and 267 U/mg protein) and had much lower activity toward carboxymethylcellulose (3.9 U/mg). The mode of action of the BG on barley beta-glucan and lichenan was studied in comparison with that of Bacillus subtilis lichenase and endo-(1-->4)-beta-glucanases (EG I, II, and III) of Trichoderma reesei. The BG behaved very similar to the bacterial lichenase, except the tri- and tetrasaccharides formed as the end products of beta-glucan hydrolysis with the BG contained the beta-(1-->3)-glucoside linkage at the non-reducing end, while the lichenase-derived oligosaccharides had the beta-(1-->3)-linkage at the reducing end. The BG was characterized by a high amino acid sequence identity to the EG of Aspergillus kawachii (UniProt entry Q12679) from a family 12 of glycoside hydrolases (96% in 162 identified aa residues out of total 223 residues) and also showed lower sequence similarity to the EglA of Aspergillus niger (O74705).

A novel β-glucanase gene fromBacillus haloduransC-125

A novel endo-beta-1,3(4)-D-glucanase gene was found in the complete genome sequence of Bacillus halodurans C-125. The gene was previously annotated as an "unknown" protein and assigned an incorrect open reading frame (ORF). However, determining the biochemical characteristics has elucidated the function and correct ORF of the gene. The gene encodes 231 amino acids, and its calculated molecular mass was estimated to be 26743.16 Da. The amino acid sequence alignment showed that the highest sequence identity was only 28% with that of the beta-1,3-1,4-glucanase from Bacillus subtilis. Moreover, the nucleotide sequence did not match any other known Bacillus beta-glucanase gene. The member of the gene cluster that includes this novel gene was apparently different from that of the gene cluster including the putative beta-glucanase genes (bh3231 and bh3232) from B. halodurans C-125. Therefore, the novel gene is not a copy of either of these genes, and in B. halodurans cells, the putative role of the encoded protein may differ from that of bh3231 and bh3232. To examine the activity of the gene product, the gene was cloned as a His-tagged protein and expressed in Escherichia coli. The purified enzyme showed activity against lichenan, barley beta-glucan, laminarin, and carboxymethyl curdlan. Thin-layer chromatography showed that the enzyme hydrolyzes substrates in an endo-type manner. When beta-glucan was used as a substrate, the pH optimum was between 6 and 8, and the temperature optimum was 60 degrees C. After 2 h incubation at 50 and 60 degrees C, the residual activity remained 100% and 50%, respectively. The enzymatic activity was abolished after 30 min incubation at 70 degrees C. Based on the results, the gene encodes an endo-type beta-1,3(4)-D-glucanase (E.C. 3.2.1.6).

Hydrolysis of beta-1,3/1,6-glucan by glycoside hydrolase family 16 endo-1,3(4)-beta-glucanase from the basidiomycete Phanerochaete chrysosporium

When Phanerochaete chrysosporium was grown with laminarin (a beta-1,3/1,6-glucan) as the sole carbon source, a beta-1,3-glucanase with a molecular mass of 36 kDa was produced as a major extracellular protein. The cDNA encoding this enzyme was cloned, and the deduced amino acid sequence revealed that this enzyme belongs to glycoside hydrolase family 16; it was named Lam16A. Recombinant Lam16A, expressed in the methylotrophic yeast Pichia pastoris, randomly hydrolyzes linear beta-1,3-glucan, branched beta-1,3/1,6-glucan, and beta-1,3-1,4-glucan, suggesting that the enzyme is a typical endo-1,3(4)-beta-glucanase (EC 3.2.1.6) with broad substrate specificity for beta-1,3-glucans. When laminarin and lichenan were used as substrates, Lam16A produced 6-O-glucosyl-laminaritriose (beta-D-Glcp-(1->6)-beta-D-Glcp-(1->3)-beta-D-Glcp-(1->3)-D-Glc) and 4-O-glucosyl-laminaribiose (beta-D-Glcp-(1->4)-beta-D-Glcp-(1->3)-D-Glc), respectively, as one of the major products. These results suggested that the enzyme strictly recognizes beta-D-Glcp-(1->3)-D-Glcp at subsites -2 and -1, whereas it permits 6-O-glucosyl substitution at subsite +1 and a beta-1,4-glucosidic linkage at the catalytic site. Consequently, Lam16A generates non-branched oligosaccharide from branched beta-1,3/1,6-glucan and, thus, may contribute to the effective degradation of such molecules in combination with other extracellular beta-1,3-glucanases.

The Phanerochaete chrysosporium secretome: Database predictions and initial mass spectrometry peptide identifications in cellulose-grown medium

The white rot basidiomycete, Phanerochaete chrysosporium, employs an array of extracellular enzymes to completely degrade the major polymers of wood: cellulose, hemicellulose and lignin. Towards the identification of participating enzymes, 268 likely secreted proteins were predicted using SignalP and TargetP algorithms. To assess the reliability of secretome predictions and to evaluate the usefulness of the current database, we performed shotgun LC-MS/MS on cultures grown on standard cellulose-containing medium. A total of 182 unique peptide sequences were matched to 50 specific genes, of which 24 were among the secretome subset. Underscoring the rich genetic diversity of P. chrysosporium, identifications included 32 glycosyl hydrolases. Functionally interconnected enzyme groups were recognized. For example, the multiple endoglucanases and processive exocellobiohydrolases observed quite probably attack cellulose in a synergistic manner. In addition, a hemicellulolytic system included endoxylanases, alpha-galactosidase, acetyl xylan esterase, and alpha-l-arabinofuranosidase. Glucose and cellobiose metabolism likely involves cellobiose dehydrogenase, glucose oxidase, and various inverting glycoside hydrolases, all perhaps enhanced by an epimerase. To evaluate the completeness of the current database, mass spectroscopy analysis was performed on a larger and more inclusive dataset containing all possible ORFs. This allowed identification of a previously undetected hypothetical protein and a putative acid phosphatase. The expression of several genes was supported by RT-PCR amplification of their cDNAs.

Gene expression during infection of wheat roots by the 'take-all' fungus Gaeumannomyces graminis

SUMMARY The infection of plants by pathogenic microbes and the subsequent establishment of disease involves substantial changes in the biochemistry and physiology of both partners. Analysis of genes that are expressed during these interactions represents a powerful strategy to obtain insights into the molecular events underlying these changes. Root diseases have considerable economic impact but have not been characterized extensively at the molecular genetic level. Here we have used two complementary approaches-suppression subtractive hybridization and expressed sequence tag analysis of an unsubtracted cDNA library-to investigate gene expression during the early stages of colonization of wheat roots by the take-all fungus, Gaeumannomyces graminis.

Purification and characterization of the (1→3)-β-glucanases fromAcremoniumsp. IMI 383068

Three extracellular (1-->3)-beta-glucanases were purified from the fungus Acremonium sp. IMI 383068. Higher activities were unexpectedly obtained with pustulan, a (1-->6)-beta-glucan as carbon source, than when grown with laminarin, a (1-->3)-beta-glucan. Preliminary evidence suggests that these enzymes are not constitutive, but are inducible, and that their synthesis is repressed by glucose. All three had the same molecular masses, similar pH and temperature optima and none were glycosylated. They all appeared to have an exo-hydrolytic mode of substrate attack. N-terminal amino acid sequence data indicate that substantial post-translational modification of these had occurred, and that while two may be encoded by the same gene, the third may be genetically different.

Investigating the role of a Verticillium fungicola beta-1,6-glucanase during infection of Agaricus bisporus using targeted gene disruption

Studies on the mycopathogen Verticillium fungicola have shown the up-regulation of beta-1,6-glucanases when grown in the presence of host cell walls and host cell wall components including chitin. These cell-wall-degrading enzymes are hypothesized to contribute to the pathogenic ability of mycopathogens. A beta-1,6-glucanase gene, VfGlu1, showing high similarity to beta-1,6-glucanase genes from Hypocrea virens, Neotyphodium sp., and Trichoderma harzianum, was isolated using degenerate PCR from V. fungicola, a serious mycopathogen of the cultivated mushroom Agaricus bisporus. Agrobacterium-mediated transformation of V. fungicola using homologous DNA from VfGlu1 resulted in homologous integration at the VfGlu1 locus in 75% of transformants, generating mutants disrupted in the VfGlu1 gene. VfGlu1 mutants displayed reduced virulence and diminished ability to utilize chitin as a carbon source, implicating VfGlu1 in the disease process. Agrobacterium-mediated transformation affords an efficient technique for the disruption of genes associated with disease symptom development in the complex V. fungicola-A. bisporus interaction.

Characterization of Alternaria alternata glucanase genes expressed during infection of resistant and susceptible persimmon fruits

Summary Preharvest treatment with gibberellic acid (GA(3)) or its inhibitor paclobutrazol (PBZ) can reduce or increase, respectively, the susceptibility of persimmon fruits to Alternaria alternata. This was suggested to be the result of the ability of the fungus and produced endoglucanases to induce symptom development. To evaluate the importance of glucanases during A. alternata attack, five glucanase genes, corresponding to the C, F, and K families, were cloned from A. alternata using 'family-specific' oligonucleotide primers. The genes, present in a single copy, encode for exoglucanases AaC1 and AaC2, endoxylanase AaF1, endoglucanase AaK1, and the mixed-linked glucanase AaMLG1. Reverse transcriptase polymerase chain reaction (RT-PCR) analysis of RNA extracted from persimmon fruits, 2 and 4 days post-infection with A. alternata, showed the expression of all five glucanase genes in GA3- and PBZ-treated fruits. However, transcription levels and enzyme production of the endoglucanase (AaK1) and one exoglucanase (AaC1) were enhanced during A. alternata growth on cell walls from susceptible PBZ-treated fruits, whereas the expression of these genes and their enzyme production were significantly reduced in resistant GA(3)-treated fruits. The present results suggest the involvement of endo- and exoglucanase in symptom development caused by A. alternata in resistant and susceptible persimmon fruits.

A beta-glucosidase/xylosidase from the phytopathogenic oomycete, Phytophthora infestans

An 85-kDa beta-glucosidase/xylosidase (BGX1) was purified from the axenically grown phytopathogenic oomycete, Phytophthora infestans. The bgx1 gene encodes a predicted 61-kDa protein product which, upon removal of a 21 amino acid leader peptide, accumulates in the apoplastic space. Extensive N-mannosylation accounts for part of the observed molecular mass difference. BGX1 belongs to family 30 of the glycoside hydrolases and is the first such oomycete enzyme deposited in public databases. The bgx1 gene was found in various Phytophthora species, but is apparently absent in species of the related genus, Pythium. Despite significant sequence similarity to human and murine lysosomal glucosylceramidases, BGX1 demonstrated neither glucocerebroside nor galactocerebroside-hydrolyzing activity. The native enzyme exhibited glucohydrolytic activity towards 4-methylumbelliferyl (4-MU) beta-D-glucopyranoside and, to lesser extent, towards 4-MU-D-xylopyranoside, but not towards 4-MU-beta-D-glucopyranoside. BGX1 did not hydrolyze carboxymethyl cellulose, cellotetraose, chitosan or xylan, suggesting high substrate specificity and/or specific cofactor requirements for enzymatic activity.

Mutational analysis of beta-glucanase genes from the plant-pathogenic fungus Cochliobolus carbonum

Two new beta-glucanase-encoding genes, EXG2 and MLG2, were isolated from the plant-pathogenic fungus Cochliobolus carbonum using polymerase chain reaction based on amino acid sequences from the purified proteins. EXG2 encodes a 46.6-kDa exo-beta1,3-glucanase and is located on the same 3.5-Mb chromosome that contains the genes of HC-toxin biosynthesis. MLG2 encodes a 26.8-kDa mixed-linked (beta1,3-beta1,4) glucanase with low activity against beta1,4-glucan and no activity against beta1,3-glucan. Specific mutants of EXG2 and MLG2 were constructed by targeted gene replacement. Strains with multiple mutations (genotypes exg1/mlg1, exg2/mlg1, mlg1/mlg2, and exg1/exg2/mlg1/mlg2) were also constructed by sequential disruption and by crossing. Total mixed-linked glucanase activity in culture filtrates of mlg1/mlg2 and exg1/exg2/mlg1/mlg2 mutants was reduced by approximately 73%. Total beta1,3-glucanase activity was reduced by 10, 54, and 96% in exg2, mlg1, and exg1/exg2/mlg1/mlg2 mutants, respectively. The quadruple mutant showed only a modest decrease in growth on beta1,3-glucan or mixed-linked glucan. None of the mutants showed any decrease in virulence.

Isolation and characterization of a thermostable endo-beta-glucanase active on 1,3-1,4-beta-D-glucans from the aerobic fungus talaromyces emersonii CBS 814.70

A novel endoglucanase active on 1,3-1,4-beta-D-glucans was purified to apparent homogeneity from submerged cultures of the moderately thermophilic aerobic fungus Talaromyces emersonii CBS 814.70. The enzyme is a single subunit glycoprotein with M(r) and pI values of 40.7 +/- 0.3 kDa and 4.4, respectively, and an estimated carbohydrate content of 77% (w/w). The purified beta-glucanase displayed activity over broad ranges of pH and temperature, yielding respective optima values of pH 4.8 and 80 degrees C. This enzyme was markedly thermostable with 15% of the original activity remaining after incubation for 15 min at 100 degrees C. Substrate specificity studies revealed the identity of the enzyme to be a 1,3-1,4-beta-D-glucanase. Identical K(m) values (13.38 mg.ml(-1)) were obtained with lichenan and BBG, while the V(max) value with lichenan (142.9 IU.mg(-1)) was approximately twice the value obtained with BBG (79.3 IU.mg(-1)). Time-course hydrolysis of barley-beta-glucan did not proceed linearly with respect to time indicating an 'endo' or more processive action for the enzyme. HPAEC fractionation of the products of hydrolysis yielded a range of oligosaccharides, with cellobiose, cellotriose and cellotetraose being the predominant oligosaccharide products.

Botrytis cinerea endopolygalacturonase genes are differentially expressed in various plant tissues

Botrytis cinerea, the causal agent of blight, rot, and gray mold on many plant species, secretes various endopolygalacturonases during all stages of infection. The expression pattern of the encoding genes (Bcpg 1-6) was studied on four hosts: tomato, broad bean, apple, and courgette (also known as zucchini). All gene family members are differentially expressed, depending on the stage of infection and the host. Bcpg1 is expressed in all tissues tested although differences in transcript levels occur. Bcpg2 expression is detected early in the infection of three of four plant tissues tested. Bcpg3 and Bcpg5 are expressed in apple fruit tissue, although probably as a result of different regulatory mechanisms. The expression patterns of Bcpg4 and 6 are in agreement with their inducibility by monogalacturonic acid. The pattern of Bcpg gene expression indicates that B. cinerea is equipped with a flexible enzymatic pectate degradation machinery. The studies pinpoint new targets for gene disruption studies.

Bacterial 1,3-1,4-beta-glucanases: structure, function and protein engineering

1,3-1,4-beta-Glucanases (or lichenases, EC 3.2.1.73) hydrolyse linear beta-glucans containing beta-1,3 and beta-1,4 linkages such as cereal beta-glucans and lichenan, with a strict cleavage specificity for beta-1,4 glycosidic bonds on 3-O-substituted glucosyl residues. The bacterial enzymes are retaining glycosyl hydrolases of family 16 with a jellyroll beta-sandwich fold and a substrate binding cleft composed of six subsites. The present paper reviews the structure-function aspects of the enzymatic action including mechanistic enzymology, protein engineering and X-ray crystallographic studies.

Characterization of a beta-1,3-glucanase encoded by chlorella virus PBCV-1

Sequence analysis of the 330-kb chlorella virus PBCV-1 genome revealed an open-reading frame, A94L, that encodes a protein with significant amino acid identity to Glycoside Hydrolase Family 16 beta-1,3-glucanases. The a94l gene was cloned and the protein was expressed as a GST-A94L fusion protein in Escherichia coli. The recombinant A94L protein hydrolyzed the beta-1,3-glucose polymer laminarin and had slightly less hydrolytic activity on beta-1,3-1, 4-glucose polymers, lichenan and barley beta-glucan. The recombinant enzyme had the highest activity at 65 degrees C and pH 8. We predicted that the a94l-encoded beta-1,3-glucanase is involved in degrading the host cell wall either during virus release and/or is packaged in the virion particle and involved in virus entry. Therefore, we expected a94l to be expressed late in virus infection. However, contrary to expectations, both the a94l mRNA and the A94L protein appeared 15 min after PBCV-1 infection and disappeared 60- and 120-min p.i. postinfection, respectively, indicating that a94l is an early gene. Twenty-seven of 42 chlorella viruses contained the a94l gene. To our knowledge, this is the first report of a virus-encoded beta-1,3-glucanase.

The Cochliobolus carbonum SNF1 gene is required for cell wall-degrading enzyme expression and virulence on maize

The production of cell wall-degrading enzymes (wall depolymerases) by plant pathogenic fungi is under catabolite (glucose) repression. In Saccharomyces cerevisiae, the SNF1 gene is required for expression of catabolite-repressed genes when glucose is limiting. An ortholog of SNF1, ccSNF1, was isolated from the maize pathogen Cochliobolus carbonum, and ccsnf1 mutants of HC toxin-producing (Tox2(+)) and HC toxin-nonproducing (Tox2(-)) strains were created by targeted gene replacement. Growth in vitro of the ccsnf1 mutants was reduced by 50 to 95% on complex carbon sources such as xylan, pectin, or purified maize cell walls. Growth on simple sugars was affected, depending on the sugar. Whereas growth on glucose, fructose, or sucrose was normal, growth on galactose, galacturonic acid, maltose, or xylose was somewhat reduced, and growth on arabinose was strongly reduced. Production of HC toxin was normal in the Tox2(+) ccsnf1 mutant, as were conidiation, conidial morphology, conidial germination, and in vitro appressorium formation. Activities of secreted beta-1,3-glucanase, pectinase, and xylanase in culture filtrates of the Tox2(+) ccsnf1 mutant were reduced by 53, 24, and 65%, respectively. mRNA expression was downregulated under conditions that induced the following genes encoding secreted wall-degrading enzymes: XYL1, XYL2, XYL3, XYL4, XYP1, ARF1, MLG1, EXG1, PGN1, and PGX1. The Tox2(+) ccsnf1 mutant was much less virulent on susceptible maize, forming fewer spreading lesions; however, the morphology of the lesions was unchanged. The Tox2(-) ccsnf1 mutant also formed fewer nonspreading lesions, which also retained their normal morphology. The results indicate that ccSNF1 is required for biochemical processes important in pathogenesis by C. carbonum and suggest that penetration is the single most important step at which ccSNF1 is required. The specific biochemical processes controlled by ccSNF1 probably include, but are not necessarily restricted to, the ability to degrade polymers of the plant cell wall and to take up and metabolize the sugars produced.

Reduced virulence caused by meiotic instability of the TOX2 chromosome of the maize pathogen Cochliobolus carbonum

The mechanisms by which pathogenic fungi evolve are poorly understood. Production of the host-selective cyclic peptide HC-toxin is controlled by a complex locus, TOX2, in the plant pathogen Cochliobolus carbonum. Crosses between toxin-producing (Tox2+) and toxin-nonproducing (Tox2-) isolates, as well as crosses between isolates in which the TOX2 genes were on chromosomes of different size, yielded progeny that had lost one or more copies of one or more of the TOX2 genes. Of approximately 200 progeny analyzed, eight (4%) had lost at least one TOX2 gene. All of them still had at least one functional copy of all of the known genes required for HC-toxin production (HTS1, TOXA, TOXC, and TOXE). Most deletion strains could be explained by simple chromosome breaks resulting in the loss of major contiguous portions (0.8 to 1.4 Mb) of the 3.5-Mb TOX2 chromosome, whereas others had more complicated patterns. All deletion strains had normal growth and were fertile, indicating that the 1.4 Mb of DNA contained no essential housekeeping genes. Most strains were also still virulent (Tox2+), but two had a novel phenotype of reduced virulence (RV), characterized by smaller lesions that expanded at a reduced rate and an inability to colonize plants systemically. Although the RV strains made no detectable HC-toxin in culture, the RV phenotype was dependent on the presence of a functional copy of HTS1, which encodes the central enzyme in HC-toxin biosynthesis. We propose that the RV strains still make a low level of HC-toxin, at least in planta, and that this is due to the loss of one or more genes that contribute to, but are not absolutely required for, HC-toxin synthesis.

EXG1p, a novel exo-beta1,3-glucanase from the fungus Cochliobolus carbonum, contains a repeated motif present in other proteins that interact with polysaccharides

Genomic and cDNA copies of EXG1, a gene encoding an exo-beta1, 3-glucanase from the plant pathogenic fungus Cochliobolus carbonum, were isolated. The gene contains two introns of 50 and 53 bp, and the mRNA has a 5'-untranslated region of 90 nt and a 3'-untranslated region of 159 nt. The deduced protein product, EXG1p, has a predicted signal peptide of 17 amino acids, but based on the known N-terminus of the mature protein is further processed to remove an additional 25 amino acids. The sequence of EXG1p is not closely related to any other known protein, but has a low similarity (29% overall amino acid identity) to BGN13.1, an endo-beta1,3-glucanase from the mycoparasitic fungus Trichoderma harzianum. EXG1p contains two imperfect copies of a 23-amino acid motif that is found in several other proteins that interact with polysaccharides, including plant and bacterial polygalacturonases, phage neck appendage protein, phage endoneuramidase, and bacterial mannuronan epimerase.

The endopolygalacturonase gene Bcpg1 is required for full virulence of Botrytis cinerea

Botrytis cinerea, a fungus that causes diseases in over 200 plant species, secretes a number of endopolygalacturonases that have been suggested to be involved in pathogenesis. However, so far the corresponding genes have not been isolated from this fungus. We cloned Bcpg1, encoding endopolygalacturonase, with the pgaII gene from Aspergillus niger as a heterologous probe. The Bcpg1 gene is expressed to similar levels in liquid cultures of B. cinerea containing either 1% polygalacturonic acid or 1% sucrose, and is expressed during infection of tomato leaves. The Bcpg1 gene was eliminated by partial gene replacement, and the resulting mutants were tested for virulence on tomato leaves and fruits, as well as on apple fruits. Although the mutants were still pathogenic and displayed similar primary infections when compared with control strains, a significant decrease in secondary infection, i.e., growth of the lesion beyond the inoculation spot, was observed on all three host tissues. These results indicate that the Bcpg1 gene is required for full virulence.