Characterization of the Lentinula edodes exg2 gene encoding a lentinan-degrading exo-beta-1,3-glucanase

The exp2 gene, which encodes a protein with two zinc finger domains, regulates cap expansion and autolysis in Coprinopsis cinerea

Cap expansion in agaricoid mushroom species is an important event for sexual reproduction because meiosis occurs in basidia under the cap, and basidiospores can be released by opening the cap. However, molecular mechanisms underlying cap expansion in basidiomycetes remain poorly understood. We aimed to elucidate the molecular mechanisms of cap expansion in basidiomycetes by analyzing the unique cap-expansionless UV mutant #13 (exp2-1) in Coprinopsis cinerea. Linkage analysis and consequent genome sequence analysis revealed that the gene responsible for the mutant phenotypes encodes a putative transcription factor with two C2H2 zinc finger motifs. The mutant that was genome-edited to lack exp2 exhibited an expansionless phenotype. Some of the genes encoding cell wall degradation-related enzymes showed decreased expression during cap expansion and autolysis in the exp2 UV and genome-edited mutant. The exp2 gene is widely conserved in Agaricomycetes, suggesting that Exp2 homologs regulate fruiting body maturation in Agaricomycetes, especially cap expansion in Agaricoid-type mushroom-forming fungi. Therefore, exp2 homologs could be a target for mushroom breeding to maintain shape after harvest for some cultivating mushrooms, presenting a promising avenue for further research in breeding techniques.

Distinct laccase expression and activity profiles of Trametes versicolor facilitate degradation of benzo[a]pyrene

A Trametes versicolor isolate from the Changbai Mountain showed promising activity in degrading benzo[a]pyrene (BaP), which is a high molecular weight (HMW) polycyclic aromatic hydrocarbon (PAH) compound. It was hypothesized that the T. versicolor isolate encode BaP-degrading enzymes, among which laccase is mostly sought after due to significant commercial potential. Genome of the T. versicolor isolate was sequenced and assembled, and seven laccase homologues were identified (TvLac1-7) as candidate genes potentially contributing to BaP degradation. In order to further identify the BaP responsive laccases, time-course transcriptomic and proteomic analyses were conducted in parallel on the T. versicolor isolate upon BaP treatment. Homologous laccases showed distinct expression patterns. Most strikingly, TvLac5 was rapidly induced in the secreted proteomes (secretomes), while TvLac2 was repressed. Recombinant laccase expression and biochemical characterization further showed corresponding enzymatic activity profiles, where TvLac5 was 21-fold more effective in BaP degradation compared to TvLac2. Moreover, TvLac5 also showed 3.6-fold higher BaP degrading activity compared to a commercial laccase product of T. versicolor origin. Therefore, TvLac5 was concluded to be a BaP-responsive enzyme from T. versicolor showing effective BaP degradation activity.

Proteomic characterization of Shiitake (Lentinula edodes) post-harvest fruit bodies grown on hardwood logs and isolation of an antibacterial serine protease inhibitor

Lentinula edodes (Shiitake) is one of the most heavily cultivated mushrooms in the world with proven antioxidant and antibacterial properties, among others. Evidence indicates that the choice of mushroom cultivation technique strongly influences the production of bioactive compounds, but to date the nature of many of these compounds has not been fully established. This work focuses on the proteomic characterization of L. edodes to highlight the main active processes two days after harvest and elucidates the proteins involved in the known antioxidant and antibacterial proprieties of Shiitake fruit bodies cultivated on oak logs. A label-free approach allowed us to identify a total of 2702 proteins which were mainly involved in carbohydrate and protein metabolism, cell growth and replication, indicating that several developmental processes remain active in fruit bodies post-harvest. Proteins with antioxidant activities were identified, indicating the contribution of proteins to the antioxidant properties of L. edodes extracts. Antibacterial assays also reveal the activity of a serine protease inhibitor that strongly accumulates in the post-harvest fruit body grown on oak logs. Overall, this study contributes to the understanding of the impact of the log cultivation method on the production of Shiitake mushrooms richest in high-value bioactive compounds.

Protein components of water extracts from fruiting bodies of the reishi mushroom Ganoderma lucidum contribute to the production of functional molecules

BACKGROUND

Mushrooms have been widely considered as health foods as their extracts have anti-hypertensive and anti-tumor activities. After a thorough literature survey, we hypothesized that enzymes in mushroom extracts play an important role in synthesizing functional molecules. Therefore, in this study, proteins extracted from reishi mushroom (Ganoderma lucidum), which is used in oriental medicine, were identified by the proteomic approach, and appropriate extraction methods for improving angiotensin-converting enzyme (ACE) inhibitory activities were investigated.

RESULTS

Various glycoside hydrolases (GHs), such as β-N-acetylhexosaminidase (GH family 20), α-1,2-mannosidase (GH family 47), endo-β-1,3-glucanase (GH family 128), and β-1,3-glucanase (GH152), that degrade glycans in the fruiting body were identified. The residual glucanase activities generated β-oligosaccharides. Additionally, the glutamic acid protease of the peptidase G1 family was determined as the major protein in the extract, and the residual peptidase activity of the extracts was found to improve ACE inhibitory activities. Finally, it was observed that extraction at 50 °C is suitable for yielding functional molecules with high ACE inhibitory activities.

CONCLUSION

Water extraction is generally believed to extract only functional macromolecules that exist in mushroom fruiting bodies. This study proposed a new concept that describes how functional molecules are produced by enzymes, including proteases and GHs, during extraction. © 2018 Society of Chemical Industry.

Comparative secretomic analysis of lignocellulose degradation by Lentinula edodes grown on microcrystalline cellulose, lignosulfonate and glucose

Lentinula edodes has the potential to degrade woody and nonwoody lignocellulosic biomass. However, the mechanism of lignocellulose degradation by L. edodes is unclear. The aim of this work is to explore the profiling of soluble secreted proteins involved in lignocellulose degradation in L. edodes. For that, we compared the secretomes of L. edodes grown on microcrystalline cellulose, cellulose with lignosulfonate and glucose. Based on nanoliquid chromatography coupled with tandem mass spectrometry of whole-protein hydrolysate, 230 proteins were identified. Label-free proteomic analysis showed that the most abundant carbohydrate-active enzymes involved in polysaccharide hydrolysis were endo-β-1,4-glucanase, α-galactosidase, polygalacturonase and glucoamylase in both cellulosic secretomes. In contrast, enzymes involved in lignin degradation were most abundant in glucose culture, with laccase 1 being the predominant protein (13.13%). When the cellulose and cellulose with lignosulfonate secretomes were compared, the abundance of cellulases and hemicellulases was higher in cellulose with lignosulfonate cultures, which was confirmed by enzyme activity assays. In addition, qRT-PCR analysis demonstrated that the expression levels of genes encoding cellulases and hemicellulases were significantly increased (by 32.2- to 1166.7-fold) when L. edodes was grown in cellulose with lignosulfonate medium.

BIOLOGICAL SIGNIFICANCE

In this article, the secretomes of L. edodes grown on three different carbon sources were compared. The presented results revealed the profiling of extracellular enzymes involved in lignocellulose degradation, which is helpful to further explore the mechanism of biomass bioconversion by L. edodes.

Lentinula edodes Genome Survey and Postharvest Transcriptome Analysis

Lentinula edodes is a popular, cultivated edible and medicinal mushroom. Lentinula edodes is susceptible to postharvest problems, such as gill browning, fruiting body softening, and lentinan degradation. We constructed a de novo assembly draft genome sequence and performed gene prediction for Lentinula edodesDe novo assembly was carried out using short reads from paired-end and mate-paired libraries and by using long reads by PacBio, resulting in a contig number of 1,951 and an N₅₀ of 1 Mb. Furthermore, we predicted genes by Augustus using transcriptome sequencing (RNA-seq) data from the whole life cycle of Lentinula edodes, resulting in 12,959 predicted genes. This analysis revealed that Lentinula edodes lacks lignin peroxidase. To reveal genes involved in the loss of quality of Lentinula edodes postharvest fruiting bodies, transcriptome analysis was carried out using serial analysis of gene expression (SuperSAGE). This analysis revealed that many cell wall-related enzymes are upregulated after harvest, such as β-1,3-1,6-glucan-degrading enzymes in glycoside hydrolase (GH) families GH5, GH16, GH30, GH55, and GH128, and thaumatin-like proteins. In addition, we found that several chitin-related genes are upregulated, such as putative chitinases in GH family 18, exochitinases in GH20, and a putative chitosanase in GH family 75. The results suggest that cell wall-degrading enzymes synergistically cooperate for rapid fruiting body autolysis. Many putative transcription factor genes were upregulated postharvest, such as genes containing high-mobility-group (HMG) domains and zinc finger domains. Several cell death-related proteins were also upregulated postharvest.IMPORTANCE Our data collectively suggest that there is a rapid fruiting body autolysis system in Lentinula edodes The genes for the loss of postharvest quality newly found in this research will be targets for the future breeding of strains that keep fresh longer than present strains. De novoLentinula edodes genome assembly data will be used for the construction of a complete Lentinula edodes chromosome map for future breeding.

Alteration in the ultrastructural morphology of mycelial hyphae and the dynamics of transcriptional activity of lytic enzyme genes during basidiomycete morphogenesis

The morphogenesis of macromycetes is a complex multilevel process resulting in a set of molecular-genetic, physiological-biochemical, and morphological-ultrastructural changes in the cells. When the xylotrophic basidiomycetes Lentinus edodes, Grifola frondosa, and Ganoderma lucidum were grown on wood waste as the substrate, the ultrastructural morphology of the mycelial hyphal cell walls differed considerably between mycelium and morphostructures. As the macromycetes passed from vegetative to generative development, the expression of the tyr1, tyr2, chi1, chi2, exg1, exg2, and exg3 genes was activated. These genes encode enzymes such as tyrosinase, chitinase, and glucanase, which play essential roles in cell wall growth and morphogenesis.

The Modes of Action of ChiIII, a Chitinase from Mushroom Coprinopsis cinerea, Shift with Changes in the Length of GlcNAc Oligomers

A putative class III endochitinase (ChiIII) was reported previously to be expressed dominantly in fruiting bodies of Coprinopsis cinerea, and its expression levels increased with the maturation of the fruiting bodies. This paper further reports that ChiIII is a novel chitinase with exo- and endoactivities. When the substrate was (GlcNAc)3-5, ChiIII exhibited exoactivity, releasing GlcNAc processively from the reducing end of (GlcNAc)3-5; when the substrate was (GlcNAc)6-7, the activity of ChiIII shifted to an endoacting enzyme, randomly splitting chitin oligosaccharides to various shorter oligosaccharides. This shift in the mode of action of ChiIII may be related to its stronger hydrolytic capacity to degrade chitin in fungal cell walls. The predicted structure of ChiIII shows that it lacks the α+β domain insertion; however, its substrate binding cleft seems to be deeper than that of common endochitinases but shallower and more open than that of common exochitinases, which may be related to its exo- and endohydrolytic activities.

Genome Sequence of the Edible Cultivated Mushroom Lentinula edodes (Shiitake) Reveals Insights into Lignocellulose Degradation

Lentinula edodes, one of the most popular, edible mushroom species with a high content of proteins and polysaccharides as well as unique aroma, is widely cultivated in many Asian countries, especially in China, Japan and Korea. As a white rot fungus with lignocellulose degradation ability, L. edodes has the potential for application in the utilization of agriculture straw resources. Here, we report its 41.8-Mb genome, encoding 14,889 predicted genes. Through a phylogenetic analysis with model species of fungi, the evolutionary divergence time of L. edodes and Gymnopus luxurians was estimated to be 39 MYA. The carbohydrate-active enzyme genes in L. edodes were compared with those of the other 25 fungal species, and 101 lignocellulolytic enzymes were identified in L. edodes, similar to other white rot fungi. Transcriptome analysis showed that the expression of genes encoding two cellulases and 16 transcription factor was up-regulated when mycelia were cultivated for 120 minutes in cellulose medium versus glucose medium. Our results will foster a better understanding of the molecular mechanism of lignocellulose degradation and provide the basis for partial replacement of wood sawdust with agricultural wastes in L. edodes cultivation.

Whole genome de novo sequencing and genome annotation of the world popular cultivated edible mushroom, Lentinula edodes

Lentinula edodes, the popular shiitake mushroom, is one of the most important cultivated edible mushrooms. It is used as a food and for medicinal purposes. Here, we present the 46.1 Mb draft genome of L. edodes, comprising 13,028 predicted gene models. The genome assembly consists of 31 scaffolds. Gene annotation provides key information about various signaling pathways and secondary metabolites. This genomic information should help establish the molecular genetic markers for MAS/MAB and increase our understanding of the genome structure and function.

Comparative Study of Nonautolytic Mutant and Wild-Type Strains of Coprinopsis cinerea Supports an Important Role of Glucanases in Fruiting Body Autolysis

Autolysis of Coprinopsis cinerea fruiting bodies affects its commercial value. In this study, a mutant of C. cinerea that exhibits pileus expansion without pileus autolysis was obtained using ultraviolet mutagenesis. This suggests that pileus expansion and pileus autolysis involve different enzymes or proteins. Among the detected hydrolytic enzymes, only β-1,3-glucanase activity increased with expansion and autolysis of pilei in the wild-type strain, but the increase was abolished in the mutant. This suggests that β-1,3-glucanases plays a major role in the autolysis. Although there are 43 possible β-1,3-glucoside hydrolases genes, only 4 known genes, which have products that are thought to act synergistically to degrade the β-1,3-glucan backbone of cell walls during fruiting body autolysis, and an unreported gene were upregulated during pileus expansion and autolysis in the wild-type stain but were suppressed in the mutant. This suggests that expression of these β-1,3-glucanases is potentially controlled by a single regulatory mechanism.

Purification, characterization and synergism in autolysis of a group of 1,3-β-glucan hydrolases from the pilei of Coprinopsis cinerea fruiting bodies

Using a combined chromatography method, we simultaneously purified three protein fractions (II-2, II-3 and II-4) with 1,3-β-glucanase activity from extraction of pilei of Coprinopsis cinerea fruiting bodies. MALDI-TOF/TOF amino acid sequencing showed that these three fractions matched a putative exo-1,3-β-glucanase, a putative glucan 1,3-β-glucosidase and a putative glycosyl hydrolase family 16 protein annotated in the C. cinerea genome, respectively; however, they were characterized as a 1,3-β-glucosidase, an exo-1,3-β-glucanase and an endo-1,3-β-glucanase, respectively, by analysis of their substrate specificities and modes of action. This study explored how these three 1,3-β-glucoside hydrolases synergistically acted on laminarin: the endo-1,3-β-glucanase hydrolysed internal glycosidic bonds of laminarin to generate 1,3-β-oligosaccharides of various lengths, the exo-1,3-β-glucanase cleaved the longer-chain laminarioligosaccharides into short-chain disaccharides, laminaribiose and gentiobiose, and the 1,3-β-glucosidase further hydrolysed laminaribiose to glucose. The remaining gentiobiose must be hydrolysed by other 1,6-β-glucosidases. Therefore, the endo-1,3-β-glucanase, exo-1,3-β-glucanase and 1,3-β-glucosidase may act synergistically to completely degrade the 1,3-β-glucan backbone of the C. cinerea cell wall during fruiting body autolysis. These three 1,3-β-glucoside hydrolases share a similar optimum pH and optimum temperature, supporting the speculation that these enzymes work together under the same conditions to degrade 1,3-β-glucan in the C. cinerea cell wall during fruiting body autolysis.

Lentinan degradation in the Lentinula edodes fruiting body during postharvest preservation is reduced by downregulation of the exo-β-1,3-glucanase EXG2

Lentinan from Lentinula edodes fruiting bodies (shiitake mushrooms) is a valuable β-glucan for medical purposes based on its anticancer activity and immunomodulating activity. However, lentinan content in fruiting bodies decreases after harvesting and storage due to an increase in glucanase activity. In this study, we downregulated the expression of an exo-β-1,3-glucanase, exg2, in L. edodes using RNA interference. In the wild-type strain, β-1,3-glucanase activity in fruiting bodies remarkably increased after harvesting, and 41.7% of the lentinan content was lost after 4 days of preservation. The EXG2 downregulated strain showed significantly lower lentinan degrading activity (60-70% of the wild-type strain) in the fruiting bodies 2-4 days after harvesting. The lentinan content of fresh fruiting bodies was similar in the wild-type and EXG2 downregulated strains, but in the downregulated strain, only 25.4% of the lentinan was lost after 4 days, indicating that downregulation of EXG2 enables keeping the lentinan content high longer.

Gene expression profiling reveals large regulatory switches between succeeding stipe stages in Volvariella volvacea

The edible mushroom Volvariella volvacea is an important crop in Southeast Asia and is predominantly harvested in the egg stage. One of the main factors that negatively affect its yield and value is the rapid transition from the egg to the elongation stage, which has a decreased commodity value and shelf life. To improve our understanding of the changes during stipe development and the transition from egg to elongation stage in particular, we analyzed gene transcription in stipe tissue of V. volvacea using 3′-tag based digital expression profiling. Stipe development turned out to be fairly complex with high numbers of expressed genes, and regulation of stage differences is mediated mainly by changes in expression levels of genes, rather than on/off modulation. Most explicit is the strong up-regulation of cell division from button to egg, and the very strong down-regulation hereof from egg to elongation, that continues in the maturation stage. Button and egg share cell division as means of growth, followed by a major developmental shift towards rapid stipe elongation based on cell extension as demonstrated by inactivation of cell division throughout elongation and maturation. Examination of regulatory genes up-regulated from egg to elongation identified three potential high upstream regulators for this switch. The new insights in stipe dynamics, together with a series of new target genes, will provide a sound base for further studies on the developmental mechanisms of mushroom stipes and the switch from egg to elongation in V. volvacea in particular.

Identification and expression analysis of a new glycoside hydrolase family 55 exo-β-1,3-glucanase-encoding gene in Volvariella volvacea suggests a role in fruiting body development

The edible straw mushroom Volvariella volvacea is an important crop in South East Asia and is predominantly harvested in the egg stage. Rapid stipe elongation and cap expansion result in a swift transition from the egg to elongation and maturation stage, which are subjected to fast senescence and deterioration. In other mushrooms, β-1,3-glucanases have been associated with degradation (softening) of the cell wall during stipe elongation and senescence. We present a new glycoside hydrolase family 55 (GH55) exo-β-1,3-glucanase gene, exg2, and highly conserved deduced EXG2 protein. The 3D model and presumed catalytic residues of V. volvacea EXG2 are identical to Lentinula edodes EXG2 and Phanerochaete chrysosporium Lam55A, supporting similar enzymatic functions. In addition to previous association to stipe elongation and senescence, our data clearly indicates a role for cap (pileus) expansion. Digital gene expression, quantitative PCR and isobaric tags for relative and absolute quantification analysis showed low exg2 and EXG2 levels in primordia, button, egg and elongation stages and significantly increased levels in the maturation stage. Subsequent relative quantitative PCR analysis designated expression of exg2 to the stipe in the elongation stage and to the pileus and stipe in the maturation stage. EXG2 cell wall softening activity, close correlation of exg2 expression with the principal expanding mushroom tissues and a strong conservation of expression patterns and protein sequences in other mushrooms, make V. volvacea exg2 an important candidate for future studies on mechanisms of fruiting body expansion and senescence causing commodity value loss.

Fungal laccase, manganese peroxidase and lignin peroxidase: gene expression and regulation

Extensive research efforts have been dedicated to characterizing expression of laccases and peroxidases and their regulation in numerous fungal species. Much attention has been brought to these enzymes broad substrate specificity resulting in oxidation of a variety of organic compounds which brings about possibilities of their utilization in biotechnological and environmental applications. Research attempts have resulted in increased production of both laccases and peroxidases by the aid of heterologous and homologous expression. Through analysis of promoter regions, protein expression patterns and culture conditions manipulations it was possible to compare and identify common pathways of these enzymes' production and secretion. Although laccase and peroxidase proteins have been crystallized and thoroughly analyzed, there are still a lot of questions remaining about their evolutionary origin and the physiological functions. This review describes the present understanding of promoter sequences and correlation between the observed regulatory effects on laccase, manganese peroxidase and lignin peroxidase genes transcript levels and the presence of specific response elements.

Characterization of β-N-acetylhexosaminidase (LeHex20A), a member of glycoside hydrolase family 20, from Lentinula edodes (shiitake mushroom)

We purified and cloned a β-N-acetylhexosaminidase, LeHex20A, with a molecular mass of 79 kDa from the fruiting body of Lentinula edodes (shiitake mushroom). The gene lehex20a gene had 1,659 nucleotides, encoding 553 amino acid residues. Sequence analysis indicated that LeHex20A belongs to glycoside hydrolase (GH) family 20, and homologues of lehex20a are broadly represented in the genomes of basidiomycetes. Purified LeHex20A hydrolyzed the terminal monosaccharide residues of β-N-acetylgalactosaminides and β-N-acetylglucosaminides, indicating that LeHex20A is a β-N-acetylhexosaminidase classified into EC 3.2.1.52. The maximum LeHex20A activity was observed at pH 4.0 and 50°C. The kinetic constants were estimated using chitooligosaccharides with degree of polymerization 2-6. GH20 β-N-acetylhexosaminidases generally prefer chitobiose among natural substrates. However, LeHex20A had the highest catalytic efficiency (kcat/Km) for chitotetraose, and the Km values for GlcNAc6 were 3.9-fold lower than for chitobiose. Furthermore, the enzyme partially hydrolyzed amorphous chitin polymers. These results indicate that LeHex20A can produce N-acetylglucosamine from long-chain chitomaterials.

Endo-β-1,3-glucanase GLU1, from the fruiting body of Lentinula edodes, belongs to a new glycoside hydrolase family

The cell wall of the fruiting body of the mushroom Lentinula edodes is degraded after harvesting by enzymes such as β-1,3-glucanase. In this study, a novel endo-type β-1,3-glucanase, GLU1, was purified from L. edodes fruiting bodies after harvesting. The gene encoding it, glu1, was isolated by rapid amplification of cDNA ends (RACE)-PCR using primers designed from the N-terminal amino acid sequence of GLU1. The putative amino acid sequence of the mature protein contained 247 amino acid residues with a molecular mass of 26 kDa and a pI of 3.87, and recombinant GLU1 expressed in Pichia pastoris exhibited β-1,3-glucanase activity. GLU1 catalyzed depolymerization of glucans composed of β-1,3-linked main chains, and reaction product analysis by thin-layer chromatography (TLC) clearly indicated that the enzyme had an endolytic mode. However, the amino acid sequence of GLU1 showed no significant similarity to known glycoside hydrolases. GLU1 has similarity to several hypothetical proteins in fungi, and GLU1 and highly similar proteins should be classified as a novel glycoside hydrolase family (GH128).

An endo-β-1,6-glucanase involved in Lentinula edodes fruiting body autolysis

A β-1,6-glucanase, LePus30A, was purified and cloned from fruiting bodies of the basidiomycete Lentinula edodes. β-1,6-glucanases degrade β-1,6-glucan polysaccharides, a unique and essential component of fungal cell walls. The complementary DNA of LePus30A includes an open reading frame of 1,575 bp encoding an 18 amino acid signal peptide and the 506 amino acid mature protein. Sequence analysis indicated that LePus30A is a member of glycoside hydrolase family 30, and highly similar genes are broadly conserved among basidiomycetes. The purified LePus30A catalyzed depolymerization of β-1,6-glucan endolytically and was highly specific toward β-1,6-glucan polysaccharide. It is known that the cell walls of fruiting bodies of basidiomycetes are autodegraded after harvesting by means of enzymatic hydrolysis. The transcript level of LePus30A gene (lepus30a) was significantly increased in fruiting bodies after harvesting. Moreover, LePus30A showed hydrolyzing activity against the cell wall components of L. edodes fruiting bodies. These results suggest that LePus30A is responsible for the degradation of the cell wall components during fruiting body autolysis after harvest.

A chimeric laccase with hybrid properties of the parental Lentinula edodes laccases

We created a chimeric laccase from two different laccases, Lcc1 and Lcc4, from Lentinula edodes. Lcc1 is a secretory lignin-degrading enzyme produced in liquid cultures of L. edodes. Lcc4 is a tissue-accumulating-type enzyme, which is thought to be involved in melanin synthesis in fruiting body after harvesting. Lcc1 and Lcc4 differ in their Km values for some substrates, especially beta-(3,4-dihydroxyphenyl) alanine (L-DOPA) and catechol. The novel chimeric laccase, Lcc4/1, has properties that are a hybrid of those of Lcc1 and Lcc4. Lcc4/1 acts upon both Lcc1 and Lcc4 substrates and most of its Km values are lower than those of Lcc1 and Lcc4. Homology modeling indicates that the deduced shape of the substrate-binding pocket of the chimeric laccase is larger than that of Lcc1 and similar to that of Lcc4. The other biochemical properties, such as temperature and pH dependency, are intermediate between those of Lcc1 and Lcc4.

Characterization of the post-harvest changes in gene transcription in the gill of the Lentinula edodes fruiting body

We compared the gene expression patterns of Lentinula edodes fresh fruiting bodies and fruiting bodies 3 days after harvest, by suppression subtractive hybridization, to characterize the physiologic changes that occur after harvest, such as gill browning and cell wall lysis of the fruiting body, which are responsible for the loss of food quality and value. We found increase of transcription levels of several enzyme encoding genes, such as, two phenol oxidases encoding genes (tyr tyrosinase, lcc4 laccase), and several cell wall degradation-related enzyme-encoding genes, such as mixed-linked glucanase (mlg1), chitinases (chi1, chi2), chitin deacetylase (chd1), and chitosanase (cho1), after harvesting. We isolated a putative transcription factor-encoding gene (L. edodes exp1) with high similarity to exp1 from Coprinopsis cinerea, which is involved in autolysis of the cap during spore diffusion. Transcription of L. edodes exp1 increased post-harvest, which suggests that its target genes are up-regulated after harvesting. These enzymes and the transcription factor may be involved in L. edodes fruiting body senescence.

The tyrosinase-encoding gene of Lentinula edodes, Letyr, is abundantly expressed in the gills of the fruit-body during post-harvest preservation

The gill browning of Lentinula edodes fruit-bodies during preservation is thought to be due to melanin biosynthesis catalyzed by tyrosinase. We isolated a genomic DNA sequence and cDNA encoding a putative tyrosinase from the white rot basidiomycete Lentinula edodes (shiitake mushroom). The gene, named Letyr, consists of a 1,854-bp open reading frame interrupted by eight introns, and encodes a putative protein of 618 amino acid residues with an estimated molecular mass of 68 kDa. Amino acid residues known to be involved in copper-binding domains were conserved in the deduced amino acid residues of LeTyr. Transcriptional and translational expression of Letyr in the gills of the fruit-body increased during preservation after harvest. This correlation between Letyr expression and fruit-body preservation suggests that tyrosinase gene expression contributes to gill browning.

Secretory expression of the non-secretory-type Lentinula edodes laccase by Aspergillus oryzae

The shiitake mushroom, Lentinula edodes, has an extracelluar secretory-type laccase, Lcc1, and a fruiting-body-accumulation-type laccase, Lcc4. We previously reported the production of Lcc1 by plant cells, but had difficulty producing Lcc4. Here, we report the production of Lcc1 and Lcc4 by Aspergillus oryzae and the extracellular secretory production of Lcc4 using a modified secretion signal peptide (SP) from Lcc1. Sp-Lcc4 produced by A. oryzae had biochemical activities similar to Lcc4 produced by L. edodes. Lcc1 did not react with beta-(3,4-dihydroxyphenol) alanine (DOPA), but Lcc4 from L. edodes and A. oryzae could oxidize DOPA. K(M) values for the substrates 2,2'-azino-di-(3-ethylbenzthiazolinsulfonate), 2,6-dimethoxyphenol, guaiacol, pyrogallol, and catechol were similar for Lcc4 and Sp-Lcc4. In conclusion, a non-secretory-type fungal laccase is secreted into the culture media with its original enzymatic properties by exploiting modified secretory signal peptide.

Purification and characterization of a novel exo-beta-1,3-1,6-glucanase from the fruiting body of the edible mushroom Enoki (Flammulina velutipes)

To elucidate the role of beta-glucanases in the cell-wall degradation involved in morphogenesis, an exo-beta-1,3-1,6-glucanase (FvBGL1) was purified from fruiting bodies of the edible mushroom Enoki (Flammulina velutipes), and its enzymatic properties were studied. At least three beta-glucanases were detected in the crude extract by zymogram assay when 1% laminarin was used as substrate. The molecular mass of FvBGL1 was estimated by SDS-PAGE to be 80 kDa. The optimum pH and temperature for the action of FvBGL1 were 6.1 and 60 degrees C respectively. FvBGL1 was completely inactivated by 1 mM mercuric ions. FvBGL1 hydrolyzed F. velutipes cell-wall beta-glucan as well as beta-1,3- and beta-1,6-glucans from various sources with glucose as the only reaction product. Transglucosylation was observed when the enzyme acted on laminarinonaose. FvBGL1 can be assumed to degrade F. velutipes cell-wall beta-1,3-glucan, but most probably acts more efficiently in concert with other endogenous beta-glucan degrading enzymes.

Heterologous expression of lcc1 from Lentinula edodes in tobacco BY-2 cells results in the production an active, secreted form of fungal laccase

Laccase (Lcc) is a lignin-degrading enzyme produced by white-rot fungi and has been the subject of much interest in the field of bioremediation due to its ability to oxidize phenolic compounds. In this report, we describe the isolation and characterization of lcc1, a novel gene of Lentinula edodes that encodes Lcc1, and demonstrate that recombinant Lcc1 is expressed in an active, secreted form in tobacco BY-2 cells in culture. The open reading frame of lcc1 was 1,557 base pairs in length and encoded a putative protein of 518 amino acids. We introduced a chimeric form of lcc1 (CaMV35Sp:clcc1) into tobacco BY-2 cells and obtained several stable clcc1 transformants that expressed active Lcc1. Lcc1 activity in BY-2 culture media was higher than in cellular extracts, which indicated that recombinant Lcc1 was produced in a secreted form. Recombinant Lcc1 had a smaller apparent molecular weight and exhibited a different pattern of posttranslational modification than Lcc1 purified from L. edodes. The substrate specificity of purified recombinant Lcc1 was similar to L. edodes Lcc1, and both enzymes were able to decolorize the same set of dyes. These results suggest that heterologous expression of fungal Lcc1 in BY-2 cells will be a valuable tool for the production of sufficient quantities of active laccase for bioremediation.

Pileus differentiation and pileus-specific protein expression in Flammulina velutipes

Fruiting bodies of Flammulina velutipes formed under complete darkness had a poorly developed pileus on top (pinhead fruiting body), and lacked a hymenium. Upon light stimulation, the pileus immediately began to develop on the apical region of the pinhead fruiting body. Swelling of the apical region caused by cell division was observed 2 days after light treatment; at day 4, the junction fracture between the pileus and stipe, and formation of the hymenium primordia were observed; at 6 days, gills were observed. We identified a cell wall-associated protein (PSH) that was specifically induced in the pileus, but not in the stipe, following light treatment of the pinhead fruiting body. Cloning and sequence analysis of the gene encoding PSH (psh) revealed a motif in the C-terminal region of the predicted amino acid sequence that was similar to hydrophobin. The level of transcription of psh was low in the stipe, but it was expressed at a high level in the pileus of the normal fruiting body. Transcription was also low in pinhead fruiting bodies, but increased after light treatment. These results indicate that psh is specifically expressed during pileus differentiation induced by light stimulation.

Lentinula edodes tlg1 encodes a thaumatin-like protein that is involved in lentinan degradation and fruiting body senescence

Lentinan is an antitumor product that is purified from fresh Lentinula edodes fruiting bodies. It is a cell wall component, comprising beta-1,3-glucan with beta-1,6-linked branches, which becomes degraded during postharvest preservation as a result of increased glucanase activity. In this study, we used N-terminal amino acid sequence to isolate tlg1, a gene encoding a thaumatin-like (TL) protein in L. edodes. The cDNA clone was approximately 1.0 kb whereas the genomic sequence was 2.1 kb, and comparison of the two indicated that tlg1 contains 12 introns. The tlg1 gene product (TLG1) was predicted to comprise 240 amino acids, with a molecular mass of 25 kD and isoelectric point value of 3.5. The putative amino acid sequence exhibits approximately 40% identity with plant TL proteins, and a fungal genome database search revealed that these TL proteins are conserved in many fungi including the basidiomycota and ascomycota. Transcription of tlg1 was not detected in vegetative mycelium or young and fresh mushrooms. However, transcription increased following harvest. Western-blot analysis demonstrated a rise in TLG1 levels following harvest and spore diffusion. TLG1 expressed in Escherichia coli and Aspergillus oryzae exhibited beta-1,3-glucanase activity and, when purified from the L. edodes fruiting body, demonstrated lentinan degrading activity. Thus, we suggest that TLG1 is involved in lentinan and cell wall degradation during senescence following harvest and spore diffusion.