Isolation and characterization of the glyceraldehyde-3-phosphate dehydrogenase gene of Lentinus edodes

Extracellular enzymes secreted in the mycelial block of Lentinula edodes during hyphal growth

Lentinula edodes (shiitake mushroom) is one of the most widely cultivated edible mushrooms and is primarily cultivated using sawdust medium. While there have been improvements in the cultivation technology, the mechanism of mycelial block cultivation, such as mycelial growth and enzymatic sawdust degradation, has not been clarified. In this study, the mycelium was elongated longitudinally in the bottle sawdust culture for 27 days, and the cultivated sawdust medium was divided into three sections (top, middle, and bottom parts). To determine spatial heterogeneity in the enzyme secretion, the enzymatic activities of each part were analyzed. Lignocellulose degradation enzymes, such as endoglucanase, xylanase, and manganese peroxidase were highly secreted in the top part of the medium. On the other hand, amylase, pectinase, fungal cell wall degradation enzyme (β-1,3-glucanase, β-1,6-glucanase, and chitinase), and laccase activities were higher in the bottom part. The results indicate that the principal sawdust degradation occurs after mycelial colonization. Proteins with the laccase activity were purified from the bottom part of the medium, and three laccases, Lcc5, Lcc6 and Lcc13, were identified. In particular, the expression of Lcc13 gene was higher in the bottom part compared with the level in the top part, suggesting Lcc13 is mainly produced from the tip region and have important roles for mycelial spread and nutrient uptake during early stage of cultivation.

Metabolic regulation mechanism of Trametes gibbosa CB_1 on lignin

White rot fungi can degrade lignin and play a significant role in the recycling of carbon resources for environmental protection. Trametes gibbosa is the main white rot fungus in Northeast China. The main acids produced by T. gibbosa degradation, include long-chain fatty acids, lactic acid, succinic acid, and some small molecular compounds for example benzaldehyde. A variety of proteins respond to lignin stress and play an important role in xenobiotics metabolism, metal ion transport, and redox. Coordinated regulation and detoxification activation of H₂O₂ produced in oxidative stress by peroxidase coenzyme system and Fenton reaction. The Dioxygenase cleavage pathway and β-ketoadipic acid pathway are the main oxidation pathways of lignin degradation, which mediate the entry of "COA" into the TCA cycle. In the joint action of hydrolase and coenzyme, cellulose, hemicellulose, and other polysaccharides are degraded and finally converted to glucose to participate in energy metabolism. The expression of the laccase (Lcc_1) protein was verified by E. coli. Also, the Lcc_1 overexpression mutant was established. The morphology of mycelium was dense and the lignin degradation rate was improved. We completed the first non-directional mutation of in T. gibbosa. It also improved the mechanism of T. gibbosa in response to lignin stress.

Research Progress on Edible Fungi Genetic System

In order to obtain strains with targeted changes in genetic characteristics, molecular biology and genetic engineering techniques are used to integrate target gene fragments into the vector and transform them into recipient cells. Due to the different target genes and functional elements on the transformation plasmids, gene silencing, gene knockout, and gene overexpression can be carried out, which provides a new way to study the gene function of edible fungi. At present, the cloning vectors used in the transformation of edible fungi are modified by bacterial plasmids, among which pCAMBIA-1300 plasmid and pAN7 plasmid are the two most commonly used basic vectors. On this basis, some basic elements such as promoters, selective marker genes, and reporter genes were added to construct silencing vectors, knockout vectors, and overexpression vectors. At the same time, different expression vector systems are needed for different transformation methods. In this chapter, the main elements of the genetic system (promoters, screening markers), the current main genetic transformation methods (Agrobacterium-mediated transformation, liposome transformation, electroporation method), and the specific application of transformation were systematically summarized, which provides a reference for the study of the genetic system of edible fungi.

De novo transcriptome analysis of Pleurotus djamor to identify genes encoding CAZymes related to the decomposition of corn stalk lignocellulose

CAZymes play a very important role in the biotransformation of corn stalk biomass, which is an important resource for sustainable development. Pleurotus djamor can produce CAZymes related to the decomposition of corn stalk lignocellulose biomass in sole corn stalk substrate; however, little is known about their encoding genes. In order to identify CAZymes encoding genes, RNA high-throughput sequencing of P. djamor was performed in this study. The results showed that a core set of 70 upregulated genes encoding putative CAZymes were revealed. They encode 19 kinds of CAZymes in total, of which there are 4 EGLs, 8 CBHs, 5 BGLs, and 12 LPMOs related to cellulose degradation, 8 XYNs, 1 XYL, 2 AGUs, 3 ABFs, 2 AGLs, and 2 AXEs related to hemicellulose degradation, and 5 LACCs, 2 MnPs, 5 VPs, 3 CDHs, 1 AAO, 1 GOX, 1 AOX, 2 GAOXs, and 3 GLOXs related to lignin degradation. This variety suggests that CAZymes may play a very important role in decomposing the lignocellulose biomass of corn stalk. This is the first study to report the de novo transcriptome sequencing of P. djamor, which will produce a dataset of genes encoding CAZymes, thereby laying the foundation to elucidate the degradation mechanism of corn stalk biomass and boost the biotransformation of corn stalk biomass resources.

Overexpression and repression of the tyrosinase gene in Lentinula edodes using the pChG vector

Tyrosinase is an industrially useful enzyme, however, it causes gill browning of Lentinula edodes fruiting bodies during preservation. In this study, we constructed two vectors, pChG-gTs and pChG-gTa, expressing sense and antisense tyrosinase gene of L. edodes, respectively, using promoters derived from the glyceraldehyde-3-phosphate dehydrogenase gene. The host strain SR-1 of L. edodes was selected because of its fast growth, high protoplast yield, and high regeneration rate. Upon transformation of the host strain SR-1 with the pChG-gTs vector, a clone with 3.6-fold and 14.5-fold higher tyrosinase activity in vegetative mycelia and in fresh gills, respectively, than that of the host strain was obtained from nine transformants. Similarly, two clones containing the pChG-gTa vector with effectively repressed tyrosinase gene expression in vegetative mycelia and gills during the late stage of post-harvest preservation of fruiting bodies were obtained from 10 transformants. However, it remained unclear whether repression of the tyrosinase gene prevented gill browning, as the host strain also showed less browning than a commercial strain. Thus, this study highlights the usefulness of the pChG vector in expressing homologous enzyme coding genes in the vegetative mycelia and fruiting bodies of 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.

Grouping of multicopper oxidases in Lentinula edodes by sequence similarities and expression patterns

The edible white rot fungus Lentinula edodes possesses a variety of lignin degrading enzymes such as manganese peroxidases and laccases. Laccases belong to the multicopper oxidases, which have a wide range of catalytic activities including polyphenol degradation and synthesis, lignin degradation, and melanin formation. The exact number of laccases in L. edodes is unknown, as are their complete properties and biological functions. We analyzed the draft genome sequence of L. edodes D703PP-9 and identified 13 multicopper oxidase-encoding genes; 11 laccases in sensu stricto, of which three are new, and two ferroxidases. lcc8, a laccase previously reported in L. edodes, was not identified in D703PP-9 genome. Phylogenetic analysis showed that the 13 multicopper oxidases can be classified into laccase sensu stricto subfamily 1, laccase sensu stricto subfamily 2 and ferroxidases. From sequence similarities and expression patterns, laccase sensu stricto subfamily 1 can be divided into two subgroups. Laccase sensu stricto subfamily 1 group A members are mainly secreted from mycelia, while laccase sensu stricto subfamily 1 group B members are expressed mainly in fruiting bodies during growth or after harvesting but are lowly expressed in mycelia. Laccase sensu stricto subfamily 2 members are mainly expressed in mycelia, and two ferroxidases are mainly expressed in the fruiting body during growth or after harvesting, and are expressed at very low levels in mycelium. Our data suggests that L. edodes laccases in same group share expression patterns and would have common biological functions.

Cloning and analysis of a functional promoter of fungal immunomodulatory protein from Flammulina velutipes

Fugal immunomodulatory protein from Flammulina velutipes (FIP-fve) belongs to FIPs family, which has precious pharmaceutical value. To understand the regulatory mechanism of FIP-fve expression, we have cloned a 900 bp genomic DNA fragment from the transcriptional start site of the FIP-fve gene using genomic walker technology. Sequence analysis showed the presence of several eukaryotic transcription factor binding motifs in the 900 bp of upstream region of the FIP-fve gene, which contains one putative TATA-boxes, four possible CAAT-boxes, one ABRE, one ARE, three CGTCA-motifs, two TGA-elements and four Skn-1 motifs. The eukaryotic expression vector pfveP:: GUS-GFP was transferred into tobacco via an agrobacterium-mediated leaf disc transformation. The results showed that the FIP-fve promoter could induce the reporter gene GUS or GFP expression in different tissues of tobaccos. This study would lay a foundation for expression regulation of FIP-fve and development of genetic-modified plant products.

Isolation of Genes Specifically Expressed in the Fruit Body of the Edible BasidiomyceteLentinula edodes

In order to isolate the genes expressed specifically and abundantly in the mature fruit body of Lentinula edodes, the cDNAs derived from the gill of the fruit body were compared with the cDNAs from the mycelia by differential screening. Consequently, six clones were identified as fruit-body-specific genes (fbg03, 08, 13, 14, 16, and 21). The deduced amino acid sequence of fbg14 (Le.cypfb) had significant homology with the cytochrome P450 protein. The transcriptional level of fbg16, which showed 29.9% identity with the riboflavin aldehyde-forming enzyme of Agaricus bisporus, was highest among all of the fbg clones. This result indicates that the promoter region of fbg16 may become a powerful candidate for the expression signal of the vector for the gene manipulation in the mature fruit body.

Constructing a new integrated genetic linkage map and mapping quantitative trait loci for vegetative mycelium growth rate in Lentinula edodes

The most saturated linkage map for Lentinula edodes to date was constructed based on a monokaryotic population of 146 single spore isolates (SSIs) using sequence-related amplified polymorphism (SRAP), target region amplification polymorphism (TRAP), insertion-deletion (InDel) markers, and the mating-type loci. Five hundred and twenty-four markers were located on 13 linkage groups (LGs). The map spanned a total length of 1006.1 cM, with an average marker spacing of 2.0 cM. Quantitative trait loci (QTLs) mapping was utilized to uncover the loci regulating and controlling the vegetative mycelium growth rate on various synthetic media, and complex medium for commercial cultivation of L. edodes. Two and 13 putative QTLs, identified respectively in the monokaryotic population and two testcross dikaryotic populations, were mapped on seven different LGs. Several vegetative mycelium growth rate-related QTLs uncovered here were clustered on LG4 (Qmgr1, Qdgr1, Qdgr2 and Qdgr9) and LG6 (Qdgr3, Qdgr4 and Qdgr5), implying the presence of main genomic areas responsible for growth rate regulation and control. The QTL hotspot region on LG4 was found to be in close proximity to the region containing the mating-type A (MAT-A) locus. Moreover, Qdgr2 on LG4 was detected on different media, contributing 8.07 %-23.71 % of the phenotypic variation. The present study provides essential information for QTL mapping and marker-assisted selection (MAS) in L. edodes.

Polysaccharide-inducible endoglucanases from Lentinula edodes exhibit a preferential hydrolysis of 1,3-1,4-β-glucan and xyloglucan

Three genes encoding glycoside hydrolase family 12 (GH12) enzymes from Lentinula edodes, namely Lecel12A, Lecel12B, and Lecel12C, were newly cloned by PCR using highly conserved sequence primers. To investigate enzymatic properties, recombinant enzymes encoded by L. edodes DNAs and GH12 genes from Postia placenta (PpCel12A and PpCel12B) and Schizophyllum commune (ScCel12A) were prepared in Brevibacillus choshinensis. Recombinant LeCel12A, PpCel12A, and PpCel12B, which were grouped in GH12 subfamily 1, preferentially hydrolyzed 1,3-1,4-β-glucan. By contrast, LeCel12B, LeCel12C, and ScCel12A, members of the subfamily 2, exhibited specific hydrolysis of xyloglucan. These results suggest that two subfamilies of GH12 are separated based on the substrate specificity. Transcript levels of L. edodes genes increased 72 h after growth of L. edodes mycelia cells in the presence of plant cell wall polymers such as xyloglucan, 1,3-1,4-β-glucan, and cellulose. These results suggest that L. edodes GH12 enzymes have evolved to hydrolyze 1,3-1,4-β-glucan and xyloglucan, which might enhance hyphal extension and nutrient acquisition.

Cloning and characterization of two allelic glyceraldehyde-3-phosphate dehydrogenase genes in Auricularia auricula-judae

Two allelic variants of the gpd gene, Gpd(a) and Gpd(b), were isolated based on a putative glyceraldehyde-3-phosphate dehydrogenase encoding sequence from the transcriptome of Auricularia auricula-judae strain Au916. The two alleles were found to have a 73 bp length discrepancy and 39 SNP variations. Both of the genomic DNA sequences of two alleles were interrupted by five introns, and encoded a same 340 aa protein. Intron positions analysis showed that the first intron was absent, but the last unique intron was gained in A. auricula-judae. Allele-specific expression analysis showed that the Gpd(a) and Gpd(b) were expressed with no significant difference in dikaryotic mycelia of A. auricula-judae. To the best of our knowledge, this is the first report about the detection of two allelic gpd genes in A. auricula-judae, as well as the application of allele-specific primers in gene expression analysis for this edible fungus.

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.

Highly Efficient Electroporation-mediated Transformation into Edible Mushroom Flammulina velutipes

In this study, we developed an efficient electroporation-mediated transformation system featuring Flammulina velutipes. The flammutoxin (ftx) gene of F. velutipes was isolated by reverse transcription-PCR. pFTXHg plasmid was constructed using the partial ftx gene (410 bp) along with the hygromycin B phosphotransferase gene (hygB) downstream of the glyceraldehydes-3-phosphate dehydrogenase (gpd) promoter. The plasmid was transformed into protoplasts of monokaryotic strain 4019-20 of F. velutipes by electroporation. High transformation efficiency was obtained with an electric-pulse of 1.25 kV/cm by using 177 transformants/µg of DNA in 1 × 10(7) protoplasts. PCR and Southern blot hybridization indicated that a single copy of the plasmid DNA was inserted at different locations in the F. velutipes genome by non-homologous recombination. Therefore, this transformation system could be used as a useful tool for gene function analysis of F. velutipes.

Sequence analysis and structural characterization of a glyceraldehyde-3-phosphate dehydrogenase gene from the phytopathogenic fungus Eremothecium ashbyi

Eremothecium ashbyi is a phytopathogenic fungus infesting cotton, soybeans and several other plants. This highly flavinogenic fungus has been phylogenetically characterized, but the genetic aspects of its central metabolic and riboflavin biosynthetic pathways are unknown. An ORF of 996 bp was obtained from E. ashbyi by using degenerate primers for glyceraldehyde-3-phosphate dehydrogenase (GPD) through reverse transcriptase polymerase chain reaction (RT-PCR) and 5'-3' rapid amplification of cDNA ends (RACE-PCR). This nucleotide sequence had a high similarity of 88% with GPD sequence of Ashbya gossypii. The putative GPD peptide of 331-aa had a high similarity of 85% with the GPD sequence from other ascomycetes. The ORF had an unusually strong codon bias with 5 amino acids showing strict preference of a single codon. The theoretical molecular weight for the putative peptide was 35.58 kDa with an estimated pI of 5.7. A neighbor-joining tree showed that the putative peptide from E. ashbyi displayed the highest similarity to GPD of A. gossypii. The gene sequence is available at the GenBank, accession number EU717696. Homology modeling done with Kluyveromyces marxianus GPD (PDB: 2I5P) as template indicated high structural similarity.

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.

The glyceraldehyde-3-phosphate dehydrogenase gene of Moniliophthoraperniciosa, the causal agent of witches' broom disease of Theobroma cacao

This report describes the cloning, sequence and expression analysis of the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene of Moniliophthora perniciosa, the most important pathogen of cocoa in Brazil. Southern blot analysis revealed the presence of a single copy of the GAPDH gene in the M. perniciosa genome (MpGAPDH). The complete MpGAPDH coding sequence contained 1,461 bp with eight introns that were conserved in the GAPDH genes of other basidiomycete species. The cis-elements in the promoter region of the MpGAPDH gene were similar to those of other basidiomycetes. Likewise, the MpGAPDH gene encoded a putative 339 amino acid protein that shared significant sequence similarity with other GAPDH proteins in fungi, plants, and metazoans. Phylogenetic analyses clustered the MPGAPDH protein with other homobasidiomycete fungi of the family Tricholomataceae. Expression analysis of the MpGAPDH gene by real-time PCR showed that this gene was more expressed (~1.3X) in the saprotrophic stage of this hemibiotrophic plant pathogen than in the biotrophic stage when grown in cacao extracts.

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.

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.

A highly efficient polyethylene glycol-mediated transformation method for mushrooms

A highly efficient transformation system mediated by polyethylene glycol was developed for the cultivated mushroom Pleurotus ostreatus. Eighty to 180 integrative and stable-resistant colonies appeared per mug of DNA per 10(7) viable protoplasts in a transformation experiment with the hygromycin B phosphotransferase gene (hph), which is about 40-1800 times higher than that previously reported in P. ostreatus. One hundred to 150 transformants emitting green fluorescence were observed per mug of DNA per 10(7) viable protoplasts in a transformation with the green fluorescent protein gene, but green fluorescence disappeared 30 h after transformation, suggesting that the green fluorescent protein gene was only transiently expressed in P. ostreatus. Plasmid pAN7-1 was also transferred into two important cultivated mushrooms, Ganoderma lucidum and Lentinus edodes, and 120-150 and 85-100 transformants per mug of DNA per 10(7) viable protoplasts were obtained, respectively, which is seven to 38 times and 24-28 times greater than previously reported. These data indicate that this new polyethylene glycol-mediated transformation procedure is highly efficient for mushrooms, and could be a useful tool in mushroom improvement by gene engineering.

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

Lentinan, an antitumor substance purified from Lentinula edodes, is degraded during post-harvest preservation as a result of increased glucanase activity. We isolated an exo-beta-1,3-glucanase encoding gene, exg2, from L. edodes which is a homologue of an exo-glucanase-encoding gene conserved in ascomycetous fungi. The exg2 gene was cloned as an approximately 2.4-kbp cDNA, and as a genomic sequence of 3.9-kbp. The product of the exg2 gene is predicted to contain 759 amino acids with a molecular weight of 79 kDa and a pI value of 4.6. The putative N-terminus of EXG2 is identical to the N-terminal sequences of lentinan-degrading enzymes, GNase I and II, and a custom-made anti-EXG2 peptide anti-serum cross-reacted with purified GNase I and II. Transcription and translation of exg2 was low in the gills of mature fruiting bodies, but increased after harvesting. We conclude that the exg2 gene is a lentinan-degrading enzyme-encoding-gene in L. edodes.

Isolation and characterization of a fruiting body-specific exo-beta-1,3-glucanase-encoding gene, exg1, from Lentinula edodes

An exo-beta-1,3-glucanase-encoding gene was isolated from Lentinula edodes to investigate the relationship between the cell wall lytic enzyme and mushroom morphogenesis. The deduced amino acid sequence of the protein corresponding to the exg1 gene displayed 67% identity to AbEXG1 of Agaricus bisporus and approximately 40% identity to yeast exo-beta-1,3-glucanases. Two conserved glutamic acids within the catalytic active site in yeast exo-beta-1,3-glucanases were conserved in exg1 of L. edodes. The exg1 gene was expressed in fruiting bodies, but not in vegetative mycelia. Expression was higher in the stipe than in the pileus of young fruiting bodies. The gene was additionally expressed in the gills of mature fruiting bodies. We purified a glucanase from the stipes of young fruiting bodies that had an N-terminus identical to that of the putative exg1 product. These results collectively indicate that exg1 is involved in L. edodes fruiting body development, including stipe elongation.

CaMV 35S promoter directs beta-glucuronidase expression in Ganoderma lucidum and Pleurotus citrinopileatus

The cauliflower mosaic virus (CaMV) 35S promoter has been most commonly used in plant transformation studies, but its activity in mushrooms has not been reported. p301-b is a binary vector containing a bialaphos resistance gene driven by the promoter of Lentinus edodes glyceraldehyde-3-phosphate dehydrogenase (GPD) gene. CaMV 35S-GUS was inserted into p301-b, and the resulting construct p301-bG was transformed to protoplasts of Ganoderma lucidum and basidiospores of Pleurotus citrinopileatus. GUS activity was observed in the transformants, indicating that CaMV 35S promoter can direct expression of exogenous gene in the mushrooms. This is the first report on the application of CaMV 35S promoter in genetic modification of mushrooms.

Cloning of glyceraldehyde-3-phosphate dehydrogenase-encoding genes in Mucor circinelloides (Syn. racemosus) and use of the gpd1 promoter for recombinant protein production

Three genes (gpd1, gpd2, and gpd3) encoding glyceraldehyde-3-phosphate dehydrogenase were isolated from the dimorphic zygomycete Mucor circinelloides by PCR using degenerated primers. Transcription of gpd1 could be detected during vegetative growth under both aerobic and anaerobic conditions, whereas neither gpd2 nor gpd3 transcription was detected, indicating that gpd1 is the major transcribed gpd gene. The transcription of gpd1 was regulated by carbon source. The gpd1 promoter was successfully used for recombinant expression of genes of both homologous (crgA encoding a regulator of carotene biosynthesis) and heterologous (gox1 from Aspergillus niger encoding glucose oxidase; GOX) nature. Growth of a gox1 transformant strain resulted in the secretion of enzymatically active GOX. The potential advantages of using a dimorphic fungus for heterologous protein production are discussed.

Isolation and characterization of the gene encoding glyceraldehyde-3-phosphate dehydrogenase

A 1.2-kb full-length cDNA sequence of a glyceraldehyde-3-phosphate dehydrogenase (GPD) gene was isolated from the mushroom, Pleurotus sajor-caju. The full-length cDNA of the GPD gene consists of 1248 nucleotides, predicted to encode a 36-kDa polypeptide consisting of 335 amino acid residues. Sequence analysis revealed that the GPD gene has more than 72-78% amino acid sequence homology with those of other Basidiomycetes. Expression of the GPD gene increased when P. sajor-caju was treated with various abiotic stresses, such as salt, cold, heat, and drought. There was an eightfold induction by drought treatment. Salt and cold stress induced four- and twofold induction of GPD gene expression, respectively. There was also a fivefold induction by heat stress. The GPD gene exhibits different expression patterns under different stress conditions. It reached its maximum expression level within two hours under cold or heat treatment. The mRNA levels of this gene increased proportionally to increasing treatment time under salt or dry conditions. Because the expression of GPD was significantly increased, we tested whether GPD could confer abiotic stress resistance when it was introduced into yeast cells. For this, a transgenic yeast harboring P. sajor-caju GPD was generated under the control of a constitutively expressed GAL promoter. The results from biofunctional analyses with GPD yeast transformants showed that GPD yeast transformants had significantly higher resistance to cold, salt, heat, and drought stresses.