Development of a Transgenic Flammulina velutipes Oral Vaccine for Hepatitis B.

Orally administered fungal vaccines show promise for the prevention of infectious diseases. Edible mushrooms are deemed appropriate hosts to produce oral vaccines due to their low production cost and low risk of gene contamination. However, their low expression level of antigens has limited the potential development of oral vaccines using mushrooms. The low expression level might result from impurity of the transgenic mycelia since dikaryotic mycelia are commonly used as transformation materials. In this study, stable transgenic hepatitis B virus surface antigen (HBsAg) in Flammulina velutipes transformants was obtained by Agrobacterium-mediated transformation, followed by fruiting and basidiospore mating. The formation of HBsAg was detected by western blot analysis. The expression levels of HBsAg in transgenic F. velutipes fruiting bodies were (129.3±15.1), (110.9±1.7) and (161.1±8.5) ng/g total soluble protein. However, the values may be underestimated due to incomplete protein extraction. Two of the four pigs in the experimental group produced positive anti-HBsAg-specific IgG after being fed the HBsAg transgenic F. velutipes fruiting bodies for 20 weeks, while no anti-HBsAg antibody was detected in the control group. One of the positive pigs had HBsAg titres of 5.36 and 14.9 mIU/mL in weeks 10 and 14, respectively, but expression faded thereafter. The other positive pig displayed HBsAg titres of 9.75, 17.86 and 39.87 mIU/mL in weeks 14, 18 and 20, respectively. The successful immunogenicity in pigs fed transgenic F. velutipes fruiting bodies demonstrated the potential of using the fungus as an oral vaccine.

Enhancing the efficiency of the Pichia pastoris AOX1 promoter via the synthetic positive feedback circuit of transcription factor Mxr1.

BACKGROUND: The methanol-regulated AOX1 promoter (PAOX1) is the most widely used promoter in the production of recombinant proteins in the methylotrophic yeast Pichia pastoris. However, as the tight regulation and methanol dependence of PAOX1 restricts its application, it is necessary to develop a flexible induction system to avoid the problems of methanol without losing the advantages of PAOX1. The availability of synthetic biology tools enables researchers to reprogram the cellular behaviour of P. pastoris to achieve this goal. RESULTS: The characteristics of PAOX1 are highly related to the expression profile of methanol expression regulator 1 (Mxr1). In this study, we applied a biologically inspired strategy to reprogram regulatory networks in P. pastoris. A reprogrammed P. pastoris was constructed by inserting a synthetic positive feedback circuit of Mxr1 driven by a weak AOX2 promoter (PAOX2). This novel approach enhanced PAOX1 efficiency by providing extra Mxr1 and generated switchable Mxr1 expression to allow PAOX1 to be induced under glycerol starvation or carbon-free conditions. Additionally, the inhibitory effect of glycerol on PAOX1 was retained because the synthetic circuit was not activated in response to glycerol. Using green fluorescent protein as a demonstration, this reprogrammed P. pastoris strain displayed stronger fluorescence intensity than non-reprogrammed cells under both methanol induction and glycerol starvation. Moreover, with single-chain variable fragment (scFv) as the model protein, increases in extracellular scFv productivity of 98 and 269% were observed in Mxr1-reprogrammed cells under methanol induction and glycerol starvation, respectively, compared to productivity in non-reprogrammed cells under methanol induction. CONCLUSIONS: We successfully demonstrate that the synthetic positive feedback circuit of Mxr1 enhances recombinant protein production efficiency in P. pastoris and create a methanol-free induction system to eliminate the potential risks of methanol.

Small P particles formed by the Taiwan-native norovirus P domain overexpressed in Komagataella pastoris.

The protrusion (P) domain of the major structural protein VP1 of norovirus (NoV) is critical for the host's immune response and receptor binding. Most heterologous P domains expressed in Escherichia coli or Komagataella pastoris (formally known as Pichia pastoris) form P particles consisting of 24 P monomers formed through intermolecular contact in the P regions and an end-linked cysteine tag. The small P particle is only found in P domains with terminal modifications. In this study, the NoV P domain of the most predominant NoV strain GII.4 isolated from Taiwan was expressed in K. pastoris. A high yield of NoV P was obtained using the high-cell density fermentation process in K. pastoris. A large amount of the small P particles and the trimer and dimer complexes formed by 12, 6, and 2 P monomers were observed in both the expression of the NoV P-His and P containing cysteine tag at the N-terminus. Dynamic light scattering and transmission electron microscopy analysis of the purified NoV P-His and P revealed that most of these small P particles are triangle-, square-, and ring-shaped with a diameter of 14-15 nm. The binding ability of purified NoV P-His and P to human histo-blood group antigen was confirmed by a saliva-binding assay. Without terminal modification, small P particles were formed in our study. The amino acid sequence analysis showed only four different amino acids (residue 84, 119, 136, and 313) between the P domain in this study and other investigated GII.4 strains suggesting that these amino acids might play an important role in the P particle formation. The small P particles formed by the Taiwan-native norovirus P domain overexpressed in K. pastoris may provide further information for morphogenesis studies and vaccine development.

Expression of enterovirus 71 virus-like particles in transgenic enoki (Flammulina velutipes).

No commercial vaccines are currently available for enterovirus 71 (EV71) infection. Oral virus-like particle (VLP) vaccines are regarded as a better choice for prevention from food-borne diseases compared with injected whole virus vaccines. Unfortunately, the application of oral VLP vaccines produced from transgenic plants was limited due to the concerns of gene contamination. Alternatively, using transgenic mushrooms retains the advantages of transgenic plants and tremendously reduce risks of gene contamination. Polycistronic expression vectors harboring the glyceraldehyde-3-phospho-dehydrogenase promoter to codrive EV71 structural protein P1 and protease 3C using the 2A peptide of porcine teschovirus-1 were constructed and introduced into Flammulina velutipes via Agrobacterium tumefaciens-mediated transformation. The analyses of the genomic PCR, Southern blotting, and RT-PCR showed that the genes of P1 and 3C were integrated into the chromosomal DNA through a single insertion, and their resulting mRNAs were transcribed. The Western blotting analysis combined with LC-MS/MS demonstrated that EV71 VLPs were composed of the four subunit proteins digested from P1 polyprotein by 3C protease. Through the use of a single particle electron microscope, images of 1705 particles with diameter similar to the EV71 viron were used for 3D reconstruction. Protrusions were observed on the surface in the 2D class averages, and a 3D reconstruction of the VLPs was obtained. In conclusion, EV71 VLPs were successfully produced in transgenic F. velutipes using a polycistronic expression strategy, which indicates that this approach is promising for the development of oral vaccines produced in mushrooms.

Cloning and characterization of a thermostable and pH-stable cellobiohydrolase from Neocallimastix patriciarum J11.

An 1888-bp cDNA designated celA, isolated from a cDNA library of Neocallimastix patriciarum J11 was cloned. The celA had an open reading frame of 1530 bp encoding J11 CelA of 510 amino acids. The primary structure analysis of J11 CelA revealed a complete cellulose-binding domain at the N-terminal, followed by an Asn, Ala, Gly, Gln and Pro-rich linker and ending with a C-terminal glycosyl hydrolase family 6 catalytic domain. The mature J11 CelA was overexpressed in Escherichia coli and purified to homogeneity. This enzyme had high specific activities towards barley ß-glucan and lichenan, low toward carboxymethyl cellulose (CMC), Avicel, and H3PO4-swollen Avicel (PSA). The product of Avicel hydrolysis was cellobiose indicating that J11 CelA is a typical cellobiohydrolase. The recombinant J11 CelA had an optimal pH of 6.0 and was stable over a wide range of pH (5.2-11.3). The enzyme showed an optimal temperature of 50°C and was still maintained approximately 50% of the maximum activity in response to the treatment at 70°C for 1h. Cobalt and Fe(3+) at 1 mM greatly activated the enzyme activity. As a thermostable and pH stable enzyme with crystalline cellulose-degrading activity, J11 CelA is a potential candidate for the bioethanol industry.

Chitosan augments photodynamic inactivation of gram-positive and gram-negative bacteria.

Antimicrobial photodynamic inactivation (PDI) was shown to be a promising treatment modality for microbial infections. This study explores the effect of chitosan, a polycationic biopolymer, in increasing the PDI efficacy against Gram-positive bacteria, including Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pyogenes, and methicillin-resistant S. aureus (MRSA), as well as the Gram-negative bacteria Pseudomonas aeruginosa and Acinetobacter baumannii. Chitosan at <0.1% was included in the antibacterial process either by coincubation with hematoporphyrin (Hp) and subjection to light exposure to induce the PDI effect or by addition after PDI and further incubation for 30 min. Under conditions in which Hp-PDI killed the microbe on a 2- to 4-log scale, treatment with chitosan at concentrations of as low as 0.025% for a further 30 min completely eradicated the bacteria (which were originally at ∼10(8) CFU/ml). Similar results were also found with toluidine blue O (TBO)-mediated PDI in planktonic and biofilm cells. However, without PDI treatment, chitosan alone did not exert significant antimicrobial activity with 30 min of incubation, suggesting that the potentiated effect of chitosan worked after the bacterial damage induced by PDI. Further studies indicated that the potentiated PDI effect of chitosan was related to the level of PDI damage and the deacetylation level of the chitosan. These results indicate that the combination of PDI and chitosan is quite promising for eradicating microbial infections.

Establishment of a two-step purification scheme for tag-free recombinant Taiwan native norovirus P and VP1 proteins.

The protruding (P) domain of the major capsid protein VP1 of norovirus (NoV) is the crucial element for immune recognition and host receptor binding. The heterologous P protein expressed by Pichia pastoris self-assembles into P particles. However, tag-free NoV protein purification schemes have rarely been reported due to the low isoelectric point of NoV proteins, which leads to highly competitive binding between the target protein and yeast host cell proteins at alkaline pH. In this study, a two-step purification scheme based on surface histidines and the charge on the NoV GII.4 strain P protein was developed. Using HisTrap and ion exchange chromatography, the P protein was directly purified, with a recovery of 28.1% and purity of 82.1%. Similarly, the NoV capsid protein VP1 was also purified using HisTrap and gel filtration chromatography based on native surface histidines and self-assembly ability, with 20% recovery and over 90% purity. Dynamic light scattering and transmission electron microscopy analyses of the purified NoV P revealed that most of these small P particles were triangle-, square- and ring-shaped, with a diameter of approximately 14 nm, and that the purified NoV VP1 self-assembles into particles with a diameter of approximately 47 nm. Both the purified NoV P and VP1 particles retained human histo-blood group antigen-binding ability, as evidenced by a saliva-binding assay.

Reishi immuno-modulation protein induces interleukin-2 expression via protein kinase-dependent signaling pathways within human T cells.

Ganoderma lucidum, a medicinal fungus is thought to possess and enhance a variety of human immune functions. An immuno-modulatory protein, Ling Zhi-8 (LZ-8) isolated from G. lucidum exhibited potent mitogenic effects upon human peripheral blood lymphocytes (PBL). However, LZ-8-mediated signal transduction in the regulation of interleukin-2 (IL-2) gene expression within human T cells is largely unknown. Here we cloned the LZ-8 gene of G. lucidum, and expressed the recombinant LZ-8 protein (rLZ-8) by means of a yeast Pichia pastoris protein expression system. We found that rLZ-8 induces IL-2 gene expression via the Src-family protein tyrosine kinase (PTK), via reactive oxygen species (ROS), and differential protein kinase-dependent pathways within human primary T cells and cultured Jurkat T cells. In essence, we have established the nature of the rLZ-8-mediated signal-transduction pathways, such as PTK/protein kinase C (PKC)/ROS, PTK/PLC/PKCalpha/ERK1/2, and PTK/PLC/PKCalpha/p38 pathways in the regulation of IL-2 gene expression within human T cells. Our current results of analyzing rLZ-8-mediated signal transduction in T cells might provide a potential application for rLZ-8 as a pharmacological immune-modulating agent.

A reliable transformation method and heterologous expression of beta-glucuronidase in Lentinula edodes.

A simple and reliable mushroom transformation procedure based on electroporation of basidiospores or mycelial fragments was developed. This method eliminated the problem of protoplast preparation, the transformation efficiency were 30-150 transformants per mug DNA and the hygromycin resistant marker gene and gus were expressed in Lentinula edodes successfully. No false positive antibiotic-resistant cultures were detected by PCR amplification and the beta-glucuronidase (GUS) expression was maintained stable during mitotic cell division without selection pressure for more than 6 months. Southern analysis of transformants indicated the integration of gene might occur by non-homologous recombination. Using the glyceraldehyde-3-phosphate dehydrogenase (gpd) promoter with the first intron of gpd gene, the average GUS activity in L. edodes reached 144.6+/-3.9 U mg(-1) soluble protein, while only 30.1+/-0.7 U mg(-1) soluble protein was detected for those without the intron. The percentage of GUS in total soluble protein was 5.67 x 10(-4) (0.06%) for the transformant with the highest GUS activity. This rapid and convenient electroporation procedure offers a new approach for the genetic manipulation and tool to tag genes of important edible mushroom species.

Evidence for two types of nrDNA existing in Chinese medicinal fungus Ophiocordyceps sinensis.

Nuclear ribosomal DNA (nrDNA) sequences are widely used in the molecular classification of fungi. Previous phylogenetic studies of highly-valued traditional Chinese medicinal fungus Ophiocordyceps sinensis were mostly based on 18S and internal transcribed spacer (ITS) regions (ITS1, 5.8S and ITS2) of nrDNA. However, the disparity manifest in the low sequences identities between different O. sinensis isolates has led to argumentative hypotheses for this phenomenon, such as the "species complex" or "cryptic species" hypotheses. In the present study, four types of nrDNA (GC, AT-1, AT-2, and T) were identified using four primer pairs to amplify the nrDNA of six O. sinensis isolates. We demonstrate that each O. sinensis isolate contained two types of nrDNA, the omnipresent GC-type and a coexistent type alternating between the remaining three. This crucial discovery challenges the established notion of one type of nrDNA per species. We therefore propose that the composition of nrDNA types should be taken into consideration in studies of fungal genetics and classification.

Effects of dockerin domains on Neocallimastix frontalis xylanases.

Two xylanase genes were cloned from the anaerobic fungus Neocallimastix frontalis. Xyn11A had a modular structure of two catalytic domains and two dockerin domains, while Xyn11B had one catalytic domain and two dockerin domains. The characteristics of the xylanases with and without dockerin domains were investigated. The deletion of dockerin domains had little influence on the optimal pH of xylanases, while it significantly affected the optimal temperatures. The optimal temperatures increased from 55 to 60 degrees C for Xyn11A and 60 to 65 degrees C for Xyn11B after the deletion of dockerin domains. The increase of optimal temperatures was attributed to the lower stability of the second structure in full length xylanase than that in the truncated one as evidenced by the circular dichroism spectroscopy. The specific activity of Xyn11A and Xyn11B increased about 64% and 330%, respectively, after the deletion of the dockerin domains. The removal of dockerin domains appeared to increase the overall efficiency of Xyn11A' (1.2-) and Xyn11B' (2.9-) fold with oat spelts xylan as reflected by the values of k(cat)/K(m). The results suggest that the dockerin domain might play an important role in the characteristics of xylanases from anaerobic fungi.

delta-Aminolaevulinic acid mediated photodynamic antimicrobial chemotherapy on Pseudomonas aeruginosa planktonic and biofilm cultures.

To demonstrate photodynamic antimicrobial chemotherapy (PACT) against planktonic and biofilm cultures of Pseudomonas aeruginosa, using photoporphyrin IX which could be endogenously synthesized by administrating delta-aminolaevulinic acid (delta-ALA), and a light emitted diode (LED) array to photoactivate the photosensitizer. P. aeruginosa suspended cells or biofilms, grown on a rotating disk reactor, were treated by different concentrations of delta-ALA in the dark for 1 h, followed by LED irradiation for various time. Regrowth experiments were conducted by placed PACT-treated disks back to a sterile reactor. Viable cells were determined by serial dilution and plate counts. Both P. aeruginosa planktonic and biofilm cells were inhibited by PACT with light doses or photosensitizer concentrations increasing. Treatments of planktonic cells with 10 mM delta-ALA and incident dose 240 J cm(-2) or 7.5 mM ALA and incident dose 360 J cm(-2) led to completely photoinactivation. No viable biofilm cells were found after treatment of 20 mM delta-ALA and incident dose 240 J cm(-2). However, regrowth was observed once PACT-treated biofilms were put back to a sterile reactor. Regrowth could be prevented only if biofilm samples were treated PACT twice. delta-ALA-mediated PACT on P. aeruginosa planktonic and biofilm cells was effective, though the detailed mechanism still required further investigation.

Compatibility balanced antibacterial modification based on vapor-deposited parylene coatings for biomaterials.

Advanced antibacterial surfaces are designed based on covalently attached antibacterial agents, avoiding potential side effects associated with overdosed or eluted agents. The technique is widely applicable regardless of the underlying substrate material. In addition, antibacterial surfaces are effective against the early stages of bacterial adhesion and can significantly reduce the formation of biofilm, without compromising biocompatibility. Here, this concept was realized by employing a benzoyl-functionalized parylene coating. The antibacterial agent chlorhexidine was used as a proof of concept. Chlorhexidine was immobilized by reaction with photoactivated benzoyl-functionalized surfaces, including titanium alloy, stainless steel, polyether ether ketone, polymethyl methacrylate, and polystyrene. A low concentration of chlorhexidine (1.4 ± 0.08 nmol cm-2) covalently bound to surfaces rendered them sufficiently resistant to an Enterobacter cloacae inoculum and its adherent biofilm. Compared to unmodified surfaces, up to a 30-fold reduction in bacterial attachment was achieved with this coating technology. The immobilization of chlorhexidine was verified with infrared reflection absorption spectroscopy (IRRAS) and X-ray photoelectron spectroscopy (XPS), and a leaching test was performed to confirm that the chlorhexidine molecules were not dislodged. Cell compatibility was examined by culturing fibroblasts and osteoblasts on the modified surfaces, revealing greater than 93% cell viability. This coating technology may be broadly applicable for a wide range of other antibacterial agents and allow the design of new biomaterials.

Enhancement of heterologous gene expression in Flammulina velutipes using polycistronic vectors containing a viral 2A cleavage sequence.

Agrobacterium tumefaciens-mediated transformation for edible mushrooms has been previously established. However, the enhancement of heterologous protein production and the expression of multi-target genes remains a challenge. In this study, heterologous protein expression in the enoki mushroom Flammulina velutipes was notably enhanced using 2A peptide-mediated cleavage to co-express multiple copies of single gene. The polycistronic expression vectors were constructed by connecting multi copies of the enhanced green fluorescent protein (egfp) gene using 2A peptides derived from porcine teschovirus-1. The P2A peptides properly self-cleaved as shown by the formation of the transformants with antibiotic resistant capacity and exciting green fluorescence levels after introducing the vectors into F. velutipes mycelia. The results of western blot analysis, epifluorescent microscopy and EGFP production showed that heterologous protein expression in F. velutipes using the polycistronic strategy increased proportionally as the gene copy number increased from one to three copies. In contrast, much lower EGFP levels were detected in the F. velutipes transformants harboring four copies of the egfp gene due to mRNA instability. The polycistronic strategy using 2A peptide-mediated cleavage developed in this study can not only be used to express single gene in multiple copies, but also to express multiple genes in a single reading frame. It is a promising strategy for the application of mushroom molecular pharming.

An immunomodulatory protein, Ling Zhi-8, induced activation and maturation of human monocyte-derived dendritic cells by the NF-kappaB and MAPK pathways.

Ganoderma lucidum, an oriental medicinal mushroom, has been widely used in Asia to promote health and longevity. LZ-8 is a protein derived from the fungus G. lucidum and has immunomodulatory capacities. In this study, we investigated the immune modulatory effects of rLZ-8 on human monocyte-derived DCs. Treatment of DC with rLZ-8 resulted in the enhanced cell-surface expression of CD80, CD86, CD83, and HLA-DR, as well as the enhanced production of IL-12 p40, IL-10, and IL-23, and the capacity for endocytosis was suppressed in DCs. In addition, treatment of DCs with rLZ-8 resulted in an enhanced, naïve T cell-stimulatory capacity and increased, naïve T cell secretion of IFN-gamma and IL-10. Neutralization with antibodies against TLR4 inhibited the rLZ-8-induced production of IL-12 p40 and IL-10 in DCs. rLZ-8 can stimulate TLR4 or TLR4/MD2-transfected HEK293 cells to produce IL-8. These results suggested an important role for TLR4 in signaling DCs upon incubation with rLZ-8. Further study showed that rLZ-8 was able to augment IKK, NF-kappaB activity, and also IkappaBalpha and MAPK phosphorylation. Further, inhibition of NF-kappaB by helenalin prevented the effects of rLZ-8 in the expression of CD80, CD86, CD83, and HLA-DR and production of IL-12 p40 and IL-10 in various degrees. To confirm the in vitro data, we investigated the effect of rLZ-8 further on antigen-specific antibody and cytokine production in BALB/c mice. Immunization with OVA/rLZ-8 showed that the anti-OVA IgG2a, IFN-gamma, and IL-2 were increased significantly compared with OVA alone in BALB/c mice. In conclusion, our experiments demonstrated that rLZ-8 can effectively promote the activation and maturation of immature DCs, preferring a Th1 response, suggesting that rLZ-8 may possess a potential effect in regulating immune responses.

Effects of quorum-sensing deficiency on Pseudomonas aeruginosa biofilm formation and antibiotic resistance.

Variations in biofilm formation by, and antibiotic resistance of, Pseudomonas aeruginosa PAO1 (wild type) and the quorum-sensing-deficient mutants PDO100 (Delta rhlI), JP1 (Delta lasI) and JP2 (Delta lasI Delta rhlI) were studied. For PAO1, the maximum-accumulation phase of biofilm formation began immediately and a plateau phase was reached after 24 h, whereas the quorum-sensing mutants showed 36-48 h lags before entering the maximum-accumulation phase. After 72 h, the cell density of the PAO1 biofilms was c. 0.8-1.2 log greater than for the mutants. On a unit protein basis, total polysaccharide production was similar for PAO1 and PDO100, whereas JP1 and JP2 biofilms accumulated only c. 36% of the PAO1 level after 72 h. Fluorescent micrographs revealed that the PAO1 biofilms were much thicker than those of the quorum-sensing-deficient mutants. In the case of the PAO1 and PDO100 biofilms, most cells were attached to the top of the biofilm layer, whereas the bottom layer consisted predominantly of polysaccharides. The JP1 and JP2 biofilms were closely packed with cells, and little polysaccharide was visible. Cells in PAO1 biofilms were little affected by kanamycin, even at 100 mg/L, whereas those in PDO100 biofilms were susceptible to the highest concentration of kanamycin (100 mg/L) but not to lower concentrations (10 and 50 mg/L). In contrast, cells in JP1 and JP2 biofilms were susceptible to kanamycin at all three concentrations.

Use of merocyanine 540 for photodynamic inactivation of Staphylococcus aureus planktonic and biofilm cells.

Photodynamic inactivation of Staphylococcus aureus planktonic and biofilm cells by a phtotosensitizer, merocyanine 540 (MC 540), was investigated. For the planktonic experiments, MC 540 binding efficiency to bacterial cells was found to increase with both increasing MC 540 concentration and increasing incubation time, but the binding became saturated following 10 min of incubation. The antimicrobial activity was enhanced with an increasing light dose, but an increase in the light dose could not further improve the antimicrobial activity if the maximum excitation level attainable was less than the necessary minimum threshold level. Complete inactivation was achieved when the excitation level of MC 540 was somewhere above the threshold level. The relationship between antimicrobial activity and the excitation level of MC 540 revealed that the more MC 540 was excited, the more S. aureus cells were killed. For the biofilm experiments, the antimicrobial activity was enhanced with an increase in the light dose. No viable cells were detected when organisms were exposed to 15 mug of MC 540 per ml and a light dose of 600 J/cm2 or to 20 mug of MC 540 per ml and a light dose of 450 J/cm2. A quantitative analysis of MC 540 bound to biofilms was also performed, and the images from confocal laser scanning microscopy provided direct evidence that revealed the difference between the MC 540 remaining in the biofilms prior to irradiation and the MC 540 remaining in the biofilms after irradiation. The results of both the planktonic and biofilm experiments suggest that the antimicrobial activity of photodynamic inactivation of S. aureus is closely related to the excitation level of MC 540.

Cloning of glyceraldehyde-3-phosphate dehydrogenase gene and use of the gpd promoter for transformation in Flammulina velutipes.

The glyceraldehyde-3-phosphate dehydrogenase gene of Flammulina velutipes was isolated. The complete gpd sequence (from ATG to TAA) was 1,489 bp in length and contained nine introns. The locations of these nine introns were similar to those of other basidiomycetes, which might reflect the evolutionary divergence of these mushrooms. The F. velutipes gpd gene was found to encode a protein of 339 amino acids and its putative amino acid sequence revealed a high similarity to an analogous protein deriving from other basidiomycetes. Results of Southern blot analysis suggested that there existed only one copy of the gpd gene in the genome of F. velutipes and that there was one typical TATA box and two CAAT boxes located in the 5' flanking region. The F. velutipes gpd promoter was fused to a hygromycin B phosphotransferase gene (hph) derived from Escherichia coli as a selection marker. Using the resulting construction, hph was efficiently transformed into F. velutipes by basidiospore electroporation. No false-positive antibiotic-resistant cultures were detected by PCR amplification and the hygromycin resistance trait was maintained stably during mitotic cell division for 3 months. Southern analysis of transformants indicated the integration of gene might occur by non-homologous recombination. This rapid and convenient electroporation procedure offers new prospects for the genetic manipulation and a tool for tagging genes of this important edible mushroom species. Sequence data will appear in the DDBJ/EMBL/GenBank nucleotide sequence database under accession number AF515622.