Expression of laccase gene lcc1 in Coprinopsis cinerea under control of various basidiomycetous promoters

An apoptosis-inducing factor controls programmed cell death and laccase expression during fungal interactions

Apoptotic-like programmed cell death (PCD) is one of the main strategies for fungi to resist environmental stresses and maintain homeostasis. The apoptosis-inducing factor (AIF) has been shown in different fungi to trigger PCD through upregulating reactive oxygen species (ROS). This study identified a mitochondrial localized AIF homolog, CcAIF1, from Coprinopsis cinerea monokaryon Okayama 7. Heterologous overexpression of CcAIF1 in Saccharomyces cerevisiae caused apoptotic-like PCD of the yeast cells. Ccaif1 was increased in transcription when C. cinerea interacted with Gongronella sp. w5, accompanied by typical apoptotic-like PCD in C. cinerea, including phosphatidylserine externalization and DNA fragmentation. Decreased mycelial ROS levels were observed in Ccaif1 silenced C. cinerea transformants during cocultivation, as well as reduction of the apoptotic levels, mycelial growth, and asexual sporulation. By comparison, Ccaif1 overexpression led to the opposite phenotypes. Moreover, the transcription and expression levels of laccase Lcc9 decreased by Ccaif1 silencing but increased firmly in Ccaif1 overexpression C. cinerea transformants in coculture. Thus, in conjunction with our previous report that intracellular ROS act as signal molecules to stimulate defense responses, we conclude that CcAIF1 is a regulator of ROS to promote apoptotic-like PCD and laccase expression in fungal-fungal interactions. In an axenic culture of C. cinerea, CcAIF1 overexpression and H2O2 stimulation together increased laccase secretion with multiplied production yield. The expression of two other normally silent isozymes, Lcc8 and Lcc13, was unexpectedly triggered along with Lcc9. KEY POINTS: • Mitochondrial CcAIF1 induces PCD during fungal-fungal interactions • CcAIF1 is a regulator of ROS to trigger the expression of Lcc9 for defense • CcAIF1 overexpression and H2O2 stimulation dramatically increase laccase production.

Enhanced extracellular production of laccase in Coprinopsis cinerea by silencing chitinase gene

Laccase, a copper-containing polyphenol oxidase, is an important green biocatalyst. In this study, Laccase Lcc5 was homologous recombinantly expressed in Coprinopsis cinerea and a novel strategy of silencing chitinase gene expression was used to enhance recombinant Lcc5 extracellular yield. Two critical chitinase genes, ChiEn1 and ChiE2, were selected by analyzing the transcriptome data of C. cinerea FA2222, and their silent expression was performed by RNA interference (RNAi). It was found that silencing either ChiEn1 or ChiE2 reduced sporulation and growth rate, and increased cell wall sensitivity, but had no significant effect on mycelial branching. Among them, the extracellular laccase activity of the ChiE2-silenced engineered strain Cclcc5-antiChiE2-5 and the control Cclcc5-13 reached the highest values (38.2 and 25.5 U/mL, respectively) at 250 and 150 rpm agitation speeds, corresponding to productivity of 0.35 and 0.19 U/mL·h, respectively, in a 3-L fermenter culture. Moreover, since Cclcc5-antiChiE2-5 could withstand greater shear forces, its extracellular laccase activity was 2.6-fold higher than that of Cclcc5-13 when the agitation speed was all at 250 rpm. To our knowledge, this is the first report of enhanced recombinant laccase production in C. cinerea by silencing the chitinase gene. This study will pave the way for laccase industrial production and accelerate the development of a C. cinerea high-expression system. KEY POINTS: • ChiEn1 and ChiE2 are critical chitinase genes in C. cinerea FA2222 genome. • Chitinase gene silencing enhanced the tolerance of C. cinerea to shear forces. • High homologous production of Lcc5 is achieved by fermentation in a 3-L fermenter.

Fungal Laccases: Fundamentals, Engineering and Classification Update

Multicopper oxidases (MCOs) share a common catalytic mechanism of activation by oxygen and cupredoxin-like folding, along with some common structural determinants. Laccases constitute the largest group of MCOs, with fungal laccases having the greatest biotechnological applicability due to their superior ability to oxidize a wide range of aromatic compounds and lignin, which is enhanced in the presence of redox mediators. The adaptation of these versatile enzymes to specific application processes can be achieved through the directed evolution of the recombinant enzymes. On the other hand, their substrate versatility and the low sequence homology among laccases make their exact classification difficult. Many of the ever-increasing amounts of MCO entries from fungal genomes are automatically (and often wrongly) annotated as laccases. In a recent comparative genomic study of 52 basidiomycete fungi, MCO classification was revised based on their phylogeny. The enzymes clustered according to common structural motifs and theoretical activities, revealing three novel groups of laccase-like enzymes. This review provides an overview of the structure, catalytic activity, and oxidative mechanism of fungal laccases and how their biotechnological potential as biocatalysts in industry can be greatly enhanced by protein engineering. Finally, recent information on newly identified MCOs with laccase-like activity is included.

Identification and characterization of a novel AA9-type lytic polysaccharide monooxygenase from a bagasse metagenome

Lytic polysaccharide monooxygenases (LPMOs) are auxiliary enzymes catalyzing oxidative cleavages of cellulose chains in crystalline regions, resulting in their increasing accessibility to the hydrolytic enzyme counterparts and hence higher released sugars from biomass saccharification. In this study, a novel auxiliary protein family 9 LPMO (BgAA9) was identified from a metagenomic library derived from a thermophilic microbial community in bagasse collection site where diverse AA9 and AA10 putative sequences were annotated. The enzyme showed highest similarity to a glycoside hydrolase family 61 from Chaetomium thermophilum. Recombinant BgAA9 expressed in Pichia pastoris cleaved cellohexaose (DP6) into shorter cellooligosaccharides (DP2, DP3, and DP4). Supplementation BgAA9 to a commercial cellulase, Accellerase® 1500 showed strong synergistic effect on saccharification of Avicel® PH101, decrystallized cellulose, filter paper, and alkaline-pretreated sugarcane bagasse, resulting in 63-93% increase in the total reducing sugar yield after incubation at 50 °C for 72 h. Strong synergism was shown between BgAA9 and the cellulase with the highest total fermentable sugar yield obtained from 75:25% of Accellerase®1500:BgAA9 which released 39 mg glucose/FPU (filter paper unit) equivalent to 38.7% higher than Accellerase®1500 alone at the same total protein dosage of 5 mg/g substrate according to the mixture design study. The enzyme represented the first characterized LPMO from environmental metagenome and a potent auxiliary component for biomass saccharification. KEY POINTS: • BgAA9 represents the first characterized LPMO from metagenome. • 12 AA families were annotated in thermophilic bagasse fosmid library by NGS. • BgAA9 showed homology to Cel61 in Chaetomium thermophilum. • BgAA9 oxidized cellohexaose and PASC to DP2, DP4, and DP6. • BgAA9 showed strong synergism to Accellerase on bagasse hydrolysis.

Selection markers for transformation of the sequenced reference monokaryon Okayama 7/#130 and homokaryon AmutBmut of Coprinopsis cinerea

BACKGROUND

Two reference strains have been sequenced from the mushroom Coprinopsis cinerea, monokaryon Okayama 7/#130 (OK130) and the self-compatible homokaryon AmutBmut. An adenine-auxotrophy in OK130 (ade8-1) and a para-aminobenzoic acid (PABA)-auxotrophy in AmutBmut (pab1-1) offer selection markers for transformations. Of these two strains, homokaryon AmutBmut had been transformed before to PABA-prototrophy and with the bacterial hygromycin resistance marker hph, respectively.

RESULTS

Gene ade8 encodes a bifunctional enzyme with an N-terminal glycinamide ribonucleotide synthase (GARS) and a C-terminal aminoimidazole ribonucleotide synthase (AIRS) domain required for steps 2 and 5 in the de novo biosynthesis of purines, respectively. In OK130, a missense mutation in ade8-1 rendered residue N231 for ribose recognition by the A loop of the GARS domain into D231. The new ade8 + vector pCcAde8 complements the auxotrophy of OK130 in transformations. Transformation rates with pCcAde8 in single-vector and co-transformations with ade8 +-selection were similarly high, unlike for trp1 + plasmids which exhibit suicidal feedback-effects in single-vector transformations with complementation of tryptophan synthase defects. As various other plasmids, unselected pCcAde8 helped in co-transformations of trp1 strains with a trp1 +-selection vector to overcome suicidal effects by transferred trp1 +. Co-transformation rates of pCcAde8 in OK130 under adenine selection with nuclear integration of unselected DNA were as high as 80% of clones. Co-transformation rates of expressed genes reached 26-42% for various laccase genes and up to 67% with lcc9 silencing vectors. The bacterial gene hph can also be used as another, albeit less efficient, selection marker for OK130 transformants, but with similarly high co-transformation rates. We further show that the pab1-1 defect in AmutBmut is due to a missense mutation which changed the conserved PIKGT motif for chorismate binding in the C-terminal PabB domain to PIEGT in the mutated 4-amino-4-deoxychorismate synthase.

CONCLUSIONS

ade8-1 and pab1-1 auxotrophic defects in C. cinerea reference strains OK130 and AmutBmut for complementation in transformation are described. pCcAde8 is a new transformation vector useful for selection in single and co-transformations of the sequenced monokaryon OK130 which was transformed for the first time. The bacterial gene hph can also be used as an additional selection marker in OK130, making in combination with ade8 + successive rounds of transformation possible.

A promoter assay system using gene targeting in agaricomycetes Pleurotus ostreatus and Coprinopsis cinerea

A novel promoter assay was developed for Agaricomycetes, using a gene-targeting approach, with or without the CRISPR/Cas9 technique. It enables precise evaluation of promoter activity at the original site of the chromosome without random and multiple integrations in conventional transformation experiments.

Identification and characterization of a novel light-induced promoter for recombinant protein production in Pleurotus ostreatus

A lectin gene (plectin) with a high level of expression was previously identified by comparative transcriptome analysis of Pleurotus ostreatus. In this study, we cloned a 733-bp DNA fragment from the start codon of the plectin gene. Sequence analysis showed that the plectin promoter (Plp) region contained several eukaryotic transcription factor binding motifs, such as the TATA-box, four possible CAAT-box, light respon-siveness motifs and MeJA-responsiveness motifs. To deter-mine whether the Plp promoter was a light-regulated promoter, we constructed an expression vector with the fused egfp-hph fragment under the control of the Plp promoter and transformed P. ostreatus mycelia via Agrobacterium tunte-faciens. PCR and Southern blot analyses confirmed the Plp-egfp-hph fragment was integrated into the chromosomal DNA of transformants. qRT-PCR, egfp visualization, and intracellular egfp determination experiments showed the Plp promoter could be a light-induced promoter that may be suitable for P. ostreatus genetic engineering. This study lays the foundation for gene homologous expression in P. ostreatus.

Stable and transient transformation, and a promoter assay in the selective lignin-degrading fungus, Ceriporiopsis subvermispora

A genetic transformation system was developed for the selective white rot basidiomycete Ceriporiopsis subvermispora using a modified protocol with polyethylene glycol and CaCl₂ treatment of the protoplasts and plasmids harboring recombinant hygromycin phosphotransferase (hph) driven by a homologous promoter. During repeated transfer on fresh potato dextrose agar plates containing 100 µg/ml hygromycin B, most transformants lost drug resistance, while the remaining isolates showed stable resistance over five transfers. No drug-resistant colonies appeared in control experiments without DNA or using a promoter-less derivative of the plasmid, indicating that a transient expression of the recombinant hph was driven by the promoter sequence in these unstable drug-resistant transformants. Southern blot analysis of the stable transformants revealed random integration of the plasmid DNA fragment in the chromosome at different copy numbers. This transformation system yielding mostly transient transformants was successfully used for promoter assay experiments, and only a 141-bp fragment was found to be essential for the basic promoter function of glyceraldehyde dehydrogenase gene (gpd) in this fungus. Subsequent mutational analyses suggested that a TATAA sequence is important for the basic promoter function of gpd gene. The promoter assay system will enable the functional analysis of gene expression control sequences quickly and easily, mostly in the absence of undesirable effects from differences in copy number and chromosomal position of an integrated reporter gene among stable transformants.

Signal peptide replacement resulted in recombinant homologous expression of laccase Lcc8 in Coprinopsis cinerea

Although the model agaricomycete Coprinopsis cinerea possess 17 different laccase genes, up to now only four C. cinerea laccases have been purified and characterized to some degree. By exchanging the nucleotide sequence of the deduced signal peptide of Lcc8 it was possible to homologously express lcc8 in C. cinerea under control of the Agaricus bisporus gdpII promoter and the C. cinerea lcc1 terminator. The purified Lcc8 showed two bands in the SDS-PAGE with a molecular weight of 64 kDa and 77 kDa, respectively. The IEF determined pI values of 3.3 and 3.4 for both bands. The optimal pH for oxidation of the substrates ABTS, 2,6-dimethoxyphenol, guaiacol and syringaldazine was pH 4.0, pH 5.0, pH 4.5 and pH 5.0, respectively. Best pH for enzyme storage was pH 8.0. The optimal temperature for oxidation of ABTS was 63 °C, while Lcc8 showed activity of at least 50% over 300 min at 50 °C. The comparable high stability of Lcc8 at alkaline pH and higher temperatures can be of interest for biotechnical applications.

Laccase production and pellet morphology of Coprinopsis cinerea transformants in liquid shake flask cultures

Laccase production and pellet formation of transformants of Coprinopsis cinerea strain FA2222 of C. cinerea laccase gene lcc1 subcloned behind the gpdII-promoter from Agaricus bisporus were compared with a control transformant carrying no extra laccase gene. At the optimum growth temperature of 37 °C, maximal laccase yields of 2.9 U/ml were obtained by the best lcc1 transformant pYSK7-26 in liquid shake flask cultures. Reduction in temperature to 25 °C increased laccase yields up to 9.2 U/ml. The control transformant had no laccase activities at 37 °C but native activity at 25 °C (3.5 U/ml). Changing the temperature had severe effects on the morphology of the mycelial pellets formed during cultivation, but links of distinct pellet morphologies to native or recombinant laccase production could not be established. Automated image analysis was used to characterise pellet formation and morphological parameters (pellet area, diameter, convexity and mycelial structure). Cross sections of selected pellets showed that they differentiated in an outer rind and an inner medulla of loosened hyphae. Pellets at 25 °C had a small and dense outer zone and adopted with time a smooth surface. Pellets at 37 °C had a broader outer zone and a fringy surface due to generation of more and larger protuberances in the rind that when released can serve for production of further pellets.

Laccases: Production, Expression Regulation, and Applications in Pharmaceutical Biodegradation

Laccases are a family of copper-containing oxidases with important applications in bioremediation and other various industrial and biotechnological areas. There have been over two dozen reviews on laccases since 2010 covering various aspects of this group of versatile enzymes, from their occurrence, biochemical properties, and expression to immobilization and applications. This review is not intended to be all-encompassing; instead, we highlighted some of the latest developments in basic and applied laccase research with an emphasis on laccase-mediated bioremediation of pharmaceuticals, especially antibiotics. Pharmaceuticals are a broad class of emerging organic contaminants that are recalcitrant and prevalent. The recent surge in the relevant literature justifies a short review on the topic. Since low laccase yields in natural and genetically modified hosts constitute a bottleneck to industrial-scale applications, we also accentuated a genus of laccase-producing white-rot fungi, Cerrena, and included a discussion with regards to regulation of laccase expression.

The good, the bad and the tasty: The many roles of mushrooms

Fungi are often inconspicuous in nature and this means it is all too easy to overlook their importance. Often referred to as the "Forgotten Kingdom", fungi are key components of life on this planet. The phylum Basidiomycota, considered to contain the most complex and evolutionarily advanced members of this Kingdom, includes some of the most iconic fungal species such as the gilled mushrooms, puffballs and bracket fungi. Basidiomycetes inhabit a wide range of ecological niches, carrying out vital ecosystem roles, particularly in carbon cycling and as symbiotic partners with a range of other organisms. Specifically in the context of human use, the basidiomycetes are a highly valuable food source and are increasingly medicinally important. In this review, seven main categories, or 'roles', for basidiomycetes have been suggested by the authors: as model species, edible species, toxic species, medicinal basidiomycetes, symbionts, decomposers and pathogens, and two species have been chosen as representatives of each category. Although this is in no way an exhaustive discussion of the importance of basidiomycetes, this review aims to give a broad overview of the importance of these organisms, exploring the various ways they can be exploited to the benefit of human society.

A native promoter and inclusion of an intron is necessary for efficient expression of GFP or mRFP in Armillaria mellea

Armillaria mellea is a significant pathogen that causes Armillaria root disease on numerous hosts in forests, gardens and agricultural environments worldwide. Using a yeast-adapted pCAMBIA0380 Agrobacterium vector, we have constructed a series of vectors for transformation of A. mellea, assembled using yeast-based recombination methods. These have been designed to allow easy exchange of promoters and inclusion of introns. The vectors were first tested by transformation into basidiomycete Clitopilus passeckerianus to ascertain vector functionality then used to transform A. mellea. We show that heterologous promoters from the basidiomycetes Agaricus bisporus and Phanerochaete chrysosporium that were used successfully to control the hygromycin resistance cassette were not able to support expression of mRFP or GFP in A. mellea. The endogenous A. mellea gpd promoter delivered efficient expression, and we show that inclusion of an intron was also required for transgene expression. GFP and mRFP expression was stable in mycelia and fluorescence was visible in transgenic fruiting bodies and GFP was detectable in planta. Use of these vectors has been successful in giving expression of the fluorescent proteins GFP and mRFP in A. mellea, providing an additional molecular tool for this pathogen.

Paradoxical performance of tryptophan synthase gene trp1 (+) in transformations of the basidiomycete Coprinopsis cinerea

Several transformation strains of Coprinopsis cinerea carry the defective tryptophan synthase allele trp1-1,1-6 which can be complemented by introduction of the trp1 (+) wild-type gene. Regularly in C. cinerea, single-trp1 (+)-vector transformations yield about half the numbers of clones than cotransformations with a non-trp1 (+)-plasmid done in parallel. The effect is also observed with the orthologous Schizophyllum commune trpB (+) gene shown here to function as a selection marker in C. cinerea. Parts of single-trp1 (+) - or single-trpB (+) -vector transformants are apparently lost. This paradoxical phenomenon relates to de-regulation of aromatic amino acid biosynthesis pathways. Adding tryptophan precursors to protoplast regeneration agar or feeding with other aromatic amino acids increases loss of single-trp1 (+)-vector transformants and also sets off loss of clones in cotransformation with a non-trp1 (+)-plasmid. Feedback control by tryptophan and cross-pathway control by tyrosine and phenylalanine are both active in the process. We deduce from the observations that more cotransformants than single-vector transformants are obtained by in average less disturbance of the tryptophan biosynthesis pathway. DNA in C. cinerea transformation usually integrates into the genome at multiple ectopic places. Integration events for a single vector per nucleus should statistically be 2-fold higher in single-vector transformations than in cotransformations in which the two different molecules compete for the same potential integration sites. Integration of more trp1 (+) copies into the genome might more likely lead to sudden tryptophan overproduction with subsequent rigid shut-down of the pathway. Blocking ectopic DNA integration in a Δku70 mutant abolished the effect of doubling clone numbers in cotransformations due to preferred single trp1 (+) integration by homologous recombination at its native genomic site.

Yeast recombination-based cloning as an efficient way of constructing vectors for Zymoseptoria tritici

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Yeast recombination-based cloning (YRBC) is a reliable and inexpensive way of generating plasmids.

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We provide 4 vectors for YRBC that a cover different resistance genes.

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Using this technique promises rapid generation of molecular tools to study Z. tritici.

Many pathogenic fungi are genetically tractable. Analysis of their cellular organization and invasion mechanisms underpinning virulence determinants profits from exploiting such molecular tools as fluorescent fusion proteins or conditional mutant protein alleles. Generation of these tools requires efficient cloning methods, as vector construction is often a rate-limiting step. Here, we introduce an efficient yeast recombination-based cloning (YRBC) method to construct vectors for the fungus Zymoseptoria tritici. This method is of low cost and avoids dependency on the availability of restriction enzyme sites in the DNA sequence, as needed in more conventional restriction/ligation-based cloning procedures. Furthermore, YRBC avoids modification of the DNA of interest, indeed this potential risk limits the use of site-specific recombination systems, such as Gateway cloning. Instead, in YRBC, multiple DNA fragments, with 30 bp overlap sequences, are transformed into Saccharomyces cerevisiae, whereupon homologous recombination generates the vector in a single step. Here, we provide a detailed experimental protocol and four vectors, each encoding a different dominant selectable marker cassette, that enable YRBC of constructs to be used in the wheat pathogen Z. tritici.

Overexpression of Laccaria bicolor aquaporin JQ585595 alters root water transport properties in ectomycorrhizal white spruce (Picea glauca) seedlings

The contribution of hyphae to water transport in ectomycorrhizal (ECM) white spruce (Picea glauca) seedlings was examined by altering expression of a major water-transporting aquaporin in Laccaria bicolor. Picea glauca was inoculated with wild-type (WT), mock transgenic or L. bicolor aquaporin JQ585595-overexpressing (OE) strains and exposed to root temperatures ranging from 5 to 20°C to examine the root water transport properties, physiological responses and plasma membrane intrinsic protein (PIP) expression in colonized plants. Mycorrhization increased shoot water potential, transpiration, net photosynthetic rates, root hydraulic conductivity and root cortical cell hydraulic conductivity in seedlings. At 20°C, OE plants had higher root hydraulic conductivity compared with WT plants and the increases were accompanied by higher expression of P. glauca PIP GQ03401_M18.1 in roots. In contrast to WT L. bicolor, the effects of OE fungi on root and root cortical cell hydraulic conductivities were abolished at 10 and 5°C in the absence of major changes in the examined transcript levels of P. glauca root PIPs. The results provide evidence for the importance of fungal aquaporins in root water transport of mycorrhizal plants. They also demonstrate links between hyphal water transport, root aquaporin expression and root water transport in ECM plants.

Oral vaccination of mice with Tremella fuciformis yeast-like conidium cells expressing HBsAg

Tremella fuciformis yeast-like conidium (YLC) cells were transformed by co-cultivation with Agrobacterium cells harboring the hepatitis B surface antigen (HBsAg) gene construct under the control of the CaMV35S promoter. Integration of HBsAg DNA into the YLC genome was confirmed by PCR and dot-blot hybridization. Immunoblotting verified expression of the recombinant protein. Oral administration of YLC cells expressing HBsAg in mice significantly increased anti-HBsAg antibody titer levels using a double prime-boost strategy that combined parenteral and oral HBsAg boosters.

Production of antibacterial peptide from bee venom via a new strategy for heterologous expression

Honey bee is important economic insect that not only pollinates fruits and crops but also provides products with various physiological activities. Bee venom is a functional agent that is widely applied in clinical treatment and pharmacy. Secapin is one of these agents that have a significant role in therapy. The functions of secapin from the bee venom have been documented, but little information is known about its heterologous expression under natural condition. Moreover, few scholars verified experimentally the functions of secapin from bee venom in vitro. In this study, we successfully constructed a heterologous expression vector, which is different from conventional expression system. A transgenic approach was established for transformation of secapin gene from the venom of Apis mellifera carnica (Ac-sec) into the edible fungi, Coprinus cinereus. Ac-sec was encoded by a 234 bp nucleotide that contained a signal peptide domain and two potential phosphorylation sites. The sequence exhibited highly homology with various secapins characterized from honey bee and related species. Southern blot data indicated that Ac-sec was present as single or multiple copy loci in the C. cinereus genome. By co-transformation and double-layer active assay, Ac-sec was expressed successfully in C. cinereus and the antibacterial activity of the recombinants was identified, showing notable antibacterial activities on different bacteria. Although Ac-sec is from the venom of Apidae, phylogenetic analysis demonstrated that Ac-sec was more closely related to that of Vespid than to bee species from Apidae. The molecular characteristics of Ac-sec and the potential roles of small peptides in biology were discussed.

A DNA damage checkpoint pathway coordinates the division of dikaryotic cells in the ink cap mushroom Coprinopsis cinerea

The fungal fruiting body or mushroom is a multicellular structure essential for sexual reproduction. It is composed of dikaryotic cells that contain one haploid nucleus from each mating partner sharing the same cytoplasm without undergoing nuclear fusion. In the mushroom, the pileus bears the hymenium, a layer of cells that includes the specialized basidia in which nuclear fusion, meiosis, and sporulation occur. Coprinopsis cinerea is a well-known model fungus used to study developmental processes associated with the formation of the fruiting body. Here we describe that knocking down the expression of Atr1 and Chk1, two kinases shown to be involved in the response to DNA damage in a number of eukaryotic organisms, dramatically impairs the ability to develop fruiting bodies in C. cinerea, as well as other developmental decisions such as sclerotia formation. These developmental defects correlated with the impairment in silenced strains to sustain an appropriated dikaryotic cell cycle. Dikaryotic cells in which chk1 or atr1 genes were silenced displayed a higher level of asynchronous mitosis and as a consequence aberrant cells carrying an unbalanced dose of nuclei. Since fruiting body initiation is dependent on the balanced mating-type regulator doses present in the dikaryon, we believe that the observed developmental defects were a consequence of the impaired cell cycle in the dikaryon. Our results suggest a connection between the DNA damage response cascade, cell cycle regulation, and developmental processes in this fungus.

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.

Lcc1 and Lcc5 are the main laccases secreted in liquid cultures of Coprinopsis cinerea strains

The litter-degrading dung fungus Coprinopsis cinerea has the high number of seventeen different laccase genes. In this work, ten different monokaryons were compared in their ability to produce laccases in two different complete media at different temperatures. Few strains showed laccase activity at the optimal growth temperature of 37 °C. Nine of the strains gave laccase activities between 0.2 and 5.9 U mL(-1) at the suboptimal temperature of 25 °C in mKjalke medium. Laccase activities in YMG/T medium were detected for only three strains (0.5-4.5 U mL(-1)). Zymograms of supernatants from mKjalke medium resulted in total in 10 different laccase bands but strains differed in distribution. LC-MS/MS analysis with Mascot searches of the annotated C. cinerea genome identified isoenzymes from five different genes (Lcc1, Lcc2, Lcc5, Lcc9 and Lcc10) and of Lcc1 three and of Lcc5 two distinct electrophoretical forms. Lcc1 and Lcc5 were expressed in all laccase positive strains, but not all forms were found in all of the strains. Lcc2, Lcc9 and Lcc10 occurred only in three strains as minor laccases, indicating that Lcc1 and Lcc5 are the main laccases of C. cinerea secreted in liquid mKjalke medium.

Enhancement of ganoderic acid accumulation by overexpression of an N-terminally truncated 3-hydroxy-3-methylglutaryl coenzyme A reductase gene in the basidiomycete Ganoderma lucidum

Ganoderic acids produced by Ganoderma lucidum, a well-known traditional Chinese medicinal mushroom, exhibit antitumor and antimetastasis activities. Genetic modification of G. lucidum is difficult but critical for the enhancement of cellular accumulation of ganoderic acids. In this study, a homologous genetic transformation system for G. lucidum was developed for the first time using mutated sdhB, encoding the iron-sulfur protein subunit of succinate dehydrogenase, as a selection marker. The truncated G. lucidum gene encoding the catalytic domain of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) was overexpressed by using the Agrobacterium tumefaciens-mediated transformation system. The results showed that the mutated sdhB successfully conferred carboxin resistance upon transformation. Most of the integrated transfer DNA (T-DNA) appeared as a single copy in the genome. Moreover, deregulated constitutive overexpression of the HMGR gene led to a 2-fold increase in ganoderic acid content. It also increased the accumulation of intermediates (squalene and lanosterol) and the upregulation of downstream genes such as those of farnesyl pyrophosphate synthase, squalene synthase, and lanosterol synthase. This study demonstrates that transgenic basidiomycete G. lucidum is a promising system to achieve metabolic engineering of the ganoderic acid pathway.

Multiple multi-copper oxidase gene families in basidiomycetes - what for?

Genome analyses revealed in various basidiomycetes the existence of multiple genes for blue multi-copper oxidases (MCOs). Whole genomes are now available from saprotrophs, white rot and brown rot species, plant and animal pathogens and ectomycorrhizal species. Total numbers (from 1 to 17) and types of mco genes differ between analyzed species with no easy to recognize connection of gene distribution to fungal life styles. Types of mco genes might be present in one and absent in another fungus. Distinct types of genes have been multiplied at speciation in different organisms. Phylogenetic analysis defined different subfamilies of laccases sensu stricto (specific to Agaricomycetes), classical Fe2+-oxidizing Fet3-like ferroxidases, potential ferroxidases/laccases exhibiting either one or both of these enzymatic functions, enzymes clustering with pigment MCOs and putative ascorbate oxidases. Biochemically best described are laccases sensu stricto due to their proposed roles in degradation of wood, straw and plant litter and due to the large interest in these enzymes in biotechnology. However, biological functions of laccases and other MCOs are generally little addressed. Functions in substrate degradation, symbiontic and pathogenic intercations, development, pigmentation and copper homeostasis have been put forward. Evidences for biological functions are in most instances rather circumstantial by correlations of expression. Multiple factors impede research on biological functions such as difficulties of defining suitable biological systems for molecular research, the broad and overlapping substrate spectrum multi-copper oxidases usually possess, the low existent knowledge on their natural substrates, difficulties imposed by low expression or expression of multiple enzymes, and difficulties in expressing enzymes heterologously.

Agrobacterium tumefaciens mediated fused egfp-hph gene expression under the control of gpd promoter in Pleurotus ostreatus

A transformation system for the basidiomycete Pleurotus ostreatus was established using agrobacterium-mediated infection. Following P. ostreatus glyceraldehyde-3-phosphate dehydrogenase gene analysis, its promoter region including two introns was used as cis-regulatory element to drive expression of enhanced green fluorescent protein (eGFP). As a selection marker, the hygromycin phosphotransferase (hph) gene cassette was used in the binary vector pPEH. Mycelia without pretreatment were found to be the most efficient recipients in transformation experiments while fruiting body tissue or basidiospores showed lower transformation rates. A transformation efficiency of 75% was achieved. After subculturing, putative transformants were screened by PCR and Southern blot analysis showing the expected ectopic integration of the transforming DNA. At the same time, the promotor region was shown to drive expression of selection marker as well as eGFP that could be visualized, which will be helpful for future investigation using Agrobacterium tumefaciens mediated transformation for functional characterization of genes in the mushroom forming basidioymcete P. ostreatus.

Heterologous expression of the immunomodulatory protein gene from Ganoderma sinense in the basidiomycete Coprinopsis cinerea

AIMS

FIP-gsi, a fungal immunomodulatory protein found in Ganoderma sinense, has antitumour, anti-allergy and immunomodulatory activities and is regulated by the fip-gsi gene. In this study, we aimed to express the fip-gsi gene from G. sinense in Coprinopsis cinerea to increase yield of FIPs-gsi.

METHODS AND RESULTS

A fungal expression vector pBfip-gsi containing the gpd promoter from Agaricus bisporus and the fip-gsi gene from the G. sinense was constructed and transformed into C. cinerea. PCR and Southern blotting analysis verified the successful integration of the exogenous gene fip-gsi into the genome of C. cinerea. RT-PCR and Northern blotting analysis confirmed that the fip-gsi gene was transcribed in C. cinerea. The yield of the FIP-gsi protein reached 314mg kg(-1) fresh mycelia. The molecular weight of the FIP-gsi was 13kDa, and the FIP-gsi was capable of hemagglutinating mouse red blood cells, but no such activity was observed towards human red blood cells in vitro.

CONCLUSIONS

The fip-gsi from G. sinense has been successfully translated in C. cinerea, and the yield of bioactive FIP-gsi protein was high.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report using the C. cinerea for the heterologous expression of FIP-gsi protein and it might supply a basis for large-scale production of the protein.

Improvement of the Coprinopsis cinerea molecular toolkit using new construct design and additional marker genes

This paper describes the optimisation of an existing basidiomycete molecular toolkit through the development of new versatile vectors. These vectors enable the straightforward and rapid construction of gene expression and silencing cassettes by allowing the easy exchange of promoters, coding regions and terminator elements. The constructs contain multiple cloning sites (MCS) allowing any gene to be inserted using a range of restriction sites, with the option of a 5' integral intron for efficient gene expression. We describe the testing of these vectors through marker gene expression in Coprinopsis cinerea. This work also extends the range of marker genes available for use in C. cinerea with the first report of DsRed and monomeric red fluorescent protein (mRFP) expression in C. cinerea and further demonstrates the requirement for an intron in the expression cassette for some marker genes. However, analysis of transformants containing either beta-glucuronidase (GUS) or luciferase (LUC) genes, with and without an intron revealed no detectable marker gene expression. The inclusion of an intron does therefore not guarantee expression and other genetic factors may be involved.

Expression of multi-functional cellulase gene mfc in Coprinus cinereus under control of different basidiomycete promoters

Multi-functional cellulase gene mfc was expressed in Coprinus cinereus under naturally non-inductive conditions using three heterologous promoters. Endo-beta-1,4-glucanase expression was achieved in solid and liquid media with promoter sequences from the Lentinula edodesgpd gene, the Flammulina velutipes gpd gene and the Volvariella volvaceagpd gene. As measured by enzyme activity in liquid cultures, a 613-bp gpd promoter fragment from L. edodes was most efficient, followed by a 752-bp gpd fragment from F. velutipes. The V. volvacea gpd promoter sequence was less active, in comparison. Irrespective of the promoter used, enzymatic activities increase 34-fold for highly active transformants and 29-fold for less active one by using cellulase-inducing medium. The highest activities of endo-beta-1,4-glucanase (34.234 U/ml) and endo-beta-1,4-xylanase (263.695 U/ml) were reached by using the L. edodesgpd promoter.

Establishing molecular tools for genetic manipulation of the pleuromutilin-producing fungus Clitopilus passeckerianus

We describe efficient polyethylene glycol (PEG)-mediated and Agrobacterium-mediated transformation systems for a pharmaceutically important basidiomycete fungus, Clitopilus passeckerianus, which produces pleuromutilin, a diterpene antibiotic. Three dominant selectable marker systems based on hygromycin, phleomycin, and carboxin selection were used to study the feasibility of PEG-mediated transformation of C. passeckerianus. The PEG-mediated transformation of C. passeckerianus protoplasts was successful and generated hygromycin-resistant transformants more efficiently than either phleomycin or carboxin resistance. Agrobacterium-mediated transformation with plasmid pBGgHg containing hph gene under the control of the Agaricus bisporus gpdII promoter led to hygromycin-resistant colonies and was successful when homogenized mycelium and fruiting body gill tissue were used as starting material. Southern blot analysis of transformants revealed the apparently random integration of the transforming DNA to be predominantly multiple copies for the PEG-mediated system and a single copy for the Agrobacterium-mediated system within the genome. C. passeckerianus actin and tubulin promoters were amplified from genomic DNA and proved successful in driving green fluorescent protein and DsRed expression in C. passeckerianus, but only when constructs contained a 5' intron, demonstrating that the presence of an intron is prerequisite for efficient transgene expression. The feasibility of RNA interference-mediated gene silencing was investigated using gfp as a target gene easily scored in C. passeckerianus. Upon transformation of gfp antisense constructs into a highly fluorescent strain, transformants were recovered that exhibited either reduced or undetectable fluorescence. This was confirmed by Northern blotting showing depletion of the target mRNA levels. This demonstrated that gene silencing is a suitable tool for modulating gene expression in C. passeckerianus. The molecular tools developed in this study should facilitate studies aimed at gene isolation or characterization in this pharmaceutically important species.

Investigating dominant selection markers for Coprinopsis cinerea: a carboxin resistance system and re-evaluation of hygromycin and phleomycin resistance vectors

Dominant selectable markers are beneficial for transformation of many fungi, particularly those model species where repeated transformations may be required. A carboxin resistance allele of the Coprinopsis cinerea sdi1 gene, encoding the iron-sulphur protein subunit of succinate dehydrogenase, was developed by introducing a suitable point mutation in the histidine block responsible for binding of the associated iron ion. This modified gene was used successfully to confer carboxin resistance upon transformation of C. cinerea protoplasts. Plasmids previously used to establish hygromycin transformation systems of several basidiomycete species, such as pAN7-1 and phph004, failed to give rise to hygromycin-resistant transformants of C. cinerea, whilst pPHT1 was successful. Sequencing of these constructs showed that the hygromycin resistance gene in pAN7-1 and phph004 had been modified removing the codons encoding two lysine residues following the N-terminal methionine. Replacement of the deleted 6 bp (AAA AAG) in the truncated hph gene led to generation of hygromycin-resistant transformants indicating the importance of these two codons for expression in C. cinerea. Phleomycin-resistant (ble) transformants were also obtained, but only with the intron-containing construct pblei004, showing that an intron is necessary to obtain phleomycin-resistant C. cinerea. This contrasts with hygromycin-resistance, where introns are not required for expression, emphasising the variability in importance of these elements.

Engineering and Applications of fungal laccases for organic synthesis

Laccases are multi-copper containing oxidases (EC 1.10.3.2), widely distributed in fungi, higher plants and bacteria. Laccase catalyses the oxidation of phenols, polyphenols and anilines by one-electron abstraction, with the concomitant reduction of oxygen to water in a four-electron transfer process. In the presence of small redox mediators, laccase offers a broader repertory of oxidations including non-phenolic substrates. Hence, fungal laccases are considered as ideal green catalysts of great biotechnological impact due to their few requirements (they only require air, and they produce water as the only by-product) and their broad substrate specificity, including direct bioelectrocatalysis.

Thus, laccases and/or laccase-mediator systems find potential applications in bioremediation, paper pulp bleaching, finishing of textiles, bio-fuel cells and more. Significantly, laccases can be used in organic synthesis, as they can perform exquisite transformations ranging from the oxidation of functional groups to the heteromolecular coupling for production of new antibiotics derivatives, or the catalysis of key steps in the synthesis of complex natural products. In this review, the application of fungal laccases and their engineering by rational design and directed evolution for organic synthesis purposes are discussed.

Molecular cloning and heterologous expression of a laccase gene from Pleurotus eryngii in free and immobilized Saccharomyces cerevisiae cells

A full length cDNA encoding an extracellular laccase was isolated by reverse transcription polymerase chain reaction from the mycelia of the mushroom Pleurotus eryngii. The isolated sequence, denoted Ery3, encodes for a mature laccase isoenzyme of 531 amino acid residues with a predicted molecular weight of 56.6 kDa. All sequence motifs, being the signature sequences used to identify the laccases, were found in the Ery3 protein sequence. The Ery3 cDNA was expressed in Saccharomyces cerevisiae and the effects of copper concentration and cultivation temperature were investigated. S. cerevisiae cells were immobilized in calcium alginate gel and the optimal immobilization parameters for the enhanced production of laccase were determined. The immobilization was most effective with 3% sodium alginate, 0.1 M calcium chloride and an initial biomass of 4.5 x 10(8) cells. The enzyme yield obtained with immobilized cells (139 mU ml(-1)) showed a 1.6-fold increase compared to the highest yield obtained with free cells. The alginate beads showed good stability and retained 84% capacity of enzyme production after seven repeated cycles of batch fermentation. The immobilization system proved to increase the proteolytic stability of the recombinant Ery3 protein. To our knowledge, this is the first report on S. cerevisiae whole-cell immobilization for recombinant laccase production.

A comparison of methods for successful triggering of gene silencing in Coprinus cinereus

Post-transcriptional gene-silencing methods (PTGS), including RNAi, are becoming increasingly pervasive in functional genomics. To advance analysis of the recently sequenced Coprinus cinereus genome, a high throughput gene silencing method is essential. We have exploited the GFP reporter gene to evaluate and quantify efficacy of three different silencing strategies. Modular constructs that encompassed antisense, untranslatable sense, and RNAi-mediating hairpin sequences, were transformed into a GFP-expressing host strain. Transformants exhibiting strong downregulation and partial suppression of GFP were recovered with all three constructs. Analyses of protein and transcriptional nucleic acids revealed that the antisense and hairpin sequences yielded similar levels of GFP suppression, and were both more efficient than untranslatable sense sequences. Our antisense vectors will expedite functional characterisation of C. cinereus and the modular nature of the constructs should permit exploitation of directional cDNA libraries for high throughput screening.

The laccase multi-gene family in Coprinopsis cinerea has seventeen different members that divide into two distinct subfamilies

Seventeen non-allelic laccase genes and one gene footprint are present in the genome of Coprinopsis cinerea. Two gene subfamilies were defined by intron positions and similarity of deduced gene products, one with 15 members (lcc1-lcc15) and one with 2 members (lcc16, lcc17). The first subfamily divides in the phylogenetic tree of deduced proteins into smaller clusters that probably reflect recent gene duplication events. Different laccase genes diverged from each other both by frequent synonymous and non-synonymous codon changes. Mainly synonymous codon changes accumulate in alleles, with up to 12% total codon differences between given pairs of alleles. Overexpression of the 17 laccase genes under the control of a constitutive promoter identified nine active enzymes from subfamily 1. All of these showed laccase activities with DMP (2,6-dimethoxy phenol) as substrate but only eight of them also with ABTS [2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)]. Lcc16 and Lcc17 share certain sequence features with ferroxidases but enzyme assays failed to show such activity. Lcc15 is expected to be non-functional in laccase activity due to an internal deletion of about 150 amino acids. Transcripts were obtained from all genes but splice junctions for three genes were not congruent with translation into a functional protein.