Isolation and characterization of the glyceraldehyde-3-phosphate dehydrogenase gene of Aspergillus nidulans

Kojic Acid Gene Clusters and the Transcriptional Activation Mechanism of Aspergillus flavus KojR on Expression of Clustered Genes

Kojic acid (KA) is a fungal metabolite and has a variety of applications in the cosmetics and food industries. Aspergillus oryzae is a well-known producer of KA, and its KA biosynthesis gene cluster has been identified. In this study, we showed that nearly all section Flavi aspergilli except for A. avenaceus had complete KA gene clusters, and only one Penicillium species, P. nordicum, contained a partial KA gene cluster. Phylogenetic inference based on KA gene cluster sequences consistently grouped section Flavi aspergilli into clades as prior studies. The Zn(II)₂Cys₆ zinc cluster regulator KojR transcriptionally activated clustered genes of kojA and kojT in Aspergillus flavus. This was evidenced by the time-course expression of both genes in kojR-overexpressing strains whose kojR expression was driven by a heterologous Aspergillus nidulans gpdA promoter or a homologous A. flavus gpiA promoter. Using sequences from the kojA and kojT promoter regions of section Flavi aspergilli for motif analyses, we identified a consensus KojR-binding motif to be an 11-bp palindromic sequence of 5'-CGRCTWAGYCG-3' (R = A/G, W = A/T, Y = C/T). A CRISPR/Cas9-mediated gene-targeting technique showed that the motif sequence, 5'-CGACTTTGCCG-3', in the kojA promoter was critical for KA biosynthesis in A. flavus. Our findings may facilitate strain improvement and benefit future kojic acid production.

Transcriptome-based Mining of the Constitutive Promoters for Tuning Gene Expression in Aspergillus oryzae

Transcriptional regulation has been adopted for developing metabolic engineering tools. The regulatory promoter is a crucial genetic element for strain optimization. In this study, a gene set of Aspergillus oryzae with highly constitutive expression across different growth stages was identified through transcriptome data analysis. The candidate promoters were functionally characterized in A. oryzae by transcriptional control of β-glucuronidase (GUS) as a reporter. The results showed that the glyceraldehyde triphosphate dehydrogenase promoter (PgpdA1) of A. oryzae with a unique structure displayed the most robust strength in constitutively controlling the expression compared to the PgpdA2 and other putative promoters tested. In addition, the ubiquitin promoter (Pubi) of A. oryzae exhibited a moderate expression strength. The deletion analysis revealed that the 5' untranslated regions of gpdA1 and ubi with the length of 1028 and 811 nucleotides, counted from the putative translation start site (ATG), respectively, could efficiently drive the GUS expression. Interestingly, both promoters could function on various carbon sources for cell growth. Glucose was the best fermentable carbon source for allocating high constitutive expressions during cell growth, and the high concentrations (6-8% glucose, w/v) did not repress their functions. It was also demonstrated that the secondary metabolite gene coding for indigoidine could express under the control of PgpdA1 or Pubi promoter. These strong and moderate promoters of A. oryzae provided beneficial options in tuning the transcriptional expression for leveraging the metabolic control towards the targeted products.

Conversion of Polyethylenes into Fungal Secondary Metabolites

Waste plastics represent major environmental and economic burdens due to their ubiquity, slow breakdown rates, and inadequacy of current recycling routes. Polyethylenes are particularly problematic, because they lack robust recycling approaches despite being the most abundant plastics in use today. We report a novel chemical and biological approach for the rapid conversion of polyethylenes into structurally complex and pharmacologically active compounds. We present conditions for aerobic, catalytic digestion of polyethylenes collected from post-consumer and oceanic waste streams, creating carboxylic diacids that can then be used as a carbon source by the fungus Aspergillus nidulans. As a proof of principle, we have engineered strains of A. nidulans to synthesize the fungal secondary metabolites asperbenzaldehyde, citreoviridin, and mutilin when grown on these digestion products. This hybrid approach considerably expands the range of products to which polyethylenes can be upcycled.

Modular Inducible Multigene Expression System for Filamentous Fungi

Inducible promoters are indispensable elements when considering the possibility to modulate gene expression on demand. Desirable traits of conditional expression systems include their capacity for tight downregulation, high overexpression, and in some instances for fine-tuning, to achieve a desired product's stoichiometry. Although the number of inducible systems is slowly increasing, suitable promoters comprising these features are rare. To date, the concomitant use of multiple regulatable promoter platforms for controlled multigene expression has been poorly explored. This work provides pioneer work in the human pathogenic fungus Aspergillus fumigatus, wherein we investigated different inducible systems, elucidated three candidate promoters, and proved for the first time that up to three systems can be used simultaneously without interfering with each other. Proof of concept was obtained by conditionally expressing three antifungal drug targets within the ergosterol biosynthetic pathway under the control of the xylose-inducible PxylP system, the tetracycline-dependent Tet-On system, and the thiamine-repressible PthiA system. IMPORTANCE In recent years, inducible promoters have gained increasing interest for industrial or laboratory use and have become key instruments for protein expression, synthetic biology, and metabolic engineering. Constitutive, high-expressing promoters can be used to achieve high expression yields; however, the continuous overexpression of specific proteins can lead to an unpredictable metabolic burden. To prevent undesirable effects on the expression host's metabolism, the utilization of tunable systems that allow expression of a gene product on demand is indispensable. Here, we elucidated several excellent tunable promoter systems and verified that each can be independently induced in a single strain to ultimately develop a unique conditional multigene expression system. This highly efficient, modular toolbox has the potential to significantly advance applications in fundamental as well as applied research in which regulatable expression of several genes is a key requirement.

The Sugar Metabolic Model of Aspergillus niger Can Only Be Reliably Transferred to Fungi of Its Phylum

Fungi play a critical role in the global carbon cycle by degrading plant polysaccharides to small sugars and metabolizing them as carbon and energy sources. We mapped the well-established sugar metabolic network of Aspergillus niger to five taxonomically distant species (Aspergillus nidulans, Penicillium subrubescens, Trichoderma reesei, Phanerochaete chrysosporium and Dichomitus squalens) using an orthology-based approach. The diversity of sugar metabolism correlates well with the taxonomic distance of the fungi. The pathways are highly conserved between the three studied Eurotiomycetes (A. niger, A. nidulans, P. subrubescens). A higher level of diversity was observed between the T. reesei and A. niger, and even more so for the two Basidiomycetes. These results were confirmed by integrative analysis of transcriptome, proteome and metabolome, as well as growth profiles of the fungi growing on the corresponding sugars. In conclusion, the establishment of sugar pathway models in different fungi revealed the diversity of fungal sugar conversion and provided a valuable resource for the community, which would facilitate rational metabolic engineering of these fungi as microbial cell factories.

The gold-standard genome of Aspergillus niger NRRL 3 enables a detailed view of the diversity of sugar catabolism in fungi

The fungal kingdom is too large to be discovered exclusively by classical genetics. The access to omics data opens a new opportunity to study the diversity within the fungal kingdom and how adaptation to new environments shapes fungal metabolism. Genomes are the foundation of modern science but their quality is crucial when analysing omics data. In this study, we demonstrate how one gold-standard genome can improve functional prediction across closely related species to be able to identify key enzymes, reactions and pathways with the focus on primary carbon metabolism.

Based on this approach we identified alternative genes encoding various steps of the different sugar catabolic pathways, and as such provided leads for functional studies into this topic. We also revealed significant diversity with respect to genome content, although this did not always correlate to the ability of the species to use the corresponding sugar as a carbon source.

Microbial Production of Recombinant Rennet

Rennet, traditionally obtained from calves, is non-vegeterian and unethical due to the slaughter of unweaned animals. Chymosin is highly specific to the Phe105-Met106 bond of κ-casein and has low proteolytic activity. Microbial aspartic proteases can partly replace chymosin. However, recombinant DNA technology has allowed chymosin itself to be produced by bacteria, yeast, and molds. Not only rennet from calf, but from animals like goat kid, lamb, buffalo, camel, and others can be used in cheesemaking. Chymosins of these animals can be cloned and successfully expressed in microorganisms and can be employed in the production of novel as well as traditional cheese products from the milk of camel, goat, and even horse and donkey. This chapter outlines the recombinant DNA techniques applied over the past few years to improve the microbial production of recombinant rennet, from animals and plants.

Discovery of McrA, a master regulator of Aspergillus secondary metabolism

Fungal secondary metabolites (SMs) are extremely important in medicine and agriculture, but regulation of their biosynthesis is incompletely understood. We have developed a genetic screen in Aspergillus nidulans for negative regulators of fungal SM gene clusters and we have used this screen to isolate mutations that upregulate transcription of the non-ribosomal peptide synthetase gene required for nidulanin A biosynthesis. Several of these mutations are allelic and we have identified the mutant gene by genome sequencing. The gene, which we designate mcrA, is conserved but uncharacterized, and it encodes a putative transcription factor. Metabolite profiles of mcrA deletant, mcrA overexpressing, and parental strains reveal that mcrA regulates at least ten SM gene clusters. Deletion of mcrA stimulates SM production even in strains carrying a deletion of the SM regulator laeA, and deletion of mcrA homologs in Aspergillus terreus and Penicillum canescens alters the secondary metabolite profile of these organisms. Deleting mcrA in a genetic dereplication strain has allowed us to discover two novel compounds as well as an antibiotic not known to be produced by A. nidulans. Deletion of mcrA upregulates transcription of hundreds of genes including many that are involved in secondary metabolism, while downregulating a smaller number of genes.

Synergistic and Dose-Controlled Regulation of Cellulase Gene Expression in Penicillium oxalicum

Filamentous fungus Penicillium oxalicum produces diverse lignocellulolytic enzymes, which are regulated by the combinations of many transcription factors. Here, a single-gene disruptant library for 470 transcription factors was constructed and systematically screened for cellulase production. Twenty transcription factors (including ClrB, CreA, XlnR, Ace1, AmyR, and 15 unknown proteins) were identified to play putative roles in the activation or repression of cellulase synthesis. Most of these regulators have not been characterized in any fungi before. We identified the ClrB, CreA, XlnR, and AmyR transcription factors as critical dose-dependent regulators of cellulase expression, the core regulons of which were identified by analyzing several transcriptomes and/or secretomes. Synergistic and additive modes of combinatorial control of each cellulase gene by these regulatory factors were achieved, and cellulase expression was fine-tuned in a proper and controlled manner. With one of these targets, the expression of the major intracellular β-glucosidase Bgl2 was found to be dependent on ClrB. The Bgl2-deficient background resulted in a substantial gene activation by ClrB and proved to be closely correlated with the relief of repression mediated by CreA and AmyR during cellulase induction. Our results also signify that probing the synergistic and dose-controlled regulation mechanisms of cellulolytic regulators and using it for reconstruction of expression regulation network (RERN) may be a promising strategy for cellulolytic fungi to develop enzyme hyper-producers. Based on our data, ClrB was identified as focal point for the synergistic activation regulation of cellulase expression by integrating cellulolytic regulators and their target genes, which refined our understanding of transcriptional-regulatory network as a “seesaw model” in which the coordinated regulation of cellulolytic genes is established by counteracting activators and repressors.

Cellulolytic fungi have evolved into sophisticated lignocellulolytic systems to adapt to their natural habitat. This trait is important for filamentous fungi, which are the main source of cellulases utilized to degrade lignocellulose to fermentable sugars. Penicillium oxalicum, which produces lignocellulolytic enzymes with more diverse components than Trichoderma reesei, has the capacity to secrete large amounts of cellulases. Meanwhile, cellulase expression is regulated by a complex network involved in many transcription factors in this organism. To better understand how cellulase genes are systematically regulated in P. oxalicum, we employed molecular genetics to uncover the cellulolytic transcription factors on a genome-wide scale. We discovered the synergistic and tunable regulation of cellulase expression by integrating cellulolytic regulators and their target genes, which refined our understanding of transcriptional-regulatory network as a “seesaw model” in which the coordinated regulation of cellulolytic genes is established by counteracting activators and repressors.

Sugar catabolism in Aspergillus and other fungi related to the utilization of plant biomass

Fungi are found in all natural and artificial biotopes and can use highly diverse carbon sources. They play a major role in the global carbon cycle by decomposing plant biomass and this biomass is the main carbon source for many fungi. Plant biomass is composed of cell wall polysaccharides (cellulose, hemicellulose, pectin) and lignin. To degrade cell wall polysaccharides to different monosaccharides, fungi produce a broad range of enzymes with a large variety in activities. Through a series of enzymatic reactions, sugar-specific and central metabolic pathways convert these monosaccharides into energy or metabolic precursors needed for the biosynthesis of biomolecules. This chapter describes the carbon catabolic pathways that are required to efficiently use plant biomass as a carbon source. It will give an overview of the known metabolic pathways in fungi, their interconnections, and the differences between fungal species.

Transcriptome changes initiated by carbon starvation in Aspergillus nidulans

Carbon starvation is a common stress for micro-organisms both in nature and in industry. The carbon starvation stress response (CSSR) involves the regulation of several important processes including programmed cell death and reproduction of fungi, secondary metabolite production and extracellular hydrolase formation. To gain insight into the physiological events of CSSR, DNA microarray analyses supplemented with real-time RT-PCR (rRT-PCR) experiments on 99 selected genes were performed. These data demonstrated that carbon starvation induced very complex changes in the transcriptome. Several genes contributing to protein synthesis were upregulated together with genes involved in the unfolded protein stress response. The balance between biosynthesis and degradation moved towards degradation in the case of cell wall, carbohydrate, lipid and nitrogen metabolism, which was accompanied by the production of several hydrolytic enzymes and the induction of macroautophagy. These processes provide the cultures with long-term survival by liberating nutrients through degradation of the cell constituents. The induced synthesis of secondary metabolites, antifungal enzymes and proteins as well as bacterial cell wall-degrading enzymes demonstrated that carbon-starving fungi should have marked effects on the micro-organisms in their surroundings. Due to the increased production of extracellular and vacuolar enzymes during carbon starvation, the importance of the endoplasmic reticulum increased considerably.

The bZIP transcription factor MeaB mediates nitrogen metabolite repression at specific loci

In Fusarium fujikuroi, bikaverin (BIK) biosynthesis is subject to repression by nitrogen. Unlike most genes subject to nitrogen metabolite repression, it has been shown that transcription of bik biosynthetic genes is not AreA dependent. Searching for additional transcription factors that may be involved in nitrogen regulation, we cloned and characterized the orthologue of Aspergillus nidulans meaB, which encodes a bZIP transcription factor. Two transcripts are derived from F. fujikuroi meaB: the large transcript (meaB(L)) predominates under nitrogen-sufficient conditions and the smaller transcript (meaB(S)) under nitrogen limitation, in an AreA-dependent manner. MeaB is specifically translocated to the nucleus under nitrogen-sufficient conditions in both F. fujikuroi and A. nidulans. Deletion of meaB resulted in partial upregulation of several nitrogen-regulated genes, but only in the ΔmeaB ΔareA double mutant were the bikaverin genes significantly upregulated in the presence of glutamine. These data demonstrate that MeaB and AreA coordinately mediate nitrogen metabolite repression and, importantly, that independently of AreA, MeaB can mediate nitrogen metabolite repression at specific loci in F. fujikuroi.

Overexpression of bacterial ethylene-forming enzyme gene in Trichoderma reesei enhanced the production of ethylene

In order to efficiently utilize natural cellulose materials to produce ethylene, three expression vectors containing the ethylene-forming enzyme (efe) gene from Pseudomonas syringae pv. glycinea were constructed. The target gene was respectively controlled by different promoters: cbh I promoter from Trichoderma reesei cellobiohydrolases I gene, gpd promoter from Aspergillus nidulans glyceraldehyde-3-phosphate dehydrogenase gene and pgk I promoter from T. reesei 3-phosphoglycerate kinase I gene. After transforming into T. reesei QM9414, 43 stable transformants were obtained by PCR amplification and ethylene determination. Southern blot analysis of 14 transformants demonstrated that the efe gene was integrated into chromosomal DNA with copy numbers from 1 to 4. Reverse transcription polymerase chain reaction (RT-PCR) analysis of 6 transformants showed that the heterologous gene was transcribed. By using wheat straw as a carbon source, the ethylene production rates of aforementioned 14 transformants were measured. Transformant C30-3 with pgk I promoter had the highest ethylene production (4,012 nl h^-1 l^-1). This indicates that agricultural wastes could be used to produce ethylene in recombinant filamentous fungus T. reesei.

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.

Functional analysis of the endoxylanase B (xynB) promoter from Penicillium purpurogenum

In Penicillium purpurogenum, the gene encoding endoxylanase B (xynB) is highly expressed by xylan and repressed by glucose at the transcriptional level. The promoter of this gene has a modular structure, with eight putative XlnR binding sites in tandem (XlnR module), and upstream from them, four putative CreA binding sites (CreA module). Promoter fragments containing different modules were inserted into a plasmid, pAN49-1, which contains a basal fungal promoter linked to a reporter gene (lacZ) and its expression was studied in vivo in Aspergillus nidulans. The XlnR module is able to trigger high beta-galactosidase activity in the presence of xylan, but the lack of most XlnR sites notoriously reduces this enzymatic activity. No enzyme induction is observed if the orientation of the promoter fragment is inverted. The presence of the CreA module is necessary for glucose repression when beta-galactosidase activity is previously induced by xylan. However, when transformant strains containing the XlnR module but lacking all CreA sites were grown in glucose without pre-induction in xylan, a low beta-galactosidase activity was observed compared with the same transformants grown in xylan. These results agree with a double-lock regulatory mechanism for both direct and indirect repression of xylanolytic genes by glucose.

Role of AREA, a regulator of nitrogen metabolism, during colonization of maize kernels and fumonisin biosynthesis in Fusarium verticillioides

Fumonisin B1 (FB(1)) biosynthesis is repressed in cultures containing ammonium as the nitrogen source and when grown on blister kernels, the earliest stages of kernel development. In this study AREA, a regulator of nitrogen metabolism, was disrupted in Fusarium verticilliodes. The mutant (DeltaareA) grew poorly on mature maize kernels, but grew similar to wild type (WT) with the addition of ammonium phosphate. FB(1) was not produced by DeltaareA under any condition or by the WT with added ammonium phosphate. Constitutive expression of AREA (strain AREA-CE) rescued the growth and FB(1) defects in DeltaareA. Growth of WT, DeltaareA, and AREA-CE on blister-stage kernels was similar. After 7 days of growth, none of the strains produced FB(1) and the pH of the kernel tissues was 8.0. Addition of amylopectin to the blister kernels resulted in a pH near 6.6 and FB(1) production by WT and AREA-CE. The results support the hypothesis that FB(1) biosynthesis is regulated by AREA. Also the failure to produce FB(1) in blister kernels is due to high pH conditions generated because of an unfavorable carbon/nitrogen environment.

A novel gene, phcA from Pseudomonas syringae induces programmed cell death in the filamentous fungus Neurospora crassa

The phytopathogen Pseudomonas syringae competes with other epiphytic organisms, such as filamentous fungi, for resources. Here we characterize a gene in P. syringae pv. syringae B728a and P. syringae pv. tomato DC3000, termed phcA, that has homology to a filamentous fungal gene called het-c. phcA is conserved in many P. syringae strains, but is absent in one of the major clades, which includes the P. syringae pathovar phaseolicola. In the filamentous fungus Neurospora crassa, HET-C regulates a conserved programmed cell death pathway called heterokaryon incompatibility (HI). Ectopic expression of phcA in N. crassa induced HI and cell death that was dependent on the presence of a functional het-c pin-c haplotype. Further, by co-immunoprecipitation experiments, a heterocomplex between N. crassa HET-C1 and PhcA was associated with phcA-induced HI. P. syringae was able to attach and extensively colonize N. crassa hyphae, while an Escherichia coli control showed no association with the fungus. We further show that the P. syringae is able to use N. crassa as a sole nutrient source. Our results suggest that P. syringae has the potential to utilize phcA to acquire nutrients from fungi in nutrient-limited environments like the phyllosphere by the novel mechanism of HI induction.

CreA mediates repression of the regulatory gene xlnR which controls the production of xylanolytic enzymes in Aspergillus nidulans

The Aspergillus nidulans xlnR gene encodes a Zn(2)Cys(6) transcription activator necessary for the synthesis of the main xylanolytic enzymes, i.e. endo-xylanases X(22), X(24) and X(34), and beta-xilosidase XlnD. Expression of xlnR is not sufficient for induction of genes encoding the xylanolytic complex, the presence of xylose is absolutely required. It has been established previously that the wide-domain carbon catabolite repressor CreA indirectly represses xlnA (encodes X(22)) and xlnB (encodes X(24)) genes as well as exerting direct repression on xlnA. This work provides evidence that CreA-mediated indirect repression occurs through repression of xlnR: (i) the xlnR gene promoter is repressed by glucose and this repression is abolished in creA(d)30 mutant strains and (ii) deregulated expression of xlnR completely relieves glucose repression of xlnA and xlnB. Thus, CreA and XlnR form a transcriptional cascade regulating A. nidulans xylanolytic genes.

Role of Hsp104 in the propagation and inheritance of the [Het-s] prion

The chaperones of the ClpB/HSP100 family play a central role in thermotolerance in bacteria, plants, and fungi by ensuring solubilization of heat-induced protein aggregates. In addition in yeast, Hsp104 was found to be required for prion propagation. Herein, we analyze the role of Podospora anserina Hsp104 (PaHsp104) in the formation and propagation of the [Het-s] prion. We show that DeltaPaHsp104 strains propagate [Het-s], making [Het-s] the first native fungal prion to be propagated in the absence of Hsp104. Nevertheless, we found that [Het-s]-propagon numbers, propagation rate, and spontaneous emergence are reduced in a DeltaPaHsp104 background. In addition, inactivation of PaHsp104 leads to severe meiotic instability of [Het-s] and abolishes its meiotic drive activity. Finally, we show that DeltaPaHSP104 strains are less susceptible than wild type to infection by exogenous recombinant HET-s(218-289) prion amyloids. Like [URE3] and [PIN(+)] in yeast but unlike [PSI(+)], [Het-s] is not cured by constitutive PaHsp104 overexpression. The observed effects of PaHsp104 inactivation are consistent with the described role of Hsp104 in prion aggregate shearing in yeast. However, Hsp104-dependency appears less stringent in P. anserina than in yeast; presumably because in Podospora prion propagation occurs in a syncitium.

Gene overexpression and biochemical characterization of the biotechnologically relevant chlorogenic acid hydrolase from Aspergillus niger

The full-length gene that encodes the chlorogenic acid hydrolase from Aspergillus niger CIRM BRFM 131 was cloned by PCR based on the genome of the strain A. niger CBS 513.88. The complete gene consists of 1,715 bp and codes for a deduced protein of 512 amino acids with a molecular mass of 55,264 Da and an acidic pI of 4.6. The gene was successfully cloned and overexpressed in A. niger to yield 1.25 g liter(-1), i.e., 330-fold higher than the production of wild-type strain A. niger CIRM BRFM131. The histidine-tagged recombinant ChlE protein was purified to homogeneity via a single chromatography step, and its main biochemical properties were characterized. The molecular size of the protein checked by mass spectroscopy was 74,553 Da, suggesting the presence of glycosylation. ChlE is assembled in a tetrameric form with several acidic isoforms with pIs of around 4.55 and 5.2. Other characteristics, such as optimal pH and temperature, were found to be similar to those determined for the previously characterized chlorogenic acid hydrolase of A. niger CIRM BRFM 131. However, there was a significant temperature stability difference in favor of the recombinant protein. ChlE exhibits a catalytic efficiency of 12.5 x 10(6) M(-1) s(-1) toward chlorogenic acid (CGA), and its ability to release caffeic acid from CGA present in agricultural by-products such as apple marc and coffee pulp was clearly demonstrated, confirming the high potential of this enzyme.

VIB-1 is required for expression of genes necessary for programmed cell death in Neurospora crassa

Nonself recognition during somatic growth is an essential and ubiquitous phenomenon in both prokaryotic and eukaryotic species. In filamentous fungi, nonself recognition is also important during vegetative growth. Hyphal fusion between genetically dissimilar individuals results in rejection of heterokaryon formation and in programmed cell death of the fusion compartment. In filamentous fungi, such as Neurospora crassa, nonself recognition and heterokaryon incompatibility (HI) are regulated by genetic differences at het loci. In N. crassa, mutations at the vib-1 locus suppress nonself recognition and HI mediated by genetic differences at het-c/pin-c, mat, and un-24/het-6. vib-1 is a homolog of Saccharomyces cerevisiae NDT80, which is a transcriptional activator of genes during meiosis. For this study, we determined that vib-1 encodes a nuclear protein and showed that VIB-1 localization varies during asexual reproduction and during HI. vib-1 is required for the expression of genes involved in nonself recognition and HI, including pin-c, tol, and het-6; all of these genes encode proteins containing a HET domain. vib-1 is also required for the production of downstream effectors associated with HI, including the production of extracellular proteases upon carbon and nitrogen starvation. Our data support a model in which mechanisms associated with starvation and nonself recognition/HI are interconnected. VIB-1 is a major regulator of responses to nitrogen and carbon starvation and is essential for the expression of genes involved in nonself recognition and death in N. crassa.

A Rho-type GTPase, rho-4, is required for septation in Neurospora crassa

Proteins in the Rho family are small monomeric GTPases primarily involved in polarization, control of cell division, and reorganization of cytoskeletal elements. Phylogenetic analysis of predicted fungal Rho proteins suggests that a new Rho-type GTPase family, whose founding member is Rho4 from the archiascomycete Schizosaccharomyces pombe, is involved in septation. S. pombe rho4Delta mutants have multiple, abnormal septa. In contrast to S. pombe rho4Delta mutants, we show that strains containing rho-4 loss-of-function mutations in the filamentous fungus Neurospora crassa lead to a loss of septation. Epitope-tagged RHO-4 localized to septa and to the plasma membrane. In other fungi, the steps required for septation include formin, septin, and actin localization followed by cell wall synthesis and the completion of septation. rho-4 mutants were unable to form actin rings, showing that RHO-4 is required for actin ring formation. Characterization of strains containing activated alleles of rho-4 showed that RHO-4-GTP is likely to initiate new septum formation in N. crassa.

Identification of the mstE gene encoding a glucose-inducible, low affinity glucose transporter in Aspergillus nidulans

The mstE gene encoding a low affinity glucose transporter active during the germination of Aspergillus nidulans conidia on glucose medium has been identified. mstE expression also occurs in hyphae, is induced in the presence of other repressing carbon sources besides glucose, and is dependent on the function of the transcriptional repressor CreA. The expression of MstE and its subcellular distribution have been studied using a MstE-sGFP fusion protein. Concordant with data on mstE expression, MstE-sGFP is synthesized in the presence of repressing carbon sources, and fluorescence at the periphery of conidia and hyphae is consistent with MstE location in the plasma membrane. Deletion of mstE has no morphological phenotype but results in the absence of low affinity glucose uptake kinetics, the latter being substituted by a high affinity system.

Cloning and sequence analysis of putative glyceraldehyde-3-phosphate dehydrogenase gene from Monascus purpureus KCCM11832

Using a synthetic oligonucleotide probe, glyceraldehyde-3-phosphate dehydrogenase gene (gpd1) was cloned from Monascus purpureus KCCM11832. The 2834 bp EcoRV-HindIII region harbored 1183 bp 5'-UTR containing such regulatory elements as CT box, common in fungal gpd's, and gpd box previously found exclusively in Aspergillus gpd's. Full-length cDNA was cloned by PCR, and its sequence was determined. Transcription starting point was located 88 bp upstream from start codon. Polyadenylation signal sequence occurred 201 bp downstream from stop codon. Region from start codon ATG to stop codon TAA including introns showed 62 approximately 69% nucleotide sequence identity to those of Aspergillus gpd's. Significant bias in third position, with pyrimidines favored over purines, was observed in codon usage. The deduced amino acid sequence had 81 approximately 85% identity to Aspergillus gpd's. Monascus purpureus GPD was located at the same clade with Aspergillus GPD's.

Visualization of interactions between a pathogenic and a beneficial Fusarium strain during biocontrol of tomato foot and root rot

The soilborne fungus Fusarium oxysporum f. sp. radicis-lycopersici causes tomato foot and root rot (TFRR), which can be controlled by the addition of the nonpathogenic fungus F. oxysporum Fo47 to the soil. To improve our understanding of the interactions between the two Fusarium strains on tomato roots during biocontrol, the fungi were labeled using different autofluorescent proteins as markers and subsequently visualized using confocal laser scanning microscopy. The results were as follows. i) An at least 50-fold excess of Fo47over F. oxysporum f. sp. radicis-lycopersici was required to obtain control of TFRR. ii) When seedlings were planted in sand infested with spores of a single fungus, Fo47 hyphae attached to the root earlier than those of F. oxysporum f. sp. radicis-lycopersici. iii) Subsequent root colonization by F. oxysporum f. sp. radicis-lycopersici was faster and to a larger extent than that by Fo47. iv) Under disease-controlling conditions, colonization of tomato roots by the pathogenic fungus was significantly reduced. v) When the inoculum concentration of Fo47 was increased, root colonization by the pathogen was arrested at the stage of initial attachment to the root. vi) The percentage of spores of Fo47 that germinates in tomato root exudate in vitro is higher than that of the pathogen F. oxysporum f. sp. radicis-lycopersici. Based on these results, the mechanisms by which Fo47 controls TFRR are discussed in terms of i) rate of spore germination and competition for nutrients before the two fungi reach the rhizoplane; ii) competition for initial sites of attachment, intercellular junctions, and nutrients on the tomato root surface; and iii) inducing systemic resistance.

Characterization of IDI-4, a bZIP transcription factor inducing autophagy and cell death in the fungus Podospora anserina

In filamentous fungi a cell death reaction occurs when hyphae of unlike genotype fuse. This phenomenon is referred to as heterokaryon incompatibility. In Podospora anserina, this cell death reaction was found to be associated with the transcriptional induction of a set of genes termed idi genes (for induced during incompatibility) and activation of autophagy. Herein, we describe the characterization of idi-4, a novel idi gene encoding a bZIP transcription factor. Expression of idi-4 is induced during cell death by incompatibility and in various stress conditions. Inactivation of idi-4 by gene replacement does not suppress incompatibility but we show that overexpression of idi-4 triggers cell death. Strains which undergo idi-4-induced cell death display cytological hallmarks of cell death by incompatibility notably induction of autophagy. We also report that increased expression of idi-4 leads to transcriptional induction of other idi genes such as idi-7, the orthologue of the yeast ATG8 autophagy gene. Together these results establish IDI-4 as one of the transcription factor regulating autophagy and cell fate in Podospora.

Genomic organization of the Neurospora crassa gsn gene: possible involvement of the STRE and HSE elements in the modulation of transcription during heat shock

Glycogen synthase, an enzyme involved in glycogen biosynthesis, is regulated by phosphorylation and by the allosteric ligand glucose-6-phosphate (G6P). In addition, enzyme levels can be regulated by changes in gene expression. We recently cloned a cDNA for glycogen synthase ( gsn) from Neurospora crassa, and showed that gsn transcription decreased when cells were exposed to heat shock (shifted from 30 degrees C to 45 degrees C). In order to understand the mechanisms that control gsn expression, we isolated the gene, including its 5' and 3' flanking regions, from the genome of N. crassa. An ORF of approximately 2.4 kb was identified, which is interrupted by four small introns (II-V). Intron I (482 bp) is located in the 5'UTR region. Three putative Transcription Initiation Sites (TISs) were mapped, one of which lies downstream of a canonical TATA-box sequence (5'-TGTATAAA-3'). Analysis of the 5'-flanking region revealed the presence of putative transcription factor-binding sites, including Heat Shock Elements (HSEs) and STress Responsive Elements (STREs). The possible involvement of these motifs in the negative regulation of gsn transcription was investigated using Electrophoretic Mobility Shift Assays (EMSA) with nuclear extracts of N. crassa mycelium obtained before and after heat shock, and DNA fragments encompassing HSE and STRE elements from the 5'-flanking region. While elements within the promoter region are involved in transcription under heat shock, elements in the 5'UTR intron may participate in transcription during vegetative growth. The results thus suggest that N. crassa possesses trans -acting elements that interact with the 5'-flanking region to regulate gsn transcription during heat shock and vegetative growth.

The sequences appended to the amyloid core region of the HET-s prion protein determine higher-order aggregate organization in vivo

The [Het-s] prion of the fungus Podospora anserina propagates as a self-perpetuating amyloid form of the HET-s protein. This protein triggers a cell death reaction termed heterokaryon incompatibility when interacting with the HET-S protein, an allelic variant of HET-s. HET-s displays two distinct domains, a N-terminal globular domain and a C-terminal unstructured prion-forming domain (residues 218-289). Here, we describe the characterization of HET-s(157-289), a truncated form of HET-s bearing an extensive deletion in the globular domain but retaining full activity in incompatibility and prion propagation. In vitro, HET-s(157-289) polymerizes into amyloid fibers displaying the same core region as full-length HET-s fibers. We have shown previously that fusions of green fluorescent protein (GFP) with HET-s or HET-s(218-289) form dot-like aggregates in vivo upon transition to the prion state. By contrast, a HET-s(157-289)/GFP fusion protein forms elongated fibrillar aggregates in vivo. Such elongated aggregates can reach up to 150 μm in length. The in vivo dynamics of these organized structures is analysed by time lapse microscopy. We find that the large elongate structures grow by lateral association of shorter fibrillar aggregates. When co-expressed with HET-s(157-289), full-length HET-s and HET-s(218-289) can be incorporated into such elongated aggregates. Together, our data indicate that HET-s(157-289) aggregates can adopt an organized higher-order structure in vivo and that the ability to adopt this supramolecular organization is conferred by the sequences appended to the amyloid core region.

Isolation, characterization and expression of the hex1 gene from Trichoderma reesei

Polymers of the HEX1 protein produce Woronin bodies in filamentous fungi. We have isolated and sequenced the hex1 gene and flanking regions from the industrially exploited fungus Trichoderma reesei. Multiple transcription start sites (TSS) and the 5' untranslated region (UTR) were identified by 5'RACE PCR. There are three hex1 transcript types, two of which originate from two TSSs at approximately -320 and -1335 from the start codon, which are separated by a 500-bp intron within the 5'UTR. The third transcript type results from alternative splicing of the intron within the coding sequence at the 3' end, which results in the inclusion or exclusion of an unconserved histidine-rich coding region. The three transcripts code for two forms of HEX1 protein. N-terminal sequencing of HEX1 separated by 2D gel electrophoresis confirms that there are two forms of HEX1 protein which are modified further by alternative cleavage of the N-terminus. The dominant form of HEX1 is coded by a cDNA with TSS at position -1335. Expression of hex1 on cellulase-inducing medium peaks strongly within 24 h of growth but the protein is expressed at a lower and more consistent level in medium containing glucose. This is the first investigation of expression of the hex1 gene encoding a protein unique to filamentous fungi.

Cercosporin-deficient mutants by plasmid tagging in the asexual fungus Cercospora nicotianae

We have successfully adapted plasmid insertion and restriction enzyme-mediated integration (REMI) to produce cercosporin toxin-deficient mutants in the asexual phytopathogenic fungus Cercospora nicotianae. The use of pre-linearized plasmid or restriction enzymes in the transformation procedure significantly decreased the transformation frequency, but promoted a complicated and undefined mode of plasmid integration that leads to mutations in the C. nicotianae genome. Vector DNA generally integrated in multiple copies, and no increase in single-copy insertion was observed when enzymes were added to the transformation mixture. Out of 1873 transformants tested, 39 putative cercosporin toxin biosynthesis ( ctb) mutants were recovered that showed altered levels of cercosporin production. Seven ctb mutants were recovered using pre-linearized plasmids without the addition of enzymes, and these were considered to be non-REMI mutants. The correlation between a specific insertion and a mutant phenotype was confirmed using rescued plasmids as gene disruption vectors in the wild-type strain. Six out of fifteen rescued plasmids tested yielded cercosporin-deficient transformants when re-introduced into the wild-type strain, suggesting a link between the insertion site and the cercosporin-deficient phenotype. Sequence analysis of a fragment flanking the insert site recovered from one insertion mutant showed it to be disrupted in sequences with high homology to the acyl transferase domain of polyketide synthases from other fungi. Disruption of this polyketide synthase gene ( CTB1) using a rescued plasmid resulted in mutants that were defective in cercosporin production. Thus, we provide the first molecular evidence that cercosporin is synthesized via a polyketide pathway as previously hypothesized.

The Aa-Pri4 gene, specifically expressed during fruiting initiation in the Agrocybe aegerita complex, contains an unusual CT-rich leader intron within the 5' uncoding region

The Aa1-Pri4 gene was cloned from the edible mushroom Agrocybe aegerita. The gene, specifically expressed during fruiting initiation, encodes a glycine-rich protein of 116 amino acids, with no homology to already known proteins. Homologous genes were amplified from two other strains belonging to the Agr. aegerita complex and originating from South-East Asia; and a comparison of the three genes revealed a high conservation of the coding sequences (72.8-97.8%). The PRI4 putative protein sequences were highly similar (87.5-100.0%); and all of them contained two protein kinase C sites, suggesting a potential supplementary regulation by phosphorylation at the protein level. The 5' uncoding regions all presented a leader intron, very variable in sequence (45.7% identity), but with a high C+T content (74.5-79.0%). The presence of such CT-rich sequences previously described in the promoter of highly expressed fungal genes suggests that the leader intron of the Aa1-Pri4 gene could be involved in the high-level, stage-specific expression.

Expression of a synthetic copy of the bovine chymosin gene in Aspergillus awamori from constitutive and pH-regulated promoters and secretion using two different pre-pro sequences

A copy of the bovine chymosin gene (chy) with a codon usage optimized for its expression in Aspergillus awamori was constructed starting from synthetic oligonucleotides. To study the ability of this filamentous fungus to secrete bovine prochymosin, two plasmids were constructed in which the transcriptional, translational, and secretory control regions of the A. nidulans gpdA gene and pepB genes were coupled to either preprochymosin or prochymosin genes. Secretion of a protein enzymatically and immunologically indistinguishable from bovine chymosin was achieved in A. awamori transformants with each of these constructions. In all cases, the primary translation product (40.5 kDa) was self-processed to a mature chymosin polypeptide having a molecular weight of 35.6 kDa. Immunological assays indicated that most of the chymosin was secreted to the extracellular medium. Hybridization analysis of genomic DNA from chymosin transformants showed chromosomal integration of prochymosin sequences and, in some transformants, multiple copies of the expression cassettes were observed. Expression from the gpdA promoter was constitutive, whereas expression from the pepB promoter was strongly influenced by pH. A very high expression from the pepB promoter was observed during the growth phase. The A. awamori pepB gene terminator was more favorable for chymosin production than the S. cerevisiae CYC1 terminator.

Domain organization and structure-function relationship of the HET-s prion protein of Podospora anserina

The [Het-s] infectious element of the fungus Podospora anserina is a prion protein involved in a genetically controlled cell death reaction termed heterokaryon incompatibility. Previous analyses indicate that [Het-s] propagates as a self-perpetuating amyloid aggregate. The HET-s protein is 289 amino acids in length. Herein, we identify the region of the HET-s protein that is responsible for amyloid formation and prion propagation. The region of HET-s spanning residues 218-289 forms amyloid fibers in vitro and allows prion propagation in vivo. Conversely, a C-terminal deletion in HET-s prevents amyloid aggregation in vitro and prion propagation in vivo, and abolishes the incompatibility function. In the soluble form of HET-s, the region from residue 1 to 227 forms a well-folded domain while the C-terminal region is highly flexible. Together, our data establish a domain structure-function relationship for HET-s amyloid formation, prion propagation and incompatibility activity.

Rapamycin mimics the incompatibility reaction in the fungus Podospora anserina

In filamentous fungi, a programmed cell death (PCD) reaction occurs when cells of unlike genotype fuse. This reaction is caused by genetic differences at specific loci termed het loci (for heterokaryon incompatibility). Although several het genes have been characterized, the mechanism of this cell death reaction and its relation to PCD in higher eukaryotes remains largely unknown. In Podospora anserina, genes induced during the cell death reaction triggered by the het-R het-V interaction have been identified and termed idi genes. Herein, we describe the functional characterization of one idi gene (idi-1) and explore the connection between incompatibility and the response to nutrient starvation. We show that IDI-1 is a cell wall protein which localizes at the septum during normal growth. We found that induction of idi-1 and of the other known idi genes is not specific of the incompatibility reaction. The idi genes are induced upon nitrogen and carbon starvation and by rapamycin, a specific inhibitor of the TOR kinase pathway. The cytological hallmarks of het-R het-V incompatibility (increased septation, vacuolization, coalescence of lipid droplets, induction of autophagy, and cell death) are also observed during rapamycin treatment. Globally the cytological alterations and modifications in gene expression occurring during the incompatibility reaction are similar to those observed during starvation or rapamycin treatment.

Autophagy is induced during cell death by incompatibility and is essential for differentiation in the filamentous fungus Podospora anserina

In filamentous fungi, a cell death reaction occurs when cells of unlike genotype fuse. This cell death reaction, known as incompatibility reaction, is genetically controlled by a set of loci termed het loci (for heterokaryon incompatibility loci). In Podospora anserina, genes induced during this cell death reaction (idi genes) have been identified. The idi-6/pspA gene encodes a serine protease that is the orthologue of the vacuolar protease B of Saccharomyces cerevisiae involved in autophagy. We report here that the PSPA protease participates in the degradative autophagic pathway in Podospora. We have identified the Podospora orthologue of the AUT7 gene of S. cerevisiae involved in the early steps of autophagy in yeast. This gene is induced during the development of the incompatibility reaction and was designated idi-7. We have used a GFP-IDI7 fusion protein as a cytological marker of the induction of autophagy. Relocalization of this fusion protein and detection of autophagic bodies inside the vacuoles during the development of the incompatibility reaction provide cytological evidence of induction of autophagy during this cell death reaction. Therefore, cell death by incompatibility in fungi appears to be related to type II programmed cell death in metazoans. In addition, we found that pspA and idi-7 null mutations confer differentiation defects such as the absence of female reproductive structures, indicating that autophagy is required for differentiation in Podospora.

Nonself recognition is mediated by HET-C heterocomplex formation during vegetative incompatibility

Nonself recognition during vegetative growth in filamentous fungi is mediated by heterokaryon incompatibility (het) loci. In Neurospora crassa, het-c is one of 11 het loci. Three allelic specificity groups, termed het-c(OR), het-c(PA) and het-c(GR), exist in natural populations. Heterokaryons or partial diploids that contain het-c alleles of alternative specificity show severe growth inhibition, repression of conidiation and hyphal compartmentation and death (HCD). Using epitope-tagged HET-C, we show that nonself recognition is mediated by the presence of a heterocomplex composed of polypeptides encoded by het-c alleles of alternative specificity. The HET-C heterocomplex localized to the plasma membrane (PM); PM-bound HET-C heterocomplexes occurred in all three het-c incompatible allelic interactions. Strains containing het-c constructs deleted for a predicted signal peptide sequence formed HET-C heterocomplexes in the cytoplasm and showed a growth arrest phenotype. Our finding is a step towards understanding nonself recognition mechanisms that operate during vegetative growth in filamentous fungi, and provides a model for investigating relationships between recognition mechanisms and cell death.

Novel aspects of tomato root colonization and infection by Fusarium oxysporum f. sp. radicis-lycopersici revealed by confocal laser scanning microscopic analysis using the green fluorescent protein as a marker

The fungus Fusarium oxysporum f. sp. radicis-lycopersici is the causal agent of tomato foot and root rot disease. The green fluorescent protein (GFP) was used to mark this fungus in order to visualize and analyze the colonization and infection processes in vivo. Transformation of F oxysporum f. sp. radicis-lycopersici was very efficient and gfp expression was stable for at least nine subcultures. Microscopic analysis of the transformants revealed homogeneity of the fluorescent signal, which was clearly visible in the hyphae as well as in the chlamydospores and conidia. To our knowledge, this is the first report in which this is shown. The transformation did not affect the pathogenicity. Using confocal laser scanning microscopy, colonization, infection, and disease development on tomato roots were visualized in detail and several new aspects of these processes were observed, such as (i) the complete colonization pattern of the tomato root system; (ii) the very first steps of contact between the fungus and the host, which takes place at the root hair zone by mingling and by the attachment of hyphae to the root hairs; (iii) the preferential colonization sites on the root surface, which are the grooves along the junctions of the epidermal cells; and (iv) the absence of specific infection sites, such as sites of emergence of secondary roots, root tips, or wounded tissue, and the absence of specific infection structures, such as appressoria. The results of this work prove that the use of GFP as a marker for F. oxysporum f. sp. radicis-lycopersici is a convenient, fast, and effective approach for studying plant-fungus interactions.

In vivo aggregation of the HET-s prion protein of the fungus Podospora anserina

We have proposed that the [Het-s] infectious cytoplasmic element of the filamentous fungus Podospora anserina is the prion form of the HET-s protein. The HET-s protein is involved in a cellular recognition phenomenon characteristic of filamentous fungi and known as heterokaryon incompatibility. Under the prion form, the HET-s protein causes a cell death reaction when co-expressed with the HET-S protein, from which it differs by only 13 amino acid residues. We show here that the HET-s protein can exist as two alternative states, a soluble and an aggregated form in vivo. As shown for the yeast prions, transition to the infectious prion form leads to aggregation of a HET-s--green fluorescent protein (GFP) fusion protein. The HET-s protein is aggregated in vivo when highly expressed. However, we could not demonstrate HET-s aggregation at wild-type expression levels, which could indicate that only a small fraction of the HET-s protein is in its aggregated form in vivo in wild-type [Het-s] strains. The antagonistic HET-S form is soluble even at high expression level. A double amino acid substitution in HET-s (D23A P33H), which abolishes prion infectivity, suppresses in vivo aggregation of the GFP fusion. Together, these results further support the model that the [Het-s] element corresponds to an abnormal self-perpetuating aggregated form of the HET-s protein.

Regulation of hisHF transcription of Aspergillus nidulans by adenine and amino acid limitation

The hisHF gene of Aspergillus nidulans encodes imidazole-glycerole-phosphate (IGP) synthase, consisting of a glutamine amidotransferase and a cyclase domain. The enzyme catalyzes the fifth and sixth steps of histidine biosynthesis, which results in an intermediate of the amino acid and an additional intermediate of purine biosynthesis. An A. nidulans hisHF cDNA complemented a Saccharomyces cerevisiae his7Delta strain and Escherichia coli hisH and hisF mutant strains. The genomic DNA encoding the hisHF gene was cloned and its sequence revealed two introns within the 1659-bp-long open reading frame. The transcription of the hisHF gene of A. nidulans is activated upon amino acid starvation, suggesting that hisHF is a target gene of cross pathway control. Adenine but not histidine, both end products of the biosynthetic pathways connected by the IGP synthase, represses hisHF transcription. In contrast to other organisms HISHF overproduction did not result in any developmental phenotype of the fungus in hyphal growth or the asexual life cycle. hisHF overexpression caused a significantly reduced osmotic tolerance and the inability to undergo the sexual life cycle leading to acleistothecial colonies.

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.

A defined sequence within the 3' UTR of the areA transcript is sufficient to mediate nitrogen metabolite signalling via accelerated deadenylation

Nitrogen metabolism in Aspergillus nidulans is regulated by AREA, a member of the GATA family of transcription factors. One mechanism that modulates AREA activity involves the rapid degradation of the areA transcript when sufficient NH4+ or Gln are available. This signalling mechanism has been shown to require a region of 218 nucleotides within the 3' untranslated region of areA mRNA. We demonstrate that this region functions independently in a heterologous transcript and acts to accelerate degradation of the poly(A) tail, which in turn leads to rapid transcript degradation in response to the addition of NH4+ or Gln to the growth medium. areA transcript degradation is inhibited by cycloheximide, but this is not a general consequence of translational inhibition. We believe that this is the first reported example in which specific physiological signals, acting through a defined sequence within a transcript, have been shown to promote accelerated poly(A) degradation, which in turn triggers transcript degradation.