Expression of Tri15 in Fusarium sporotrichioides

Virulence factors of the genus Fusarium with targets in plants

Fusarium spp. comprise various species of filamentous fungi that cause severe diseases in plant crops of both agricultural and forestry interest. These plant pathogens produce a wide range of molecules with diverse chemical structures and biological activities. Genetic functional analyses of some of these compounds have shown their role as virulence factors (VF). However, their mode of action and contributions to the infection process for many of these molecules are still unknown. This review aims to analyze the state of the art in Fusarium VF, emphasizing their biological targets on the plant hosts. It also addresses the current experimental approaches to improve our understanding of their role in virulence and suggests relevant research questions that remain to be answered with a greater focus on species of agroeconomic importance. In this review, a total of 37 confirmed VF are described, including 22 proteinaceous and 15 non-proteinaceous molecules, mainly from Fusarium oxysporum and Fusarium graminearum and, to a lesser extent, in Fusarium verticillioides and Fusarium solani.

Two Satellite Gene Clusters Enhance Ergot Alkaloid Biosynthesis Capacity of Aspergillus leporis

Ergot alkaloids are fungal specialized metabolites that are important in agriculture and serve as sources of several pharmaceuticals. Aspergillus leporis is a soil saprotroph that possesses two ergot alkaloid biosynthetic gene clusters encoding lysergic acid amide production. We identified two additional, partial biosynthetic gene clusters within the A. leporis genome containing some of the ergot alkaloid synthesis (eas) genes required to make two groups of clavine ergot alkaloids, fumigaclavines and rugulovasines. Clavines possess unique biological properties compared to lysergic acid derivatives. Bioinformatic analyses indicated the fumigaclavine cluster contained functional copies of easA, easG, easD, easM, and easN. Genes resembling easQ and easH, which are required for rugulovasine production, were identified in a separate gene cluster. The pathways encoded by these partial, or satellite, clusters would require intermediates from the previously described lysergic acid amide pathway to synthesize a product. Chemical analyses of A. leporis cultures revealed the presence of fumigaclavine A. However, rugulovasine was only detected in a single sample, prompting a heterologous expression approach to confirm functionality of easQ and easH. An easA knockout strain of Metarhizium brunneum, which accumulates the rugulovasine precursor chanoclavine-I aldehyde, was chosen as expression host. Strains of M. brunneum expressing easQ and easH from A. leporis accumulated rugulovasine as demonstrated through mass spectrometry analysis. These data indicate that A. leporis is exceptional among fungi in having the capacity to synthesize products from three branches of the ergot alkaloid pathway and for utilizing an unusual satellite cluster approach to achieve that outcome. IMPORTANCE Ergot alkaloids are chemicals produced by several species of fungi and are notable for their impacts on agriculture and medicine. The ability to make ergot alkaloids is typically encoded by a clustered set of genes that are physically adjacent on a chromosome. Different ergot alkaloid classes are formed via branching of a complex pathway that begins with a core set of the same five genes. Most ergot alkaloid-producing fungi have a single cluster of genes that is complete, or self-sufficient, and produce ergot alkaloids from one or occasionally two branches from that single cluster. Our data show that Aspergillus leporis is exceptional in having the genetic capacity to make products from three pathway branches. Moreover, it uses a satellite cluster approach, in which gene products of partial clusters rely on supplementation with a chemical intermediate produced via another gene cluster, to diversify its biosynthetic potential without duplicating all the steps.

Comparative transcriptome analysis reveals the biocontrol mechanism of Bacillus velezensis E68 against Fusarium graminearum DAOMC 180378, the causal agent of Fusarium head blight

Fusarium graminearum is the causal agent of Fusarium Head Blight, a serious disease affecting grain crops worldwide. Biological control involves the use of microorganisms to combat plant pathogens such as F. graminearum. Strains of Bacillus velezensis are common biological control candidates for use against F. graminearum and other plant pathogens, as they can secrete antifungal secondary metabolites. Here we study the interaction between B. velezensis E68 and F. graminearum DAOMC 180378 by employing a dual RNA-seq approach to assess the transcriptional changes in both organisms. In dual culture, B. velezensis up-regulated genes related to sporulation and phosphate stress and down-regulated genes related to secondary metabolism, biofilm formation and the tricarboxylic acid cycle. F. graminearum up-regulated genes encoding for killer protein 4-like proteins and genes relating to heavy metal tolerance, and down-regulated genes relating to trichothecene biosynthesis and phenol metabolism. This study provides insight into the molecular mechanisms involved in the interaction between a biocontrol bacterium and a phytopathogenic fungus.

Transcriptomic Response of Fusarium verticillioides to Variably Inhibitory Environmental Isolates of Streptomyces

Fusarium verticillioides is a mycotoxigenic fungus that is a threat to food and feed safety due to its common infection of maize, a global staple crop. A proposed strategy to combat this threat is the use of biological control bacteria that can inhibit the fungus and reduce mycotoxin contamination. In this study, the effect of multiple environmental isolates of Streptomyces on F. verticillioides was examined via transcriptome analysis. The Streptomyces strains ranged from inducing no visible response to dramatic growth inhibition. Transcriptionally, F. verticillioides responded proportionally to strain inhibition with either little to no transcript changes to thousands of genes being differentially expressed. Expression changes in multiple F. verticillioides putative secondary metabolite gene clusters was observed. Interestingly, genes involved in the fusaric acid gene cluster were suppressed by inhibitory strains of Streptomyces. A F. verticillioides beta-lactamase encoding gene (FVEG_13172) was found to be highly induced by specific inhibitory Streptomyces strains and its deletion increased visible response to those strains. This study demonstrates that F. verticillioides does not have an all or nothing response to bacteria it encounters but rather a measured response that is strain specific and proportional to the strength of inhibition.

Effect of Compactin on the Mycotoxin Production and Expression of Related Biosynthetic and Regulatory Genes in Toxigenic Fusarium culmorum

Zearalenone (ZEN) and deoxynivalenol (DON) are mycotoxins produced by various species of Fusarium fungi. They contaminate agricultural products and negatively influence human and animal health, thus representing a serious problem of the agricultural industry. Earlier we showed that compactin, a secondary metabolite of Penicillium citrinum, is able to completely suppress the aflatoxin B1 biosynthesis by Aspergillus flavus. Using the F. culmorum strain FC-19 able to produce DON and ZEN, we demonstrated that compactin also significantly suppressed both DON (99.3%) and ZEN (100%) biosynthesis. The possible mechanisms of this suppression were elucidated by qPCR-based analysis of expression levels of 48 biosynthetic and regulatory genes. Expression of eight of 13 TRI genes, including TRI4, TRI5, and TRI101, was completely suppressed. A significant down-regulation was revealed for the TRI10, TRI9, and TRI14 genes. TRI15 was the only up-regulated gene from the TRI cluster. In the case of the ZEN cluster, almost complete suppression was observed for PKS4, PKS13, and ZEB1 genes, and the balance between two ZEB2 isoforms was altered. Among regulatory genes, an increased expression of GPA1 and GPA2 genes encoding α- and β-subunits of a G-protein was shown, whereas eight genes were down-regulated. The obtained results suggest that the main pathway for a compactin-related inhibition of the DON and ZEN biosynthesis affects the transcription of genes involved in the G-protein-cAMP-PKA signaling pathway. The revealed gene expression data may provide a better understanding of genetic mechanisms underlying mycotoxin production and its regulation.

Verification of TRI3 Acetylation of Trichodermol to Trichodermin in the Plant Endophyte Trichoderma taxi

Trichodermin, a trichothecene first isolated in Trichoderma species, is a sesquiterpenoid antibiotic that exhibits significant inhibitory activity to the growth of many pathogenic fungi such as Candida albicans, Rhizoctonia solani, and Botrytis cinerea by inhibiting the peptidyl transferase involved in eukaryotic protein synthesis. Trichodermin has also been shown to selectively induce cell apoptosis in several cancer cell lines and thus can act as a potential lead compound for developing anticancer therapeutics. The biosynthetic pathway of trichodermin in Trichoderma has been identified, and most of the involved genes have been functionally characterized. An exception is TRI3, which encodes a putative acetyltransferase. Here, we report the identification of a gene cluster that contains seven genes expectedly involved in trichodermin biosynthesis (TRI3, TRI4, TRI6, TRI10, TRI11, TRI12, and TRI14) in the trichodermin-producing endophytic fungus Trichoderma taxi. As in Trichoderma brevicompactum, TRI5 is not included in the cluster. Functional analysis provides evidence that TRI3 acetylates trichodermol, the immediate precursor, to trichodermin. Disruption of TRI3 gene eliminated the inhibition to R. solani by T. taxi culture filtrates and significantly reduced the production of trichodermin but not of trichodermol. Both the inhibitory activity and the trichodermin production were restored when native TRI3 gene was reintroduced into the disruption mutant. Furthermore, a His-tag-purified TRI3 protein, expressed in Escherichia coli, was able to convert trichodermol to trichodermin in the presence of acetyl-CoA. The disruption of TRI3 also resulted in lowered expression of both the upstream biosynthesis TRI genes and the regulator genes. Our data demonstrate that T. taxi TRI3 encodes an acetyltransferase that catalyzes the esterification of the C-4 oxygen atom on trichodermol and thus plays an essential role in trichodermin biosynthesis in this fungus.

Sequencing of non-virulent strains of Fusarium fujikuroi reveals genes putatively involved in bakanae disease of rice

Bakanae, one of the most important diseases of rice, is caused by the fungal pathogen Fusarium fujikuroi. The elongation of internodes is the most common symptom induced by the pathogen, and it is related to the production of gibberellins. Despite this, the pathogenicity mechanism of F. fujikuroi is still not completely clear, and there are some strains inducing stunting instead of elongation. Even if there are relatively many genomes of F. fujikuroi strains available in online databases, none of them belongs to an isolate of proven non-virulence, and therefore there has been no comparative genomics study conducted between virulent and non-virulent strains. In the present work, the genomes of non-virulent strain SG4 and scarcely virulent strain C2S were compared to the ones of 12 available virulent isolates. Genes present in the majority of available virulent strains, but not in the non-virulent one, underwent functional annotation with multiple tools, and their expression level during rice infection was checked using pre-existing data. Nine genes putatively related to pathogenicity in F. fujikuroi were identified throughout comparative and functional analyses. Among these, many are involved in the degradation of plant cell wall, which is poorly studied in F. fujikuroi-rice interactions. Three of them were validated through qPCR, showing higher expression in the virulent strain and low to no expression in the low virulent and non virulent strains during rice infection. This work helps to clarify the mechanisms of pathogenicity of F. fujikuroi on rice.

Comparative acetylome analysis reveals the potential roles of lysine acetylation for DON biosynthesis in Fusarium graminearum

Background

Fusarium graminearum is a destructive fungal pathogen of wheat, barley and other small grain cereals. During plant infection, the pathogen produces trichothecene mycotoxin deoxynivalenol (DON), which is harmful to human and livestock. FgGCN5 encodes a GCN5 acetyltransferase. The gene deletion mutant Fggcn5 failed to produce DON. We assumed that lysine acetylation might play a key regulatory role in DON biosynthesis in the fungus.

Results

In this study, the acetylome comparison between Fggcn5 mutant and wild-type strain PH-1 was performed by using affinity enrichment and high resolution LC-MS/MS analysis. Totally, 1875 acetylated proteins were identified in Fggcn5 mutant and PH-1. Among them, 224 and 267 acetylated proteins were identified exclusively in Fggcn5 mutant and PH-1, respectively. Moreover, 95 differentially acetylated proteins were detected at a significantly different level in the gene deletion mutant:43 were up-regulated and 52 were down-regulated. GO enrichment and KEGG-pathways enrichment analyses revealed that acetylation plays a key role in metabolism process in F. graminearum.

Conclusions

Seeing that the gens playing critical roles in DON biosynthesis either in Fggcn5 mutant or PH-1. Therefore, we can draw the conclusion that the regulatory roles of lysine acetylation in DON biosynthesis in F. graminearum results from the positive and negative regulation of the related genes. The study would be a foundation to insight into the regulatory mechanism of lysine acetylation on DON biosynthesis.

Trichothecenes in Cereal Grains - An Update

Trichothecenes are sesquiterpenoid mycotoxins produced by fungi from the order Hypocreales, including members of the Fusarium genus that infect cereal grain crops. Different trichothecene-producing Fusarium species and strains have different trichothecene chemotypes belonging to the Type A and B class. These fungi cause a disease of small grain cereals, called Fusarium head blight, and their toxins contaminate host tissues. As potent inhibitors of eukaryotic protein synthesis, trichothecenes pose a health risk to human and animal consumers of infected cereal grains. In 2009, Foroud and Eudes published a review of trichothecenes in cereal grains for human consumption. As an update to this review, the work herein provides a comprehensive and multi-disciplinary review of the Fusarium trichothecenes covering topics in chemistry and biochemistry, pathogen biology, trichothecene toxicity, molecular mechanisms of resistance or detoxification, genetics of resistance and breeding strategies to reduce their contamination of wheat and barley.

The prevalence of selected genes involved in the biosynthesis of trichothecenes assessed with the specific PCR tests in Fusarium spp. isolated from cereals in southern Poland

The analysis was conducted using 50 isolates of fungi of the genus Fusarium belonging to the species classified as major trichothecene mycotoxin producers: F. graminearum, F. culmorum, F. sporotrichioides, and F. poae. The tested fungi were isolated from ears of cereal crops in southern Poland during the two growing seasons (2011 and 2012). The aim of this study was to evaluate the prevalence of genes involved in the biosynthesis of trichothecene mycotoxins using the specific PCR tests. Molecular analyses indicated that the genes responsible for the production of trichothecenes (Tri3, Tri5, Tri7, Tri13) were abundant in the examined genetic material. The tested fungal isolates were characterized by a large diversity in terms of the number and composition of the possessed Tri genes. On the other hand, 14 of 50 isolates were found not to carry any of Tri genes.

Molecular and Genetic Studies ofFusariumTrichothecene Biosynthesis: Pathways, Genes, and Evolution

Trichothecenes are a large family of sesquiterpenoid secondary metabolites of Fusarium species (e.g., F. graminearum) and other molds. They are major mycotoxins that can cause serious problems when consumed via contaminated cereal grains. In the past 20 years, an outline of the trichothecene biosynthetic pathway has been established based on the results of precursor feeding experiments and blocked mutant analyses. Following the isolation of the pathway gene Tri5 encoding the first committed enzyme trichodiene synthase, 10 biosynthesis genes (Tri genes; two regulatory genes, seven pathway genes, and one transporter gene) were functionally identified in the Tri5 gene cluster. At least three pathway genes, Tri101 (separated alone), and Tri1 and Tri16 (located in the Tri1-Tri16 two-gene cluster), were found outside of the Tri5 gene cluster. In this review, we summarize the current understanding of the pathways of biosynthesis, the functions of cloned Tri genes, and the evolution of Tri genes, focusing on Fusarium species.

The velvet gene, FgVe1, affects fungal development and positively regulates trichothecene biosynthesis and pathogenicity in Fusarium graminearum

Trichothecenes are a group of toxic secondary metabolites produced mainly by Fusarium graminearum (teleomorph: Gibberella zeae) during the infection of crop plants, including wheat, maize, barley, oats, rye and rice. Some fungal genes involved in trichothecene biosynthesis have been shown to encode regulatory proteins. However, the global regulation of toxin biosynthesis is still enigmatic. In addition to the production of secondary metabolites belonging to the trichothecene family, F. graminearum produces the red pigment aurofusarin. The gene regulation underlying the production of aurofusarin is not well understood. The velvet gene (veA) is conserved in various genera of filamentous fungi. Recently, the veA gene from Aspergillus nidulans has been shown to be the key component of the velvet complex regulating development and secondary metabolism. Using blast analyses, we identified the velvet gene from F. graminearum, FgVe1. Disruption of FgVe1 causes several phenotypic effects. However, the complementation of this mutant with the FgVe1 gene restores the wild-type phenotypes. The in vitro phenotypes include hyperbranching of the mycelium, suppression of aerial hyphae formation, reduced hydrophobicity of the mycelium and highly reduced sporulation. Our data also show that FgVe1 modulates the production of the aurofusarin pigment and is essential for the expression of Tri genes and the production of trichothecenes. Pathogenicity studies performed on flowering wheat plants indicate that FgVe1 is a positive regulator of virulence in F. graminearum.

OmniMapFree: a unified tool to visualise and explore sequenced genomes

• Background

Acquiring and exploring whole genome sequence information for a species under investigation is now a routine experimental approach. On most genome browsers, typically, only the DNA sequence, EST support, motif search results, and GO annotations are displayed. However, for many species, a growing volume of additional experimental information is available but this is rarely searchable within the landscape of the entire genome.

• Results

We have developed a generic software which permits users to view a single genome in entirety either within its chromosome or supercontig context within a single window. This software permits the genome to be displayed at any scales and with any features. Different data types and data sets are displayed onto the genome, which have been acquired from other types of studies including classical genetics, forward and reverse genetics, transcriptomics, proteomics and improved annotation from alternative sources. In each display, different types of information can be overlapped, then retrieved in the desired combinations and scales and used in follow up analyses. The displays generated are of publication quality.

• Conclusions

OmniMapFree provides a unified, versatile and easy-to-use software tool for studying a single genome in association with all the other datasets and data types available for the organism.

Trichothecenes: from simple to complex mycotoxins

As the world's population grows, access to a safe food supply will continue to be a global priority. In recent years, the world has experienced an increase in mycotoxin contamination of grains due to climatic and agronomic changes that encourage fungal growth during cultivation. A number of the molds that are plant pathogens produce trichothecene mycotoxins, which are known to cause serious human and animal toxicoses. This review covers the types of trichothecenes, their complexity, and proposed biosynthetic pathways of trichothecenes.

Regulation of trichothecene biosynthesis in Fusarium: recent advances and new insights

Trichothecenes are toxic secondary metabolites produced by filamentous fungi mainly belonging to the Fusarium genus. Production of these mycotoxins occurs during infection of crops and is a threat to human and animal health. Although the pathway for biosynthesis of trichothecenes is well established, the regulation of the Tri genes implicated in the pathway remains poorly understood. Most of the Tri genes are gathered in a cluster which contains two transcriptional regulators controlling the expression of the other Tri genes. The regulation of secondary metabolites biosynthesis in most fungal genera has been recently shown to be controlled by various regulatory systems in response to external environment. The control of the "Tri cluster" by non-cluster regulators in Fusarium was not clearly demonstrated until recently. This review covers the recent advances concerning the regulation of trichothecene biosynthesis in Fusarium and highlights the potential implication of various general regulatory circuits. Further studies on the role of these regulatory systems in the control of trichothecene biosynthesis might be useful in designing new strategies to reduce mycotoxin accumulation.

A partial chromosomal deletion caused by random plasmid integration resulted in a reduced virulence phenotype in Fusarium graminearum

Fusarium graminearum (teleomorph: Gibberella zeae) is an Ascomycete fungal plant pathogen which infects a range of agriculturally important crops, including wheat, barley, and maize. A random plasmid insertion mutagenesis approach was used to analyze the pathogenicity of the PH-1 strain, for which full genomic information is available. Fungal transformants were initially screened for their ability to infect wheat ears. From a total of 1,170 transformants screened, eight were confirmed to be highly reduced in pathogenicity toward wheat ears and roots. These were designated disease-attenuated F. graminearum (daf) mutants. The in vitro growth rate and appearance of each daf mutant was equivalent to the parental strain. Deoxynivalenol (DON) was not detected in threshed grain recovered from ears inoculated with the daf10 mutant. Plasmid rescue and sequencing of the mutant daf10 revealed a deletion of approximately 350 kb from one end of chromosome 1. This chromosome segment is predicted to contain 146 genes. Microarray analysis of daf10 gene expression during growth in DON-inducing conditions confirmed the large deletion. The identities of the genes deleted and their potential role in DON production, pathogenesis, and other life processes are discussed.

Novel genes of Fusarium graminearum that negatively regulate deoxynivalenol production and virulence

Fusarium head blight of wheat, caused by Fusarium graminearum, is a serious disease resulting in both reduced yields and contamination of grain with trichothecene toxins, with severe consequences for mammalian health. Recently, we have identified several related amine compounds such as agmatine and putrescine that promote the production of high levels of trichothecene toxins, such as deoxynivalenol (DON), in culture by F. graminearum and F. sporotrichioides. Here, a global analysis of fungal gene expression using the Affymetrix Fusarium GeneChip during culture under DON-inducing conditions compared with noninducing conditions is reported. Agmatine differentially regulated a large number of fungal genes, including both known and previously uncharacterized putative secondary metabolite biosynthetic gene clusters. In silico prediction of binding sites for the transcriptional regulator (TRI6) controlling TRI gene expression and gene expression analysis in a TRI6 mutant of F. graminearum showed that three of the differentially regulated genes were under the control of TRI6. Gene knock-out mutations of two of these genes resulted in mutants with massively increased production of DON and increased aggressiveness toward wheat. Our results not only identify a novel mechanism of negative regulation of DON production and virulence in F. graminearum but also point out the potential of this pathogen to evolve with an ability to produce massively increased amounts of toxins and increased virulence.

Application of a master equation for quantitative mRNA analysis using qRT-PCR

The qRT-PCR has been widely accepted as the assay of choice for mRNA quantification. For conventional practice, housekeeping genes have been applied as internal reference for data normalization and analysis since the technology appeared. However, housekeeping genes vary under different conditions and environmental stimuli and no commonly accepted housekeeping gene references are available. Accurate data acquisition and data reproducibility remain challenging and it is difficult to compare results from different experimental sources. Using yeast and a Fusarium fungus as examples, we demonstrate the independent performance of a sole reference gene, CAB, designated as a constant manual threshold for data acquisition, normalization, and analysis for multiple plate reactions. A robust master equation based on the CAB reference and the set of calibration control genes thereafter was established to estimate mRNA abundance for the same RNA background reactions. A valid range of amplification efficiency between 95% and 100% was observed for the control genes in different RNA background applied on an ABI real time PCR 7500 system. This newly developed robust quality control system provides a reliable means for absolute quantification of mRNA using the qRT-PCR, simplifies the conventional qRT-PCR procedures, and increases data reliability, reproducibility, and throughput of the assay.

Alignment of genetic and physical maps of Gibberella zeae

We previously published a genetic map of Gibberella zeae (Fusarium graminearum sensu lato) based on a cross between Kansas strain Z-3639 (lineage 7) and Japanese strain R-5470 (lineage 6). In this study, that genetic map was aligned with the third assembly of the genomic sequence of G. zeae strain PH-1 (lineage 7) using seven structural genes and 108 sequenced amplified fragment length polymorphism markers. Several linkage groups were combined based on the alignments, the nine original linkage groups were reduced to six groups, and the total size of the genetic map was reduced from 1,286 to 1,140 centimorgans. Nine supercontigs, comprising 99.2% of the genomic sequence assembly, were anchored to the genetic map. Eight markers (four markers from each parent) were not found in the genome assembly, and four of these markers were closely linked, suggesting that >150 kb of DNA sequence is missing from the PH-1 genome assembly. The alignments of the linkage groups and supercontigs yielded four independent sets, which is consistent with the four chromosomes reported for this fungus. Two proposed heterozygous inversions were confirmed by the alignments; otherwise, the colinearity of the genetic and physical maps was high. Two of four regions with segregation distortion were explained by the two selectable markers employed in making the cross. The average recombination rates for each chromosome were similar to those previously reported for G. zeae. Despite an inferred history of genetic isolation of lineage 6 and lineage 7, the chromosomes of these lineages remain homologous and are capable of recombination along their entire lengths, even within the inversions. This genetic map can now be used in conjunction with the physical sequence to study phenotypes (e.g., fertility and fitness) and genetic features (e.g., centromeres and recombination frequency) that do not have a known molecular signature in the genome.

The TRI101 story: engineering wheat and barley to resist Fusarium head blight

Fusarium head blight (FHB), caused primarily by Fusarium graminearum, is a major disease of wheat and barley in the United States and Canada. FHB epidemics have been on the increase since 1993 and have caused severe monetary damage for the growers and seed industry. Along with reduced yields, the presence of mycotoxins in moldy grain constitutes a major problem for the grain industry. These mycotoxins pose health hazards to humans and animals upon ingestion. The acute phytotoxicity of these mycotoxins and their occurrence in plant tissues correlates with their role in pathogenesis and the production of plant disease. Transgenic plants incorporating the Fusarium sporotrichioides Tri101 gene, a gene that reduces toxicity of trichothecenes, have reduced levels of disease, thus demonstrating that FHB severity and deoxynivalenol (DON) accumulation can be reduced in small grains by the introduction of a toxin-modification gene.

Fusarium graminearum gene deletion mutants map1 and tri5 reveal similarities and differences in the pathogenicity requirements to cause disease on Arabidopsis and wheat floral tissue

The Ascomycete pathogen Fusarium graminearum can infect all cereal species and lower grain yield, quality and safety. The fungus can also cause disease on Arabidopsis thaliana. In this study, the disease-causing ability of two F. graminearum mutants was analysed to further explore the parallels between the wheat (Triticum aestivum) and Arabidopsis floral pathosystems. Wild-type F. graminearum (strain PH-1) and two isogenic transformants lacking either the mitogen-activated protein kinase MAP1 gene or the trichodiene synthase TRI5 gene were individually spray- or point-inoculated onto Arabidopsis and wheat floral tissue. Disease development was quantitatively assessed both macroscopically and microscopically and deoxynivalenol (DON) mycotoxin concentrations determined by enzyme-linked immunosorbent assay (ELISA). Wild-type strain inoculations caused high levels of disease in both plant species and significant DON production. The map1 mutant caused minimal disease and DON accumulation in both hosts. The tri5 mutant, which is unable to produce DON, exhibited reduced pathogenicity on wheat ears, causing only discrete eye-shaped lesions on spikelets which failed to infect the rachis. By contrast, the tri5 mutant retained full pathogenicity on Arabidopsis floral tissue. This study reveals that DON mycotoxin production is not required for F. graminearum to colonize Arabidopsis floral tissue.

A microarray for monitoring the production of mycotoxins in food

A microarray, which covers most of the known relevant mycotoxin biosynthesis genes, has been developed. The microarray carries oligonucleotides of the fumonisin, the aflatoxin, the ochratoxin, the trichothecene (type A and B) and the patulin biosynthesis pathways. For trichothecene producing Fusaria the biosynthesis cluster of trichothecene producing Fusarium sporotrichioides (type A) and of Gibberrella zeae (type B, teleomorph of F. graminearum) have been spotted. The aflatoxin cluster carries oligonucleotides specific for Aspergillus flavus. The ochratoxin pattern is specific for ochratoxin A producing Penicillia, the fumonisin cluster is specific for G. moniliformis (teleomorph of F. verticillioides) and the patulin genes have been obtained from Penicillium expansum. The microarray is designed in a way that newly identified pathway genes can be added easily at any time. The microarray was used to detect the activation of all gene clusters under conditions conducive for mycotoxin biosynthesis. According to the results the obtained signals were specific under the hybridization conditions used and only insignificant cross-hybridizations occurred. The microarray was used to demonstrate differences in mycotoxin pathway gene expressions after growth on various media for trichothecene and ochratoxin A biosynthesis. It was used further to study and compare the expression kinetics of the trichothecene biosynthesis genes of Fusarium on different trichothecene supporting media. An expression pattern indicative for trichothecene biosynthesis could be identified.

Exogenous H2O2and catalase treatments interfere withTrigenes expression in liquid cultures ofFusarium graminearum

Effect of exogenous H(2)O(2) and catalase was tested in liquid cultures of the deoxynivalenol and 15-acetyldeoxynivalenol-producing fungus Fusarium graminearum. Accordingly to previous results, H(2)O(2) supplementation of the culture medium leads to increased toxin production. This study indicates that this event seems to be linked to a general up regulation of genes involved in the deoxynivalenol and 15-acetyldeoxynivalenol biosynthesis pathway, commonly named Tri genes. In catalase-treated cultures, toxin accumulation is reduced, and Tri genes expression is significantly down regulated. Furthermore, kinetics of expression of several Tri genes is proposed in relation to toxin accumulation. Biological meanings of these findings are discussed.

Fusarium Tri4 encodes a multifunctional oxygenase required for trichothecene biosynthesis

Fusarium graminearum and Fusarium sporotrichioides produce the trichothecene mycotoxins 15-acetyldeoxynivalenol and T-2 toxin, respectively. In both species, disruption of the P450 monooxygenase-encoding gene, Tri4, blocks production of the mycotoxins and leads to the accumulation of the trichothecene precursor trichodiene. To further characterize its function, the F. graminearum Tri4 (FgTri4) was heterologously expressed in the trichothecene-nonproducing species Fusarium verticillioides. Transgenic F. verticillioides carrying the FgTri4 converted exogenous trichodiene to the trichothecene biosynthetic intermediates isotrichodermin and trichothecene. Conversion of trichodiene to isotrichodermin requires seven biochemical steps. The fifth and sixth steps can occur nonenzymatically. Precursor feeding studies done in the current study indicate that wild-type F. verticillioides has the enzymatic activity necessary to carry out the seventh step, the C-3 acetylation of isotrichodermol to form isotrichodermin. Together, the results of this study indicate that the Tri4 protein catalyzes the remaining four steps and is therefore a multifunctional monooxygenase required for trichothecene biosynthesis.

Identification of an abscisic acid gene cluster in the grey mold Botrytis cinerea

Like several other phytopathogenic fungi, the ascomycete Botrytis cinerea is known to produce the plant hormone abscisic acid (ABA) in axenic culture. Recently, bcaba1, the first fungal gene involved in ABA biosynthesis, was identified. Neighborhood analysis of bcaba1 revealed three further candidate genes of this pathway: a putative P450 monooxygenase-encoding gene (bcaba2), an open reading frame without significant similarities (bcaba3), and a gene probably coding for a short-chain dehydrogenase/reductase (bcaba4). Targeted inactivation of the genes proved the involvement of BcABA2 and BcABA3 in ABA biosynthesis and suggested a contribution of BcABA4. The close linkage of at least three ABA biosynthetic genes is strong evidence for the presence of an abscisic acid gene cluster in B. cinerea.

Patterns of trichothecene production, genetic variability, and virulence to wheat of Fusarium graminearum from smallholder farms in Nepal

Fusarium graminearum causes wheat head blight and contaminates grain with the trichothecenes 4-deoxynivalenol and nivalenol. Sequence analysis of trichothecene genes indicates that nivalenol production is the ancestral trait; however, deoxynivalenol producers occur worldwide and predominate in North and South America and in Europe. Analysis of a large field population (>500 strains) from Nepal identified three groups that were both genetically distinct and polymorphic for trichothecene production: SCAR1 comprising 95% deoxynivalenol producers, SCAR2 comprising 94% nivalenol producers, and SCAR3/5 comprising 34% deoxynivalenol producers/63% nivalenol producers. The ability to cause wheat head blight differed between SCAR groups and trichothecene chemotypes: deoxynivalenol producers were more virulent than nivalenol producers across all three SCAR groups and within the SCAR3/5 genetic background. These data support the hypothesis that production of deoxynivalenol rather than nivalenol confers a selective advantage to this important wheat pathogen.