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PubMed2006

Emerging antifungal azoles and effects on Magnaporthe grisea.

Derivatives of pyrazolo[1,5-a][1, 3, 5]triazine-2,4-dione,pyrazolo[1,5-c][1, 3, 5]thiadiazine-2-one, pyrazolo[3,4-d][1, 3]thiazine-4-one, and pyrazolo[3,4-d][1, 3]thiazine-4-thione were screened for antifungal activity against the causal agent of rice blast disease, Magnaporthe grisea. The compounds were tested at doses ranging from 10 to 200mugml(-1), using the commercial fungicide tricyclazole as reference compound. All triazine derivatives inhibited the growth and pigmentation of the mycelia less effectively than tricyclazole. The thiadiazine derivatives proved to be more effective than their triazine counterparts, but only 4-(butylimino)-7-methylpyrazolo[1,5-c][1,3,5]thiadiazine-2-one (2h) and 4-(cyclohexylimino)-7-methylpyrazolo[1,5-c][1,3,5]thiadiazine-2-one (2j) were more effective than tricyclazole. Pyrazolo[3,4-d][1,3]thiazine-4-one derivatives were active only at the highest doses, whereas members of the pyrazolo[3,4-d][1,3]thiazine-4-thione series inhibited fungal growth at the lowest concentrations used, at which tricyclazole had no effect. A dose-dependent mechanism might be responsible for this effect, with lipophilicity as the governing factor. Within a given set, the presence of a cyclohexyl or an n-butyl group generally increased antifungal activity, with respect to both growth inhibition and cell de-pigmentation of the mycelium, suggesting that a higher lipophilicity might improve transport inside the cells. SEM and TEM of M. grisea hyphae showed that treatment with the most active substance (2h) caused significant ultrastructural effects, particularly on the endomembrane system, suggesting a mechanism of action similar to that of most azole fungicides. Dissimilarities were also observed, with no alterations of the cell wall evident. In conclusion, several compounds showed greater inhibition than tricyclazole, and therefore provide useful new chemistry for control of M. grisea infections.

Antifungal Agents↗
PubMed2006

Estimates of biomechanical forces in Magnaporthe grisea.

The mechanical actions of the fungus Magnaporthe grisea raise many intriguing questions concerning the forces involved. These include: (1) the material properties of the appressorial wall; (2) the strength of the adhesive that keeps the appressorium anchored to the rice leaf surface; and (3) the forces involved in the penetration process whereby a peg is driven through the host cell wall. In this paper we give order of magnitude estimates for all three of these quantities. A simple Young-Laplace law type argument is used to show that the appressorial wall elastic modulus is of order 10-100 MPa; and an adaptation of standard adhesion theory indicates a lower bound on the strength of the appressorial adhesive to be of the order 500 J/m(2). Drawing on ideas from plasticity theory and ballistics, estimates of the penetration force raise interesting questions about experiments performed on the penetration of inert substrates by the fungus.

Biomechanical Phenomena↗
PubMed2006

The 1.6Mb chromosome carrying the avirulence gene AvrPik in Magnaporthe oryzae isolate 84R-62B is a chimera containing chromosome 1 sequences.

A genetic map was constructed previously from a cross between Magnaporthe oryzae isolates 84R-62B and Y93-245c-2, and genetic markers closely linked to the cultivar-specific avirulence (Avr) gene, AvrPik, were assigned to a 1.6Mb small chromosome of 84R-62B that is absent from Y93-245c-2. In the present study, the 1.6Mb chromosome was characterized by using contour-clamped homogeneous electric fields (CHEF) electrophoresis and hybridization analysis. CHEF electrophoresis analysis showed that the 1.6Mb chromosome was inherited in Mendelian fashion, and co-segregated with AvrPik. Southern hybridization analysis revealed that the 1.6Mb chromosome carried sequences only distributed to the supernumerary chromosome in M. oryzae isolates, as well as sequences corresponding to those in the supercontig 17 of chromosome 1 in the M. grisea database. Thus, we conclude that the Mendelian 1.6Mb chromosome is a chimera containing sequences from chromosome 1 and from supernumerary chromosomes in M. oryzae.

Blotting, Southern↗
PubMed2006

High level production of the Magnaporthe grisea fructose 1,6-bisphosphate aldolase enzyme in Escherichia coli using a small volume bench-top fermentor.

The Class II fructose 1,6-bisphosphate aldolase from the Rice Blast causative agent Magnaporthe grisea was subcloned in the Escherichia coli vector pT7-7. The enzyme was overexpressed using fed-batch fermentation in a small bench-top reactor. A total of 275 g of cells and 1.3 g of highly purified enzyme with a specific activity of 70 U/mg were obtained from a 1.5L culture. The purified enzyme is a homodimer of 39.6 kDa subunits with a zinc ion at the active site. Kinetic characterization indicates that the enzyme has a K(m) of 51 microM, a k(cat) of 46 s(-1), and a pH optimum of 7.8 for fructose 1,6-bisphosphate cleavage. The fermentation system procedure reported exemplifies the potential of using a lab-scale bioreactor for the large scale production of recombinant enzymes.

Amino Acid Sequence↗
PubMed2002

Glycosphingolipids from Magnaporthe grisea cells: expression of a ceramide dihexoside presenting phytosphingosine as the long-chain base.

Magnaporthe grisea is a fungal pathogen that infects rice leaves and causes rice blast, a devastating crop disease. M. grisea produces active elicitors of the hypersensitive response in rice that were previously identified as ceramide monohexosides (CMHs). Using several chromatographic approaches, mass spectrometry, and nuclear magnetic resonance, we identified ceramide mono- and dihexosides (CDH) in purified lipid extracts from M. grisea cells. As described by other authors, CMH consists of a ceramide moiety containing 9-methyl-4,8-sphingadienine in amidic linkage to 2-hydroxyoctadecenoic or 2-hydroxyhexadecenoic acids and a carbohydrate segment consisting of one residue of glucose. CDHs, however, contain beta-galactose (1-->4)-linked to beta-glucose as sugar units and phytosphingosine as the long-chain base, bound to a C24 alpha-hydroxylated fatty acid. To our knowledge, this is the first report on the occurrence of CDH in a fungal species and illustrates the existence of an alternative path of ceramide glycosylation in fungal cells.

Carbohydrate Conformation↗
PubMed1998

Transcriptional activation of the alternative oxidase gene of the fungus Magnaporthe grisea by a respiratory-inhibiting fungicide and hydrogen peroxide.

Alternative oxidase (AOX) is dramatically induced when the fungus Magnaporthe grisea is incubated with the fungicide SSF-126, which interacts with the cytochrome bc1 complex in the electron transport system of mitochondria. A full-length cDNA for the alternative oxidase gene (AOX) was obtained, and the deduced amino acid sequence revealed marked similarity to other AOXs, but lacks two cysteine residues at corresponding sites which are conserved in plant AOXs and play essential roles in the post-translational regulation. Northern blot experiments showed that treatment of M. grisea cells with SSF-126 induces accumulation of AOX mRNA in a dose-dependent manner, and the level was correlated with the activity of alternative respiration. H2O2 also induced the accumulation of the transcript with a short half-life (<15 min). Nuclear run-on experiments showed that the AOX gene was transcribed constitutively in unstimulated cells. Cycloheximide did not change the basal level of transcription, but induced the accumulation of the transcript, indicating that active degradation of the transcript occurs by factor(s) sensitive to cycloheximide. On the other hand, SSF-126 enhanced the transcriptional activity of AOX gene threefold compared to that of control cells, and H2O2 was also potent for enhancement of the transcription. From these results, it is concluded that the respiratory inhibitor-dependent activation of the transcription is a primary determinant for the induction of alternative respiration in M. grisea. Because we have previously shown that SSF-126 treatment of M. grisea mitochondria induced the generation of superoxide, active oxygen species are thought to be signal mediators to activate AOX gene transcription in M. grisea.

Amino Acid Sequence↗
PubMedDate not supplied

A hybrid machine model of rice blast fungus, Magnaporthe grisea.

The fungus, Magnaporthe grisea (Rice blast fungus) is a major agricultural problem affecting rice and related food crops. The way that the fungus invades the host plant and propagates itself is a very important scientific problem and recent advances in research into the genetic basis of these processes can be used to build a simple partial model using hybrid computational modelling techniques. The possible potential benefits of doing this include the use of computer simulation and automated analysis through techniques such as model checking to understand the complex behaviour of such systems. The example is a metaphor for the process of trying to integrate and understand much of the vast amounts of genomic and other data that is being produced in current molecular biology research.

Magnaporthe↗
PubMed2003

Purification and characterization of laccase from the rice blast fungus, Magnaporthe grisea.

A 70-kDa extracellular laccase was purified from the rice blast fungus Magnaporthe grisea using gel filtration and ion exchange chromatography The procedure provided 282-fold purification with a specific enzyme activity of 225.91 U mg(-1) and a yield of 11.92%. The enzyme oxidized a wide range of substrates. The highest level of oxidation was detected with syringaldazine as the substrate. Using syringaldazine as the substrate, the enzyme exhibited a pH optimum of 6 and temperature optimum of 30 degrees C, and its K(m) was 0.118 mM. The enzyme was strongly inhibited by Cu-chelating agents.

Chromatography, High Pressure Liquid↗
PubMed2004

Cloning, sequencing and functional analysis of Magnaporthe grisea MVP1 gene, a hex-1 homolog encoding a putative 'woronin body' protein.

A hex-1 homolog named MVP1 was isolated from an appressoria cDNA library of the rice blast fungus Magnaporthe grisea. The transcript of approximately 1.6 kb contains 546 bp of coding sequence with a 3' untranslated region about 168 bp long and a 5' untranslated region about 870 bp long. Southern gel blot analysis of genomic DNA following digestion with three restriction enzymes (BamHI, EcoRI, HindIII) indicated that the gene exists as a single copy in M. grisea genome. RNA gel blot analyses showed that MVP1 was highly expressed in germinating conidia and the mycelial stage compared to appressoria or non-germinated conidia. MVP1 showed a high degree of homology to the hex-1 gene recently described to encode a major protein in the woronin bodies of Neurospora crassa. Double homologous recombination was used to replace MVP1 with the hyg(R) gene. MVP1 knockout mutants showed apical swellings when grown on agar plates containing 2% sorbose but they were not impaired in any other vegetative or pathogenic properties evaluated. The pathological and other phenotypic consequences of gene disruption are discussed.

Cloning, Molecular↗
PubMed2002

Effects of signaling molecules, protein phosphatase inhibitors and blast pathogen (Magnaporthe grisea) on the mRNA level of a rice (Oryza sativa L.) phospholipid hydroperoxide glutathione peroxidase (OsPHGPX) gene in seedling leaves.

With a specific focus on rice self-defense response(s), the effects of global signaling molecules, jasmonic acid (JA), salicylic acid (SA), abscisic acid (ABA), and ethylene (using the ethylene generator, ethephon), and protein phosphatase (PP) inhibitors, cantharidin and endothall on expression of a rice phospholipid hydroperoxide glutathione peroxidase (OsPHGPX) gene in rice seedling leaves were investigated. We provide first evidence for a potent up-regulation of the OsPHGPX mRNA accumulation by these signaling molecules and PP inhibitors that strongly suggest its potential role in defense/stress. The OsPHGPX gene also showed a weak constitutive expression and responsiveness to cut. These inductions were influenced by light signal(s), and did not show a requirement for de novo synthesized protein factor(s). A potential interaction amongst these signaling molecules, especially JA, SA, ABA and kinetin, in modulating the OsPHGPX expression was found. The blast pathogen, Magnaporthe grisea also elicited the accumulation of OsPHGPX mRNA in leaves. This is a first systematic report in rice (and in plants) demonstrating the inducible nature (and expression) of the OsPHGPX gene by a variety of defense/stress-related stimuli, and modulation by the PPs of the kinase-signaling cascade(s).

Abscisic Acid↗
PubMed1999

Fungal proteinase expression in the interaction of the plant pathogen Magnaporthe poae with its host.

Infection by pathogenic fungi involves breaching the outer layer of the host by either mechanical or enzymatic means. Subtilisin-like proteinases are considered to be important in the infection process of entomopathogenic, nematophagous, and mycoparasitic fungi. Little is known regarding the expression of such proteinases by plant pathogenic fungi. Magnaporthe poae, a fungal pathogen of Kentucky bluegrass, expressed a subtilisin-like proteinase, proteinase Mp1, in the infected roots. Antibody was produced against the purified enzyme. From immunoblot analysis, expression of the proteinase in infected roots correlated with increasing severity of disease symptoms. Sequence analysis of a genomic clone indicated proteinase Mp1 was homologous to other fungal subtilisin-like proteinases. DNA gel blot analysis indicated proteinase Mp1 was encoded by a small gene family.

Amino Acid Sequence↗
PubMed2000

Crystal structure of saccharopine reductase from Magnaporthe grisea, an enzyme of the alpha-aminoadipate pathway of lysine biosynthesis.

BACKGROUND: The biosynthesis of the essential amino acid lysine in higher fungi and cyanobacteria occurs via the alpha-aminoadipate pathway, which is completely different from the lysine biosynthetic pathway found in plants and bacteria. The penultimate reaction in the alpha-aminoadipate pathway is catalysed by NADPH-dependent saccharopine reductase. We set out to determine the structure of this enzyme as a first step in exploring the structural biology of fungal lysine biosynthesis. RESULTS: We have determined the three-dimensional structure of saccharopine reductase from the plant pathogen Magnaporthe grisea in its apo form to 2.0 A resolution and as a ternary complex with NADPH and saccharopine to 2.1 A resolution. Saccharopine reductase is a homodimer, and each subunit consists of three domains, which are not consecutive in amino acid sequence. Domain I contains a variant of the Rossmann fold that binds NADPH. Domain II folds into a mixed seven-stranded beta sheet flanked by alpha helices and is involved in substrate binding and dimer formation. Domain III is all-helical. The structure analysis of the ternary complex reveals a large movement of domain III upon ligand binding. The active site is positioned in a cleft between the NADPH-binding domain and the second alpha/beta domain. Saccharopine is tightly bound to the enzyme via a number of hydrogen bonds to invariant amino acid residues. CONCLUSIONS: On the basis of the structure of the ternary complex of saccharopine reductase, an enzymatic mechanism is proposed that includes the formation of a Schiff base as a key intermediate. Despite the lack of overall sequence homology, the fold of saccharopine reductase is similar to that observed in some enzymes of the diaminopimelate pathway of lysine biosynthesis in bacteria. These structural similarities suggest an evolutionary relationship between two different major families of amino acid biosynthetic pathway, the glutamate and aspartate families.

2-Aminoadipic Acid↗
PubMed2002

Live-cell imaging of endocytosis during conidial germination in the rice blast fungus, Magnaporthe grisea.

Although there is growing evidence that endocytosis is important in hyphal tip growth, it has not previously been shown to occur during fungal spore germination. We have analysed and characterized endocytosis during the germination of living conidia of the rice blast fungus, Magnaporthe grisea. Conidia treated with the endocytic markers Lucifer Yellow carbohydrazide, FITC-dextran, and FM4-64 were imaged by confocal microscopy. Internalization of these fluorescent marker dyes by conidia was blocked by chemical and temperature treatments that inhibit endocytosis, and the sequential staining of organelles by the membrane-selective dye FM4-64 was consistent with dye internalization by endocytosis. FM4-64 uptake occurred within 2-3 min of conidial hydration, more than 40 min before the emergence of the germ tube. The times at which each of the three conidial cells initiated dye internalization were different as were the rates of dye uptake by each cell. Using these techniques we have demonstrated for the first time that ungerminated and germinated spores of filamentous fungi undergo endocytosis. Furthermore, internalization of FITC-dextran and Lucifer Yellow carbohydrazide by germinating conidia provides the first direct evidence for fluid-phase endocytosis in a filamentous fungus. FM4-64 was internalized by both ungerminated conidia and conidial germlings on the rice leaf suggesting that endocytosis might play a significant role in spore germination and germ tube growth during the pre-penetration phase of infection.

Endocytosis↗
PubMed1998

Infection-related development in the rice blast fungus Magnaporthe grisea.

Recent developments have been made in the identification of signal transduction pathways and gene products involved in the infection-related development of the rice blast fungus, Magnaporthe grisea. It has been established that cAMP-dependent and MAP kinase-mediated signaling are both critical for appressorium morphogenesis and function. These signaling pathways may act downstream of hydrophobin-mediated surface sensing by the growing germ tube. Several genes have been identified that are required for invasive growth of M. grisea including genes that allow adaptation of fungal metabolism to growth within plant tissues.

Gene Expression Regulation, Fungal↗
PubMed2002

Development of new fungicides against Magnaporthe grisea: synthesis and biological activity of pyrazolo[3,4-d][1,3]thiazine, pyrazolo[1,5-c][1,3,5]thiadiazine, and pyrazolo[3,4-d]pyrimidine derivatives.

Some pyrazolo[3,4-d]pyrimidin-4(5H)-thione, pyrazolo[3,4-d][1,3]thiazin-4-one/thione, and pyrazolo[1,5-c][1,3,5]thiadiazine-4-one/thione derivatives were synthesized and screened for antifungal activity against the causal agent of rice blast disease, Magnaporthe grisea. In all cases a remarkable inhibition of fungal growth was found in the range from 10 to 200 microg x mL(-1). Several compounds were able to control mycelium growth at a rate of 10 microg x mL(-1), a concentration at which the reference compound tricyclazole was completely ineffective. At least in the case of the most active substance, at the same dose the growth of seedlings or cultured cells of rice was substantially unaffected. Results allowed definition of structural requirements either to maintain or to enhance mycotoxic activity.

Fungicides, Industrial↗
PubMed2000

Constitutive expression of the defense-related Rir1b gene in transgenic rice plants confers enhanced resistance to the rice blast fungus Magnaporthe grisea.

The Rirlb gene of rice (Oryza sativa) is one of a set of putative defense genes whose transcripts accumulate upon inoculation of rice with the non-host pathogen Pseudomonas syringae pv. syringae. It belongs to a family of genes encoding small extracellular proteins so far only identified in cereals. To assess the function of the Rirlb gene in rice blast resistance, it was placed under the control of the CaMV 35S promoter and transferred into rice plants of the japonica variety Taipei 309 by biolistic transformation of immature embryos. Two out of 12 hygromycin-resistant regenerated plants (OE1 and OE3) were fertile. DNA gel blot analysis suggested that these two T0 plants were independent transformants, each of which had stably incorporated one complete copy of the transgene into the genome. In addition, the OE1 plant appeared also a contain a rearranged copy or incomplete copy. T1 plants homozygous for the transgene were identified by DNA gel blot analysis of individual T2 progeny and further propagated. Expression analysis of the transgene showed that the transgene was active both in T1 plants and homozygous decendants. Challenge inoculation of homozygous transgenic plants with Magnaporthe grisea, the causal agent of rice blast disease, revealed that both independent transgenic lines were more resistant than the untransformed wild type, suggesting that over-expression of the Rirlb gene confers partial resistance against this important pathogen.

Gene Expression Regulation, Plant↗
PubMed2004

Transgenic rice plants expressing the antifungal AFP protein from Aspergillus giganteus show enhanced resistance to the rice blast fungus Magnaporthe grisea.

The Aspergillus giganteus antifungal protein (AFP), encoded by the afp gene, has been reported to possess in vitro antifungal activity against various economically important fungal pathogens, including the rice blast fungus Magnaporthe grisea. In this study, transgenic rice ( Oryza sativa ) constitutively expressing the afp gene was generated by Agrobacterium -mediated transformation. Two different DNA constructs containing either the afp cDNA sequence from Aspergillus or a chemically synthesized codon-optimized afp gene were introduced into rice plants. In both cases, the DNA region encoding the signal sequence from the tobacco AP24 gene was N-terminally fused to the coding sequence of the mature AFP protein. Transgenic rice plants showed stable integration and inheritance of the transgene. No effect on plant morphology was observed in the afp -expressing rice lines. The inhibitory activity of protein extracts prepared from leaves of afp plants on the in vitro growth of M. grisea indicated that the AFP protein produced by the trangenic rice plants was biologically active. Several of the T(2) homozygous afp lines were challenged with M. grisea in a detached leaf infection assay. Transformants exhibited resistance to rice blast at various levels. Altogether, the results presented here indicate that AFP can be functionally expressed in rice plants for protection against the rice blast fungus M. grisea.

Animals↗
PubMed2005

The genome sequence of the rice blast fungus Magnaporthe grisea.

Magnaporthe grisea is the most destructive pathogen of rice worldwide and the principal model organism for elucidating the molecular basis of fungal disease of plants. Here, we report the draft sequence of the M. grisea genome. Analysis of the gene set provides an insight into the adaptations required by a fungus to cause disease. The genome encodes a large and diverse set of secreted proteins, including those defined by unusual carbohydrate-binding domains. This fungus also possesses an expanded family of G-protein-coupled receptors, several new virulence-associated genes and large suites of enzymes involved in secondary metabolism. Consistent with a role in fungal pathogenesis, the expression of several of these genes is upregulated during the early stages of infection-related development. The M. grisea genome has been subject to invasion and proliferation of active transposable elements, reflecting the clonal nature of this fungus imposed by widespread rice cultivation.

Fungal Proteins↗