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PLOS ONE: Comparative Transcriptome Profiling of the Early Response to Magnaporthe oryzae in Durable Resistant vs Susceptible Rice (Oryza sativa L.) Genotypes

PLOS ONE: Comparative Transcriptome Profiling of the Early Response to Magnaporthe oryzae in Durable Resistant vs Susceptible Rice (Oryza sativa L.) Genotypes | Rice Blast | Scoop.it
PLOS ONE: an inclusive, peer-reviewed, open-access resource from the PUBLIC LIBRARY OF SCIENCE. Reports of well-performed scientific studies from all disciplines freely available to the whole world.
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Rice Blast
Scientific articles on rice blast and wheat blast 20 new articles each month !
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The small GTPase MoYpt7 is required for membrane fusion in autophagy and pathogenicity of Magnaporthe oryzae

The small GTPase MoYpt7 is required for membrane fusion in autophagy and pathogenicity of Magnaporthe oryzae | Rice Blast | Scoop.it
Rab GTPases are required for vesicle-vacuolar fusion during vacuolar biogenesis in fungi. To date, little is known about the biological functions of the Rab small GTPase components in Magnaporthe oryzae. In this study, we investigated MoYpt7 of M. oryzae, a homologue of the small Ras-like GTPase Ypt7 in Saccharomyces cerevisiae. Cellular localization assays showed that MoYpt7 was predominantly localized to vacuolar membranes. Using a targeted gene disruption strategy, a ΔMoYPT7 mutant was generated that exhibited defects in mycelial growth and production of conidia. The conidia of the ΔMoYPT7 mutant were malformed and defective in the formation of appressoria. Consequently, the ΔMoYPT7 mutant failed to cause disease in rice and barley. Furthermore, the ΔMoYPT7 mutant showed impairment in autophagy, breached cell wall integrity, and higher sensitivity to both calcium and heavy metal stress. Transformants constitutively expressing an active MoYPT7 allele (MoYPT7-CA, Gln67Leu) exhibited distinct phenotypes from the ΔMoYPT7 mutant. Expression of MoYPT7-CA in MoYpt7 reduced pathogenicity and produced more appressoria-forming single-septum conidia. These results indicate that MoYPT7 is required for fungal morphogenesis, vacuole fusion, autophagy, stress resistance, and pathogenicity in M. oryzae.
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Phosphoproteome analysis links protein phosphorylation to cellular remodeling and metabolic adaptation during Magnaporthe oryzae appressorium development.

Phosphoproteome analysis links protein phosphorylation to cellular remodeling and metabolic adaptation during Magnaporthe oryzae appressorium development. | Rice Blast | Scoop.it
The rice pathogen, Magnaporthe oryzae, undergoes a complex developmental process leading to formation of an appressorium prior to plant infection. In an effort to better understand phosphoregulation during appressorium development, a mass spectrometry based phosphoproteomics study was undertaken. A total of 2924 class I phosphosites were identified from 1514 phosphoproteins from mycelia, conidia, germlings and appressoria of the wild type and a protein kinase A (PKA) mutant. Phosphoregulation during appressorium development was observed for 448 phosphosites on 320 phosphoproteins. In addition, a set of candidate PKA targets was identified encompassing 253 phosphosites on 227 phosphoproteins. Network analysis incorporating regulation from transcriptomic, proteomic and phosphoproteomic data revealed new insights into the regulation of the metabolism of conidial storage reserves and phospholipids, autophagy, actin dynamics and cell wall metabolism during appressorium formation. In particular, protein phosphorylation appears to play a central role in the regulation of autophagic recycling and actin dynamics during appressorium formation. Changes in phosphorylation were observed in multiple components of the cell wall integrity pathway providing evidence that this pathway is highly active during appressorium development. Several transcription factors were phosphoregulated during appressorium formation including the bHLH domain transcription factor MGG_05709. Functional analysis of MGG_05709 provided further evidence for the role of protein phosphorylation in regulation of glycerol metabolism and the metabolic reprogramming characteristic of appressorium formation. The data presented here represent a comprehensive investigation of the M. oryzae phosphoproteome and provide key insights on the role of protein phosphorylation during infection-related development.
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Antifungal Activity of Piper caninum against Pyricularia oryzae Cav. the Cause of Rice Blast Disease on Rice

Rice blast caused by Pyricularia oryzae Cav.is one of important and destructive disease on rice in most areas where susceptible rice cultivars are grown. This study was done in order to find alternative measure to control the disease by using leaf extract of Piper caninum Blume. Antifungal activity of P. caninum against P. oryzae was done under laboratory condition on potato dextrose agar (PDA) medium. Results of this study showed that the crude extract of P. caninum exhibited a very strong inhibitory activity against P. oryzae with diameter of inhibition zone by 44 mm. Minimum inhibitory concentration (MIC) of this extract was 0.5% (w/v). Treatment with leaf extract of P. caninum significantly (P<0.05) inhibited fungal radial growth, spores formation, and biomass formation.

The growth inhibition resulted from this extract is due to the lysis of fungal cells indicated by the zize of  mycelia, in which the size of mycelia treated with extract is obviously smaller than that of control. It is necessary to purify and identify the substances in the leaf extract of P. caninum that responsible the most for the antifungal activity against P. oryzae. In addition, a field trial is necessary to be done to evaluate the effectiveness of the leaf extract of P. caninum to control rice blast disease under field condition.
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FEMS Microbiology Reviews (2015): The battle for chitin recognition in plant-microbe interactions

FEMS Microbiology Reviews (2015): The battle for chitin recognition in plant-microbe interactions | Rice Blast | Scoop.it

Fungal cell walls play dynamic functions in interaction of fungi with their surroundings. In pathogenic fungi, the cell wall is the first structure to make physical contact with host cells. An important structural component of fungal cell walls is chitin, a well-known elicitor of immune responses in plants. Research into chitin perception has sparked since the chitin receptor from rice was cloned nearly a decade ago. Considering the widespread nature of chitin perception in plants, pathogens evidently evolved strategies to overcome detection, including alterations in the composition of cell walls, modification of their carbohydrate chains and secretion of effectors to provide cell wall protection or target host immune responses. Also non-pathogenic fungi contain chitin in their cell walls and are recipients of immune responses. Intriguingly, various mutualists employ chitin-derived signaling molecules to prepare their hosts for the mutualistic relationship. Research on the various types of interactions has revealed different molecular components that play crucial roles and, moreover, that various chitin-binding proteins contain dissimilar chitin-binding domains across species that differ in affinity and specificity. Considering the various strategies from microbes and hosts focused on chitin recognition, it is evident that this carbohydrate plays a central role in plant–fungus interactions.


Via WU_Phyto
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Fungal diversity notes 1–110: taxonomic and phylogenetic contributions to fungal species

Fungal diversity notes 1–110: taxonomic and phylogenetic contributions to fungal species | Rice Blast | Scoop.it
This paper is a compilation of notes on 110 fungal taxa, including one new family, 10 new genera, and 76 new species, representing a wide taxonomic and geographic range.
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Pike, a rice blast resistance allele consisting of two adjacent NBS–LRR genes, was identified as a novel allele at the Pik locus - Springer

Pike, a rice blast resistance allele consisting of two adjacent NBS–LRR genes, was identified as a novel allele at the Pik locus - Springer | Rice Blast | Scoop.it
Rice (Oryza sativa L.) blast caused by fungus Magnaporthe oryzae is one of the most devastating diseases throughout the world. In the current study, a rice blast resistance gene, designated as Pike, was identified from an indica breeding line Xiangzao143 conferring a durable resistance to rice blast. A map-based cloning strategy was then employed to locate Pike to a 306-kb genomic interval in proximity of the telomeric region of the long arm of chromosome 11. Candidate gene analysis and transgenic complementation test demonstrated that two Xiangzao143-derived adjacent CC–NBS–LRR genes (Pike-1 and Pike-2) at the previously identified Pik locus were required for the Pike-mediated resistance. As compared to the previously identified Pik alleles, the putative Pike-1 peptide was found to be unique in three highly polymorphic sites, two amino acid residue sites (D153 and D229) in the CC domain and one site (L442-W443-P465) in the NBS domain. In addition, against a set of 215 M. oryzae isolates collected from diverse rice cropping areas of China, the Pike carrier Xiangzao143 showed a unique resistance spectrum and a high resistance frequency of 86.1 %. These results thus declared Pike as a novel allele of the Pik locus. Two SNPs G1328C and A3017T in Pike DNA sequence were identified and based on the SNPs, two Pike-specific dCAPS markers d-G1328C and d-A3017T were developed and have been used to effectively distinguish Pike from all of the previously identified Pik alleles.
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Effects of biosurfactants, mannosylerythritol lipids, on the hydrophobicity of solid surfaces and infection behaviors of plant pathogenic fungi

The changes in the hydrophobicity of plastic film surfaces resulting from treatments with MEL solutions (MEL-A, MEL-B, MEL-C, and isoMEL-B) and synthetic surfactant solutions were evaluated based on the changes in contact angles of water droplets placed on the surfaces. The droplet angles on surfaces treated with MELs were verified to decrease within 100 s after placement, with contact angles similar to those observed on Tween 20-treated surfaces, indicating decreases in surface hydrophobicity after MEL treatments. Next, conidial germination, germ tube elongation, and formation of appressorium of Blumeria graminis f. sp. tritici, Colletotrichum dematium, Glomerella cingulata, and Magnaporthe grisea were evaluated on plastic surfaces that were pretreated with surfactant solutions. On the surfaces of MEL-treated plastic film, inhibition of conidial germination, germ tube elongation, and suppression of appressoria formation tended to be observed, although the level of effect was dependent on the combination of fungal species and type of MEL. Inoculation tests revealed that the powdery mildew symptom caused by B. graminis f. sp. tritici was significantly suppressed on wheat leaf segments treated with MELs.
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Introgression of blast resistance genes into the elite variety mr263 through marker-assisted backcrossing

Introgression of blast resistance genes into the elite variety mr263 through marker-assisted backcrossing | Rice Blast | Scoop.it
The improved MR263-BR-3-2, MR263-BR-4-3, MR263-BR-13-1 and MR263-BR-26-4 lines carrying the Pi-7(t), Pi-d (t), Pir2-3(t) genes and qLN2 QTL were developed using the SSR markers RM5961 and RM263 (linked to the blast resistance genes and QTL) for foreground selection and a collection of 65 polymorphic SSR markers for background selection in backcrossed and selfed generations. A background analysis revealed that the highest rate of recurrent parent genome recovery was 96.0% in MR263-BR-4-3 and 94.1% in MR263-BR-3-2.
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Front. Plant Sci.: Decision tools for bacterial blight resistance gene deployment in rice-based agricultural ecosystems (2015)

Front. Plant Sci.: Decision tools for bacterial blight resistance gene deployment in rice-based agricultural ecosystems (2015) | Rice Blast | Scoop.it

Attempting to achieve long-lasting and stable resistance using uniformly deployed rice varieties is not a sustainable approach. The real situation appears to be much more complex and dynamic, one in which pathogens quickly adapt to resistant varieties. To prevent disease epidemics, deployment should be customized and this decision will require interdisciplinary actions. This perspective article aims to highlight the current progress on disease resistance deployment to control bacterial blight in rice. Although the model system rice−Xanthomonas oryzae pv. oryzae has distinctive features that underpin the need for a case-by-case analysis, strategies to integrate those elements into a unique decision tool could be easily extended to other crops.

 

Gerbert Sylvestre Dossa, Adam H. Sparks, Casiana Vera Cruz and Ricardo Oliva


Via Nicolas Denancé, CP
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Development and evaluation of near-isogenic lines for major blast resistance gene(s) in Basmati rice

Development and evaluation of near-isogenic lines for major blast resistance gene(s) in Basmati rice | Rice Blast | Scoop.it
A set of NILs carrying major blast resistance genes in a Basmati rice variety has been developed. Also, the efficacy of pyramids over monogenic NILs against rice blast pathogen Magnaporthe oryzae has been demonstrated.
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Identification of UV-induced Diterpenes Including a New Diterpene Phytoalexin, Phytocassane F, from Rice Leaves by Complementary GC/MS and LC/MS Approaches

Rice phytoalexins are regarded as one of the most important weapons against pathogenic microorganisms. We attempted to identify novel phytoalexins and their derivatives using GC/MS and LC/MS analyses. Diterpene derivatives, 9β-pimara-7,15-diene-3β,6β,19-triol, 1, stemar-13-en-2α-ol, 2, and 1α,2α-dihydroxy-ent-12,15-cassadiene-3,11-dione, 3, were isolated from UV-irradiated rice leaves by chromatographic methods. These structures were confirmed by 1D- and 2D-NMR and MS analyses. Interestingly, all three compounds were accumulated following an infection by the rice blast pathogen Magnaporthe oryzae. Compounds 1 and 2 exhibited weak antifungal activity and may be the biosynthetic intermediates of rice phytoalexins momilactones and oryzalexin S, respectively. Compound 3 exhibited relatively high inhibitory activity against the fungal mycelial growth of M. oryzae to the same extent as the known phytoalexin phytocassane A. We conclude that 3 is a member of the cassane-type phytoalexin family and propose the name phytocassane F.
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Treasure Your Exceptions: Unusual Domains in Immune Receptors Reveal Host Virulence Targets: Cell

Treasure Your Exceptions: Unusual Domains in Immune Receptors Reveal Host Virulence Targets: Cell | Rice Blast | Scoop.it

Summary:

A mechanistic understanding of how plant pathogens modulate their hosts is critical for rationally engineered disease resistance in agricultural systems. Two new studies show that genomically paired plant immune receptors have incorporated decoy domains that structurally mimic pathogen virulence targets to monitor attempted host immunosuppression.


Via Freddy Monteiro
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Freddy Monteiro's curator insight, May 21, 1:02 PM

This is a short introduction to the back-to-back pieces:

 

1. A Plant Immune Receptor Detects Pathogen Effectors that Target WRKY Transcription Factors www.cell.com/cell/abstract/S0092-8674(15)00441-9

 

2. A Receptor Pair with an Integrated Decoy Converts Pathogen Disabling of Transcription Factors to Immunity http://www.cell.com/cell/abstract/S0092-8674%2815%2900442-0

 

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Cloning and characterization of two major blast resistance genes Pi-b and Pi-kh from Malaysian rice variety Pongsu Seribu 2

In order to ensure the resistance of Pongsu Seribu 2, virulent pathotype of M. oryzae P7.2 was inoculated on Pongsu Seribu 2 and MR219 (susceptible used as control) where Pongsu Seribu 2 was found strongly resistance and MR219 susceptible. To determine the mechanism of resistance in PS2 cultivar, cloning and characterization of major blast resistance gene, Pi-b and Pi-kh were carried out. The results revealed that nucleotide sequence contain an open reading frame (ORF) and the same is also highly conserved in nature. Deduced amino acid sequence indicates that Pi-b contains zinc finger-containing protein domain and Pi-kh have Leucine rich repeat domain. The translated nucleotide sequence into amino acid produces significant homology average 76.8% with Pi-kh and 93.4% with Pi-b blast resistance genes present in different cultivars of rice.
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The putative Gγ subunit gene MGG1 is required for conidiation, appressorium formation, mating and pathogenicity in Magnaporthe oryzae

The putative Gγ subunit gene MGG1 is required for conidiation, appressorium formation, mating and pathogenicity in Magnaporthe oryzae | Rice Blast | Scoop.it
Heterotrimeric G-proteins play key roles in the transduction of extracellular signals to various downstream effectors in eukaryotes. In our previous study, a T-DNA insertional mutant A1-412, in which the promoter of a putative Gγ subunit gene MGG1 was disrupted, was impaired in asexual/sexual sporulation, appressorium formation, and pathogenicity in Magnaporthe oryzae. Here the roles of MGG1 in regulating fungal development and plant infection were further investigated and verified using a gene deletion strategy. Targeted gene deletion mutants of MGG1 exhibited similar phenotypes to those of A1-412. The Δmgg1 mutants were unable to differentiate appressorium on hydrophobic surfaces and nonpathogenic to susceptible hosts. The defects of the Δmgg1 mutants in appressorium formation were partially restored by adding exogenous cAMP or IBMX (a phosphodiesterase inhibitor), although the induced appressoria were still nonfunctional. Expressing Mgg1-GFP fusion protein in an Δmgg1 mutant could complement all phenotypes of the mutant, and bright GFP fluorescence was observed at the periphery of fungal cells, indicating that Mgg1 mainly localizes to plasma membrane. Quantitative RT-PCR analysis revealed that deletion of MGG1 resulted in a significant reduction in mRNA levels of the genes encoding Gα (MagA, MagB, and MagC), Gβ (Mgb1), and adenylate cyclase (Mac1). Moreover, intracellular cAMP accumulation was significantly reduced in Δmgg1 mutants compared to that in the wild-type strain. Taken together, our results suggested that Gγ subunit Mgg1 might act upstream of cAMP signaling pathway and play critical roles in regulation of conidiation, appressorium formation, mating, and plant infection in M. oryzae.
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Jasmonates Induce Both Defense Responses and Communication in Monocotyledonous and Dicotyledonous Plants

Jasmonates Induce Both Defense Responses and Communication in Monocotyledonous and Dicotyledonous Plants | Rice Blast | Scoop.it
Jasmonic acid (JA) and its derivatives (jasmonates, JAs) are phytohormones with essential roles in plant defense against pathogenesis and herbivorous arthropods. Both the up- and down-regulation of defense responses are dependent on signaling pathways mediated by JAs as well as other stress hormones (e.g. salicylic acid), generally those involving the transcriptional and post-transcriptional regulation of transcription factors via protein modification and epigenetic regulation. In addition to the typical model plant Arabidopsis (a dicotyledon), advances in genetics research have made rice a model monocot in which innovative pest control traits can be introduced and whose JA signaling pathway can be studied. In this review, we introduce the dynamic functions of JAs in plant defense strategy using defensive substances (e.g. indole alkaloids and terpenoid phytoalexins) and airborne signals (e.g. green leaf volatiles and volatile terpenes) in response to biotrophic and necrotrophic pathogens as well as above-ground and below-ground herbivores. We then discuss the important issue of how the mutualism of herbivorous arthropods with viruses or bacteria can cause cross-talk between JA and other phytohormones to counter the defense systems.

Via Christophe Jacquet, Tatsuya Nobori
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OsHUB1 and OsHUB2 interact with SPIN6 and form homo- and hetero-dimers in rice

Ubiquitin-mediated protein degradation is involved in various cellular processes including plant–microbe interactions and defense responses. Although there are many E3 ubiquitin ligases in rice, the functions of their targets in defense responses are unclear. We recently found that SPIN6 (SPL11-interacting Protein 6) is a Rho GTPase-activating protein and acts as the target of the E3 ligase SPL11, a negative regulator of plant cell death and innate immunity. Our results showed that that SPIN6 serves as a link between the SPL11-mediated ubiquitination pathway and the OsRac1-associated defense system. Here, we show that SPIN6 interacts with OsHUB1 and OsHUB2, the homologous proteins of Arabidopsis RING finger E3 ligases HUB1 and HUB2. OsHub1 and OsHub2 are down-regulated in the Spin6 RNAi plants and during the compatible interaction between rice and Magnaporthe oryzae. OsHub1 and OsHub2 are induced by hormone treatments. Like HUB1 and HUB2 in Arabidopsis, OsHUB1 and OsHUB2 in rice form homo- and hetero-dimers. Our results suggest that OsHUB1 and OsHUB2 may be associated with the SPIN6/OsRac1 pathway in rice immunity.
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Genome-Wide Distribution, Organisation and Functional Characterization of Disease Resistance and Defence Response Genes across Rice Species

Genome-Wide Distribution, Organisation and Functional Characterization of Disease Resistance and Defence Response Genes across Rice Species | Rice Blast | Scoop.it

The resistance (R) genes and defense response (DR) genes have become very important resources for the development of disease resistant cultivars. In the present investigation, genome-wide identification, expression, phylogenetic and synteny analysis was done for R and DR-genes across three species of rice viz: Oryza sativa ssp indica cv 93-11, Oryza sativa ssp japonica and wild rice species, Oryza brachyantha. We used the in silico approach to identify and map 786 R -genes and 167 DR-genes, 672 R-genes and 142 DR-genes, 251 R-genes and 86 DR-genes in the japonica, indica and O. brachyanth a genomes, respectively. Our analysis showed that 60.5% and 55.6% of the R-genes are tandemly repeated within clusters and distributed over all the rice chromosomes in indica and japonica genomes, respectively. The phylogenetic analysis along with motif distribution shows high degree of conservation of R- and DR-genes in clusters. In silico expression analysis of R-genes and DR-genes showed more than 85% were expressed genes showing corresponding EST matches in the databases. This study gave special emphasis on mechanisms of gene evolution and duplication for R and DR genes across species. Analysis of paralogs across rice species indicated 17% and 4.38% R-genes, 29% and 11.63% DR-genes duplication in indica and Oryza brachyantha, as compared to 20% and 26% duplication of R-genes and DR-genes in japonica respectively. We found that during the course of duplication only 9.5% of R- and DR-genes changed their function and rest of the genes have maintained their identity. Syntenic relationship across three genomes inferred that more orthology is shared between indica and japonica genomes as compared to brachyantha genome. Genome wide identification of R-genes and DR-genes in the rice genome will help in allele mining and functional validation of these genes, and to understand molecular mechanism of disease resistance and their evolution in rice and related species.


Via Christophe Jacquet, Biswapriya Biswavas Misra
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In-vitro vs in-vivo Inoculation: Screening for Resistance of Australian Rice Genotypes Against Blast Fungus

Rice blast is caused by Magnaporthe oryzae. In order to assist with rapid screening as a precursor to a breeding program, the susceptibility of 13 rice genotypes from Australia was evaluated in May 2013 using three distinct inoculation methods (spot and filter paper and standard method, all at seedling, vegetative and reproductive stage of plant growth). The results revealed that the filter paper and spot inoculation methods were successful in discerning susceptibility to the rice blast disease (p ≤ 0.05). Disease susceptibility declined significantly from the tillering to the reproductive stage. The standard method was conducted at three different stages for pot plants grown inside the mist house but, due to low temperatures did not produce disease symptoms except in a few genotypes. Among the 13 rice genotypes screened, AAT9 expressed a highly resistant response, and genotypes AAT4, AAT6, AAT10, AAT11, AAT13, AAT17 and AAT18 cultivars expressed resistance at various stages of plant growth. The results obtained from this study will be useful when selecting elite genotypes for disease tolerance for commercial production where rice blast is prevalent. In addition, the resistant genotypes can serve as a gene pool that can be used in breeding programmes to develop new resistant genotypes.
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GATA-Dependent Glutaminolysis Drives Appressorium Formation in Magnaporthe oryzae by Suppressing TOR Inhibition of cAMP/PKA Signaling

GATA-Dependent Glutaminolysis Drives Appressorium Formation in  Magnaporthe oryzae  by Suppressing TOR Inhibition of cAMP/PKA Signaling | Rice Blast | Scoop.it
Fungal plant pathogens are persistent and global food security threats. To invade their hosts they often form highly specialized infection structures, known as appressoria. The cAMP/ PKA- and MAP kinase-signaling cascades have been functionally delineated as positive-acting pathways required for appressorium development. Negative-acting regulatory pathways that block appressorial development are not known. Here, we present the first detailed evidence that the conserved Target of Rapamycin (TOR) signaling pathway is a powerful inhibitor of appressorium formation by the rice blast fungus Magnaporthe oryzae. We determined TOR signaling was activated in an M. oryzae mutant strain lacking a functional copy of the GATA transcription factor-encoding gene ASD4. Δasd4 mutant strains could not form appressoria and expressed GLN1, a glutamine synthetase-encoding orthologue silenced in wild type. Inappropriate expression of GLN1 increased the intracellular steady-state levels of glutamine in Δasd4 mutant strains during axenic growth when compared to wild type. Deleting GLN1 lowered glutamine levels and promoted appressorium formation by Δasd4 strains. Furthermore, glutamine is an agonist of TOR. Treating Δasd4 mutant strains with the specific TOR kinase inhibitor rapamycin restored appressorium development. Rapamycin was also shown to induce appressorium formation by wild type and Δcpka mutant strains on non-inductive hydrophilic surfaces but had no effect on the MAP kinase mutant Δpmk1. When taken together, we implicate Asd4 in regulating intracellular glutamine levels in order to modulate TOR inhibition of appressorium formation downstream of cPKA. This study thus provides novel insight into the metabolic mechanisms that underpin the highly regulated process of appressorium development.
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Influence of magnesium on physiological responses of wheat infected by Pyricularia oryzae

Influence of magnesium on physiological responses of wheat infected by Pyricularia oryzae | Rice Blast | Scoop.it
Although magnesium (Mg) is considered an essential element for wheat growth, its importance for disease control often has been overlooked and the physiological features of diseased plants mediated by Mg remain elusive. In this study, the effect of three Mg concentrations (0.25, 2.5 and 4 mM) on wheat resistance to leaf blast (Pyricularia oryzae), leaf gas exchange, invertase activity, cellular damage and foliar concentration of photosynthetic pigments and nutrients was investigated. Foliar Mg increased from 1.9 to 3.9 g kg−1, whereas calcium (Ca) decreased from 7.8 to 4.9 g kg−1 as the Mg applied increased from 0.25 to 4 mM. Blast severity increased from 11.3 to 39.6% as the Mg applied increased from 0.25 to 4 mM. Photosynthesis, stomatal conductance, transpiration and photosynthetic pigment concentrations decreased in inoculated plants compared to non-inoculated plants regardless of the Mg concentration; however, the reductions were more pronounced for plants grown with 4 mM Mg than those grown with 0.25 mM Mg. On the other hand, a higher internal CO2 concentration, invertase activity and malondialdehyde concentration was recorded in inoculated plants grown with 4 mM Mg compared to those grown with 0.25 mM Mg. In conclusion, reduced Ca uptake may partially explain the increased susceptibility of wheat to leaf blast with the highest Mg concentration. Mg-induced susceptibility to leaf blast appeared responsible for the photosynthetic impairments which were most likely due to biochemical constraints since plants grown with the highest Mg concentration suffered extensive cellular damage and degradation of photosynthetic pigments as a result of high disease severity.
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Regulation of plant polysaccharide utilisation in Magnaporthe oryzae and other ascomycetous fungi

Regulation of plant polysaccharide utilisation in Magnaporthe oryzae and other ascomycetous fungi | Rice Blast | Scoop.it
Magnaporthe oryzae is a fungal plant pathogen of many grasses including rice. Since arabinoxylan is one of the major components of the plant cell wall of grasses, M. oryzae is likely to degrade this polysaccharide for supporting its growth in infected leaves. D-xylose is released from arabinoxylan by fungal xylanolytic enzymes and catabolised through the pentose pathway. This PhD thesis describes the characterisation of the pathway for pentose utilisation in M. oryzae and the discovery of a novel pentose reductase. In fungi, the expression of genes involved in xylan degradation and D-xylose utilisation is under control of the transcriptional activator XlnR. A detailed characterisation of the homolog of XlnR in M. oryzae, Xlr1, was performed in the course of this thesis. Investigation of an XLR1 disruption strain demonstrated that XLR1 encodes the transcriptional activator of the pentose catabolic pathway in M. oryzae. However, the xylanolytic system of this fungus was induced even in the absence of Xlr1. A detailed transcriptome analysis demonstrated that a number of genes involved in xylan degradation were strongly dependent on Xlr1 while a second set of xylanolytic genes appeared to be under control of another yet unknown regulatory system.

XlnR homologs are commonly found in filamentous ascomycetes and often assumed to have the same function in different fungi. A comparison of five filamentous fungi showed significant differences in the proteome secreted by these fungi in response to xylan as well as regarding the set of genes that is controlled by XlnR in the individual species. This comparison emphasizes the functional diversity of a fine-tuned (hemi-) cellulolytic regulatory system in filamentous fungi, which might be related to the adaptation of fungi to their specific biotopes.



This PhD thesis deepens our knowledge about regulation of plant polysaccharide degradation and utilisation in filamentous fungi with a special focus on the rice blast fungus M. oryzae. The family, to which M. oryzae belongs to (Magnaporthaceae), also includes other important plant pathogens (e.g. rice stem rot fungus, summer patch). The taxonomic relationships of Magnaporthe and Pyricularia species were investigated which led to the identification of novel species, which are also described in this PhD thesis.
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Appressorium-mediated penetration of Magnaporthe oryzae and Colletotrichum orbiculare into surface-cross-linked agar media

Appressorium-mediated penetration of Magnaporthe oryzae and Colletotrichum orbiculare into surface-cross-linked agar media | Rice Blast | Scoop.it
Many phytopathogenic fungi form appressoria on some artificial substances. However, it is difficult to induce appressorium-mediated penetration into artificial substances. In the present study, novel artificial agar media were developed to investigate the in vitro penetration process of phytopathogenic fungi. The media contained sodium carboxymethyl cellulose or sodium alginate, and the surfaces were subjected to ionic cross-linking using trivalent metal ions. The hemibiotrophic phytopathogenic fungi, rice blast fungus and cucurbit anthracnose fungus, formed appressoria and penetrated into the surface cross-linked artificial agar media from the base of appressoria. These artificial media appeared to induce fungal infection behavior that occurred on host plants.
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Rmg7, a New Gene for Resistance to Triticum Isolates of Pyricularia oryzae Identified in Tetraploid Wheat

Rmg7, a New Gene for Resistance to Triticum Isolates of Pyricularia oryzae Identified in Tetraploid Wheat | Rice Blast | Scoop.it
A single gene for resistance, designated Rmg7 (Resistance to Magnaporthe grisea 7), was identified in a tetraploid wheat accession, St24 (Triticum dicoccum, KU120), against Br48, a Triticum isolate of Pyricularia oryzae. Two other wheat accessions, St17 (T. dicoccum, KU112) and St25 (T. dicoccum, KU122), were also resistant against Br48 and showed a similar disease reaction pattern to St24. Crosses between these resistant accessions yielded no susceptible F2 seedlings, suggesting that St24, St17, and St25 carry the same resistance gene. Furthermore, a single avirulence gene corresponding to Rmg7 was detected in a segregation analysis of random F1 progenies between Br48 and MZ5-1-6, an Eleusine isolate virulent to St24 at a higher temperature. This avirulence gene was recognized not only by St24, but also by St17 and St25, thus supporting the preceding results indicating that all three accessions carry Rmg7. This resistance gene may have potential in future wheat breeding programs.
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