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Expression of hpa1 Gene Encoding a Bacterial Harpin Protein in Xanthomona oryzae pv. oryzae Enhances Disease Resistance to Both Fungal and Bacteria Pathogens in Rice and Arabidopsis

In this study, we expressed hpa1 gene in rice and Arabidopsis to examine
the effects of Hpa1 expression on disease resistance to both fungal and bacterial pathogens. Expression of hpa1 gene in rice enhanced disease resistance to both X.oryzae pv. oryzae and Magnaporthe grisea. Interestingly,
individual transgenic rice plants could be divided into four groups, depending on responses to both pathogens.

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Rice Blast
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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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Methionine Biosynthesis is Essential for Infection in the Rice Blast Fungus Magnaporthe oryzae

Methionine Biosynthesis is Essential for Infection in the Rice Blast Fungus  Magnaporthe oryzae | Rice Blast | Scoop.it
Methionine is a sulfur amino acid standing at the crossroads of several biosynthetic pathways. In fungi, the last step of methionine biosynthesis is catalyzed by a cobalamine-independent methionine synthase (Met6, EC 2.1.1.14). In the present work, we studied the role of Met6 in the infection process of the rice blast fungus, Magnaporthe oryzae. To this end MET6 null mutants were obtained by targeted gene replacement. On minimum medium, MET6 null mutants were auxotrophic for methionine. Even when grown in presence of excess methionine, these mutants displayed developmental defects, such as reduced mycelium pigmentation, aerial hypha formation and sporulation. They also displayed characteristic metabolic signatures such as increased levels of cysteine, cystathionine, homocysteine, S-adenosylmethionine, S-adenosylhomocysteine while methionine and glutathione levels remained unchanged. These metabolic perturbations were associated with the over-expression of MgCBS1 involved in the reversed transsulfuration pathway that metabolizes homocysteine into cysteine and MgSAM1 and MgSAHH1 involved in the methyl cycle. This suggests a physiological adaptation of M. oryzae to metabolic defects induced by the loss of Met6, in particular an increase in homocysteine levels. Pathogenicity assays showed that MET6 null mutants were non-pathogenic on both barley and rice leaves. These mutants were defective in appressorium-mediated penetration and invasive infectious growth. These pathogenicity defects were rescued by addition of exogenous methionine and S-methylmethionine. These results show that M. oryzae cannot assimilate sufficient methionine from plant tissues and must synthesize this amino acid de novo to fulfill its sulfur amino acid requirement during infection.
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Pseudo-backcrossing design for rapidly pyramiding multiple traits into a preferential rice variety

Four resistance donors with five target genes (Sub1A-C, xa5, Xa21, TPS and SSIIa) and three QTLs (qBph3, qBL1 and qBL11) were backcrossed individually using markers into the pseudo-recurrent parent ‘PinK3’ via one cycle of backcrossing followed by two cycles of pseudo-backcrossing and three selfings with rigorous foreground marker-assisted selection. In total, 29 pseudo-backcross inbred lines (BILs) were developed. Genome composition was surveyed using 61 simple sequence repeats (SSRs), 35 of which were located on six carrier chromosomes, with the remainder located on six non-carrier chromosomes. The recurrent genome content (%RGC) and donor genome content (%DGC), which were based on the physical positions of BC1F2, ranged from 69.99 to 88.98% and 11.02 to 30.01%, respectively. For the pseudo-BC3F3BILs, the %RGC and %DGC ranged from 74.50 to 81.30% and 18.70 to 25.50%, respectively. These results indicated that without direct background selection, no further increases in %RGC were obtained during pseudo-backcrossing, whereas rigorous foreground marker-assisted selection tended to reduce linkage drag during pseudo-backcrossing. The evaluation of new traits in selected pseudo-BC3F3BILs indicated significant improvements in resistance to BB, BL, BPH and Sub compared with PinK3, as well as significant improvements in grain yield (21-68%) over the donors, although yield was 7-26% lower than in ‘PinK3’. All pyramided lines were aromatic and exhibited improved starch profiles, rendering them suitable for industrial food applications.
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Current advance methods for the identification of blast resistance genes in rice

Current advance methods for the identification of blast resistance genes in rice | Rice Blast | Scoop.it
Rice blast caused by Magnaporthe oryzae is one of the most devastating diseases of rice around the world and crop losses due to blast are considerably high. Many blast resistant rice varieties have been developed by classical plant breeding and adopted by farmers in various rice-growing countries. However, the variability in the pathogenicity of the blast fungus according to environment made blast disease a major concern for farmers, which remains a threat to the rice industry. With the utilization of molecular techniques, plant breeders have improved rice production systems and minimized yield losses. In this article, we have summarized the current advanced molecular techniques used for controlling blast disease. With the advent of new technologies like marker-assisted selection, molecular mapping, map-based cloning, marker-assisted backcrossing and allele mining, breeders have identified more than 100 Pi loci and 350 QTL in rice genome responsible for blast disease. These Pi genes and QTLs can be introgressed into a blast-susceptible cultivar through marker-assisted backcross breeding. These molecular techniques provide timesaving, environment friendly and labour-cost-saving ways to control blast disease. The knowledge of host–plant interactions in the frame of blast disease will lead to develop resistant varieties in the future.
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Global Genome and Transcriptome Analyses of Magnaporthe oryzae Epidemic Isolate 98-06 Uncover Novel Effectors and Pathogenicity-Related Genes, Revealing Gene Gain and Lose Dynamics in Genome Evol...

Global Genome and Transcriptome Analyses of  Magnaporthe oryzae  Epidemic Isolate 98-06 Uncover Novel Effectors and Pathogenicity-Related Genes, Revealing Gene Gain and Lose Dynamics in Genome Evol... | Rice Blast | Scoop.it
Genetic variations in pathogens, such as the causal agent of rice blast Magnaporthe oryzae, often lead to circumvention of disease-resistance cultivars. Previous genome-wide analyses of model organisms suggest that pathogen effectors are also rapidly evolving, especially in regions with high genome plasticity. However, genetic variations among different isolates remain largely unknown in M. oryzae, particularly at the genome and transcriptome levels. In this study, we provided a systematic genomic and interaction transcriptome profile for a dominant rice blast field isolate, resulting in identification of 134 candidate effectors. Two effectors, Iug6 and Iug9, and one pathogenicity-related (PaR) gene product, Iug18, were subjected to functional characterization. We found that Iug6 and Iug9 are located in the biotrophic interfacial complex (BIC) and their overexpression leads to suppression of defense-related gene expression in rice, while Iug18 appears to be a novel PaR protein. Our studies support the hypothesis that isolate-unique genes may serve as a source of genetic variability in the M. oryzae population encountering different environments. Our studies also facilitate further understanding of effectors and genomic variations in pathogenicity of M. oryzae.
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Phytochemical screening and antimicrobial activities of the constituents isolated from Koelreuteria paniculata leaves

Methanolic extract of Golden rain leaves was fractionated by column chromatography on silica gel and 18 fractions were obtained. Antimicrobial activities of fractions were investigated against Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa as quality control bacteria and fungus Pyricularia grisea which causes Blast disease in rice. Fractions showed more antibacterial activity at 0.04 g/mL concentration only on B. subtilis and S. aureus as gram positive bacteria. Also, three fractions indicated excellent antifungal effect on fungus P. grisea. Moreover, in the present study, fractions that showed very good effect on microorganisms were used for gas chromatography-mass spectrometry analysis to identify different phytochemicals.
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Population structure, pathogenicity and mating type distribution of Magnaporthe oryzae isolates from East Africa

Population structure, pathogenicity and mating type distribution of Magnaporthe oryzae isolates from East Africa | Rice Blast | Scoop.it
Rice blast, caused by Magnaporthe oryzae, is one of the emergent threats to rice production in East Africa (EA), where yet little is known about the population genetics and pathogenicity of this pathogen. We investigated the genetic diversity and mating type distribution of 88 isolates of Magnaporthe oryzae from EA and representative isolates from West Africa (WA) and the Philippines (Asia) using amplified fragment length polymorphism (AFLP) markers and mating type specific primer sets. In addition, the aggressiveness of each isolate was evaluated by inoculating on the susceptible Oryza sativa indica cultivar Co39, scoring the disease severity and calculating the disease progress. Hierarchical analysis of molecular variance revealed a low level of genetic differentiation at two levels (FST 0.12 and FCT 0.11). No evidence of population structure was found among the 65 isolates from EA, and gene flow among EA populations was high. Moreover, pair wise population differentiation (GST) in EA populations ranged from 0.03-0.04, suggesting that >96% of genetic variation is derived from within populations. The populations from Asia and WA were however moderately differentiated from EA ones. The spatial analysis of principal coordinates (PCoA) and STRUCTURE revealed overlapping between individual M. oryzae isolates from EA, with limited distinctness according to the geographic origin. All the populations were clonal, given the positive and significant index of association (IA) and standardized index of association (rd), which indicates a significant (P<0.001) departure from panmixia (IA and rd =0). Both mating types (Mat1-1 and Mat1-2) were detected. However, MAT 1-1 was more prevalent than MAT 1-2. Pathogenicity analysis revealed variability in aggressiveness, suggesting a potential existence of different races. Our data suggest that M. oryzae populations from EA could be either distributed as a single genetic population or that gene flow is exerting a significant influence, effectively swamping the action of selection. This is the first study on genetic differentiation of rice infecting M. oryzae strains from EA, and may guide further studies on the pathogen as well as resistance breeding efforts.
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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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RiceVarMap: a comprehensive database of rice genomic variations

RiceVarMap: a comprehensive database of rice genomic variations | Rice Blast | Scoop.it
Rice Variation Map (RiceVarMap, http:/ricevarmap.ncpgr.cn) is a database of rice genomic variations. The database provides comprehensive information of 6 551 358 single nucleotide polymorphisms (SNPs) and 1 214 627 insertions/deletions (INDELs) identified from sequencing data of 1479 rice accessions. The SNP genotypes of all accessions were imputed and evaluated, resulting in an overall missing data rate of 0.42% and an estimated accuracy greater than 99%. The SNP/INDEL genotypes of all accessions are available for online query and download. Users can search SNPs/INDELs by identifiers of the SNPs/INDELs, genomic regions, gene identifiers and keywords of gene annotation. Allele frequencies within various subpopulations and the effects of the variation that may alter the protein sequence of a gene are also listed for each SNP/INDEL. The database also provides geographical details and phenotype images for various rice accessions. In particular, the database provides tools to construct haplotype networks and design PCR-primers by taking into account surrounding known genomic variations. These data and tools are highly useful for exploring genetic variations and evolution studies of rice and other species.
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Molecular breeding of thermo-sensitive genic male sterile (TGMS) lines of rice for blast resistance using Pi2 gene

Four new TGMS lines with blast resistance gene Pi2 were developed from C815S (an elite TGMS line susceptible to the blast, used as recurrent parent) and VE6219 (a blast resistant line harboring Pi2, used as donor parent). The pathogenicity assays inoculated with 53 blast prevalent isolates in glasshouse showed that the blast resistant frequency of the four TGMS lines was 94.3%-98.1% that is equivalent to blast resistant donor parent VE6219. The field evaluation of the new lines and hybrids made from them at a blast epidemic site also showed high resistant levels against the blast. The genetic background of the newly developed TGMS lines were examined using a whole-genome single nucleotide polymorphism (SNP) array (RICE6K) that turned out more than 83% of the genomic markers were derived from the recurrent parent. The critical temperature points of fertility-sterility alteration of the new TGMS lines were between 22°C and 23°C of daily mean temperature, which is similar to that of C815S. The complete male sterility under natural growth conditions at Wuhan last more than 80 days. Their agronomic and grain quality traits meet the requirement for two-line hybrid rice production.
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Genetic and physical mapping of a new allele of Pik locus from japonica rice ‘Liziangxintuanheigu

Genetic and physical mapping of a new allele of Pik locus from japonica rice ‘Liziangxintuanheigu’ | Rice Blast | Scoop.it
The Chinese rice “Liziangxintuanheigu (LTH)” has been used as a universal susceptible background for the development of international monogenic blast differentials by the JIRCAS–IRRI network. Few reports on the occurrence of LTH incompatible blast isolates from the Philippines and India indicate that the genotype harbours unknown blast resistance gene(s). We report identification, mapping and physical delimitation of the chromosomal location of a new blast resistance gene from LTH. Preliminary linkage analysis of an F2 mapping population generated from a cross between a susceptible cv. ‘Dular’ and LTH localized the blast resistance gene between simple sequence repeat (SSR) markers RM224 and RM6293 on the distal end of the long arm of chromosome 11. Further mapping with polymorphic SSR and sequence tagged site (STS) markers developed from the interval RM224–RM6293 delimited the resistance gene to a 2 cM interval flanked by STS markers STS-7 and STS-13. By aligning the sequences of linked markers on the sequence of cv. Nipponbare, a ~168.05 kb region at the telomeric end of long of chromosome 11 was delineated as the region of the blast resistance gene. Six putatively expressed NBS–LRR genes were identified in the target region by surveying the equivalent genomic region of Nipponbare and two of these, LOC_Os11g46200 and LOC_Os11g46210, were short-listed as a potential candidate for the resistance gene. The new blast resistance gene designated as Pik-l was inferred to be a new allele of Pik locus based on its genomic position and distinct resistance spectra compared to previously known Pik alleles
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Plant NB-LRR proteins: tightly regulated sensors in a complex manner

As plants are sessile, they have evolved hundreds of resistance (R) genes to defend themselves against multiple pathogens. Most of plant R genes encode proteins with the nucleotide-binding and leucine-rich repeat (NB-LRR) domains that interact with pathogen effectors to induce defense responses. Recent findings describing R proteins structures, host interactors and transcriptional and posttranscriptional regulators have broadened our understanding of R gene activity regulation. Genome-wide analyses of NB-LRR genes are useful for identifying host and nonhost R genes and elucidating complex resistance mechanisms. This review provides an overview of the functions of identified NB-LRRs and intra- and intermolecular R gene regulators
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Phylogenomic analysis uncovers the evolutionary history of nutrition and infection mode in rice blast fungus and other Magnaporthales

Phylogenomic analysis uncovers the evolutionary history of nutrition and infection mode in rice blast fungus and other Magnaporthales | Rice Blast | Scoop.it
The order Magnaporthales (Ascomycota, Fungi) includes devastating pathogens of cereals, such as the rice blast fungus Pyricularia (Magnaporthe) oryzae, which is a model in host-pathogen interaction studies. Magnaporthales also includes saprotrophic species associated with grass roots and submerged wood. Despite its scientific and economic importance, the phylogenetic position of Magnaporthales within Sordariomycetes and the interrelationships of its constituent taxa, remain controversial. In this study, we generated novel transcriptome data from 21 taxa that represent key Magnaporthales lineages of different infection and nutrition modes and phenotypes. Phylogenomic analysis of >200 conserved genes allowed the reconstruction of a robust Sordariomycetes tree of life that placed the monophyletic group of Magnaporthales sister to Ophiostomatales. Among Magnaporthales, three major clades were recognized: 1) an early diverging clade A comprised of saprotrophs associated with submerged woods; 2) clade B that includes the rice blast fungus and other pathogens that cause blast diseases of monocot plants. These species infect the above-ground tissues of host plants using the penetration structure, appressorium; and 3) clade C comprised primarily of root-associated species that penetrate the root tissue with hyphopodia. The well-supported phylogenies provide a robust framework for elucidating evolution of pathogenesis, nutrition modes, and phenotypic characters in Magnaporthales
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