• Proceedings of the Botanical Society of Korea Conference
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• 1999.07a
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• pp.41-44
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• 1999

Magnaporthe grisea (Hebert) Barr (anamorph: Pyricularia grisea) is a typical heterothallic Ascomycete and the causal agent of rice blast, one of the most destructive diseases on rice (Oryza sativa L.) worldwide. The interactions between cells of the pathogen and those of the host involve a complex of biological influences which can lead to blast disease. The early stages of infection process in particular may be viewed as a sequence of discrete and critical events. These include conidial attachment, gemination, and the formation of an appressorium, a dome-shaped and melanized infection structure. Disruption of this process at any point will result in failure of the pathogen to colonize host tissues. This may offer a new avenue for developing innovative crop protection strategies. To recognize and capture such opportunities, understanding the very bases of the pathogenesis at the cellular and molecular level is prerequisite. Much has been learned about environmental cues and endogenous signaling systems for the early infection-related morphogenesis in M. grisea during last several years. The study of signal transduction system in phytopathogenic filamentous fungi offers distinct advantages over traditional mammalian systems. Mammalian systems often contain multiple copies of important genes active in the same tissue under the same physiological processes. Functional redundancy, alternate gene splicing, and specilized isoforms make defining the role of any single gene difficult. Fungi and animals are closely related kingdoms [3], so inferences between these organisms are often justified. For many genes, fungi frequently possess only a single copy, thus phenotype can be attributed directly to the mutation or deletion of any particular gene of interest.

• Research in Plant Disease
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• v.25 no.3
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• pp.103-107
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• 2019

Roles of nutrients in controlling plant diseases have been documented for a long time. Among the nutrients having impact on susceptibility/resistance to crop diseases, nitrogen is one of the most important nutrients for plant growth and development. In rice plants, excess nitrogen via fertilization in agricultural systems is known to increase susceptibility to the rice blast disease. Mechanisms underlying such phenomenon, despite its implication in yield and sustainable agriculture, have not been fully elucidated yet. A few research efforts attempted to link nitrogen-induced susceptibility to concomitant changes in rice plant and rice blast fungus in response to excess nitrogen. However, recent studies focusing on phytobiome are offering new insights into effects of nitrogen on interaction between plants and pathogens. In this review, I will first briefly describe importance of nitrogen as a key nutrient for plants and what changes excess nitrogen can bring about in rice and the fungal pathogen. Next, I will highlight some of the recent phytobiome studies relevant to nitrogen utilization and immunity of plants. Finally, I propose the hypothesis that changes in phytobiome upon excessive nitrogen fertilization contribute to nitrogen-induced susceptibility, and discuss empirical evidences that are needed to support the hypothesis.

• Research in Plant Disease
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• v.19 no.4
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• pp.243-253
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• 2013

Rice blast is one of the most serious disease threatening stable production of rice. Breeding of resistant cultivars has been used as the most effective and useful method to controll rice blast caused by Magnaporthe oryzae. To collect rice blast isolates in fields and test their pathogenicity on new cultivars are important for establishment of new resistant cultivars breeding program of rice. Pathotypes of Korean rice blast isolates have been categorized to Korean differential race system developed in 1985. However, it is little known about genetic background of Korean differential cultivars, so that it is hard to understand for relationship between each pathogen and each host plant at genetic level. In this study, we suggested necessity of a new differential system by analyzing pathogenic responses between 24 monogenic rice lines and 200 Korean rice blast isolates. In addition, we determined the nine representative resistant genes based on the resistance responses of the monogenic lines to rice blast isolates, indexed resistant responses of the monogenic lines to ten representative rice blast isolates and selected 30 Korean representative rice blast isolates proper to Korean system. We think the newly developed differential race system can be broadly used to select resistant cultivars to rice blast in Korea.

• Proceedings of the Korean Society of Plant Pathology Conference
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• 2000.10a
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• pp.24.1-24
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• 2000

• The Plant Pathology Journal
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• v.19 no.1
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• pp.34-42
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• 2003

The ascomycete Magnaporthe grisea is a pathogen of rice blast and is known to form specialized infection structures called appressoria for successful infection into host cells. To understand the molecular mechanism underlying infection process, appressorium-related genes were identified through global approaches including EST sequencing, differential hybridization, and sup-pression subtractive hybridization. EST database was generated on >2,000 cDNA clones randomly selected from appressorium stage cDNA library. Large number of ESTs showed homology to known proteins possibly involved in infection-related cellular development (attachment, germination, appressorium formation, and colonization) of rice blast fungus. The 1051 ESTs showing significant homology to known genes were assigned to 11 functional categories. Differential hybridization and suppression subtractive hybridization were applied to identify genes showing an appressorium stage specific expression pattern. A number of genes were selected as up-regulated during appressorium formation compared with the vegetative growing stage. Clones from various cDNA libraries constructed in different developmental stages were arrayed on slide glass for further expression profiling study. functional characterization of genes identified from these global approaches may lead to a better understand-ing of the infection process of this devastating plant disease, and the development of novel ways to protect host plant.

• The Plant Pathology Journal
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• v.34 no.2
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• pp.126-138
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• 2018

Rice blast caused by Magnaporthe oryzae is a major disease. In the present study, we aimed to identify and evaluate the novel bacterial isolates from rice rhizosphere for biocontrol of M. oryzae pathogen. Sixty bacterial strains from the rice plant's rhizosphere were tested for their biocontrol activity against M. oryzae under in vitro and in vivo. Among them, B. amyloliquefaciens had significant high activity against the pathogen. The least disease severity and highest germination were recorded in seeds treated with B. amyloliquefaciens UASBR9 (0.96 and 98.00%) compared to untreated control (3.43 and 95.00%, respectively) under in vivo condition. These isolates had high activity of enzymes in relation to growth promoting activity upon challenge inoculation of the pathogen. The potential strains were identified based on 16S rRNA gene sequencing and dominance of these particular genes were associated in Bacillus strains. These strains were also confirmed for the presence of antimicrobial peptide biosynthetic genes viz., srfAA (surfactin), fenD (fengycin), spaS (subtilin), and ituC (iturin) related to secondary metabolite production (e.g., AMPs). Overall, the results suggested that application of potential bacterial strains like B. amyloliquefaciens UASBR9 not only helps in control of the biological suppression of one of the most devastating rice pathogens, M. grisea but also increases plant growth along with a reduction in application of toxic chemical pesticides.

• Proceedings of the Korean Society of Plant Pathology Conference
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• 2003.10a
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• pp.105.3-106
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• 2003

Bacillus subtilis strain BAC02-4 was tested for its ability induced systemic resistance(ISR) in rice against Magnaporthe grisea We extend these studies to investigate the biological induction of systemic resistance in rice following treatment with the inducer isolate BAC02-4 and naturally infested with Pyricularia oryzae. We also determine levels of ISR activity during the period between disease development and the onset of systemic resistance. Comparition of lesion number according to applied concentration of BAC02-4 to 'Nagdongbyeo' when naturally infested with the conidia of P. grisea. Results from the blast nusery trial using the 'Nagdongbyeo' showed very low rice blast severity with the inducer concentration of 10$\^$8/ cfu level. Considering the low level of treatment and untreated control were observed to have developed typical susceptible lesion type. Highest protection against the rice blast pathogen when applied three times with 5 days interval as root drench at 5 to 6 leaf stage before pathogen challenge. But higher dose of bacterial inducer produced a little stunted plants with less number lesions and delayed disease development. Diseased leaf area of treated with suspension of the isolate which gave about 80％ of control efficacy at 20 days later comparable to that in noninfested, inducer-free soil.

• Journal of Crop Science and Biotechnology
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• v.11 no.3
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• pp.205-214
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• 2008

Blast disease caused by the fungal pathogen, Magnaporthe oryzae, is one of the most damaging diseases in rice. The use of resistant varieties is an effective measure to control the disease, however, many resistant varieties were broken down to their resistance effects by the differentiating of new virulent isolates. This study was done to analyze the haplotypes of 31 microsatellite markers linked to five major R genes and two QTLs and to identify the alleles for the putatively novel genes related to durable resistance to blast in 56 Korean japonica and four indica varieties. The 31 microsatellite markers produced 2 to 13 alleles(mean = 5.4) and had PICi values ranging from 0.065 to 0.860(mean=0.563) among the 60 rice accessions. Cluster analysis based on allele diversities of 31 microsatellite markers grouped into 60 haplotypes and ten major clusters in 0.810 genetic similarity. A subcluster IV-1 grouped of early flowering varieties harboring Piz and/or Pi9(t) on chromosome 6 and Pita/Pita-2 gene on chromosome 12. The other subcluster V-1 consisted of four stable resistance varieties Donghae, Seomjin, Palgong and Milyang20. The analysis of putative QTLs associated with seven blast resistance genes using ANOVA and linear regression showed high significance to blast resistance across regions and isolates in the markers of two genes Piz and/or Pi9(t) and Pita/Pita-2. These results illustrate the utility of microsatellite markers to identify rice varieties is likely carrying the same R genes and QTLs and rice lines with potentially novel resistant gene.

• Mycobiology
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• v.46 no.4
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• pp.361-369
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• 2018

The rice blast fungus, Magnaporthe oryzae, is an important pathogen of rice plants. It is well known that genes encoded in the genome have different evolutionary histories that are related to their functions. Phylostratigraphy is a method that correlates the evolutionary origin of genes with evolutionary transitions. Here we applied phylostratigraphy to partition total gene content of M. oryzae into distinct classes (phylostrata), which we designated PS1 to PS7, based on estimation of their emergence time. Genes in individual phylostrata did not show significant biases in their global distribution among seven chromosomes, but at the local level, clustering of genes belonging to the same phylostratum was observed. Our phylostrata-wide analysis of genes revealed that genes in the same phylostratum tend to be similar in many physical and functional characteristics such as gene length and structure, GC contents, codon adaptation index, and level of transcription, which correlates with biological functions in evolutionary context. We also found that a significant proportion of genes in the genome are orphans, for which no orthologs can be detected in the database. Among them, we narrowed down to seven orphan genes having transcriptional and translational evidences, and showed that one of them is implicated in asexual reproduction and virulence, suggesting ongoing evolution in this fungus through lineage-specific genes. Our results provide genomic basis for linking functions of pathogenicity factors and gene emergence time.

• 한국균학회소식:학술대회논문집
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• 2015.05a
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• pp.13-13
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• 2015

Rice blast fungus, Magnaporthe oryzae, is the most destructive pathogen of rice in the world. This fungus has a biotrophic phase early in infection and switches to a necrotrophic lifestyle after host cell death. During the biotrophic phase, the fungus competes with host for nutrients and oxygen. Continuous uptake of oxygen is essential for successful establishment of blast disease of this pathogen. Here, we report transcriptional responses of the fungus to oxygen limitation. Transcriptome analysis using RNA-Seq identified 1,047 up-regulated genes in response to hypoxia. Those genes were involved in mycelial development, sterol biosynthesis, and metal ion transport based on hierarchical GO terms and well-conserved among three different fungal species. In addition, null mutants of three hypoxia-responsive genes were generated and tested for their roles on fungal development and pathogenicity. The mutants for a sterol regulatory element-binding protein gene, MoSRE1, and C4 methyl sterol oxidase gene, ERG25, exhibited increased sensitivity to hypoxia-mimetic agent, increased conidiation, and delayed invasive growth within host cells, suggesting important roles in fungal development. However, such defects did not cause any significant decrease in disease severity. The other null mutant for alcohol dehydrogenase gene, MoADH1, showed no defect in the hypoxia-mimic condition and fungal development. Taken together, this comprehensive transcriptional profiling in response to a hypoxia condition with experimental validations would provide new insights on fungal development and pathogenicity in plant pathogenic fungi.