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Li Z, Wu L, Wu H, Zhang X, Mei J, Zhou X, Wang GL, Liu W. Arginine methylation is required for remodelling pre-mRNA splicing and induction of autophagy in rice blast fungus. New Phytol 2020; 225:413-429. [PMID: 31478201 DOI: 10.1111/nph.16156] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/24/2019] [Accepted: 08/18/2019] [Indexed: 06/10/2023]
Abstract
Protein arginine methyltransferases (PRMTs) regulate many physiological processes, including autophagy. However, the direct roles of the various PRMTs during autophagosome formation remain unclear. Here, we characterised the function of MoHMT1 in the rice blast fungus, Magnaporthe oryzae. Knockout of MoHMT1 results in inhibited growth and a decreased ability to cause disease lesions on rice seedlings. MoHMT1 catalyses the di-methylation of arginine 247, 251, 261 and 271 residues of MoSNP1, a U1 small nuclear ribonucleoprotein (snRNP) component, likely in a manner dependent on direct interaction. RNA-seq analysis revealed that alternative splicing of pre-mRNAs of 558 genes, including the autophagy-related (ATG) gene MoATG4, was altered in MoHMT1 deletion mutants, compared with wild-type strains under normal growth conditions. During light exposure or nitrogen starvation, MoHMT1 localises to autophagosomes and MoHMT1 mutants display defects in autophagy induction. Under nitrogen starvation, six additional MoATG genes were identified with retained introns in their mRNA transcripts, corresponding with a significant reduction in transcripts of intron-spliced isoforms in the MoHMT1 mutant strain. Our study shows that arginine methylation plays an essential role in accurate pre-mRNA splicing necessary for a range of developmental processes, including autophagosome formation.
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Affiliation(s)
- Zhiqiang Li
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, 100193, China
| | - Liye Wu
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, 100193, China
| | - Hang Wu
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, 100193, China
| | - Xixi Zhang
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, 100193, China
| | - Jie Mei
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, 100193, China
| | - Xueping Zhou
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, 100193, China
| | - Guo-Liang Wang
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, 100193, China
- Department of Plant Pathology, Ohio State University, Columbus, OH, 43210, USA
| | - Wende Liu
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, 100193, China
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Fukada F, Kodama S, Nishiuchi T, Kajikawa N, Kubo Y. Plant pathogenic fungi Colletotrichum and Magnaporthe share a common G 1 phase monitoring strategy for proper appressorium development. New Phytol 2019; 222:1909-1923. [PMID: 30715740 DOI: 10.1111/nph.15728] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2018] [Accepted: 01/24/2019] [Indexed: 06/09/2023]
Abstract
To breach the plant cuticle, many plant pathogenic fungi differentiate specialized infection structures (appressoria). In Colletotrichum orbiculare (cucumber anthracnose fungus), this differentiation requires unique proper G1 /S phase progression, regulated by two-component GTPase activating protein CoBub2/CoBfa1 and GTPase CoTem1. Since their homologues regulate mitotic exit, cytokinesis, or septum formation from yeasts to mammals, we asked whether the BUB2 function in G1 /S progression is specific to plant pathogenic fungi. Colletotrichum higginsianum and Magnaporthe oryzae were genetically analyzed to investigate conservation of BUB2 roles in cell cycle regulation, septum formation, and virulence. Expression profile of cobub2Δ was analyzed using a custom microarray. In bub2 mutants of both fungi, S phase initiation was earlier, and septum formation coordinated with a septation initiation network protein and contractile actin ring was impaired. Earlier G1 /S transition in cobub2Δ results in especially high expression of DNA replication genes and differing regulation of virulence-associated genes that encode proteins such as carbohydrate-active enzymes and small secreted proteins. The virulence of chbub2Δ and mobub2Δ was significantly reduced. Our evidence shows that BUB2 regulation of G1 /S transition and septum formation supports its specific requirement for appressorium development in plant pathogenic fungi.
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Affiliation(s)
- Fumi Fukada
- Laboratory of Plant Pathology, Life and Environmental Sciences, Graduate School of Kyoto Prefectural University, Sakyo, Kyoto, 606-8522, Japan
| | - Sayo Kodama
- Laboratory of Plant Pathology, Life and Environmental Sciences, Graduate School of Kyoto Prefectural University, Sakyo, Kyoto, 606-8522, Japan
| | - Takumi Nishiuchi
- Division of Functional Genomics, Advanced Science Research Centre, Kanazawa University, Kanazawa, 920-0934, Japan
| | - Naoki Kajikawa
- Laboratory of Plant Pathology, Life and Environmental Sciences, Graduate School of Kyoto Prefectural University, Sakyo, Kyoto, 606-8522, Japan
| | - Yasuyuki Kubo
- Laboratory of Plant Pathology, Life and Environmental Sciences, Graduate School of Kyoto Prefectural University, Sakyo, Kyoto, 606-8522, Japan
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Liu C, Li Z, Xing J, Yang J, Wang Z, Zhang H, Chen D, Peng YL, Chen XL. Global analysis of sumoylation function reveals novel insights into development and appressorium-mediated infection of the rice blast fungus. New Phytol 2018; 219:1031-1047. [PMID: 29663402 DOI: 10.1111/nph.15141] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/03/2018] [Accepted: 03/02/2018] [Indexed: 05/23/2023]
Abstract
Protein post-translational modifications play critical roles in cellular processes, development and stress response. The small ubiquitin-like modifier (SUMO) to proteins is one of the essential modifications in eukaryotes, but its function remains largely unknown in plant pathogenic fungi. We present a comprehensive analysis combined with proteomic, molecular and cellular approaches to explore the roles of sumoylation in the model plant fungal pathogen, Magnaporthe oryzae. We found the SUMO pathway plays key roles in colony growth, conidia formation and virulence to the host, as well as cell-cycle-related phenotypes. Sumoylation is also involved in responding to different stresses. Affinity purification identified 940 putative SUMO substrates, many of which were reported to be involved in development, stress response and infection. Interestingly, four septins were also shown to be sumoylated. Mutation of consensus sumoylation sites in each septin all resulted in reduced virulence to the host and dislocation of septins in appressoria. Moreover, sumoylation is also involved in extracellular secretion of different effector proteins. Our study on the functions of sumoylation provides novel insight into development and infection of the rice blast fungus.
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Affiliation(s)
- Caiyun Liu
- College of Plant Science and Technology, Huazhong Agricultural University, The Provincial Key Laboratory of Plant Pathology of Hubei Province, Wuhan, 430070, China
| | - Zhigang Li
- College of Plant Science and Technology, Huazhong Agricultural University, The Provincial Key Laboratory of Plant Pathology of Hubei Province, Wuhan, 430070, China
- College of Plant Protection, China Agricultural University, State Key Laboratory of Agrobiotechnology, Ministry of Agriculture Key Laboratory of Pest Monitoring and Green Management, Beijing, 100193, China
| | - Junjie Xing
- State Key Laboratory of Hybrid Rice, Hunan Hybrid Rice Research Center, Changsha, 410125, China
| | - Jun Yang
- College of Plant Protection, China Agricultural University, State Key Laboratory of Agrobiotechnology, Ministry of Agriculture Key Laboratory of Pest Monitoring and Green Management, Beijing, 100193, China
| | - Zhao Wang
- College of Plant Science and Technology, Huazhong Agricultural University, The Provincial Key Laboratory of Plant Pathology of Hubei Province, Wuhan, 430070, China
| | - Hong Zhang
- College of Plant Science and Technology, Huazhong Agricultural University, The Provincial Key Laboratory of Plant Pathology of Hubei Province, Wuhan, 430070, China
| | - Deng Chen
- State Key Laboratory of Hybrid Rice, Hunan Hybrid Rice Research Center, Changsha, 410125, China
| | - You-Liang Peng
- College of Plant Protection, China Agricultural University, State Key Laboratory of Agrobiotechnology, Ministry of Agriculture Key Laboratory of Pest Monitoring and Green Management, Beijing, 100193, China
| | - Xiao-Lin Chen
- College of Plant Science and Technology, Huazhong Agricultural University, The Provincial Key Laboratory of Plant Pathology of Hubei Province, Wuhan, 430070, China
- State Key Laboratory of Hybrid Rice, Hunan Hybrid Rice Research Center, Changsha, 410125, China
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Goh J, Jeon J, Lee YH. ER retention receptor, MoERR1 is required for fungal development and pathogenicity in the rice blast fungus, Magnaporthe oryzae. Sci Rep 2017; 7:1259. [PMID: 28455525 PMCID: PMC5430845 DOI: 10.1038/s41598-017-01237-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2017] [Accepted: 03/23/2017] [Indexed: 01/01/2023] Open
Abstract
ER retention receptor is a seven trans-membrane protein that plays pivotal roles in function and integrity of endoplasmic reticulum (ER). Insertional mutagenesis of Magnaporthe oryzae identified MoERR1 as a pathogenicity gene encoding putative ER retention receptor orthologous to ERD2 in Saccharomyces cerevisiae. Search through the genome identified that M. oryzae possesses another ortholog of ERD2, which is designated as MoERR2. When MoERR1 and MoERR2 were tagged with GFP, both were localized to ER. Targeted disruption of MoERR1 showed pleiotropic effects on phenotypes, while deletion of MoERR2 had no effect on phenotypes we examined. The disruption mutant of MoERR1 showed growth retardation and produced significantly reduced number of conidia with aberrant morphology. Appressoria from the mutant were unable to penetrate into plant tissues presumably due to defect in cell wall integrity, thereby rendering the mutant non-pathogenic. The MoERR1 mutant also appeared to display abnormal ER structure and mis-regulation of genes involved in chaperone function and unfolded protein response under ER stress condition. Taken together, these results suggest that MoERR1 is a ER retention receptor required for function and integrity of ER, and that MoERR1-mediated ER functionalities are essential for fungal development and pathogenesis.
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Affiliation(s)
- Jaeduk Goh
- Department of Agricultural Biotechnology, College of Agriculture and Life Sciences, Seoul National University, Seoul, 08826, Korea
- Fungal Resources Research Division, Nakdonggang National Institute of Biological Resources, Sangju, 37242, Korea
| | - Junhyun Jeon
- Department of Biotechnology, College of Life and Applied Sciences, Yeungnam University, Gyeongsan, Gyeongbuk, 38541, Korea
| | - Yong-Hwan Lee
- Department of Agricultural Biotechnology, College of Agriculture and Life Sciences, Seoul National University, Seoul, 08826, Korea.
- National Center for Fungal Genetic Resources, Plant Genomics and Breeding Institute, and Research Institute of Agriculture and Life Sciences, Seoul National University, Seoul, 08826, Korea.
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Marroquin-Guzman M, Sun G, Wilson RA. Glucose-ABL1-TOR Signaling Modulates Cell Cycle Tuning to Control Terminal Appressorial Cell Differentiation. PLoS Genet 2017; 13:e1006557. [PMID: 28072818 PMCID: PMC5266329 DOI: 10.1371/journal.pgen.1006557] [Citation(s) in RCA: 49] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2016] [Revised: 01/25/2017] [Accepted: 12/29/2016] [Indexed: 01/02/2023] Open
Abstract
The conserved target of rapamycin (TOR) pathway integrates growth and development with available nutrients, but how cellular glucose controls TOR function and signaling is poorly understood. Here, we provide functional evidence from the devastating rice blast fungus Magnaporthe oryzae that glucose can mediate TOR activity via the product of a novel carbon-responsive gene, ABL1, in order to tune cell cycle progression during infection-related development. Under nutrient-free conditions, wild type (WT) M. oryzae strains form terminal plant-infecting cells (appressoria) at the tips of germ tubes emerging from three-celled spores (conidia). WT appressorial development is accompanied by one round of mitosis followed by autophagic cell death of the conidium. In contrast, Δabl1 mutant strains undergo multiple rounds of accelerated mitosis in elongated germ tubes, produce few appressoria, and are abolished for autophagy. Treating WT spores with glucose or 2-deoxyglucose phenocopied Δabl1. Inactivating TOR in Δabl1 mutants or glucose-treated WT strains restored appressorium formation by promoting mitotic arrest at G1/G0 via an appressorium- and autophagy-inducing cell cycle delay at G2/M. Collectively, this work uncovers a novel glucose-ABL1-TOR signaling axis and shows it engages two metabolic checkpoints in order to modulate cell cycle tuning and mediate terminal appressorial cell differentiation. We thus provide new molecular insights into TOR regulation and cell development in response to glucose.
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Affiliation(s)
- Margarita Marroquin-Guzman
- Department of Plant Pathology, University of Nebraska-Lincoln, Lincoln, Nebraska, United States of America
| | - Guangchao Sun
- Department of Plant Pathology, University of Nebraska-Lincoln, Lincoln, Nebraska, United States of America
| | - Richard A. Wilson
- Department of Plant Pathology, University of Nebraska-Lincoln, Lincoln, Nebraska, United States of America
- * E-mail:
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Gong X, Hurtado O, Wang B, Wu C, Yi M, Giraldo M, Valent B, Goodin M, Farman M. pFPL Vectors for High-Throughput Protein Localization in Fungi: Detecting Cytoplasmic Accumulation of Putative Effector Proteins. Mol Plant Microbe Interact 2015; 28:107-121. [PMID: 25390188 DOI: 10.1094/mpmi-05-14-0144-ta] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
As part of a large-scale project whose goal was to identify candidate effector proteins in Magnaporthe oryzae, we developed a suite of vectors that facilitate high-throughput protein localization experiments in fungi. These vectors utilize Gateway recombinational cloning to place a gene's promoter and coding sequences upstream and in frame with enhanced cyan fluorescent protein, green fluorescent protein (GFP), monomeric red fluorescence protein (mRFP), and yellow fluorescent protein or a nucleus-targeted mCHERRY variant. The respective Gateway cassettes were incorporated into Agrobacterium-based plasmids to allow efficient fungal transformation using hygromycin or geneticin resistance selection. mRFP proved to be more sensitive than the GFP spectral variants for monitoring proteins secreted in planta; and extensive testing showed that Gateway-derived fusion proteins produced localization patterns identical to their "directly fused" counterparts. Use of plasmid for fungal protein localization (pFPL) vectors with two different selectable markers provided a convenient way to label fungal cells with different fluorescent proteins. We demonstrate the utility of the pFPL vectors for identifying candidate effector proteins and we highlight a number of important factors that must be taken into consideration when screening for proteins that are translocated across the host plasma membrane.
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Zhou X, Zhao X, Xue C, Dai Y, Xu JR. Bypassing both surface attachment and surface recognition requirements for appressorium formation by overactive ras signaling in Magnaporthe oryzae. Mol Plant Microbe Interact 2014; 27:996-1004. [PMID: 24835254 DOI: 10.1094/mpmi-02-14-0052-r] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Magnaporthe oryzae forms a highly specialized infection structure called an appressorium for plant penetration. In M. oryzae and many other plant-pathogenic fungi, surface attachment and surface recognition are two essential requirements for appressorium formation. Development of appressoria in the air has not been reported. In this study, we found that expression of a dominant active MoRAS2(G18V) allele in M. oryzae resulted in the formation of morphologically abnormal appressoria on nonconducive surfaces, in liquid suspensions, and on aerial hyphae without attachment to hard surfaces. Both the Pmk1 mitogen-activated protein kinase cascade and cAMP signaling pathways that regulate surface recognition and appressorium morphogenesis in M. oryzae were overactivated in the MoRAS2(G18V) transformant. In mutants deleted of PMK1 or CPKA, expression of MoRAS2(G18V) had no significant effects on appressorium morphogenesis. Furthermore, expression of dominant MoRAS2 in Colletotrichum graminicola and C. gloeosporioides also caused the formation of appressorium-like structures in aerial hyphae. Overall, our data indicate that MoRas2 functions upstream from both the cAMP-PKA and Pmk1 pathways and overactive Ras signaling leads to improper activation of these two pathways and appressorium formation without surface attachment in appressorium-forming pathogens.
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Zhang H, Zhao Q, Guo X, Guo M, Qi Z, Tang W, Dong Y, Ye W, Zheng X, Wang P, Zhang Z. Pleiotropic function of the putative zinc-finger protein MoMsn2 in Magnaporthe oryzae. Mol Plant Microbe Interact 2014; 27:446-60. [PMID: 24405033 DOI: 10.1094/mpmi-09-13-0271-r] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
The mitogen-activated protein kinase MoOsm1-mediated osmoregulation pathway plays crucial roles in stress responses, asexual and sexual development, and pathogenicity in Magnaporthe oryzae. Utilizing an affinity purification approach, we identified the putative transcriptional activator MoMsn2 as a protein that interacts with MoOsm1 in vivo. Disruption of the MoMSN2 gene resulted in defects in aerial hyphal growth, conidial production, and infection of host plants. Quantitative reverse transcription-polymerase chain reaction analysis showed that the expression of several genes involved in conidiophore formation was reduced in ΔMomsn2, suggesting that MoMsn2 might function as a transcriptional regulator of these genes. Subsequently, MoCos1 was identified as one of the MoMsn2 targets through yeast one-hybrid analysis in which MoMsn2 binds to the AGGGG and CCCCT motif of the MoCOS1 promoter region. Phenotypic characterization showed that MoMsn2 was required for appressorium formation and penetration and pathogenicity. Although the ΔMomsn2 mutant was tolerant to the cell-wall stressor Calcofluor white, it was sensitive to common osmotic stressors. Further analysis suggests that MoMsn2 is involved in the regulation of the cell-wall biosynthesis pathway. Finally, transcriptome data revealed that MoMsn2 modulates numerous genes participating in conidiation, infection, cell-wall integrity, and stress response. Collectively, our results led to a model in which MoMsn2 mediates a series of downstream genes that control aerial hyphal growth, conidiogenesis, appressorium formation, cell-wall biosynthesis, and infection and that also offer potential targets for the development of new disease management strategies.
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Li L, Wang J, Zhang Z, Wang Y, Liu M, Jiang H, Chai R, Mao X, Qiu H, Liu F, Sun G. MoPex19, which is essential for maintenance of peroxisomal structure and woronin bodies, is required for metabolism and development in the rice blast fungus. PLoS One 2014; 9:e85252. [PMID: 24454828 PMCID: PMC3891873 DOI: 10.1371/journal.pone.0085252] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2013] [Accepted: 11/24/2013] [Indexed: 11/19/2022] Open
Abstract
Peroxisomes are present ubiquitously and make important contributions to cellular metabolism in eukaryotes. They play crucial roles in pathogenicity of plant fungal pathogens. The peroxisomal matrix proteins and peroxisomal membrane proteins (PMPs) are synthesized in the cytosol and imported post-translationally. Although the peroxisomal import machineries are generally conserved, some species-specific features were found in different types of organisms. In phytopathogenic fungi, the pathways of the matrix proteins have been elucidated, while the import machinery of PMPs remains obscure. Here, we report that MoPEX19, an ortholog of ScPEX19, was required for PMPs import and peroxisomal maintenance, and played crucial roles in metabolism and pathogenicity of the rice blast fungus Magnaporthe oryzae. MoPEX19 was expressed in a low level and Mopex19p was distributed in the cytoplasm and newly formed peroxisomes. MoPEX19 deletion led to mislocalization of peroxisomal membrane proteins (PMPs), as well peroxisomal matrix proteins. Peroxisomal structures were totally absent in Δmopex19 mutants and woronin bodies also vanished. Δmopex19 exhibited metabolic deficiency typical in peroxisomal disorders and also abnormality in glyoxylate cycle which was undetected in the known mopex mutants. The Δmopex19 mutants performed multiple disorders in fungal development and pathogenicity-related morphogenesis, and lost completely the pathogenicity on its hosts. These data demonstrate that MoPEX19 plays crucial roles in maintenance of peroxisomal and peroxisome-derived structures and makes more contributions to fungal development and pathogenicity than the known MoPEX genes in the rice blast fungus.
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Affiliation(s)
- Ling Li
- Department of Plant Pathology, College of Plant Protection, Nanjing Agricultural University, Nanjing, China
- State Key Laboratory Breeding Base for Zhejiang Sustainable Pest and Disease Control, Institute of Plant Protection Microbiology, Zhejiang Academy of Agricultural Sciences, Hangzhou, China
| | - Jiaoyu Wang
- State Key Laboratory Breeding Base for Zhejiang Sustainable Pest and Disease Control, Institute of Plant Protection Microbiology, Zhejiang Academy of Agricultural Sciences, Hangzhou, China
| | - Zhen Zhang
- State Key Laboratory Breeding Base for Zhejiang Sustainable Pest and Disease Control, Institute of Plant Protection Microbiology, Zhejiang Academy of Agricultural Sciences, Hangzhou, China
| | - Yanli Wang
- State Key Laboratory Breeding Base for Zhejiang Sustainable Pest and Disease Control, Institute of Plant Protection Microbiology, Zhejiang Academy of Agricultural Sciences, Hangzhou, China
| | - Maoxin Liu
- Department of Plant Pathology, College of Plant Protection, Nanjing Agricultural University, Nanjing, China
- State Key Laboratory Breeding Base for Zhejiang Sustainable Pest and Disease Control, Institute of Plant Protection Microbiology, Zhejiang Academy of Agricultural Sciences, Hangzhou, China
| | - Hua Jiang
- State Key Laboratory Breeding Base for Zhejiang Sustainable Pest and Disease Control, Institute of Plant Protection Microbiology, Zhejiang Academy of Agricultural Sciences, Hangzhou, China
| | - Rongyao Chai
- State Key Laboratory Breeding Base for Zhejiang Sustainable Pest and Disease Control, Institute of Plant Protection Microbiology, Zhejiang Academy of Agricultural Sciences, Hangzhou, China
| | - Xueqin Mao
- State Key Laboratory Breeding Base for Zhejiang Sustainable Pest and Disease Control, Institute of Plant Protection Microbiology, Zhejiang Academy of Agricultural Sciences, Hangzhou, China
| | - Haiping Qiu
- State Key Laboratory Breeding Base for Zhejiang Sustainable Pest and Disease Control, Institute of Plant Protection Microbiology, Zhejiang Academy of Agricultural Sciences, Hangzhou, China
| | - Fengquan Liu
- Department of Plant Pathology, College of Plant Protection, Nanjing Agricultural University, Nanjing, China
- * E-mail: (FL); (GS)
| | - Guochang Sun
- State Key Laboratory Breeding Base for Zhejiang Sustainable Pest and Disease Control, Institute of Plant Protection Microbiology, Zhejiang Academy of Agricultural Sciences, Hangzhou, China
- * E-mail: (FL); (GS)
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Giraldo MC, Dagdas YF, Gupta YK, Mentlak TA, Yi M, Martinez-Rocha AL, Saitoh H, Terauchi R, Talbot NJ, Valent B. Two distinct secretion systems facilitate tissue invasion by the rice blast fungus Magnaporthe oryzae. Nat Commun 2013; 4:1996. [PMID: 23774898 PMCID: PMC3709508 DOI: 10.1038/ncomms2996] [Citation(s) in RCA: 251] [Impact Index Per Article: 22.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2012] [Accepted: 05/09/2013] [Indexed: 12/30/2022] Open
Abstract
To cause plant diseases, pathogenic micro-organisms secrete effector proteins into host tissue to suppress immunity and support pathogen growth. Bacterial pathogens have evolved several distinct secretion systems to target effector proteins, but whether fungi, which cause the major diseases of most crop species, also require different secretory mechanisms is not known. Here we report that the rice blast fungus Magnaporthe oryzae possesses two distinct secretion systems to target effectors during plant infection. Cytoplasmic effectors, which are delivered into host cells, preferentially accumulate in the biotrophic interfacial complex, a novel plant membrane-rich structure associated with invasive hyphae. We show that the biotrophic interfacial complex is associated with a novel form of secretion involving exocyst components and the Sso1 t-SNARE. By contrast, effectors that are secreted from invasive hyphae into the extracellular compartment follow the conventional secretory pathway. We conclude that the blast fungus has evolved distinct secretion systems to facilitate tissue invasion.
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Affiliation(s)
- Martha C. Giraldo
- Department of Plant Pathology, Kansas State University, Manhattan, Kansas 66506, USA
- These authors contributed equally to this work
| | - Yasin F. Dagdas
- School of Biosciences, University of Exeter, Exeter, EX4 4QD, UK
- These authors contributed equally to this work
| | - Yogesh K. Gupta
- School of Biosciences, University of Exeter, Exeter, EX4 4QD, UK
| | - Thomas A. Mentlak
- School of Biosciences, University of Exeter, Exeter, EX4 4QD, UK
- Present address: Cambridge Consultants Ltd, Cambridge, CB4 0DW, UK
| | - Mihwa Yi
- Department of Plant Pathology, Kansas State University, Manhattan, Kansas 66506, USA
| | - Ana Lilia Martinez-Rocha
- School of Biosciences, University of Exeter, Exeter, EX4 4QD, UK
- Present address: Department of Molecular Phytopathology and Genetics, University of Hamburg, Biozentrum Klein Flottbek, D-22609 Hamburg, Germany
| | - Hiromasa Saitoh
- Iwate Biotechnology Research Center, Kitakami, Iwate 024-0003, Japan
| | - Ryohei Terauchi
- Iwate Biotechnology Research Center, Kitakami, Iwate 024-0003, Japan
| | | | - Barbara Valent
- Department of Plant Pathology, Kansas State University, Manhattan, Kansas 66506, USA
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Bhadauria V, Banniza S, Vandenberg A, Selvaraj G, Wei Y. Peroxisomal alanine: glyoxylate aminotransferase AGT1 is indispensable for appressorium function of the rice blast pathogen, Magnaporthe oryzae. PLoS One 2012; 7:e36266. [PMID: 22558413 PMCID: PMC3338719 DOI: 10.1371/journal.pone.0036266] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2012] [Accepted: 04/04/2012] [Indexed: 11/18/2022] Open
Abstract
The role of β-oxidation and the glyoxylate cycle in fungal pathogenesis is well documented. However, an ambiguity still remains over their interaction in peroxisomes to facilitate fungal pathogenicity and virulence. In this report, we characterize a gene encoding an alanine, glyoxylate aminotransferase 1 (AGT1) in Magnaporthe oryzae, the causative agent of rice blast disease, and demonstrate that AGT1 is required for pathogenicity of M. oryzae. Targeted deletion of AGT1 resulted in the failure of penetration via appressoria; therefore, mutants lacking the gene were unable to induce blast symptoms on the hosts rice and barley. This penetration failure may be associated with a disruption in lipid mobilization during conidial germination as turgor generation in the appressorium requires mobilization of lipid reserves from the conidium. Analysis of enhanced green fluorescent protein expression using the transcriptional and translational fusion with the AGT1 promoter and open reading frame, respectively, revealed that AGT1 expressed constitutively in all in vitro grown cell types and during in planta colonization, and localized in peroxisomes. Peroxisomal localization was further confirmed by colocalization with red fluorescent protein fused with the peroxisomal targeting signal 1. Surprisingly, conidia produced by the Δagt1 mutant were unable to form appressoria on artificial inductive surfaces, even after prolonged incubation. When supplemented with nicotinamide adenine dinucleotide (NAD+)+pyruvate, appressorium formation was restored on an artificial inductive surface. Taken together, our data indicate that AGT1-dependent pyruvate formation by transferring an amino group of alanine to glyoxylate, an intermediate of the glyoxylate cycle is required for lipid mobilization and utilization. This pyruvate can be converted to non-fermentable carbon sources, which may require reoxidation of NADH generated by the β-oxidation of fatty acids to NAD+ in peroxisomes. Therefore, it may provide a means to maintain redox homeostasis in appressoria.
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Affiliation(s)
- Vijai Bhadauria
- Department of Biology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
- Crop Development Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Sabine Banniza
- Crop Development Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
- * E-mail: (SB); (YW)
| | - Albert Vandenberg
- Crop Development Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Gopalan Selvaraj
- Plant Biotechnology Institute, National Research Council of Canada, Saskatoon, Saskatchewan, Canada
| | - Yangdou Wei
- Department of Biology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
- * E-mail: (SB); (YW)
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Shimono M, Koga H, Akagi A, Hayashi N, Goto S, Sawada M, Kurihara T, Matsushita A, Sugano S, Jiang CJ, Kaku H, Inoue H, Takatsuji H. Rice WRKY45 plays important roles in fungal and bacterial disease resistance. Mol Plant Pathol 2012; 13:83-94. [PMID: 21726399 PMCID: PMC6638719 DOI: 10.1111/j.1364-3703.2011.00732.x] [Citation(s) in RCA: 138] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Plant 'activators', such as benzothiadiazole (BTH), protect plants from various diseases by priming the plant salicylic acid (SA) signalling pathway. We have reported previously that a transcription factor identified in rice, WRKY45 (OsWRKY45), plays a pivotal role in BTH-induced disease resistance by mediating SA signalling. Here, we report further functional characterization of WRKY45. Different plant activators vary in their action points, either downstream (BTH and tiadinil) or upstream (probenazole) of SA. Rice resistance to Magnaporthe grisea, induced by both types of plant activator, was markedly reduced in WRKY45-knockdown (WRKY45-kd) rice, indicating a universal role for WRKY45 in chemical-induced resistance. Fungal invasion into rice cells was blocked at most attempted invasion sites (pre-invasive defence) in WRKY45-overexpressing (WRKY45-ox) rice. Hydrogen peroxide accumulated within the cell wall underneath invading fungus appressoria or between the cell wall and the cytoplasm, implying a possible role for H(2)O(2) in pre-invasive defence. Moreover, a hypersensitive reaction-like reaction was observed in rice cells, in which fungal growth was inhibited after invasion (post-invasive defence). The two levels of defence mechanism appear to correspond to Type I and II nonhost resistances. The leaf blast resistance of WRKY45-ox rice plants was much higher than that of other known blast-resistant varieties. WRKY45-ox plants also showed strong panicle blast resistance. BTH-induced resistance to Xanthomonas oryzae pv. oryzae was compromised in WRKY45-kd rice, whereas WRKY45-ox plants were highly resistant to this pathogen. However, WRKY45-ox plants were susceptible to Rhizoctonia solani. These results indicate the versatility and limitations of the application of this gene.
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Affiliation(s)
- Masaki Shimono
- Disease Resistant Crops Research Unit, GMO Research Center, National Institute of Agrobiological Sciences, Kannondai 2-1-2, Tsukuba, Ibaraki 305-8602, Japan
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Saunders DG, Dagdas YF, Talbot NJ. Spatial uncoupling of mitosis and cytokinesis during appressorium-mediated plant infection by the rice blast fungus Magnaporthe oryzae. Plant Cell 2010; 22:2417-28. [PMID: 20639448 PMCID: PMC2929119 DOI: 10.1105/tpc.110.074492] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/03/2010] [Revised: 06/08/2010] [Accepted: 06/28/2010] [Indexed: 05/07/2023]
Abstract
To infect plants, many pathogenic fungi develop specialized infection structures called appressoria. Here, we report that appressorium development in the rice blast fungus Magnaporthe oryzae involves an unusual cell division, in which nuclear division is spatially uncoupled from the site of cytokinesis and septum formation. The position of the appressorium septum is defined prior to mitosis by formation of a heteromeric septin ring complex, which was visualized by spatial localization of Septin4:green fluorescent protein (GFP) and Septin5:GFP fusion proteins. Mitosis in the fungal germ tube is followed by long-distance nuclear migration and rapid formation of an actomyosin contractile ring in the neck of the developing appressorium, at a position previously marked by the septin complex. By contrast, mutants impaired in appressorium development, such as Deltapmk1 and DeltacpkA regulatory mutants, undergo coupled mitosis and cytokinesis within the germ tube. Perturbation of the spatial control of septation, by conditional mutation of the SEPTATION-ASSOCIATED1 gene of M. oryzae, prevented the fungus from causing rice blast disease. Overexpression of SEP1 did not affect septation during appressorium formation, but instead led to decoupling of nuclear division and cytokinesis in nongerminated conidial cells. When considered together, these results indicate that SEP1 is essential for determining the position and frequency of cell division sites in M. oryzae and demonstrate that differentiation of appressoria requires a cytokinetic event that is distinct from cell divisions within hyphae.
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Affiliation(s)
| | | | - Nicholas J. Talbot
- School of Biosciences, University of Exeter, Exeter EX4 4QD, United Kingdom
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Oh Y, Donofrio N, Pan H, Coughlan S, Brown DE, Meng S, Mitchell T, Dean RA. Transcriptome analysis reveals new insight into appressorium formation and function in the rice blast fungus Magnaporthe oryzae. Genome Biol 2008; 9:R85. [PMID: 18492280 PMCID: PMC2441471 DOI: 10.1186/gb-2008-9-5-r85] [Citation(s) in RCA: 144] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2007] [Revised: 03/18/2008] [Accepted: 05/20/2008] [Indexed: 11/22/2022] Open
Abstract
BACKGROUND Rice blast disease is caused by the filamentous Ascomycetous fungus Magnaporthe oryzae and results in significant annual rice yield losses worldwide. Infection by this and many other fungal plant pathogens requires the development of a specialized infection cell called an appressorium. The molecular processes regulating appressorium formation are incompletely understood. RESULTS We analyzed genome-wide gene expression changes during spore germination and appressorium formation on a hydrophobic surface compared to induction by cAMP. During spore germination, 2,154 (approximately 21%) genes showed differential expression, with the majority being up-regulated. During appressorium formation, 357 genes were differentially expressed in response to both stimuli. These genes, which we refer to as appressorium consensus genes, were functionally grouped into Gene Ontology categories. Overall, we found a significant decrease in expression of genes involved in protein synthesis. Conversely, expression of genes associated with protein and amino acid degradation, lipid metabolism, secondary metabolism and cellular transportation exhibited a dramatic increase. We functionally characterized several differentially regulated genes, including a subtilisin protease (SPM1) and a NAD specific glutamate dehydrogenase (Mgd1), by targeted gene disruption. These studies revealed hitherto unknown findings that protein degradation and amino acid metabolism are essential for appressorium formation and subsequent infection. CONCLUSION We present the first comprehensive genome-wide transcript profile study and functional analysis of infection structure formation by a fungal plant pathogen. Our data provide novel insight into the underlying molecular mechanisms that will directly benefit efforts to identify fungal pathogenicity factors and aid the development of new disease management strategies.
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Affiliation(s)
- Yeonyee Oh
- North Carolina State University, Center for Integrated Fungal Research, Raleigh, NC 27695-7251, USA
| | - Nicole Donofrio
- North Carolina State University, Center for Integrated Fungal Research, Raleigh, NC 27695-7251, USA
- Current address: University of Delaware, Department of Plant and Soil Science, Newark, DE 19716, USA
| | - Huaqin Pan
- North Carolina State University, Center for Integrated Fungal Research, Raleigh, NC 27695-7251, USA
- Current address: RTI international, Research Triangle Park, NC 27709-2194, USA
| | - Sean Coughlan
- Agilent Technologies, Little Falls, DE 19808-1644, USA
| | - Douglas E Brown
- North Carolina State University, Center for Integrated Fungal Research, Raleigh, NC 27695-7251, USA
| | - Shaowu Meng
- North Carolina State University, Center for Integrated Fungal Research, Raleigh, NC 27695-7251, USA
| | - Thomas Mitchell
- North Carolina State University, Center for Integrated Fungal Research, Raleigh, NC 27695-7251, USA
- Current address: Ohio State University, Department of Plant Pathology, Columbus, OH 43210, USA
| | - Ralph A Dean
- North Carolina State University, Center for Integrated Fungal Research, Raleigh, NC 27695-7251, USA
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Bae CY, Kim S, Choi WB, Lee YH. Involvement of extracellular matrix and integrin-like proteins on conidial adhesion and appressorium differentiation in Magnaporthe oryzae. J Microbiol Biotechnol 2007; 17:1198-1203. [PMID: 18051333] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Conidial adhesion and appressorium formation of Magnaporthe oryzae on the rice surface are important early events in the infection process. As an initiative step to understand the mechanisms underlying these cellular processes at a biochemical level, the effect of a human fibronectin antibody (HFA) and RGD peptides on conidial adhesion and appressorium formation was evaluated. HFA inhibited conidial adhesion and appressorium formation in a dosage-dependent manner. RGD peptides also inhibited these cellular events. Conidial adhesion and appressorium formation inhibited by RGD peptides were restored by chemicals involved in the cyclic AMP-dependent signaling pathway. These results suggest that extracellular matrix proteins might be involved in conidial adhesion and appressorium formation through integrin-like receptor mediation and modulation of cAMP-dependent signaling in the cells.
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Affiliation(s)
- Cheol-Yong Bae
- Department of Agricultural Biotechnology, Center for Fungal Genetic Resources, Seoul National University, Seoul 151-921, Korea
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Abstract
In order to cause disease in plants, many fungal pathogens develop a specialized structure called an appressorium. We have recently shown that the rice blast fungus Magnaporthe grisea undergoes a regulated form of programmed cell death during appressorium development involving autophagy. Significantly, this form of cell death is a prerequisite for plant infection and fungal pathogenesis and part of a growing body of evidence implicating autophagy as a key process in fungal developmental biology.
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Kankanala P, Czymmek K, Valent B. Roles for rice membrane dynamics and plasmodesmata during biotrophic invasion by the blast fungus. Plant Cell 2007; 19:706-24. [PMID: 17322409 PMCID: PMC1867340 DOI: 10.1105/tpc.106.046300] [Citation(s) in RCA: 377] [Impact Index Per Article: 22.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2006] [Revised: 01/05/2007] [Accepted: 01/30/2007] [Indexed: 05/14/2023]
Abstract
Rice blast disease is caused by the hemibiotrophic fungus Magnaporthe oryzae, which invades living plant cells using intracellular invasive hyphae (IH) that grow from one cell to the next. The cellular and molecular processes by which this occurs are not understood. We applied live-cell imaging to characterize the spatial and temporal development of IH and plant responses inside successively invaded rice (Oryza sativa) cells. Loading experiments with the endocytotic tracker FM4-64 showed dynamic plant membranes around IH. IH were sealed in a plant membrane, termed the extra-invasive hyphal membrane (EIHM), which showed multiple connections to peripheral rice cell membranes. The IH switched between pseudohyphal and filamentous growth. Successive cell invasions were biotrophic, although each invaded cell appeared to have lost viability when the fungus moved into adjacent cells. EIHM formed distinct membrane caps at the tips of IH that initially grew in neighboring cells. Time-lapse imaging showed IH scanning plant cell walls before crossing, and transmission electron microscopy showed IH preferentially contacting or crossing cell walls at pit fields. This and additional evidence strongly suggest that IH co-opt plasmodesmata for cell-to-cell movement. Analysis of biotrophic blast invasion will significantly contribute to our understanding of normal plant processes and allow the characterization of secreted fungal effectors that affect these processes.
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Affiliation(s)
- Prasanna Kankanala
- Department of Plant Pathology, Kansas State University, Manhattan, Kansas 66506, USA
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Abstract
Rice blast is caused by the fungus Magnaporthe grisea, which elaborates specialized infection cells called appressoria to penetrate the tough outer cuticle of the rice plant Oryza sativa. We found that the formation of an appressorium required, sequentially, the completion of mitosis, nuclear migration, and death of the conidium (fungal spore) from which the infection originated. Genetic intervention during mitosis prevented both appressorium development and conidium death. Impairment of autophagy, by the targeted mutation of the MgATG8 gene, arrested conidial cell death but rendered the fungus nonpathogenic. Thus, the initiation of rice blast requires autophagic cell death of the conidium.
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Affiliation(s)
- Claire Veneault-Fourrey
- School of Biosciences, University of Exeter, Washington Singer Laboratories, Perry Road, Exeter EX4 4QG, UK
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Moreno AB, Martínez Del Pozo A, San Segundo B. Biotechnologically relevant enzymes and proteins. Antifungal mechanism of the Aspergillus giganteus AFP against the rice blast fungus Magnaporthe grisea. Appl Microbiol Biotechnol 2006; 72:883-95. [PMID: 16557374 DOI: 10.1007/s00253-006-0362-1] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2005] [Revised: 01/25/2006] [Accepted: 01/31/2006] [Indexed: 10/24/2022]
Abstract
The mold Aspergillus giganteus produces a basic, low molecular weight protein showing antifungal properties against economically important plant pathogens, the AFP (Antifungal Protein). In this study, we investigated the mechanisms by which AFP exerts its antifungal activity against Magnaporthe grisea. M. grisea is the causal agent of rice blast, one of the most devastating diseases of cultivated rice worldwide. AFP was purified from the extracellular medium of A. giganteus cultures. The AFP protein was found to induce membrane permeabilization in M. grisea cells. Electron microscopy studies revealed severe cellular degradation and damage of plasma membranes in AFP-treated fungal cells. AFP however failed to induce membrane permeabilization on rice or human HeLa cells. Furthermore, AFP enters the fungal cell and targets to the nucleus, as revealed by co-localization experiments of Alexa-labeled AFP with the SYTOX Green dye. Finally, AFP binds to nucleic acids, including M. grisea DNA. Our results suggest that the combination of fungal cell permeabilization, cell-penetrating ability and nucleic acid-binding activity of AFP determines its potent antifungal activity against M. grisea. These results are discussed in relation to the potential of the AFP protein to enhance crop protection against fungal diseases.
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Affiliation(s)
- Ana Beatriz Moreno
- Laboratorio de Genética Molecular Vegetal, Consorcio CSIC-IRTA, Departamento de Genética Molecular, Instituto de Biología Molecular de Barcelona, CSIC, Jordi Girona 18, 08034, Barcelona, Spain
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Palková Z, Váchová L, Valer M, Preckel T. Single-cell analysis of yeast, mammalian cells, and fungal spores with a microfluidic pressure-driven chip-based system. Cytometry A 2004; 59:246-53. [PMID: 15170604 DOI: 10.1002/cyto.a.20049] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
BACKGROUND Cytomics aims at understanding the function of cellular systems by analysis of single cells. Recently, there has been a growing interest in single cell measurements being performed in microfluidic systems. These systems promise to integrate staining, measurement, and analysis in a single system. One important aspect is the limitation of allowable cell sizes due to microfluidic channel dimensions. Here we want to demonstrate the broad applicability of microfluidic chip technology for the analysis of many different cell types. METHODS We have developed a microfluidic chip and measurement system that allows flow cytometric analysis of fluorescently stained cells from different organisms. In this setup, the cells are moved by pressure-driven flow inside a network of microfluidic channels and are analyzed individually by fluorescence detection. RESULTS We have successfully applied the system to develop a methodology to detect viable and dead cells in yeast cell populations. Also, we have measured short interfering RNA (siRNA) mediated silencing of protein expression in mammalian cells. In addition, we have characterized the infection state of Magnaportae grisea fungal spores. CONCLUSIONS Results obtained with the microfluidic system demonstrate a broad applicability of microfluidic flow cytometry to measurement of various cell types.
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Affiliation(s)
- Zdena Palková
- Department of Genetics and Microbiology, Charles University, Prague, Czech Republic
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Abstract
Trimeric G-proteins transmit extracellular signals to various downstream effectors (e.g. MAP kinases) in eukaryotes. In the rice blast fungus Magnaporthe grisea, the Pmk1 MAP kinase is essential for appressorium formation and infectious growth. The pmk1 deletion mutant fails to form appressoria but still responds to exogenous cAMP for tip deformation. Since gene disruption mutants of three Galpha subunits still form appressoria and are phenotypically different from pmk1 mutants, it is likely that the Pmk1 pathway is activated by Gbeta in M. grisea. In this study, we isolated and characterized the MGB1 gene that encodes the G subunit in M. grisea. Mutants disrupted in MGB1 were reduced in conidiation. Conidia from mgb1 mutants were defective in appressorium formation and failed to penetrate or grow invasively on rice leaves. Exogenous cAMP induced appressorium formation in mgb1 mutants, but these appressoria were abnormal in shape and could not penetrate. The intracellular cAMP level was reduced in mgb1 mutants and the defects in conidiation and hyphal growth were partially suppressed with 1 mM cAMP. Transformants expressing multiple copies of MGB1 were able to form appressoria on hydrophilic surfaces. Our results suggest that MGB1 may be involved in the cAMP signalling for regulating conidiation, surface recognition and appressorium formation. The Pmk1 pathway may be the downstream target of MGB1 for regulating penetration and infectious hyphae growth in M. grisea.
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Affiliation(s)
- Marie Nishimura
- National Institute of Agrobiological Sciences, 2-1-2, Kan' non dai, Tsukuba, Ibaraki, 305-8602, Japan
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Abstract
The Magnaporthe grisea BUF1 gene suffers high-frequency mutation in certain genetic crosses, resulting in buff-colored progeny. Analysis of 16 buf1 mutants arising from a cross with a mutation frequency of 25% revealed that, in every case, the BUF1 gene was deleted. The deletions occurred in only one of the parental chromosomes and were due to intrachromosomal recombination. Tetrad analysis revealed that deletions occurred in 44% of meioses and usually affected both chromatids of the mutable chromosome. This suggests that they happen before the premeiotic round of DNA synthesis. However, they were also almost entirely restricted to heteroallelic crosses. This, together with the discovery of numerous repetitive elements that were present only in the mutable BUF1 locus, suggests that the deletion process is sensitive to pairing interactions between homologous chromosomes, such that only unpaired loci are subject to deletion. Given that karyogamy is not supposed to occur until after premeiotic DNA replication in Pyrenomycetous fungi such as M. grisea, this latter observation would place the time of deletion during, or after, DNA synthesis. These conflicting results suggest that karyogamy might actually precede DNA replication in Pyrenomycetous fungi or that parts of the genome remain unreplicated until after karyogamy and subsequent chromosome pairing have taken place.
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Affiliation(s)
- Mark L Farman
- Department of Plant Pathology, University of Kentucky, Lexington, Kentucky 40546, USA.
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Abstract
G protein signaling is commonly involved in regulating growth and differentiation of eukaryotic cells. We previously identified MAGB, encoding a Galpha subunit, from Magnaporthe grisea, and disruption of MAGB led to defects in a number of cellular responses, including appressorium formation, conidiation, sexual development, mycelial growth, and surface sensing. In this study, site-directed mutagenesis was used to further dissect the pleiotropic effects controlled by MAGB. Conversion of glycine 42 to arginine was predicted to abolish GTPase activity, which in turn would constitutively activate G protein signaling in magB(G42R). This dominant mutation caused autolysis of aged colonies, misscheduled melanization, reduction in both sexual and asexual reproduction, and reduced virulence. Furthermore, magB(G42R) mutants were able to produce appressoria on both hydrophobic and hydrophilic surfaces, although development on the hydrophilic surface was delayed. A second dominant mutation, magB(G203R) (glycine 203 converted to arginine), was expected to block dissociation of the Gbetagamma from the Galpha subunit, thus producing a constitutively inactive G protein complex. This mutation did not cause drastic phenotypic changes in the wild-type genetic background, other than increased sensitivity to repression of conidiation by osmotic stress. However, magB(G203R) is able to complement phenotypic defects in magB mutants. Comparative analyses of the phenotypical effects of different magB mutations are consistent with the involvement of the Gbetagamma subunit in the signaling pathways regulating cellular development in M. grisea.
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Affiliation(s)
- E G Fang
- Department of Plant Pathology and Physiology and Clemson University Genomics Institute, Clemson University, SC 29634, USA
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