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Wang H, Guo Y, Luo Z, Gao L, Li R, Zhang Y, Kalaji HM, Qiang S, Chen S. Recent Advances in Alternaria Phytotoxins: A Review of Their Occurrence, Structure, Bioactivity and Biosynthesis. J Fungi (Basel) 2022; 8:jof8020168. [PMID: 35205922 PMCID: PMC8878860 DOI: 10.3390/jof8020168] [Citation(s) in RCA: 24] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2021] [Revised: 02/06/2022] [Accepted: 02/07/2022] [Indexed: 12/04/2022] Open
Abstract
Alternaria is a ubiquitous fungal genus in many ecosystems, consisting of species and strains that can be saprophytic, endophytic, or pathogenic to plants or animals, including humans. Alternaria species can produce a variety of secondary metabolites (SMs), especially low molecular weight toxins. Based on the characteristics of host plant susceptibility or resistance to the toxin, Alternaria phytotoxins are classified into host-selective toxins (HSTs) and non-host-selective toxins (NHSTs). These Alternaria toxins exhibit a variety of biological activities such as phytotoxic, cytotoxic, and antimicrobial properties. Generally, HSTs are toxic to host plants and can cause severe economic losses. Some NHSTs such as alternariol, altenariol methyl-ether, and altertoxins also show high cytotoxic and mutagenic activities in the exposed human or other vertebrate species. Thus, Alternaria toxins are meaningful for drug and pesticide development. For example, AAL-toxin, maculosin, tentoxin, and tenuazonic acid have potential to be developed as bioherbicides due to their excellent herbicidal activity. Like altersolanol A, bostrycin, and brefeldin A, they exhibit anticancer activity, and ATX V shows high activity to inhibit the HIV-1 virus. This review focuses on the classification, chemical structure, occurrence, bioactivity, and biosynthesis of the major Alternaria phytotoxins, including 30 HSTs and 50 NHSTs discovered to date.
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Affiliation(s)
- He Wang
- Weed Research Laboratory, College of Life Science, Nanjing Agricultural University, Nanjing 210095, China; (H.W.); (Y.G.); (Z.L.); (L.G.); (Y.Z.); (S.Q.)
| | - Yanjing Guo
- Weed Research Laboratory, College of Life Science, Nanjing Agricultural University, Nanjing 210095, China; (H.W.); (Y.G.); (Z.L.); (L.G.); (Y.Z.); (S.Q.)
| | - Zhi Luo
- Weed Research Laboratory, College of Life Science, Nanjing Agricultural University, Nanjing 210095, China; (H.W.); (Y.G.); (Z.L.); (L.G.); (Y.Z.); (S.Q.)
| | - Liwen Gao
- Weed Research Laboratory, College of Life Science, Nanjing Agricultural University, Nanjing 210095, China; (H.W.); (Y.G.); (Z.L.); (L.G.); (Y.Z.); (S.Q.)
| | - Rui Li
- Agricultural and Animal Husbandry Ecology and Resource Protection Center, Ordos Agriculture and Animal Husbandry Bureau, Ordos 017010, China;
| | - Yaxin Zhang
- Weed Research Laboratory, College of Life Science, Nanjing Agricultural University, Nanjing 210095, China; (H.W.); (Y.G.); (Z.L.); (L.G.); (Y.Z.); (S.Q.)
| | - Hazem M. Kalaji
- Department of Plant Physiology, Institute of Biology, Warsaw University of Life Sciences SGGW, 159 Nowoursynowska 159, 02-776 Warsaw, Poland;
- Institute of Technology and Life Sciences—National Research Institute, Falenty, Al. Hrabska 3, 05-090 Raszyn, Poland
| | - Sheng Qiang
- Weed Research Laboratory, College of Life Science, Nanjing Agricultural University, Nanjing 210095, China; (H.W.); (Y.G.); (Z.L.); (L.G.); (Y.Z.); (S.Q.)
| | - Shiguo Chen
- Weed Research Laboratory, College of Life Science, Nanjing Agricultural University, Nanjing 210095, China; (H.W.); (Y.G.); (Z.L.); (L.G.); (Y.Z.); (S.Q.)
- Correspondence: ; Tel.: +86-25-84395117
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Wang Y, Wu J, Yan J, Guo M, Xu L, Hou L, Zou Q. Comparative genome analysis of plant ascomycete fungal pathogens with different lifestyles reveals distinctive virulence strategies. BMC Genomics 2022; 23:34. [PMID: 34996360 PMCID: PMC8740420 DOI: 10.1186/s12864-021-08165-1] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2021] [Accepted: 11/10/2021] [Indexed: 12/21/2022] Open
Abstract
BACKGROUND Pathogens have evolved diverse lifestyles and adopted pivotal new roles in both natural ecosystems and human environments. However, the molecular mechanisms underlying their adaptation to new lifestyles are obscure. Comparative genomics was adopted to determine distinct strategies of plant ascomycete fungal pathogens with different lifestyles and to elucidate their distinctive virulence strategies. RESULTS We found that plant ascomycete biotrophs exhibited lower gene gain and loss events and loss of CAZyme-encoding genes involved in plant cell wall degradation and biosynthesis gene clusters for the production of secondary metabolites in the genome. Comparison with the candidate effectome detected distinctive variations between plant biotrophic pathogens and other groups (including human, necrotrophic and hemibiotrophic pathogens). The results revealed the biotroph-specific and lifestyle-conserved candidate effector families. These data have been configured in web-based genome browser applications for public display ( http://lab.malab.cn/soft/PFPG ). This resource allows researchers to profile the genome, proteome, secretome and effectome of plant fungal pathogens. CONCLUSIONS Our findings demonstrated different genome evolution strategies of plant fungal pathogens with different lifestyles and explored their lifestyle-conserved and specific candidate effectors. It will provide a new basis for discovering the novel effectors and their pathogenic mechanisms.
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Affiliation(s)
- Yansu Wang
- School of Electronic and Communication Engineering, Shenzhen Polytechnic, 518000, Shenzhen, P. R. China
- Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China, 610054, Chengdu, P. R. China
| | - Jie Wu
- Key Laboratory of Biotechnology for Medicinal Plants of Jiangsu Province, School of Life Sciences, Jiangsu Normal University, 221116, Xuzhou, P. R. China
| | - Jiacheng Yan
- Key Laboratory of Biotechnology for Medicinal Plants of Jiangsu Province, School of Life Sciences, Jiangsu Normal University, 221116, Xuzhou, P. R. China
| | - Ming Guo
- Department of Agronomy and Horticulture, University of Nebraska, Lincoln, USA
| | - Lei Xu
- School of Electronic and Communication Engineering, Shenzhen Polytechnic, 518000, Shenzhen, P. R. China
| | - Liping Hou
- Beidahuang Industry Group General Hospital, Harbin, China.
| | - Quan Zou
- Institute of Fundamental and Frontier Sciences, University of Electronic Science and Technology of China, 610054, Chengdu, P. R. China.
- State Key Laboratory of Tree Genetics and Breeding, Northeast Forestry University, Harbin, China.
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Meena M, Samal S. Alternaria host-specific (HSTs) toxins: An overview of chemical characterization, target sites, regulation and their toxic effects. Toxicol Rep 2019; 6:745-758. [PMID: 31406682 PMCID: PMC6684332 DOI: 10.1016/j.toxrep.2019.06.021] [Citation(s) in RCA: 80] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2019] [Revised: 06/18/2019] [Accepted: 06/22/2019] [Indexed: 02/05/2023] Open
Abstract
Alternaria causes pathogenic disease on various economically important crops having saprophytic to endophytic lifecycle. Pathogenic fungi of Alternaria species produce many primary and secondary metabolites (SMs). Alternaria species produce more than 70 mycotoxins. Several species of Alternaria produce various phytotoxins that are host-specific (HSTs) and non-host-specific (nHSTs). These toxins have various negative impacts on cell organelles including chloroplast, mitochondria, plasma membrane, nucleus, Golgi bodies, etc. Non-host-specific toxins such as tentoxin (TEN), Alternaric acid, alternariol (AOH), alternariol 9-monomethyl ether (AME), brefeldin A (dehydro-), Alternuene (ALT), Altertoxin-I, Altertoxin-II, Altertoxin-III, zinniol, tenuazonic acid (TeA), curvularin and alterotoxin (ATX) I, II, III are known toxins produced by Alternaria species. In other hand, Alternaria species produce numerous HSTs such as AK-, AF-, ACT-, AM-, AAL- and ACR-toxin, maculosin, destruxin A, B, etc. are host-specific and classified into different family groups. These mycotoxins are low molecular weight secondary metabolites with various chemical structures. All the HSTs have different mode of actions, biochemical reactions, and signaling mechanisms to causes diseases in the host plants. These HSTs have devastating effects on host plant tissues by affecting biochemical and genetic modifications. Host-specific mycotoxins such as AK-toxin, AF-toxin, and AC-toxin have the devastating effect on plants which causes DNA breakage, cytotoxic, apoptotic cell death, interrupting plant physiology by mitochondrial oxidative phosphorylation and affect membrane permeability. This article will elucidate an understanding of the disease mechanism caused by several Alternaria HSTs on host plants and also the pathways of the toxins and how they caused disease in plants.
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Key Words
- 1O2, singlet oxygen
- AA, ascorbic acid
- ALT, alternuene
- AME, alternariol 9-monomethyl ether
- AOH, alternariol
- APX, ascorbate peroxidase
- ATX, alterotoxin
- Alternaria species
- CAT, catalase
- CDCs, conditionally dispensable chromosomes
- DHAR, dehydroascorbate reductase
- DHT, dihydrotentoxin
- GPX, guaiacol peroxidase
- GR, glutathione reductase
- GSH, glutathione
- H2O2, hydrogen peroxide
- HR, hypersensitive response
- HSTs, host specific toxins
- Host-specific toxins
- MDHAR, monodehydroascorbate reductase
- NO, nitric oxide
- NRPS, nonribosomal peptide synthetase
- Non-host-specific toxins
- O2˙ˉ, superoxide anion
- PCD, programmed cell death
- PKS, polyketide synthase gene
- Pathogenicity
- REMI, restriction enzyme-mediated integration
- ROS, reactive oxygen species
- SMs, secondary metabolites
- SOD, superoxide dismutase
- Secondary metabolites
- TEN, tentoxin
- TeA, tenuazonic acid
- UGT, UDP-Glucuronosyltransferases
- nHSTs, non-host specific toxins
- ˙OH, hydroxyl radical
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Affiliation(s)
- Mukesh Meena
- Department of Botany, University College of Science, Mohanlal Sukhadia University, Udaipur, 313001, India
- Centre of Advanced Study in Botany, Institute of Science, Banaras Hindu University, Varanasi, 221005, India
| | - Swarnmala Samal
- Centre of Advanced Study in Botany, Institute of Science, Banaras Hindu University, Varanasi, 221005, India
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Romero-Cortes T, Pérez España VH, López Pérez PA, Rodríguez-Jimenes GDC, Robles-Olvera VJ, Aparicio Burgos JE, Cuervo-Parra JA. Antifungal activity of vanilla juice and vanillin against Alternaria alternata. CYTA - JOURNAL OF FOOD 2019. [DOI: 10.1080/19476337.2019.1586776] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Affiliation(s)
- Teresa Romero-Cortes
- Escuela Superior de Apan, Universidad Autónoma del Estado de Hidalgo, Chimalpa Tlalayote, Hgo, Mexico
| | - Víctor Hugo Pérez España
- Escuela Superior de Apan, Universidad Autónoma del Estado de Hidalgo, Chimalpa Tlalayote, Hgo, Mexico
| | - Pablo Antonio López Pérez
- Escuela Superior de Apan, Universidad Autónoma del Estado de Hidalgo, Chimalpa Tlalayote, Hgo, Mexico
| | | | - Víctor J. Robles-Olvera
- Unidad de Investigación y Desarrollo en Alimentos, Instituto Tecnológico de Veracruz, Veracruz, Ver, Mexico
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Derbyshire MC, Gohari AM, Mehrabi R, Kilaru S, Steinberg G, Ali S, Bailey A, Hammond-Kosack K, Kema GHJ, Rudd JJ. Phosphopantetheinyl transferase (Ppt)-mediated biosynthesis of lysine, but not siderophores or DHN melanin, is required for virulence of Zymoseptoria tritici on wheat. Sci Rep 2018; 8:17069. [PMID: 30459352 PMCID: PMC6244202 DOI: 10.1038/s41598-018-35223-8] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2018] [Accepted: 10/30/2018] [Indexed: 12/19/2022] Open
Abstract
Zymoseptoria tritici is the causal agent of Septoria tritici blotch (STB) disease of wheat. Z. tritici is an apoplastic fungal pathogen, which does not penetrate plant cells at any stage of infection, and has a long initial period of symptomless leaf colonisation. During this phase it is unclear to what extent the fungus can access host plant nutrients or communicate with plant cells. Several important primary and secondary metabolite pathways in fungi are regulated by the post-translational activator phosphopantetheinyl transferase (Ppt) which provides an essential co-factor for lysine biosynthesis and the activities of non-ribosomal peptide synthases (NRPS) and polyketide synthases (PKS). To investigate the relative importance of lysine biosynthesis, NRPS-based siderophore production and PKS-based DHN melanin biosynthesis, we generated deletion mutants of ZtPpt. The ∆ZtPpt strains were auxotrophic for lysine and iron, non-melanised and non-pathogenic on wheat. Deletion of the three target genes likely affected by ZtPpt loss of function (Aar- lysine; Nrps1-siderophore and Pks1- melanin), highlighted that lysine auxotrophy was the main contributing factor for loss of virulence, with no reduction caused by loss of siderophore production or melanisation. This reveals Ppt, and the lysine biosynthesis pathway, as potential targets for fungicides effective against Z. tritici.
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Affiliation(s)
- Mark C Derbyshire
- BioIntercations and Crop Protection, Rothamsted Research, Harpenden, Hertfordshire, UK.,Centre for Crop and Disease Management, Curtin University, Perth, Australia
| | - Amir Mirzadi Gohari
- Department of Plant Pathology, Faculty of Agricultural Sciences and Engineering, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran.,Wageningen University and Research, Wageningen Plant Research, PO Box 16, 6700AA, Wageningen, The Netherlands
| | - Rahim Mehrabi
- Department of Biotechnology, College of Agriculture, Isfahan University of Technology, Isfahan, 84156-83111, Iran
| | | | | | - Solaf Ali
- Technical College of Health, Sulaimani Polytechnic University, Qrga, Wrme Street, Mardin 327, Alley 76, Sulaimaniyah, Kurdistan Region of Iraq, Sulaimani Governorate, Iraq
| | - Andy Bailey
- School of Biological Sciences, Bristol University, 24 Tyndall Avenue, Bristol, UK
| | - Kim Hammond-Kosack
- BioIntercations and Crop Protection, Rothamsted Research, Harpenden, Hertfordshire, UK
| | - Gert H J Kema
- Wageningen University and Research, Wageningen Plant Research, PO Box 16, 6700AA, Wageningen, The Netherlands. .,Wageningen University and Research, Laboratory of Phytopathology, PO box 16, 6700AA, Wageningen, The Netherlands.
| | - Jason J Rudd
- BioIntercations and Crop Protection, Rothamsted Research, Harpenden, Hertfordshire, UK.
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Petrov V, Qureshi MK, Hille J, Gechev T. Occurrence, biochemistry and biological effects of host-selective plant mycotoxins. Food Chem Toxicol 2017; 112:251-264. [PMID: 29288760 DOI: 10.1016/j.fct.2017.12.047] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2017] [Revised: 12/21/2017] [Accepted: 12/22/2017] [Indexed: 02/08/2023]
Abstract
Host-selective mycotoxins (HSTs) are various secondary metabolites or proteinaceous compounds secreted by pathogenic necrotrophic fungi that feed off on dead tissues of certain plants. Research on the HSTs has not only fundamental but also practical importance. On one hand they are implicated in the onset of devastating crop diseases. On the other hand, they have been studied as a good model for revealing the intricate mechanisms of plant-pathogen interactions. At the cellular level, HSTs target different compartments and in most instances induce programmed cell death (PCD) by a wide range of mechanisms. Often the responses provoked by HSTs resemble the effector-triggered immunity used by plant cells to combat biotrophic pathogens, which suggests that HST-producing fungi exploit the plants' own defensive systems to derive benefits. Although by definition HSTs are active only in tissues of susceptible plant genotypes, it has been demonstrated that some of them are able to influence animal cells as well. The possible effects, like cytotoxicity or cytostasis, can be harmful or beneficial and thus HSTs may either pose a health risk for humans and livestock, or be of prospective use in the fields of pharmacology, medicine and agriculture.
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Affiliation(s)
- Veselin Petrov
- Center of Plant Systems Biology and Biotechnology, 139 Ruski blvd., Plovdiv 4000, Bulgaria; Department of Plant Physiology and Biochemistry, Agricultural University, 12 Mendeleev str., Plovdiv 4000, Bulgaria.
| | - Muhammad Kamran Qureshi
- Department of Plant Breeding & Genetics, Faculty of Agricultural Sciences & Technology, Bahauddin Zakariya University, Bosan Road, 60800, Multan, Punjab, Pakistan.
| | - Jacques Hille
- Department of Pharmacy, University of Groningen, Antonius Deusinglaan 1, 9713 AV Groningen, The Netherlands.
| | - Tsanko Gechev
- Center of Plant Systems Biology and Biotechnology, 139 Ruski blvd., Plovdiv 4000, Bulgaria; Institute of Molecular Biology and Biotechnology, 105 Ruski blvd., Plovdiv 4000, Bulgaria; Department of Plant Physiology and Molecular Biology, Plovdiv University, 24 Tsar Assen str., Plovdiv 4000, Bulgaria.
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7
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Jacob S, Grötsch T, Foster AJ, Schüffler A, Rieger PH, Sandjo LP, Liermann JC, Opatz T, Thines E. Unravelling the biosynthesis of pyriculol in the rice blast fungus Magnaporthe oryzae. MICROBIOLOGY-SGM 2017; 163:541-553. [PMID: 27902426 DOI: 10.1099/mic.0.000396] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Pyriculol was isolated from the rice blast fungus Magnaporthe oryzae and found to induce lesion formation on rice leaves. These findings suggest that it could be involved in virulence. The gene MoPKS19 was identified to encode a polyketide synthase essential for the production of the polyketide pyriculol in the rice blast fungus M. oryzae. The transcript abundance of MoPKS19 correlates with the biosynthesis rate of pyriculol in a time-dependent manner. Furthermore, gene inactivation of MoPKS19 resulted in a mutant unable to produce pyriculol, pyriculariol and their dihydro derivatives. Inactivation of a putative oxidase-encoding gene MoC19OXR1, which was found to be located in the genome close to MoPKS19, resulted in a mutant exclusively producing dihydropyriculol and dihydropyriculariol. By contrast, overexpression of MoC19OXR1 resulted in a mutant strain only producing pyriculol. The MoPKS19 cluster, furthermore, comprises two transcription factors MoC19TRF1 and MoC19TRF2, which were both found individually to act as negative regulators repressing gene expression of MoPKS19. Additionally, extracts of ΔMopks19 and ΔMoC19oxr1 made from axenic cultures failed to induce lesions on rice leaves compared to extracts of the wild-type strain. Consequently, pyriculol and its isomer pyriculariol appear to be the only lesion-inducing secondary metabolites produced by M. oryzae wild-type (MoWT) under these culture conditions. Interestingly, the mutants unable to produce pyriculol and pyriculariol were as pathogenic as MoWT, demonstrating that pyriculol is not required for infection.
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Affiliation(s)
- Stefan Jacob
- Institut für Biotechnologie und Wirkstoff-Forschung gGmbH (IBWF), Erwin-Schrödinger Str. 56, D-67663 Kaiserslautern, Germany
| | - Thomas Grötsch
- Institut für Biotechnologie und Wirkstoff-Forschung gGmbH (IBWF), Erwin-Schrödinger Str. 56, D-67663 Kaiserslautern, Germany
| | - Andrew J Foster
- Institut für Biotechnologie und Wirkstoff-Forschung gGmbH (IBWF), Erwin-Schrödinger Str. 56, D-67663 Kaiserslautern, Germany
| | - Anja Schüffler
- Institut für Biotechnologie und Wirkstoff-Forschung gGmbH (IBWF), Erwin-Schrödinger Str. 56, D-67663 Kaiserslautern, Germany
| | - Patrick H Rieger
- Institut für Biotechnologie und Wirkstoff-Forschung gGmbH (IBWF), Erwin-Schrödinger Str. 56, D-67663 Kaiserslautern, Germany
| | - Louis P Sandjo
- Institute of Organic Chemistry, Johannes Gutenberg University of Mainz, Duesbergweg 10-14, D-55128 Mainz, Germany
| | - Johannes C Liermann
- Institute of Organic Chemistry, Johannes Gutenberg University of Mainz, Duesbergweg 10-14, D-55128 Mainz, Germany
| | - Till Opatz
- Institute of Organic Chemistry, Johannes Gutenberg University of Mainz, Duesbergweg 10-14, D-55128 Mainz, Germany
| | - Eckhard Thines
- Institut für Mikrobiologie und Weinforschung, Johannes Gutenberg University of Mainz, Johann-Joachim-Becherweg 15, D-55128 Mainz, Germany.,Institut für Biotechnologie und Wirkstoff-Forschung gGmbH (IBWF), Erwin-Schrödinger Str. 56, D-67663 Kaiserslautern, Germany
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Garganese F, Schena L, Siciliano I, Prigigallo MI, Spadaro D, De Grassi A, Ippolito A, Sanzani SM. Characterization of Citrus-Associated Alternaria Species in Mediterranean Areas. PLoS One 2016; 11:e0163255. [PMID: 27636202 PMCID: PMC5026349 DOI: 10.1371/journal.pone.0163255] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2016] [Accepted: 09/05/2016] [Indexed: 01/05/2023] Open
Abstract
Alternaria brown spot is one of the most important diseases of tangerines and their hybrids worldwide. Recently, outbreaks in Mediterranean areas related to susceptible cultivars, refocused attention on the disease. Twenty representatives were selected from a collection of 180 isolates of Alternaria spp. from citrus leaves and fruit. They were characterized along with reference strains of Alternaria spp. Micro- and macroscopic characteristics separated most Alternaria isolates into six morphotypes referable to A. alternata (5) and A. arborescens (1). Phylogenetic analyses, based on endopolygalacturonase (endopg) and internal transcribed spacer (ITS), confirmed this finding. Moreover, a five-gene phylogeny including two anonymous genomics regions (OPA 1-3 and OPA 2-1), and the beta-tubulin gene (ß-tub), produced a further clustering of A. alternata into three clades. This analysis suggested the existence of intra-species molecular variability. Investigated isolates showed different levels of virulence on leaves and fruit. In particular, the pathogenicity on fruit seemed to be correlated with the tissue of isolation and the clade. The toxigenic behavior of Alternaria isolates was also investigated, with tenuazonic acid (TeA) being the most abundant mycotoxin (0.2-20 mg/L). Isolates also synthesized the mycotoxins alternariol (AOH), its derivate alternariol monomethyl ether (AME), and altenuene (ALT), although to a lesser extent. AME production significantly varied among the six morphotypes. The expression of pksJ/pksH, biosynthetic genes of AOH/AME, was not correlated with actual toxin production, but it was significantly different between the two genotypes and among the four clades. Finally, ten isolates proved to express the biosynthetic genes of ACTT1 phytotoxin, and thus to be included in the Alternaria pathotype tangerine. A significant correlation between pathogenicity on leaves and ACTT1 gene expression was recorded. The latter was significantly dependent on geographical origin. The widespread occurrence of Alternaria spp. on citrus fruit and their ability to produce mycotoxins might represent a serious concern for producers and consumers.
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Affiliation(s)
- Francesca Garganese
- Dipartimento di Scienze del Suolo, della Pianta e degli Alimenti, Università degli Studi Aldo Moro, Bari, Italy
| | - Leonardo Schena
- Dipartimento di Agraria, Università Mediterranea, Reggio Calabria, Italy
| | - Ilenia Siciliano
- Centro di Competenza per l'Innovazione in campo agro-ambientale-AGROINNOVA, Università degli Studi di Torino, Grugliasco (TO), Italy
| | | | - Davide Spadaro
- Centro di Competenza per l'Innovazione in campo agro-ambientale-AGROINNOVA, Università degli Studi di Torino, Grugliasco (TO), Italy
- Dipartimento di Scienze Agrarie, Forestali e Alimentari, Università degli Studi di Torino, Grugliasco (TO), Italy
| | - Anna De Grassi
- Dipartimento di Bioscienze, Biotecnologie e Biofarmaceutica, Università degli Studi Aldo Moro, Bari, Italy
| | - Antonio Ippolito
- Dipartimento di Scienze del Suolo, della Pianta e degli Alimenti, Università degli Studi Aldo Moro, Bari, Italy
| | - Simona Marianna Sanzani
- Dipartimento di Scienze del Suolo, della Pianta e degli Alimenti, Università degli Studi Aldo Moro, Bari, Italy
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Leo AE, Linde CC, Ford R. Defence gene expression profiling to Ascochyta rabiei aggressiveness in chickpea. TAG. THEORETICAL AND APPLIED GENETICS. THEORETISCHE UND ANGEWANDTE GENETIK 2016; 129:1333-1345. [PMID: 27083569 DOI: 10.1007/s00122-016-2706-2] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/17/2015] [Accepted: 03/12/2016] [Indexed: 05/11/2023]
Abstract
Significant differences in defence pathway-related gene expression were observed among chickpea cultivars following A. rabiei infection. Differential gene expression is indicative of diverse resistances, a theoretical tool for selective breeding. A high number of Ascochyta rabiei pathotypes infecting chickpea in Australia has severely hampered efforts towards breeding for sustained quantitative resistance in chickpea. Breeding for sustained resistance will be aided by detailed knowledge of defence responses to isolates with different aggressiveness. As an initial step, the conserved and differential expressions of a suit of previously characterised genes known to be involved in fungal defence mechanisms were assessed among resistant and susceptible host genotypes following inoculation with high or low aggressive A. rabiei isolates. Using quantitative Real-Time PCR (qRT-PCR), 15 defence-related genes, normalised with two reference genes, were temporally differentially expressed (P < 0.005) as early as 2 h post inoculation of Genesis090 (resistant) or Kaniva (susceptible). The highly aggressive isolate, 09KAL09, induced vastly different expression profiles of eight key defence-related genes among resistant and susceptible genotypes. Six of these same genes were differentially expressed among ten host genotypes, inclusive of the best resistance sources within the Australian chickpea breeding program, indicating potential use for discrimination and selection of resistance "type" in future breeding pursuits.
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Affiliation(s)
- Audrey E Leo
- Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Melbourne, VIC, 3010, Australia
| | - Celeste C Linde
- Evolution, Ecology and Genetics, Research School of Biology, The Australian National University, 116 Daley Rd, Canberra, ACT, 2601, Australia
| | - Rebecca Ford
- School of Natural Sciences, Griffith University, Nathan Campus, Brisbane, QLD, 4111, Australia.
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Torres MF, Ghaffari N, Buiate EAS, Moore N, Schwartz S, Johnson CD, Vaillancourt LJ. A Colletotrichum graminicola mutant deficient in the establishment of biotrophy reveals early transcriptional events in the maize anthracnose disease interaction. BMC Genomics 2016; 17:202. [PMID: 26956617 PMCID: PMC4782317 DOI: 10.1186/s12864-016-2546-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2015] [Accepted: 02/26/2016] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Colletotrichum graminicola is a hemibiotrophic fungal pathogen that causes maize anthracnose disease. It progresses through three recognizable phases of pathogenic development in planta: melanized appressoria on the host surface prior to penetration; biotrophy, characterized by intracellular colonization of living host cells; and necrotrophy, characterized by host cell death and symptom development. A "Mixed Effects" Generalized Linear Model (GLM) was developed and applied to an existing Illumina transcriptome dataset, substantially increasing the statistical power of the analysis of C. graminicola gene expression during infection and colonization. Additionally, the in planta transcriptome of the wild-type was compared with that of a mutant strain impaired in the establishment of biotrophy, allowing detailed dissection of events occurring specifically during penetration, and during early versus late biotrophy. RESULTS More than 2000 fungal genes were differentially transcribed during appressorial maturation, penetration, and colonization. Secreted proteins, secondary metabolism genes, and membrane receptors were over-represented among the differentially expressed genes, suggesting that the fungus engages in an intimate and dynamic conversation with the host, beginning prior to penetration. This communication process probably involves reception of plant signals triggering subsequent developmental progress in the fungus, as well as production of signals that induce responses in the host. Later phases of biotrophy were more similar to necrotrophy, with increased production of secreted proteases, inducers of plant cell death, hydrolases, and membrane bound transporters for the uptake and egress of potential toxins, signals, and nutrients. CONCLUSIONS This approach revealed, in unprecedented detail, fungal genes specifically expressed during critical phases of host penetration and biotrophic establishment. Many encoded secreted proteins, secondary metabolism enzymes, and receptors that may play roles in host-pathogen communication necessary to promote susceptibility, and thus may provide targets for chemical or biological controls to manage this important disease. The differentially expressed genes could be used as 'landmarks' to more accurately identify developmental progress in compatible versus incompatible interactions involving genetic variants of both host and pathogen.
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Affiliation(s)
- Maria F Torres
- Department of Plant Pathology, University of Kentucky, 201F Plant Science Building, 1405 Veterans Drive, Lexington, KY, 40546-0312, USA.
- Present Address: Functional Genomics Laboratory, Weill Cornell Medical College, Cornell University, Qatar Foundation - Education City, Doha, Qatar.
| | - Noushin Ghaffari
- AgriLife Genomics and Bioinformatics, Texas A&M AgriLife Research, Texas A&M University, College Station, TX, 77845, USA.
| | - Ester A S Buiate
- Department of Plant Pathology, University of Kentucky, 201F Plant Science Building, 1405 Veterans Drive, Lexington, KY, 40546-0312, USA.
- Present Address: Monsanto Company Brazil, Uberlândia, Minas Gerais, Brazil.
| | - Neil Moore
- Department of Computer Science, University of Kentucky, Davis Marksbury Building, 328 Rose Street, Lexington, KY, 40506-0633, USA.
| | - Scott Schwartz
- AgriLife Genomics and Bioinformatics, Texas A&M AgriLife Research, Texas A&M University, College Station, TX, 77845, USA.
- Present Address: Department of Integrative Biology, University of Texas, Austin, TX, 78712, USA.
| | - Charles D Johnson
- AgriLife Genomics and Bioinformatics, Texas A&M AgriLife Research, Texas A&M University, College Station, TX, 77845, USA.
| | - Lisa J Vaillancourt
- Department of Plant Pathology, University of Kentucky, 201F Plant Science Building, 1405 Veterans Drive, Lexington, KY, 40546-0312, USA.
- Present Address: Department of Integrative Biology, University of Texas, Austin, TX, 78712, USA.
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12
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Pusztahelyi T, Holb IJ, Pócsi I. Secondary metabolites in fungus-plant interactions. FRONTIERS IN PLANT SCIENCE 2015; 6:573. [PMID: 26300892 PMCID: PMC4527079 DOI: 10.3389/fpls.2015.00573] [Citation(s) in RCA: 254] [Impact Index Per Article: 28.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/29/2015] [Accepted: 07/13/2015] [Indexed: 05/18/2023]
Abstract
Fungi and plants are rich sources of thousands of secondary metabolites. The genetically coded possibilities for secondary metabolite production, the stimuli of the production, and the special phytotoxins basically determine the microscopic fungi-host plant interactions and the pathogenic lifestyle of fungi. The review introduces plant secondary metabolites usually with antifungal effect as well as the importance of signaling molecules in induced systemic resistance and systemic acquired resistance processes. The review also concerns the mimicking of plant effector molecules like auxins, gibberellins and abscisic acid by fungal secondary metabolites that modulate plant growth or even can subvert the plant defense responses such as programmed cell death to gain nutrients for fungal growth and colonization. It also looks through the special secondary metabolite production and host selective toxins of some significant fungal pathogens and the plant response in form of phytoalexin production. New results coming from genome and transcriptional analyses in context of selected fungal pathogens and their hosts are also discussed.
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Affiliation(s)
- Tünde Pusztahelyi
- Central Laboratory, Faculty of Agricultural and Food Sciences and Environmental Management, University of DebrecenDebrecen, Hungary
| | - Imre J. Holb
- Faculty of Agricultural and Food Sciences and Environmental Management, Institute of Horticulture, University of DebrecenDebrecen, Hungary
- Department of Plant Pathology, Centre for Agricultural Research, Plant Protection Institute, Hungarian Academy of SciencesDebrecen, Hungary
| | - István Pócsi
- Department of Biotechnology and Microbiology, Faculty of Science and Technology, University of DebrecenDebrecen, Hungary
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Hatsugai N, Yamada K, Goto-Yamada S, Hara-Nishimura I. Vacuolar processing enzyme in plant programmed cell death. FRONTIERS IN PLANT SCIENCE 2015; 6:234. [PMID: 25914711 PMCID: PMC4390986 DOI: 10.3389/fpls.2015.00234] [Citation(s) in RCA: 123] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/11/2014] [Accepted: 03/24/2015] [Indexed: 05/19/2023]
Abstract
Vacuolar processing enzyme (VPE) is a cysteine proteinase originally identified as the proteinase responsible for the maturation and activation of vacuolar proteins in plants, and it is known to be an ortholog of animal asparaginyl endopeptidase (AEP/VPE/legumain). VPE has been shown to exhibit enzymatic properties similar to that of caspase 1, which is a cysteine protease that mediates the programmed cell death (PCD) pathway in animals. Although there is limited sequence identity between VPE and caspase 1, their predicted three-dimensional structures revealed that the essential amino-acid residues for these enzymes form similar pockets for the substrate peptide YVAD. In contrast to the cytosolic localization of caspases, VPE is localized in vacuoles. VPE provokes vacuolar rupture, initiating the proteolytic cascade leading to PCD in the plant immune response. It has become apparent that the VPE-dependent PCD pathway is involved not only in the immune response, but also in the responses to a variety of stress inducers and in the development of various tissues. This review summarizes the current knowledge on the contribution of VPE to plant PCD and its role in vacuole-mediated cell death, and it also compares VPE with the animal cell death executor caspase 1.
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Affiliation(s)
- Noriyuki Hatsugai
- Department of Plant Biology, Microbial and Plant Genomics Institute, University of MinnesotaSt. Paul, MN, USA
| | - Kenji Yamada
- Department of Botany, Graduate School of Science, Kyoto UniversityKyoto, Japan
| | - Shino Goto-Yamada
- Department of Botany, Graduate School of Science, Kyoto UniversityKyoto, Japan
| | - Ikuko Hara-Nishimura
- Department of Botany, Graduate School of Science, Kyoto UniversityKyoto, Japan
- *Correspondence: Ikuko Hara-Nishimura, Department of Botany, Graduate School of Science, Kyoto University, Kita-Shirakawa, Sakyo-ku, Kyoto 606-8502, Japan
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Tudzynski B. Nitrogen regulation of fungal secondary metabolism in fungi. Front Microbiol 2014; 5:656. [PMID: 25506342 PMCID: PMC4246892 DOI: 10.3389/fmicb.2014.00656] [Citation(s) in RCA: 170] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2014] [Accepted: 11/13/2014] [Indexed: 11/13/2022] Open
Abstract
Fungi occupy diverse environments where they are constantly challenged by stressors such as extreme pH, temperature, UV exposure, and nutrient deprivation. Nitrogen is an essential requirement for growth, and the ability to metabolize a wide variety of nitrogen sources enables fungi to colonize different environmental niches and survive nutrient limitations. Favored nitrogen sources, particularly ammonium and glutamine, are used preferentially, while the expression of genes required for the use of various secondary nitrogen sources is subject to a regulatory mechanism called nitrogen metabolite repression. Studies on gene regulation in response to nitrogen availability were carried out first in Saccharomyces cerevisiae, Aspergillus nidulans, and Neurospora crassa. These studies revealed that fungi respond to changes in nitrogen availability with physiological and morphological alterations and activation of differentiation processes. In all fungal species studied, the major GATA transcription factor AreA and its co-repressor Nmr are central players of the nitrogen regulatory network. In addition to growth and development, the quality and quantity of nitrogen also affects the formation of a broad range of secondary metabolites (SMs). Recent studies, mainly on species of the genus Fusarium, revealed that AreA does not only regulate a large set of nitrogen catabolic genes, but can also be involved in regulating production of SMs. Furthermore, several other regulators, e.g., a second GATA transcription factor, AreB, that was proposed to negatively control nitrogen catabolic genes by competing with AreA for binding to GATA elements, was shown to act as activator of some nitrogen-repressed as well as nitrogen-induced SM gene clusters. This review highlights our latest understanding of canonical (AreA-dependent) and non-canonical nitrogen regulation mechanisms by which fungi may regulate biosynthesis of certain SMs in response to nitrogen availability.
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Affiliation(s)
- Bettina Tudzynski
- Institute of Biology and Biotechnology of Plants, Westfaelische Wilhelms-University Muenster Muenster, Germany
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15
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Takaoka S, Kurata M, Harimoto Y, Hatta R, Yamamoto M, Akimitsu K, Tsuge T. Complex regulation of secondary metabolism controlling pathogenicity in the phytopathogenic fungus Alternaria alternata. THE NEW PHYTOLOGIST 2014; 202:1297-1309. [PMID: 24611558 DOI: 10.1111/nph.12754] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2013] [Accepted: 02/03/2014] [Indexed: 05/10/2023]
Abstract
The filamentous fungus Alternaria alternata includes seven pathogenic variants (pathotypes), which produce different host-selective toxins and cause disease on different plants. The Japanese pear, strawberry and tangerine pathotypes produce AK-toxin, AF-toxin and ACT-toxin, respectively, which have a common structural moiety, 9,10-epoxy-8-hydroxy-9-methyl-decatrienoic acid (EDA). Here, we identified a new gene, AKT7 (AK-toxin biosynthetic gene 7), from the Japanese pear pathotype, which encodes a cytochrome P450 monooxygenase and functions to limit AK-toxin production. AKT7 homologs were found in the strawberry pathotype, but not the tangerine pathotype. However, the strawberry pathotype homolog appeared to include a premature stop codon. Although the Japanese pear pathotype strain has multiple copies of AKT7, a single-copy disruption resulted in mutants with increased production of AK-toxin and EDA. AKT7 overexpression in the three pathotypes caused marked reductions of toxin and EDA production, suggesting that Akt7 catalyzes a side reaction of EDA or its precursor. AKT7 overexpression caused reduced virulence in these pathotypes. We also found that AKT7 transcripts predominantly include misspliced mRNAs, which have premature stop codons. Our observations suggest that the AK-toxin production required for full virulence is regulated in a complex way by the copy number and intron information content of AKT7.
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Affiliation(s)
- Shinya Takaoka
- Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Nagoya, 464-8601, Japan
| | - Mariko Kurata
- Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Nagoya, 464-8601, Japan
| | - Yoshiaki Harimoto
- Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Nagoya, 464-8601, Japan
| | - Rieko Hatta
- Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Nagoya, 464-8601, Japan
| | - Mikihiro Yamamoto
- Graduate School of Environmental and Life Science, Okayama University, Okayama, 700-8530, Japan
| | - Kazuya Akimitsu
- Faculty of Agriculture, Kagawa University, Miki, Kagawa, 761-0795, Japan
| | - Takashi Tsuge
- Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Nagoya, 464-8601, Japan
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Slavov S, Mayama S, Atanassov A. Toxin Production ofAlternaria AlternataTobacco Pathotype. BIOTECHNOL BIOTEC EQ 2014. [DOI: 10.1080/13102818.2004.10817126] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
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17
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Mase K, Ishihama N, Mori H, Takahashi H, Kaminaka H, Kodama M, Yoshioka H. Ethylene-responsive AP2/ERF transcription factor MACD1 participates in phytotoxin-triggered programmed cell death. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2013; 26:868-79. [PMID: 23617414 DOI: 10.1094/mpmi-10-12-0253-r] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
To investigate plant programmed cell death (PCD), we developed the model system using phytotoxin AAL, which is produced by necrotrophic pathogen Alternaria alternata f. sp. lycopersici, and AAL-sensitive Nicotiana umbratica. We previously reported that ethylene (ET) signaling plays a pivotal role in AAL-triggered cell death (ACD). However, downstream signaling of ET to ACD remains unclear. Here, we show that the modulator of AAL cell death 1 (MACD1), which is an APETALA2/ET response factor (ERF) transcription factor, participates in ACD and acts downstream of ET signaling during ACD. MACD1 is a transcriptional activator and MACD1 overexpression plants showed earlier ACD induction than control plants, suggesting that MACD1 positively regulates factors affecting cell death. To investigate the role of MACD1 in PCD, we used Arabidopsis thaliana and a structural analog of AAL, fumonisin B1 (FB1). FB1-triggered cell death was compromised in ET signaling and erf102 mutants. The loh2 mutants showed sensitivity to AAL, and the loh2-1/erf102 double mutant compromised ACD, indicating that ERF102 also participates in ACD. To investigate the PCD-associated genes regulated by ERF102, we compared our microarray data using ERF102 overexpression plants with the database of upregulated genes by AAL treatment in loh2 mutants, and found genes under the control of ERF102 in ACD.
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18
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Wiemann P, Sieber CMK, von Bargen KW, Studt L, Niehaus EM, Espino JJ, Huß K, Michielse CB, Albermann S, Wagner D, Bergner SV, Connolly LR, Fischer A, Reuter G, Kleigrewe K, Bald T, Wingfield BD, Ophir R, Freeman S, Hippler M, Smith KM, Brown DW, Proctor RH, Münsterkötter M, Freitag M, Humpf HU, Güldener U, Tudzynski B. Deciphering the cryptic genome: genome-wide analyses of the rice pathogen Fusarium fujikuroi reveal complex regulation of secondary metabolism and novel metabolites. PLoS Pathog 2013; 9:e1003475. [PMID: 23825955 PMCID: PMC3694855 DOI: 10.1371/journal.ppat.1003475] [Citation(s) in RCA: 321] [Impact Index Per Article: 29.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2013] [Accepted: 05/18/2013] [Indexed: 12/17/2022] Open
Abstract
The fungus Fusarium fujikuroi causes "bakanae" disease of rice due to its ability to produce gibberellins (GAs), but it is also known for producing harmful mycotoxins. However, the genetic capacity for the whole arsenal of natural compounds and their role in the fungus' interaction with rice remained unknown. Here, we present a high-quality genome sequence of F. fujikuroi that was assembled into 12 scaffolds corresponding to the 12 chromosomes described for the fungus. We used the genome sequence along with ChIP-seq, transcriptome, proteome, and HPLC-FTMS-based metabolome analyses to identify the potential secondary metabolite biosynthetic gene clusters and to examine their regulation in response to nitrogen availability and plant signals. The results indicate that expression of most but not all gene clusters correlate with proteome and ChIP-seq data. Comparison of the F. fujikuroi genome to those of six other fusaria revealed that only a small number of gene clusters are conserved among these species, thus providing new insights into the divergence of secondary metabolism in the genus Fusarium. Noteworthy, GA biosynthetic genes are present in some related species, but GA biosynthesis is limited to F. fujikuroi, suggesting that this provides a selective advantage during infection of the preferred host plant rice. Among the genome sequences analyzed, one cluster that includes a polyketide synthase gene (PKS19) and another that includes a non-ribosomal peptide synthetase gene (NRPS31) are unique to F. fujikuroi. The metabolites derived from these clusters were identified by HPLC-FTMS-based analyses of engineered F. fujikuroi strains overexpressing cluster genes. In planta expression studies suggest a specific role for the PKS19-derived product during rice infection. Thus, our results indicate that combined comparative genomics and genome-wide experimental analyses identified novel genes and secondary metabolites that contribute to the evolutionary success of F. fujikuroi as a rice pathogen.
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Affiliation(s)
- Philipp Wiemann
- Institut für Biologie und Biotechnologie der Pflanzen, Molecular Biology and Biotechnology of Fungi, Westfälische Wilhelms-Universität Münster, Münster, Germany
| | - Christian M. K. Sieber
- Institute of Bioinformatics and Systems Biology, Helmholtz Zentrum München, German Research Center for Environmental Health (GmbH), Neuherberg, Germany
| | - Katharina W. von Bargen
- Institute for Food Chemistry, Westfälische Wilhelms-Universität Münster, Corrensstraße 45, Münster, Germany
| | - Lena Studt
- Institut für Biologie und Biotechnologie der Pflanzen, Molecular Biology and Biotechnology of Fungi, Westfälische Wilhelms-Universität Münster, Münster, Germany
- Institute for Food Chemistry, Westfälische Wilhelms-Universität Münster, Corrensstraße 45, Münster, Germany
| | - Eva-Maria Niehaus
- Institut für Biologie und Biotechnologie der Pflanzen, Molecular Biology and Biotechnology of Fungi, Westfälische Wilhelms-Universität Münster, Münster, Germany
| | - Jose J. Espino
- Institut für Biologie und Biotechnologie der Pflanzen, Molecular Biology and Biotechnology of Fungi, Westfälische Wilhelms-Universität Münster, Münster, Germany
| | - Kathleen Huß
- Institut für Biologie und Biotechnologie der Pflanzen, Molecular Biology and Biotechnology of Fungi, Westfälische Wilhelms-Universität Münster, Münster, Germany
| | - Caroline B. Michielse
- Institut für Biologie und Biotechnologie der Pflanzen, Molecular Biology and Biotechnology of Fungi, Westfälische Wilhelms-Universität Münster, Münster, Germany
| | - Sabine Albermann
- Institut für Biologie und Biotechnologie der Pflanzen, Molecular Biology and Biotechnology of Fungi, Westfälische Wilhelms-Universität Münster, Münster, Germany
| | - Dominik Wagner
- Institut für Biologie und Biotechnologie der Pflanzen, Molecular Biology and Biotechnology of Fungi, Westfälische Wilhelms-Universität Münster, Münster, Germany
| | - Sonja V. Bergner
- Institut für Biologie und Biotechnologie der Pflanzen, Plant Biochemistry and Biotechnology, Westfälische Wilhelms-Universität Münster, Münster, Germany
| | - Lanelle R. Connolly
- Department of Biochemistry and Biophysics, Center for Genome Research and Biocomputing, Oregon State University, Corvallis, Oregon, United States of America
| | - Andreas Fischer
- Institut of Genetics/Developmental Genetics, Martin-Luther-Universität Halle-Wittenberg, Halle, Germany
| | - Gunter Reuter
- Institut of Genetics/Developmental Genetics, Martin-Luther-Universität Halle-Wittenberg, Halle, Germany
| | - Karin Kleigrewe
- Institute for Food Chemistry, Westfälische Wilhelms-Universität Münster, Corrensstraße 45, Münster, Germany
| | - Till Bald
- Institut für Biologie und Biotechnologie der Pflanzen, Plant Biochemistry and Biotechnology, Westfälische Wilhelms-Universität Münster, Münster, Germany
| | - Brenda D. Wingfield
- Department of Genetics, University of Pretoria, Hatfield, Pretoria, South Africa
| | - Ron Ophir
- Institute of Plant Sciences, Genomics, Agricultural Research Organization (ARO), The Volcani Center, Bet-Dagan, Israel
| | - Stanley Freeman
- Department of Plant Pathology, Agricultural Research Organization (ARO), The Volcani Center, Bet-Dagan, Israel
| | - Michael Hippler
- Institut für Biologie und Biotechnologie der Pflanzen, Plant Biochemistry and Biotechnology, Westfälische Wilhelms-Universität Münster, Münster, Germany
| | - Kristina M. Smith
- Department of Biochemistry and Biophysics, Center for Genome Research and Biocomputing, Oregon State University, Corvallis, Oregon, United States of America
| | - Daren W. Brown
- National Center for Agricultural Utilization Research, United States Department of Agriculture, Peoria, Illinois, United States of America
| | - Robert H. Proctor
- National Center for Agricultural Utilization Research, United States Department of Agriculture, Peoria, Illinois, United States of America
| | - Martin Münsterkötter
- Institute of Bioinformatics and Systems Biology, Helmholtz Zentrum München, German Research Center for Environmental Health (GmbH), Neuherberg, Germany
| | - Michael Freitag
- Department of Biochemistry and Biophysics, Center for Genome Research and Biocomputing, Oregon State University, Corvallis, Oregon, United States of America
| | - Hans-Ulrich Humpf
- Institute for Food Chemistry, Westfälische Wilhelms-Universität Münster, Corrensstraße 45, Münster, Germany
| | - Ulrich Güldener
- Institute of Bioinformatics and Systems Biology, Helmholtz Zentrum München, German Research Center for Environmental Health (GmbH), Neuherberg, Germany
| | - Bettina Tudzynski
- Institut für Biologie und Biotechnologie der Pflanzen, Molecular Biology and Biotechnology of Fungi, Westfälische Wilhelms-Universität Münster, Münster, Germany
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Tsuge T, Harimoto Y, Akimitsu K, Ohtani K, Kodama M, Akagi Y, Egusa M, Yamamoto M, Otani H. Host-selective toxins produced by the plant pathogenic fungusAlternaria alternata. FEMS Microbiol Rev 2013; 37:44-66. [DOI: 10.1111/j.1574-6976.2012.00350.x] [Citation(s) in RCA: 247] [Impact Index Per Article: 22.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2011] [Revised: 06/14/2012] [Accepted: 07/19/2012] [Indexed: 12/19/2022] Open
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20
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Manning VA, Pandelova I, Dhillon B, Wilhelm LJ, Goodwin SB, Berlin AM, Figueroa M, Freitag M, Hane JK, Henrissat B, Holman WH, Kodira CD, Martin J, Oliver RP, Robbertse B, Schackwitz W, Schwartz DC, Spatafora JW, Turgeon BG, Yandava C, Young S, Zhou S, Zeng Q, Grigoriev IV, Ma LJ, Ciuffetti LM. Comparative genomics of a plant-pathogenic fungus, Pyrenophora tritici-repentis, reveals transduplication and the impact of repeat elements on pathogenicity and population divergence. G3 (BETHESDA, MD.) 2013; 3:41-63. [PMID: 23316438 PMCID: PMC3538342 DOI: 10.1534/g3.112.004044] [Citation(s) in RCA: 129] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/16/2012] [Accepted: 11/02/2012] [Indexed: 12/31/2022]
Abstract
Pyrenophora tritici-repentis is a necrotrophic fungus causal to the disease tan spot of wheat, whose contribution to crop loss has increased significantly during the last few decades. Pathogenicity by this fungus is attributed to the production of host-selective toxins (HST), which are recognized by their host in a genotype-specific manner. To better understand the mechanisms that have led to the increase in disease incidence related to this pathogen, we sequenced the genomes of three P. tritici-repentis isolates. A pathogenic isolate that produces two known HSTs was used to assemble a reference nuclear genome of approximately 40 Mb composed of 11 chromosomes that encode 12,141 predicted genes. Comparison of the reference genome with those of a pathogenic isolate that produces a third HST, and a nonpathogenic isolate, showed the nonpathogen genome to be more diverged than those of the two pathogens. Examination of gene-coding regions has provided candidate pathogen-specific proteins and revealed gene families that may play a role in a necrotrophic lifestyle. Analysis of transposable elements suggests that their presence in the genome of pathogenic isolates contributes to the creation of novel genes, effector diversification, possible horizontal gene transfer events, identified copy number variation, and the first example of transduplication by DNA transposable elements in fungi. Overall, comparative analysis of these genomes provides evidence that pathogenicity in this species arose through an influx of transposable elements, which created a genetically flexible landscape that can easily respond to environmental changes.
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Affiliation(s)
- Viola A. Manning
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon 97331
| | - Iovanna Pandelova
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon 97331
| | - Braham Dhillon
- Department of Forest Sciences, University of British Columbia, Vancouver, British Columbia, Canada, V6T 1Z4
| | - Larry J. Wilhelm
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon 97331
- Carbone/Ferguson Laboratories, Division of Neuroscience, Oregon National Primate Research Center (ONPRC), Beaverton, Oregon 97006
| | - Stephen B. Goodwin
- USDA–Agricultural Research Service, Purdue University, West Lafayette, Indiana 47907
| | | | - Melania Figueroa
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon 97331
- USDA-Agricultural Research Service, Forage Seed and Cereal Research Unit, Oregon State University, Corvallis, Oregon 97331
| | - Michael Freitag
- Department of Biochemistry and Biophysics, Oregon State University, Corvallis, Oregon 97331
- Center for Genome Research and Biocomputing, Oregon State University, Corvallis, Oregon 97331
| | - James K. Hane
- Commonwealth Scientific and Industrial Research Organization−Plant Industry, Centre for Environment and Life Sciences, Floreat, Western Australia 6014, Australia
| | - Bernard Henrissat
- Architecture et Fonction des Macromolécules Biologiques, Aix-Marseille Université, Centre National de la Recherche Scientifique, 13288 Marseille cedex 9, France
| | - Wade H. Holman
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon 97331
| | - Chinnappa D. Kodira
- The Broad Institute, Cambridge, Massachusetts 02142
- Roche 454, Branford, Connecticut 06405
| | - Joel Martin
- US DOE Joint Genome Institute, Walnut Creek, California 94598
| | - Richard P. Oliver
- Australian Centre for Necrotrophic Fungal Pathogens, Department of Environment and Agriculture, Curtin University, Bentley, Western Australia 6845, Australia
| | - Barbara Robbertse
- Architecture et Fonction des Macromolécules Biologiques, Aix-Marseille Université, Centre National de la Recherche Scientifique, 13288 Marseille cedex 9, France
| | | | - David C. Schwartz
- Laboratory for Molecular and Computational Genomics, Department of Chemistry, Laboratory of Genetics, UW Biotechnology Center, University of Wisconsin–Madison, Madison, Wisconsin 53706
| | - Joseph W. Spatafora
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon 97331
| | - B. Gillian Turgeon
- Department of Plant Pathology and Plant-Microbe Biology, Cornell University, Ithaca, New York 14850
| | | | - Sarah Young
- The Broad Institute, Cambridge, Massachusetts 02142
| | - Shiguo Zhou
- Laboratory for Molecular and Computational Genomics, Department of Chemistry, Laboratory of Genetics, UW Biotechnology Center, University of Wisconsin–Madison, Madison, Wisconsin 53706
| | | | | | - Li-Jun Ma
- The Broad Institute, Cambridge, Massachusetts 02142
- Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, Massachusetts 01003
| | - Lynda M. Ciuffetti
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon 97331
- Center for Genome Research and Biocomputing, Oregon State University, Corvallis, Oregon 97331
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Rotondo F, Collina M, Brunelli A, Pryor BM. Comparison of Alternaria spp. collected in Italy from apple with A. mali and other AM-toxin producing strains. PHYTOPATHOLOGY 2012; 102:1130-1142. [PMID: 22934716 DOI: 10.1094/phyto-04-12-0076-r] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Since 1999, a disease of apple caused by an Alternaria sp. has been affecting orchards in northern Italy resulting in necrotic spots on leaves and on fruit. Forty-four single-spored isolates were obtained from diseased plant materials to investigate the diversity of this fungus in Italy and to compare these isolates to isolates of Alternaria associated with apple disease in previous studies, including A. mali, causal agent of apple blotch. All isolates, including the reference strains, were tested for pathogenicity utilizing in vitro bioassays on detached leaf or on fruit ('Golden Delicious'). In addition, morphological characterizations were conducted describing both the three-dimensional sporulation pattern and the colony morphology of each isolate. In order to assess the genetic diversity within the Italian Alternaria population, sequence characterization of specific loci and anonymous regions (endoPG, OPA1-3, OPA2-1, and OPA10-2) and genetic fingerprinting based on amplified fragment length polymorphism and inter simple sequence repeat markers were performed. The single spore isolates exhibited differential pathogenicity, which did not correlate with the morphological groupings or to groupings defined by molecular approaches. Moreover, 10 pathogenic isolates out of the 44 single-spored tested were positive for the host-specific AM-toxin gene based upon polymerase chain reaction amplification using specific primers for the AM-toxin gene. This suggests that the production of the AM-toxin may be involved in pathogenesis by some of the Italian isolates of A. alternata from apple. However, this research also suggests that a number of different Alternaria genotypes and morphotypes may be responsible for the apple disease in Italy and that a single taxon cannot be defined as the sole causal agent.
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Affiliation(s)
- F Rotondo
- Department of Agri-food Protection and Improvement, Studiorum University of Bologna, Italy
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Clergeot PH, Schuler H, Mørtz E, Brus M, Vintila S, Ekengren S. The corky root rot pathogen Pyrenochaeta lycopersici secretes a proteinaceous inducer of cell death affecting host plants differentially. PHYTOPATHOLOGY 2012; 102:878-891. [PMID: 22708726 DOI: 10.1094/phyto-01-12-0004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Pathogenic isolates of Pyrenochaeta lycopersici, the causal agent of corky root rot of tomato, secrete cell death in tomato 1 (CDiT1), a homodimeric protein of 35 kDa inducing cell death after infiltration into the leaf apoplast of tomato. CDiT1 was purified by fast protein liquid chromatography, characterized by mass spectrometry and cDNA cloning. Its activity was confirmed after infiltration of an affinity-purified recombinant fusion of the protein with a C-terminal polyhistidine tag. CDiT1 is highly expressed during tomato root infection compared with axenic culture, and has a putative ortholog in other pathogenic Pleosporales species producing proteinaceous toxins that contribute to virulence. Infiltration of CDiT1 into leaves of other plants susceptible to P. lycopersici revealed that the protein affects them differentially. All varieties of cultivated tomato (Solanum lycopersicum) tested were more sensitive to CDiT1 than those of currant tomato (S. pimpinellifolium). Root infection assays showed that varieties of currant tomato are also significantly less prone to intracellular colonization of their root cells by hyphae of P. lycopersici than varieties of cultivated tomato. Therefore, secretion of this novel type of inducer of cell death during penetration of the fungus inside root cells might favor infection of host species that are highly sensitive to this molecule.
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Mase K, Mizuno T, Ishihama N, Fujii T, Mori H, Kodama M, Yoshioka H. Ethylene signaling pathway and MAPK cascades are required for AAL toxin-induced programmed cell death. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2012; 25:1015-25. [PMID: 22512379 DOI: 10.1094/mpmi-02-12-0036-r] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Programmed cell death (PCD), known as hypersensitive response cell death, has an important role in plant defense response. The signaling pathway of PCD remains unknown. We employed AAL toxin and Nicotiana umbratica to analysis plant PCD. AAL toxin is a pathogenicity factor of the necrotrophic pathogen Alternaria alternata f. sp. lycopersici. N. umbratica is sensitive to AAL toxin, susceptible to pathogens, and effective in Tobacco rattle virus-based virus-induced gene silencing (VIGS). VIGS analyses indicated that AAL toxin-triggered cell death (ACD) is dependent upon the mitogen-activated protein (MAP) kinase kinase MEK2, which is upstream of both salicylic acid-induced protein kinase (SIPK) and wound-induced protein kinase (WIPK) responsible for ethylene (ET) synthesis. ET treatment of MEK2-silenced N. umbratica re-established ACD. In SIPK- and WIPK-silenced N. umbratica, ACD was compromised and ET accumulation was not observed. However, in contrast to the case of MEK2-silenced plants, ET treatment did not induce cell death in SIPK- and WIPK-silenced plants. This work showed that ET-dependent pathway and MAP kinase cascades are required in ACD. Our results suggested that MEK2-SIPK/WIPK cascades have roles in ET biosynthesis; however, SIPK and WIPK have other roles in ET signaling or another pathway leading to cell death by AAL toxin.
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Genomic characterization of the conditionally dispensable chromosome in Alternaria arborescens provides evidence for horizontal gene transfer. BMC Genomics 2012; 13:171. [PMID: 22559316 PMCID: PMC3443068 DOI: 10.1186/1471-2164-13-171] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2011] [Accepted: 03/08/2012] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Fungal plant pathogens cause serious agricultural losses worldwide. Alternaria arborescens is a major pathogen of tomato, with its virulence determined by the presence of a conditionally dispensable chromosome (CDC) carrying host-specific toxin genes. Genes encoding these toxins are well-studied, however the genomic content and organization of the CDC is not known. RESULTS To gain a richer understanding of the molecular determinants of virulence and the evolution of pathogenicity, we performed whole genome sequencing of A. arborescens. Here we present the de-novo assembly of the CDC and its predicted gene content. Also presented is hybridization data validating the CDC assembly. Predicted genes were functionally annotated through BLAST. Gene ontology terms were assigned, and conserved domains were identified. Differences in nucleotide usage were found between CDC genes and those on the essential chromosome (EC), including GC3-content, codon usage bias, and repeat region load. Genes carrying PKS and NRPS domains were identified in clusters on the CDC and evidence supporting the origin of the CDC through horizontal transfer from an unrelated fungus was found. CONCLUSIONS We provide evidence supporting the hypothesis that the CDC in A. arborescens was acquired through horizontal transfer, likely from an unrelated fungus. We also identified several predicted CDC genes under positive selection that may serve as candidate virulence factors.
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Zhao J, Li S, Jiang T, Liu Z, Zhang W, Jian G, Qi F. Chilling stress--the key predisposing factor for causing Alternaria alternata infection and leading to cotton (Gossypium hirsutum L.) leaf senescence. PLoS One 2012; 7:e36126. [PMID: 22558354 PMCID: PMC3338599 DOI: 10.1371/journal.pone.0036126] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2012] [Accepted: 03/26/2012] [Indexed: 11/19/2022] Open
Abstract
Leaf senescence plays a vital role in nutrient recycling and overall capacity to assimilate carbon dioxide. Cotton premature leaf senescence, often accompanied with unexpected short-term low temperature, has been occurring with an increasing frequency in many cotton-growing areas and causes serious reduction in yield and quality of cotton. The key factors for causing and promoting cotton premature leaf senescence are still unclear. In this case, the relationship between the pre-chilling stress and Alternaria alternata infection for causing cotton leaf senescence was investigated under precisely controlled laboratory conditions with four to five leaves stage cotton plants. The results showed short-term chilling stress could cause a certain degree of physiological impairment to cotton leaves, which could be recovered to normal levels in 2-4 days when the chilling stresses were removed. When these chilling stress injured leaves were further inoculated with A. alternata, the pronounced appearance and development of leaf spot disease, and eventually the pronounced symptoms of leaf senescence, occurred on these cotton leaves. The onset of cotton leaf senescence at this condition was also reflected in various physiological indexes such as irreversible increase in malondialdehyde (MDA) content and electrolyte leakage, irreversible decrease in soluble protein content and chlorophyll content, and irreversible damage in leaves' photosynthesis ability. The presented results demonstrated that chilling stress acted as the key predisposing factor for causing A. alternata infection and leading to cotton leaf senescence. It could be expected that the understanding of the key factors causing and promoting cotton leaf senescence would be helpful for taking appropriate management steps to prevent cotton premature leaf senescence.
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Affiliation(s)
- Jingqing Zhao
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, People's Republic of China
| | - Sha Li
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, People's Republic of China
| | - Tengfei Jiang
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, People's Republic of China
| | - Zhi Liu
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, People's Republic of China
| | - Wenwei Zhang
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, People's Republic of China
| | - Guiliang Jian
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, People's Republic of China
| | - Fangjun Qi
- State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, People's Republic of China
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Differential transcript accumulation in chickpea during early phases of compatible interaction with a necrotrophic fungus Ascochyta rabiei. Mol Biol Rep 2011; 39:4635-46. [PMID: 21956755 DOI: 10.1007/s11033-011-1255-7] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2011] [Accepted: 09/14/2011] [Indexed: 12/18/2022]
Abstract
The initial phases of the disease establishment are very crucial for the compatible interactions. Pathogens must overcome the responses generated by the host for the onset of disease invasion. The compatible interaction is inadequately represented in plant-pathogen interaction studies. To gain broader insight into the early responses elicited by chickpea blight fungus Ascochyta rabiei during compatible interaction; we isolated early responsive genes of chickpea using PCR based suppression subtractive hybridization (SSH) strategy. We obtained ~250 unique genes after homology search and redundancy elimination. Based on their potential cellular functions, these genes were broadly classified into eleven different categories viz. stress, signaling, gene regulation, cellular metabolism and genes of unknown functions. Present study revealed few unexpected genes which have a possible role in induced immunity and disease progression. We employed macroarray, northern blot, real-time PCR and cluster analysis to develop transcript profiles. Most of the genes analyzed were early induced and were transcriptionally upregulated upon 24 h post inoculation. Our approach has rendered the isolation of early responsive genes involved in signaling and regulation of metabolic changes upon fungal infection. The information obtained will help to dissect the molecular mechanisms during compatible chickpea-Ascochyta interactions.
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Lin TC, Fan MC, Wang SY, Huang JW. Identification of the Solanum nigrum extract component involved in controlling cabbage black leaf spot disease. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 2011; 59:1667-1672. [PMID: 21294509 DOI: 10.1021/jf103698b] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
In this study, we discovered that an ethanol (EtOH) extract of Solanum nigrum inhibited spore germination of Alternaria brassicicola, the causative agent of cabbage black leaf spot disease. At a concentration of 500 mg/L, this ethanol extract also caused the germ tubes to become completely swollen. Detached cabbage leaves were then used to evaluate the effects of the extract in controlling the disease. It was observed that the extract-induced swelling of A. brassicicola germ-tube spores did not cause the symptoms of black spot disease on cabbage leaves. Furthermore, an n-butanol fraction of the EtOH extract exhibited strong antifungal activity; at a concentration of 25 mg/L, a derived subfraction (Bu-11-13) showed complete inhibition of spore germination. A white powder was collected from fraction Bu-11-13, and its minimum inhibitory concentration was determined to be 8 mg/L. Using NMR and LC-MS/MS analysis, this white powder compound was identified as degalactotigonin.
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Affiliation(s)
- Tsung-Chun Lin
- Department of Plant Pathology and ‡Department of Forestry, National Chung Hsing University, Taichung 402, Taiwan
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28
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Sánchez-Rangel D, Plasencia J. The role of sphinganine analog mycotoxins on the virulence of plant pathogenic fungi. TOXIN REV 2010. [DOI: 10.3109/15569543.2010.515370] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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Horizontal chromosome transfer, a mechanism for the evolution and differentiation of a plant-pathogenic fungus. EUKARYOTIC CELL 2009; 8:1732-8. [PMID: 19749175 DOI: 10.1128/ec.00135-09] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
The tomato pathotype of Alternaria alternata produces host-specific AAL toxin and causes Alternaria stem canker on tomato. A polyketide synthetase (PKS) gene, ALT1, which is involved in AAL toxin biosynthesis, resides on a 1.0-Mb conditionally dispensable chromosome (CDC) found only in the pathogenic and AAL toxin-producing strains. Genomic sequences of ALT1 and another PKS gene, both of which reside on the CDC in the tomato pathotype strains, were compared to those of tomato pathotype strains collected worldwide. This revealed that the sequences of both CDC genes were identical among five A. alternata tomato pathotype strains having different geographical origins. On the other hand, the sequences of other genes located on chromosomes other than the CDC are not identical in each strain, indicating that the origin of the CDC might be different from that of other chromosomes in the tomato pathotype. Telomere fingerprinting and restriction fragment length polymorphism analyses of the A. alternata strains also indicated that the CDCs in the tomato pathotype strains were identical, although the genetic backgrounds of the strains differed. A hybrid strain between two different pathotypes was shown to harbor the CDCs derived from both parental strains with an expanded range of pathogenicity, indicating that CDCs can be transmitted from one strain to another and stably maintained in the new genome. We propose a hypothesis whereby the ability to produce AAL toxin and to infect a plant could potentially be distributed among A. alternata strains by horizontal transfer of an entire pathogenicity chromosome. This could provide a possible mechanism by which new pathogens arise in nature.
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30
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Collemare J, Billard A, Böhnert HU, Lebrun MH. Biosynthesis of secondary metabolites in the rice blast fungus Magnaporthe grisea: the role of hybrid PKS-NRPS in pathogenicity. ACTA ACUST UNITED AC 2008; 112:207-15. [DOI: 10.1016/j.mycres.2007.08.003] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2007] [Accepted: 08/09/2007] [Indexed: 01/22/2023]
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31
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Harimoto Y, Hatta R, Kodama M, Yamamoto M, Otani H, Tsuge T. Expression profiles of genes encoded by the supernumerary chromosome controlling AM-toxin biosynthesis and pathogenicity in the apple pathotype of Alternaria alternata. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2007; 20:1463-1476. [PMID: 17990954 DOI: 10.1094/mpmi-20-12-1463] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
The apple pathotype of Alternaria alternata produces host-specific AM-toxin and causes Alternaria blotch of apple. Previously, we cloned two genes, AMT1 and AMT2, required for AM-toxin biosynthesis and found that these genes are encoded by small, supernumerary chromosomes of <1.8 Mb in the apple pathotype strains. Here, we performed expressed sequence tag analysis of the 1.4-Mb chromosome encoding AMT genes in strain IFO8984. A cDNA library was constructed using RNA from AM-toxin-producing cultures. A total of 40,980 clones were screened with the 1.4-Mb chromosome probe, and 196 clones encoded by the chromosome were isolated. Sequence analyses of these clones identified 80 unigenes, including AMT1 and AMT2, and revealed that the functions of 43 (54%) genes are unknown. The expression levels of the 80 genes in AM-toxin-producing and nonproducing cultures were analyzed by real-time quantitative polymerase chain reaction (PCR). Most of the genes were found to be expressed in both cultures at markedly lower levels than the translation elongation factor 1-alpha gene used as an internal control. Comparison of the expression levels of these genes between two cultures showed that 21 genes, including AMT1 and AMT2, were upregulated (>10-fold) in AM-toxin-producing cultures. Two of the upregulated genes were newly identified to be involved in AM-toxin biosynthesis by the gene disruption experiments and were named AMT3 and AMT4. Thus, the genes upregulated in AM-toxin-producing cultures contain ideal candidates for novel AM-toxin biosynthetic genes.
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Affiliation(s)
- Yoshiaki Harimoto
- Graduate School of Bioagricultural Sciences, Nagoya University, Japan
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32
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Andrie RM, Schoch CL, Hedges R, Spatafora JW, Ciuffetti LM. Homologs of ToxB, a host-selective toxin gene from Pyrenophora tritici-repentis, are present in the genome of sister-species Pyrenophora bromi and other members of the Ascomycota. Fungal Genet Biol 2007; 45:363-77. [PMID: 18226934 DOI: 10.1016/j.fgb.2007.10.014] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2007] [Revised: 10/20/2007] [Accepted: 10/23/2007] [Indexed: 11/29/2022]
Abstract
Pyrenophora tritici-repentis requires the production of host-selective toxins (HSTs) to cause the disease tan spot of wheat, including Ptr ToxA, Ptr ToxB, and Ptr ToxC. Pyrenophora bromi, the species most closely related to P. tritici-repentis, is the causal agent of brown leaf spot of bromegrass. Because of the relatedness of P. bromi and P. tritici-repentis, we investigated the possibility that P. bromi contains sequences homologous to ToxA and/or ToxB, the products of which may be involved in its interaction with bromegrass. Multiplex polymerase chain reaction (PCR) revealed the presence of ToxB-like sequences in P. bromi and high-fidelity PCR was used to clone several of these loci, which were subsequently confirmed to be homologous to ToxB. Additionally, Southern analysis revealed ToxB from P. bromi to have a multicopy nature similar to ToxB from P. tritici-repentis. A combination of phylogenetic and Southern analyses revealed that the distribution of ToxB extends further into the Pleosporaceae, and a search of available fungal genomes identified a distant putative homolog in Magnaporthe grisea, causal agent of rice blast. Thus, unlike most described HSTs, ToxB homologs are present across a broad range of plant pathogenic ascomycetes, suggesting that it may have arose in an early ancestor of the Ascomycota.
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Affiliation(s)
- Rachael M Andrie
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331, USA
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Stukenbrock EH, McDonald BA. Geographical variation and positive diversifying selection in the host-specific toxin SnToxA. MOLECULAR PLANT PATHOLOGY 2007; 8:321-32. [PMID: 20507502 DOI: 10.1111/j.1364-3703.2007.00396.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
SUMMARY The host-specific toxin ToxA produced by the wheat pathogens Pyrenophora tritici-repentis and Phaeosphaeria nodorum interacts with the product of the dominant plant gene Tsn1 to induce necrosis. The ToxA gene is thought to have been acquired by Py. tritici-repentis from Ph. nodorum through a recent horizontal gene transfer event. PCR and sequence analysis indicate that the level of ToxA variation, including gene deletion, in Ph. nodorum (SnToxA) is significantly higher than in Py. tritici-repentis (PtrToxA). We PCR-screened 788 isolates of Ph. nodorum originating from eight geographical regions to infer the pattern of SnToxA deletions. The frequency of deletions differed significantly among populations, ranging from 0% (Australia) to 98% (China). Sequence analysis of the SnToxA gene in 123 Ph. nodorum isolates revealed 13 distinct haplotypes. The distribution and diversity of haplotypes varied significantly among populations. The majority of SnToxA mutations were non-synonymous resulting in changes at the protein level. We applied different models of selection to infer the mode of evolution operating at the ToxA locus. Evidence for positive diversifying selection supports the hypothesis that evolution of the ToxA locus is driven by selection imposed by the host. The distribution of SnToxA alleles and deletions may reflect the distribution of different Tsn1 alleles in the corresponding host populations.
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Affiliation(s)
- Eva H Stukenbrock
- Plant Pathology, Institute of Integrative Biology, ETH Zurich LFW, Universitätstrasse 2, CH-8092 Zurich, Switzerland
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Yamagishi D, Otani H, Kodama M. G protein signaling mediates developmental processes and pathogenesis of Alternaria alternata. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2006; 19:1280-8. [PMID: 17073310 DOI: 10.1094/mpmi-19-1280] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
A G protein alpha subunit gene (AGA1) has been cloned and characterized from a toxigenic and necrotrophic Alternaria alternata pathogen. Targeted disruption of AGA1 in the apple pathotype of A. alternata gave rise to mutants that differed in colony and conidial morphology as well as sporulation. The conidia of wild type and deltaAGA1 mutants showed equal germination on cellulose membranes. However, wild-type germ tubes formed readily from different points around the conidia, grew randomly, and were often branched, whereas those of the mutants formed only at one or both ends of the conidia and tended to grow in straight paths. Targeted disruption of AGA1 also resulted in reduction of pathogenicity on apple leaves, although the mutant produced host-specific AM-toxin, a fungal secondary metabolite associated with pathogenicity of the pathogen, at levels similar to the wild-type strain. Measurement of the intracellular cAMP levels of the mutant revealed that it was consistently higher than that of the wild type, indicating that AGA1 negatively regulates cAMP levels similar to mammalian Galphai systems. These results indicate that the signal transduction pathway represented by AGA1 appears to be involved in developmental pathways leading to sporulation and pathogenesis of A. alternata.
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Affiliation(s)
- Daisuke Yamagishi
- Laboratory of Plant Pathology, Faculty of Agriculture, Tottori University, 4-101 Koyama-Minami, Tottori 680-8553, Japan
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35
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Howlett BJ. Secondary metabolite toxins and nutrition of plant pathogenic fungi. CURRENT OPINION IN PLANT BIOLOGY 2006; 9:371-5. [PMID: 16713733 DOI: 10.1016/j.pbi.2006.05.004] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/10/2006] [Accepted: 05/03/2006] [Indexed: 05/05/2023]
Abstract
Fungal pathogens derive nutrition from the plants they invade. Some fungi can subvert plant defence responses such as programmed cell death to provide nutrition for their growth and colonisation. Secondary metabolite toxins produced by fungi often play a role in triggering these responses. Knowledge of the biosynthesis of these toxins, and the availability of fungal genome sequences and gene disruption techniques, allows the development of tools for experiments aimed at discovering the role of such toxins in triggering plant cell death and plant disease.
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Affiliation(s)
- Barbara J Howlett
- School of Botany, The University of Melbourne, 3010 Victoria, Australia.
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El Hadrami A, El Idrissi-Tourane A, El Hassni M, Daayf F, El Hadrami I. Toxin-based in-vitro selection and its potential application to date palm for resistance to the bayoud Fusarium wilt. C R Biol 2005; 328:732-44. [PMID: 16125651 DOI: 10.1016/j.crvi.2005.05.007] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2004] [Revised: 05/12/2005] [Accepted: 05/16/2005] [Indexed: 11/30/2022]
Abstract
Date palm (Phoenix dactylifera L.) is qualified as a 'tree' of great ecological and socio-economical importance in desert oases. Unfortunately, it is being decimated, especially in Morocco and Algeria, by a fusariosis wilt called bayoud and caused by Fusarium oxysporum f. sp. albedinis (Fao). Controlling this disease requires the implementation of an integrated management program. Breeding for resistance is one of the most promising component strategies of this program. Few naturally resistant cultivars with a mediocre fruit quality (dates) are known. Conventional and non-conventional methods are under development and have to use the simplest and easiest methods to screen for resistant individuals. The use of pathogen toxins as selective agents at the tissue culture step might be a source of variability that can lead to the selection of individuals with suitable levels of resistance to the toxin and/or to the pathogen among the genetic material available. Foa produces toxins such as fusaric, succinic, 3-phenyl lactic acids and their derivatives, marasmins and peptidic toxins. These toxins can be used bulked or separately as selective agents. The aim of this contribution was to give a brief overview on toxins and their use as a mean to select resistant lines and to initiate a discussion about the potential use of this approach for the date palm-Foa pathosystem. This review does not pretend to be comprehensive or exhaustive and was prepared mainly to highlight the potential use of Foa toxins for selecting date palm individuals with a suitable resistance level to bayoud using toxin-based selective media.
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Affiliation(s)
- Abdelbasset El Hadrami
- Laboratoire de physiologie végétale, équipe 'Biotechnologies et Physiologie végétales', faculté des sciences Semlalia, université Cadi-Ayyad, BP 2390, 40 001 Marrakech, Morocco.
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Varga J, Kocsubé S, Tóth B, Mesterházy A. Nonribosomal peptide synthetase genes in the genome of Fusarium graminearum, causative agent of wheat head blight. ACTA BIOLOGICA HUNGARICA 2005; 56:375-88. [PMID: 16196211 DOI: 10.1556/abiol.56.2005.3-4.19] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Fungal nonribosomal peptide synthetases (NRPSs) are responsible for the biosynthesis of numerous metabolites which serve as virulence factors in several plant-pathogen interactions. The aim of our work was to investigate the diversity of these genes in a Fusarium graminearum sequence database using bioinformatic techniques. Our search identified 15 NRPS sequences, among which two were found to be closely related to peptide synthetases of various fungi taking part in ferrichrome biosynthesis. Another peptide synthetase gene was similar to that identified in Aspergillus oryzae which is possibly responsible for the biosynthesis of fusarinine, an extracellular iron-chelating siderophore. To our knowledge, this is the first report on the identification of a putative NRPS gene possibly responsible for the biosynthesis of fusarinine-type siderophores. The other NRPSs were found to be related to peptide synthetases taking part in the biosynthesis of various peptides in other fungi. Transcription factors carrying ankyrin repeats were observed in the vicinity of four of the identified peptide synthetase genes. Additionally, NRPS related genes similar to putative long-chain fatty acid CoA ligases, acyl CoA ligases, ABC transport proteins, a highly conserved putative transmembrane protein of Aspergillus nidulans, and alpha-aminoadipate reductases have also been identified. Further studies are in progress to clarify the role of some of the identified NRPS genes in plant pathogenesis.
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Affiliation(s)
- J Varga
- Department of Microbiology, Faculty of Sciences, University of Szeged, P.O. Box 533, H-6701 Szeged, Hungary.
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Ito K, Tanaka T, Hatta R, Yamamoto M, Akimitsu K, Tsuge T. Dissection of the host range of the fungal plant pathogen Alternaria alternata by modification of secondary metabolism. Mol Microbiol 2004; 52:399-411. [PMID: 15066029 DOI: 10.1111/j.1365-2958.2004.04004.x] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The filamentous fungus Alternaria alternata contains seven pathogenic variants (pathotypes), which produce different host-specific toxins and cause diseases on different plants. The strawberry pathotype produces host-specific AF-toxin and causes Alternaria black spot of strawberry. This pathotype is also pathogenic to Japanese pear cultivars susceptible to the Japanese pear pathotype that produces AK-toxin. The strawberry pathotype produces two related molecular species, AF-toxins I and II: toxin I is toxic to both strawberry and pear, and toxin II is toxic only to pear. Previously, we isolated a cosmid clone pcAFT-1 from the strawberry pathotype that contains three genes involved in AF-toxin biosynthesis. Here, we have identified a new gene, designated AFTS1, from pcAFT-1. AFTS1 encodes a protein with similarity to enzymes of the aldo-ketoreductase superfamily. Targeted mutation of AFTS1 diminished the host range of the strawberry pathotype: Delta aftS1 mutants were pathogenic to pear, but not to strawberry, as is the Japanese pear pathotype. These mutants were found to produce AF-toxin II, but not AF-toxin I. These data represent a novel example of how the host range of a plant pathogenic fungus can be restricted by modification of secondary metabolism.
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Affiliation(s)
- Kaoru Ito
- Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Nagoya 464-8601, Japan
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Bakkeren G, Gold S. The path in fungal plant pathogenicity: many opportunities to outwit the intruders? GENETIC ENGINEERING 2004; 26:175-223. [PMID: 15387298 DOI: 10.1007/978-0-306-48573-2_10] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/30/2023]
Abstract
The number of genes implicated in the infection and disease processes of phytopathogenic fungi is increasing rapidly. Forward genetic approaches have identified mutated genes that affect pathogenicity, host range, virulence and general fitness. Likewise, candidate gene approaches have been used to identify genes of interest based on homology and recently through 'comparative genomic approaches' through analysis of large EST databases and whole genome sequences. It is becoming clear that many genes of the fungal genome will be involved in the pathogen-host interaction in its broadest sense, affecting pathogenicity and the disease process in planta. By utilizing the information obtained through these studies, plants may be bred or engineered for effective disease resistance. That is, by trying to disable pathogens by hitting them where it counts.
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Affiliation(s)
- Guus Bakkeren
- Agriculture & Agri-Food Canada,Pacific Agri-Food Research Centre, Summerland, BC, Canada V0H 1Z0
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Thomma BPHJ. Alternaria spp.: from general saprophyte to specific parasite. MOLECULAR PLANT PATHOLOGY 2003; 4:225-36. [PMID: 20569383 DOI: 10.1046/j.1364-3703.2003.00173.x] [Citation(s) in RCA: 344] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
UNLABELLED SUMMARY Alternaria species are mainly saprophytic fungi. However, some species have acquired pathogenic capacities collectively causing disease over a broad host range. This review summarizes the knowledge on pathogenic strategies employed by the fungus to plunder the host. Furthermore, strategies employed by potential host plants in order to ward off an attack are discussed. TAXONOMY Alternaria spp. kingdom Fungi, subkingdom Eumycotera, phylum Fungi Imperfecti (a non-phylogenetic or artificial phylum of fungi without known sexual stages whose members may or may not be related; taxonomy does not reflect relationships), form class Hypomycetes, Form order Moniliales, form family Dematiaceae, genus Alternaria. Some species of Alternaria are the asexual anamorph of the ascomycete Pleospora while others are speculated to be anamorphs of Leptosphaeria. HOST RANGE Most Alternaria species are common saprophytes that derive energy as a result of cellulytic activity and are found in a variety of habitats as ubiquitous agents of decay. Some species are plant pathogens that cause a range of economically important diseases like stem cancer, leaf blight or leaf spot on a large variety of crops. Latent infections can occur and result in post-harvest diseases or damping-off in case of infected seed. Useful Website: <http://ag.arizona.edu/PLP/alternaria/online.htm>
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Affiliation(s)
- Bart P H J Thomma
- Centre of Microbial and Plant Genetics (CMPG), Katholieke Universiteit Leuven, Kasteelpark Arenberg 20, B-3001 Heverlee-Leuven, Belgium
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Spassieva SD, Markham JE, Hille J. The plant disease resistance gene Asc-1 prevents disruption of sphingolipid metabolism during AAL-toxin-induced programmed cell death. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2002; 32:561-572. [PMID: 12445127 DOI: 10.1046/j.1365-313x.2002.01444.x] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The nectrotrophic fungus Alternaria alternata f.sp. lycopersici infects tomato plants of the genotype asc/asc by utilizing a host-selective toxin, AAL-toxin, that kills the host cells by inducing programmed cell death. Asc-1 is homologous to genes found in most eukaryotes from yeast to humans, suggesting a conserved function. A yeast strain with deletions in the homologous genes LAG1 and LAC1 was functionally complemented by Asc-1, indicating that Asc-1 functions in an analogous manner to the yeast homologues. Examination of the yeast sphingolipids, which are almost absent in the lag1Deltalac1Delta mutant, showed that Asc-1 was able to restore the synthesis of sphingolipids. We therefore examined the biosynthesis of sphingolipids in tomato by labeling leaf discs with l-[3-3H]serine. In the absence of AAL-toxin, there was no detectable difference in sphingolipid labeling between leaf discs from Asc/Asc or asc/asc leaves. In the presence of pathologically significant concentrations of AAL-toxin however, asc/asc leaf discs showed severely reduced labeling of sphingolipids and increased label in dihydrosphingosine (DHS) and 3-ketodihydrosphingosine (3-KDHS). Leaf discs from Asc/Asc leaves responded to AAL-toxin treatment by incorporating label into different sphingolipid species. The effects of AAL-toxin on asc/asc leaflets could be partially blocked by the simultaneous application of AAL-toxin and myriocin. Leaf discs simultaneously treated with AAL-toxin and myriocin showed no incorporation of label into sphingolipids or long-chain bases as expected. These results indicate that the presence of Asc-1 is able to relieve an AAL-toxin-induced block on sphingolipid synthesis that would otherwise lead to programmed cell death.
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Affiliation(s)
- Stefka D Spassieva
- Department of Molecular Biology of Plants, Research School GBB, University of Groningen, Kerklaan 30, 9751NN Haren, the Netherlands
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Wolpert TJ, Dunkle LD, Ciuffetti LM. Host-selective toxins and avirulence determinants: what's in a name? ANNUAL REVIEW OF PHYTOPATHOLOGY 2002; 40:251-85. [PMID: 12147761 DOI: 10.1146/annurev.phyto.40.011402.114210] [Citation(s) in RCA: 279] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Host-selective toxins, a group of structurally complex and chemically diverse metabolites produced by plant pathogenic strains of certain fungal species, function as essential determinants of pathogenicity or virulence. Investigations into the molecular and biochemical responses to these disease determinants reveal responses typically associated with host defense and incompatibility induced by avirulence determinants. The characteristic responses that unify these disparate disease phenotypes are numerous, yet the evidence implicating a causal relationship of these responses, whether induced by host-selective toxins or avirulence factors, in determining the consequences of the host-pathogen interaction is equivocal. This review summarizes some examples of the action of host-selective toxins to illustrate the similarity in responses with those to avirulence determinants.
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Affiliation(s)
- Thomas J Wolpert
- Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331, USA.
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