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Park J, Son H. Antioxidant Systems of Plant Pathogenic Fungi: Functions in Oxidative Stress Response and Their Regulatory Mechanisms. THE PLANT PATHOLOGY JOURNAL 2024; 40:235-250. [PMID: 38835295 PMCID: PMC11162859 DOI: 10.5423/ppj.rw.01.2024.0001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/02/2024] [Revised: 03/21/2024] [Accepted: 03/23/2024] [Indexed: 06/06/2024]
Abstract
During the infection process, plant pathogenic fungi encounter plant-derived oxidative stress, and an appropriate response to this stress is crucial to their survival and establishment of the disease. Plant pathogenic fungi have evolved several mechanisms to eliminate oxidants from the external environment and maintain cellular redox homeostasis. When oxidative stress is perceived, various signaling transduction pathways are triggered and activate the downstream genes responsible for the oxidative stress response. Despite extensive research on antioxidant systems and their regulatory mechanisms in plant pathogenic fungi, the specific functions of individual antioxidants and their impacts on pathogenicity have not recently been systematically summarized. Therefore, our objective is to consolidate previous research on the antioxidant systems of plant pathogenic fungi. In this review, we explore the plant immune responses during fungal infection, with a focus on the generation and function of reactive oxygen species. Furthermore, we delve into the three antioxidant systems, summarizing their functions and regulatory mechanisms involved in oxidative stress response. This comprehensive review provides an integrated overview of the antioxidant mechanisms within plant pathogenic fungi, revealing how the oxidative stress response contributes to their pathogenicity.
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Affiliation(s)
- Jiyeun Park
- Department of Agricultural Biotechnology, Seoul National University, Seoul 08826, Korea
| | - Hokyoung Son
- Department of Agricultural Biotechnology, Seoul National University, Seoul 08826, Korea
- Research Institute of Agriculture and Life Sciences, Seoul National University, Seoul 08826, Korea
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Wang Y, Wu W, Zhang L, Jiang H, Mei L. Variations in amino acids caused by drought stress mediate the predisposition of Carya cathayensis to Botryosphaeria canker disease. JOURNAL OF EXPERIMENTAL BOTANY 2023; 74:4628-4641. [PMID: 37129574 DOI: 10.1093/jxb/erad161] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2022] [Accepted: 04/28/2023] [Indexed: 05/03/2023]
Abstract
Abiotic stresses can affect the outcome of plant-pathogen interactions, mostly by predisposing the host plant to infection; however, the crosstalk between pathogens and plants related to such predisposition remains unclear. Here, we investigated the predisposition of Carya cathayensis to infection by the fungal pathogen Botryosphaeria dothidea (Bd) caused by drought in the host plant. High levels of drought stress resulted in a significant increase in plant susceptibility to Bd. Drought significantly induced the accumulation of H2O2 and the free amino acids Pro, Leu, and Ile, and in the phloem tissues of plants, and decreased the content of non-structural carbohydrates. In vitro assays showed that Bd was sensitive to H2O2; however, Pro played a protective role against exogenous H2O2. Leu, Ile, and Pro induced asexual reproduction of Bd. Our results provide the first analysis of how drought predisposes C. cathayensis to Botrysphaeria canker via amino acid accumulation in the host plant, and we propose a model that integrates the plant-pathogen interactions involved.
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Affiliation(s)
- Yongjun Wang
- College of Forestry and Biotechnology, Zhejiang A&F University, Hangzhou, 311300, Zhejiang, China
| | - Wenbin Wu
- College of Forestry and Biotechnology, Zhejiang A&F University, Hangzhou, 311300, Zhejiang, China
| | - Liqin Zhang
- Key Laboratory of Vector Biology and Pathogen Control of Zhejiang Province, Huzhou University, Huzhou, 313000, Zhejiang, China
| | - Hong Jiang
- College of Forestry and Biotechnology, Zhejiang A&F University, Hangzhou, 311300, Zhejiang, China
| | - Li Mei
- College of Forestry and Biotechnology, Zhejiang A&F University, Hangzhou, 311300, Zhejiang, China
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3
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Romero-Aguilar L, Vázquez-Meza H, Guerra-Sánchez G, Luqueño-Bocardo OI, Pardo JP. The Mitochondrial Alternative Oxidase in Ustilago maydis Is Not Involved in Response to Oxidative Stress Induced by Paraquat. J Fungi (Basel) 2022; 8:1221. [PMID: 36422042 PMCID: PMC9693204 DOI: 10.3390/jof8111221] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2022] [Revised: 11/10/2022] [Accepted: 11/17/2022] [Indexed: 07/29/2023] Open
Abstract
It has been shown that the alternative oxidase in mitochondria of fungi and plants has important functions in the response against stress conditions, although their role in some organisms is still unknown. This is the case of Ustilago maydis. There is no evidence of the participation of the U. maydis Aox1 in stressful conditions such as desiccation, high or low temperature, and low pH, among others. Therefore, in this work, we studied the role of the U. maydis Aox1 in cells exposed to oxidative stress induced by methyl viologen (paraquat). To gain insights into the role of this enzyme, we took advantage of four strains: the FB2 wild-type, a strain without the alternative oxidase (FB2aox1Δ), other with the Aox1 fused to the Gfp under the control of the original promoter (FB2aox1-Gfp), and one expressing constitutively de Aox1-Gfp (FB2Potef:aox1-Gfp). Cells were incubated for various times in the presence of 1 mM paraquat and growth, replicative capacities, mitochondrial respiratory activity, Aox1 capacity, and the activities of several antioxidant enzymes (catalase, glutathione peroxidase, glutathione reductase, and superoxide dismutase) were assayed. The results show that (1) the response of U. maydis against oxidative stress was the same in the presence or absence of the Aox1; (2) the activities of the antioxidant enzymes remained constant despite the oxidative stress; and (3) there was a decrease in the GSH/GSSG ratio in U. maydis cells incubated with paraquat.
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Affiliation(s)
- Lucero Romero-Aguilar
- Departamento de Bioquímica, Facultad de Medicina, Universidad Nacional Autónoma de México, Circuito Interior, Ciudad Universitaria, Coyoacán, Ciudad de México C.P. 04510, Mexico
| | - Héctor Vázquez-Meza
- Departamento de Bioquímica, Facultad de Medicina, Universidad Nacional Autónoma de México, Circuito Interior, Ciudad Universitaria, Coyoacán, Ciudad de México C.P. 04510, Mexico
| | - Guadalupe Guerra-Sánchez
- Instituto Politécnico Nacional, Escuela Nacional de Ciencias Biológicas, Departamento de Microbiología, Plan de Carpio y Plan de Ayala S/N Santo Tomás, Miguel Hidalgo, Ciudad de México C.P. 11340, Mexico
| | - Oscar Ivan Luqueño-Bocardo
- Departamento de Bioquímica, Facultad de Medicina, Universidad Nacional Autónoma de México, Circuito Interior, Ciudad Universitaria, Coyoacán, Ciudad de México C.P. 04510, Mexico
| | - Juan Pablo Pardo
- Departamento de Bioquímica, Facultad de Medicina, Universidad Nacional Autónoma de México, Circuito Interior, Ciudad Universitaria, Coyoacán, Ciudad de México C.P. 04510, Mexico
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Juárez-Montiel M, Clark-Flores D, Tesillo-Moreno P, de la Vega-Camarillo E, Andrade-Pavón D, Hernández-García JA, Hernández-Rodríguez C, Villa-Tanaca L. Vacuolar proteases and autophagy in phytopathogenic fungi: A review. FRONTIERS IN FUNGAL BIOLOGY 2022; 3:948477. [PMID: 37746183 PMCID: PMC10512327 DOI: 10.3389/ffunb.2022.948477] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/19/2022] [Accepted: 10/11/2022] [Indexed: 09/26/2023]
Abstract
Autophagy (macroautophagy) is a survival and virulence mechanism of different eukaryotic pathogens. Autophagosomes sequester cytosolic material and organelles, then fuse with or enter into the vacuole or lysosome (the lytic compartment of most fungal/plant cells and many animal cells, respectively). Subsequent degradation of cargoes delivered to the vacuole via autophagy and endocytosis maintains cellular homeostasis and survival in conditions of stress, cellular differentiation, and development. PrA and PrB are vacuolar aspartyl and serine endoproteases, respectively, that participate in the autophagy of fungi and contribute to the pathogenicity of phytopathogens. Whereas the levels of vacuolar proteases are regulated by the expression of the genes encoding them (e.g., PEP4 for PrA and PRB1 for PrB), their activity is governed by endogenous inhibitors. The aim of the current contribution is to review the main characteristics, regulation, and role of vacuolar soluble endoproteases and Atg proteins in the process of autophagy and the pathogenesis of three fungal phytopathogens: Ustilago maydis, Magnaporthe oryzae, and Alternaria alternata. Aspartyl and serine proteases are known to participate in autophagy in these fungi by degrading autophagic bodies. However, the gene responsible for encoding the vacuolar serine protease of U. maydis has yet to be identified. Based on in silico analysis, this U. maydis gene is proposed to be orthologous to the Saccharomyces cerevisiae genes PRB1 and PBI2, known to encode the principal protease involved in the degradation of autophagic bodies and its inhibitor, respectively. In fungi that interact with plants, whether phytopathogenic or mycorrhizal, autophagy is a conserved cellular degradation process regulated through the TOR, PKA, and SNF1 pathways by ATG proteins and vacuolar proteases. Autophagy plays a preponderant role in the recycling of cell components as well as in the fungus-plant interaction.
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Affiliation(s)
| | | | | | | | | | | | | | - Lourdes Villa-Tanaca
- Laboratorio de Biología Molecular de Bacterias y Levaduras, Departamento de Microbiología, Instituto Politécnico Nacional, Escuela Nacional de Ciencias Biológicas, Mexico City, Mexico
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Molina-Hernandez JB, Capelli F, Laurita R, Tappi S, Laika J, Gioia L, Valbonetti L, Chaves-López C. A comparative study on the antifungal efficacy of cold atmospheric plasma at low and high surface density on Aspergillus chevalieri and mechanisms of action. INNOV FOOD SCI EMERG 2022. [DOI: 10.1016/j.ifset.2022.103194] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Wu P, Choo CYL, Lu H, Wei X, Chen Y, Yago JI, Chung K. Pexophagy is critical for fungal development, stress response, and virulence in Alternaria alternata. MOLECULAR PLANT PATHOLOGY 2022; 23:1538-1554. [PMID: 35810316 PMCID: PMC9452759 DOI: 10.1111/mpp.13247] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/12/2022] [Revised: 06/16/2022] [Accepted: 06/22/2022] [Indexed: 06/09/2023]
Abstract
Alternaria alternata can resist high levels of reactive oxygen species (ROS). The protective roles of autophagy or autophagy-mediated degradation of peroxisomes (termed pexophagy) against oxidative stress remain unclear. The present study, using transmission electron microscopy and fluorescence microscopy coupled with a GFP-AaAtg8 proteolysis assay and an mCherry tagging assay with peroxisomal targeting tripeptides, demonstrated that hydrogen peroxide (H2 O2 ) and nitrogen depletion induced autophagy and pexophagy. Experimental evidence showed that H2 O2 triggered autophagy and the translocation of peroxisomes into the vacuoles. Mutational inactivation of the AaAtg8 gene in A. alternata led to autophagy impairment, resulting in the accumulation of peroxisomes, increased ROS sensitivity, and decreased virulence. Compared to the wild type, ΔAaAtg8 failed to detoxify ROS effectively, leading to ROS accumulation. Deleting AaAtg8 down-regulated the expression of genes encoding an NADPH oxidase and a Yap1 transcription factor, both involved in ROS resistance. Deleting AaAtg8 affected the development of conidia and appressorium-like structures. Deleting AaAtg8 also compromised the integrity of the cell wall. Reintroduction of a functional copy of AaAtg8 in the mutant completely restored all defective phenotypes. Although ΔAaAtg8 produced wild-type toxin levels in axenic culture, the mutant induced a lower level of H2 O2 and smaller necrotic lesions on citrus leaves. In addition to H2 O2 , nitrogen starvation triggered peroxisome turnover. We concluded that ΔAaAtg8 failed to degrade peroxisomes effectively, leading to the accumulation of peroxisomes and the reduction of the stress response. Autophagy-mediated peroxisome turnover could increase cell adaptability and survival under oxidative stress and starvation conditions.
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Affiliation(s)
- Pei‐Ching Wu
- Department of Plant Pathology, College of Agriculture and Natural ResourcesNational Chung Hsing UniversityTaichungTaiwan
| | - Celine Yen Ling Choo
- Department of Plant Pathology, College of Agriculture and Natural ResourcesNational Chung Hsing UniversityTaichungTaiwan
| | - Hsin‐Yu Lu
- Department of Plant Pathology, College of Agriculture and Natural ResourcesNational Chung Hsing UniversityTaichungTaiwan
| | - Xian‐Yong Wei
- Department of Plant Pathology, College of Agriculture and Natural ResourcesNational Chung Hsing UniversityTaichungTaiwan
| | - Yu‐Kun Chen
- Department of Plant Pathology, College of Agriculture and Natural ResourcesNational Chung Hsing UniversityTaichungTaiwan
| | - Jonar I. Yago
- Plant Science Department, College of AgricultureNueva Vizcaya State UniversityBayombongPhilippines
| | - Kuang‐Ren Chung
- Department of Plant Pathology, College of Agriculture and Natural ResourcesNational Chung Hsing UniversityTaichungTaiwan
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Lu HY, Huang YL, Wu PC, Wei XY, Yago JI, Chung KR. A zinc finger suppressor involved in stress resistance, cell wall integrity, conidiogenesis, and autophagy in the necrotrophic fungal pathogen Alternaria alternata. Microbiol Res 2022; 263:127106. [PMID: 35839700 DOI: 10.1016/j.micres.2022.127106] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2022] [Revised: 05/18/2022] [Accepted: 06/22/2022] [Indexed: 10/17/2022]
Abstract
The tangerine pathotype of Alternaria alternata can withstand high-level reactive oxygen species (ROS). By analyzing loss- and gain-of-function mutants, this study demonstrated that a Cys2His2 zinc finger-containing transcription regulator, A. alternata Stress Response Regulator 1 (AaSRR1), plays a negative role in resistance to peroxides and singlet-oxygen-generating compounds. AaSRR1 plays no role in cellular susceptibility or resistance to superoxide-producing compounds. AaSRR1 also negatively regulates conidiogenesis, maintenance of cell wall and membrane integrities, and chitin biosynthesis. Some wild-type hyphae displayed necrosis after exposure to 30 mM H2O2, whereas AaSRR1 deficient mutant (ΔAaSRR1) hyphae had visible granules and vacuoles. sGFP-AaATG8 proteolysis assays revealed that H2O2 and starvation could trigger autophagy formation in both wild type and ΔAaSRR1. Autophagy occurred at higher rates in ΔAaSRR1 than wild type under both conditions, particularly after H2O2 treatments, indicating that autophagy might contribute to ROS resistance. Upon exposure to H2O2 or under starvation, AaSRR1 was translocated into the nucleus, even though the expression of AaSRR1 was decreased. AaSRR1 is required for vegetative growth but is dispensable for fungal virulence as assayed on detached calamondin leaves. AaSRR1 suppressed the expression of the gene encoding a HOG1 mitogen-activated protein (MAP) kinase implicated in ROS resistance. Mutation of AaSRR1 increased catalase activity but decreased superoxide dismutase activity, leading to fewer ROS accumulation in the cytosol. Nevertheless, our results indicated that AaSRR1 is a transcription suppressor for ROS resistance. This study also revealed tradeoffs between stress responses and hyphal growth in A. alternata.
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Affiliation(s)
- Hsin-Yu Lu
- Department of Plant Pathology, College of Agriculture and Natural Resources, National Chung Hsing University, Taichung 40227, Taiwan
| | - Yu-Ling Huang
- Department of Plant Pathology, College of Agriculture and Natural Resources, National Chung Hsing University, Taichung 40227, Taiwan
| | - Pei-Ching Wu
- Department of Plant Pathology, College of Agriculture and Natural Resources, National Chung Hsing University, Taichung 40227, Taiwan.
| | - Xian-Yong Wei
- Department of Plant Pathology, College of Agriculture and Natural Resources, National Chung Hsing University, Taichung 40227, Taiwan
| | - Jonar I Yago
- Plant Science Department, College of Agriculture, Nueva Vizcaya State University, Bayombong, Nueva Vizcaya 3700, Philippines
| | - Kuang-Ren Chung
- Department of Plant Pathology, College of Agriculture and Natural Resources, National Chung Hsing University, Taichung 40227, Taiwan.
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Wu PC, Chen YK, Yago JI, Chung KR. Peroxisomes Implicated in the Biosynthesis of Siderophores and Biotin, Cell Wall Integrity, Autophagy, and Response to Hydrogen Peroxide in the Citrus Pathogenic Fungus Alternaria alternata. Front Microbiol 2021; 12:645792. [PMID: 34262533 PMCID: PMC8273606 DOI: 10.3389/fmicb.2021.645792] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2020] [Accepted: 05/25/2021] [Indexed: 11/13/2022] Open
Abstract
Little is known about the roles of peroxisomes in the necrotrophic fungal plant pathogens. In the present study, a Pex6 gene encoding an ATPase-associated protein was characterized by analysis of functional mutations in the tangerine pathotype of Alternaria alternata, which produces a host-selective toxin. Peroxisomes were observed in fungal cells by expressing a mCherry fluorescent protein tagging with conserved tripeptides serine-lysing-leucine and transmission electron microscopy. The results indicated that Pex6 plays no roles in peroxisomal biogenesis but impacts protein import into peroxisomes. The number of peroxisomes was affected by nutritional conditions and H2O2, and their degradation was mediated by an autophagy-related machinery termed pexophagy. Pex6 was shown to be required for the formation of Woronin bodies, the biosynthesis of biotin, siderophores, and toxin, the uptake and accumulation of H2O2, growth, and virulence, as well as the Slt2 MAP kinase-mediated maintenance of cell wall integrity. Adding biotin, oleate, and iron in combination fully restored the growth of the pex6-deficient mutant (Δpex6), but failed to restore Δpex6 virulence to citrus. Adding purified toxin could only partially restore Δpex6 virulence even in the presence of biotin, oleate, and iron. Sensitivity assays revealed that Pex6 plays no roles in resistance to H2O2 and superoxide, but plays a negative role in resistance to 2-chloro-5-hydroxypyridine (a hydroxyl radical-generating compound), eosin Y and rose Bengal (singlet oxygen-generating compounds), and 2,3,5-triiodobenzoic acid (an auxin transport inhibitor). The diverse functions of Pex6 underscore the importance of peroxisomes in physiology, pathogenesis, and development in A. alternata.
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Affiliation(s)
- Pei-Ching Wu
- Department of Plant Pathology, College of Agriculture and Natural Resources, National Chung Hsing University, Taichung, Taiwan
| | - Yu-Kun Chen
- Department of Plant Pathology, College of Agriculture and Natural Resources, National Chung Hsing University, Taichung, Taiwan
| | - Jonar I. Yago
- Plant Science Department, College of Agriculture, Nueva Vizcaya State University, Bayombong, Philippines
| | - Kuang-Ren Chung
- Department of Plant Pathology, College of Agriculture and Natural Resources, National Chung Hsing University, Taichung, Taiwan
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Wu PC, Chen CW, Choo CYL, Chen YK, Yago JI, Chung KR. Proper Functions of Peroxisomes Are Vital for Pathogenesis of Citrus Brown Spot Disease Caused by Alternaria alternata. J Fungi (Basel) 2020; 6:jof6040248. [PMID: 33114679 PMCID: PMC7712655 DOI: 10.3390/jof6040248] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2020] [Revised: 10/14/2020] [Accepted: 10/24/2020] [Indexed: 11/27/2022] Open
Abstract
In addition to the production of a host-selective toxin, the tangerine pathotype of Alternaria alternata must conquer toxic reactive oxygen species (ROS) in order to colonize host plants. The roles of a peroxin 6-coding gene (pex6) implicated in protein import into peroxisomes was functionally characterized to gain a better understanding of molecular mechanisms in ROS resistance and fungal pathogenicity. The peroxisome is a vital organelle involved in metabolisms of fatty acids and hydrogen peroxide in eukaryotes. Targeted deletion of pex6 had no impacts on the biogenesis of peroxisomes and cellular resistance to ROS. The pex6 deficient mutant (Δpex6) reduced toxin production by 40% compared to wild type and barely induce necrotic lesions on citrus leaves. Co-inoculation of purified toxin with Δpex6 conidia on citrus leaves, however, failed to fully restore lesion formation, indicating that toxin only partially contributed to the loss of Δpex6 pathogenicity. Δpex6 conidia germinated poorly and formed fewer appressorium-like structures (nonmelanized enlargement of hyphal tips) than wild type. Δpex6 hyphae grew slowly and failed to penetrate beyond the epidermal layers. Moreover, Δpex6 had thinner cell walls and lower viability. All of these defects resulting from deletion of pex6 could also account for the loss of Δpex6 pathogenicity. Overall, our results have demonstrated that proper peroxisome functions are of vital importance to pathogenesis of the tangerine pathotype of A. alternata.
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Affiliation(s)
- Pei-Ching Wu
- Department of Plant Pathology, College of Agriculture and Natural Resources, National Chung Hsing University, Taichung 40227, Taiwan; (C.-W.C.); (C.Y.L.C.); (Y.-K.C.)
- Correspondence: (P.-C.W.); (K.-R.C.); Tel.: +886-4-22840780 (ext. 316) (P.-C.W.); +886-4-22840780 (ext. 301) (K.-R.C.)
| | - Chia-Wen Chen
- Department of Plant Pathology, College of Agriculture and Natural Resources, National Chung Hsing University, Taichung 40227, Taiwan; (C.-W.C.); (C.Y.L.C.); (Y.-K.C.)
| | - Celine Yen Ling Choo
- Department of Plant Pathology, College of Agriculture and Natural Resources, National Chung Hsing University, Taichung 40227, Taiwan; (C.-W.C.); (C.Y.L.C.); (Y.-K.C.)
| | - Yu-Kun Chen
- Department of Plant Pathology, College of Agriculture and Natural Resources, National Chung Hsing University, Taichung 40227, Taiwan; (C.-W.C.); (C.Y.L.C.); (Y.-K.C.)
| | - Jonar I. Yago
- Plant Science Department, College of Agriculture, Nueva Vizcaya State University, Bayombong, Nueva Vizcaya 3700, Philippines;
| | - Kuang-Ren Chung
- Department of Plant Pathology, College of Agriculture and Natural Resources, National Chung Hsing University, Taichung 40227, Taiwan; (C.-W.C.); (C.Y.L.C.); (Y.-K.C.)
- Correspondence: (P.-C.W.); (K.-R.C.); Tel.: +886-4-22840780 (ext. 316) (P.-C.W.); +886-4-22840780 (ext. 301) (K.-R.C.)
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Lu K, Zhang M, Yang R, Zhang M, Guo Q, Baek KH, Xu H. The MAP Kinase Kinase Gene AbSte7 Regulates Multiple Aspects of Alternaria brassicicola Pathogenesis. THE PLANT PATHOLOGY JOURNAL 2019; 35:91-99. [PMID: 31007639 PMCID: PMC6464198 DOI: 10.5423/ppj.oa.07.2018.0125] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/05/2018] [Revised: 11/15/2018] [Accepted: 12/06/2018] [Indexed: 05/13/2023]
Abstract
Mitogen-activated protein kinase (MAPK) cascades in fungi are ubiquitously conserved signaling pathways that regulate stress responses, vegetative growth, pathogenicity, and many other developmental processes. Previously, we reported that the AbSte7 gene, which encodes a mitogen-activated protein kinase kinase (MAPKK) in Alternaria brassicicola, plays a central role in pathogenicity against host cabbage plants. In this research, we further characterized the role of AbSte7 in the pathogenicity of this fungus using ΔAbSte7 mutants. Disruption of the AbSte7 gene of A. brassicicola reduced accumulation of metabolites toxic to the host plant in liquid culture media. The ΔAbSte7 mutants could not efficiently detoxify cruciferous phytoalexin brassinin, possibly due to reduced expression of the brassinin hydrolase gene involved in detoxifying brassinin. Disruption of the AbSte7 gene also severely impaired fungal detoxification of reactive oxygen species. AbSte7 gene disruption reduced the enzymatic activity of cell wall-degrading enzymes, including cellulase, β-glucosidase, pectin methylesterase, polymethyl-galacturonase, and polygalacturonic acid transeliminase, during host plant infection. Altogether, the data strongly suggest the MAPKK gene AbSte7 plays a pivotal role in A. brassicicola during host infection by regulating multiple steps, and thus increasing pathogenicity and inhibiting host defenses.
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Affiliation(s)
- Kai Lu
- Department of Plant Protection, Shandong Agricultural University, Tai’an 271018,
China
| | - Min Zhang
- Department of Plant Protection, Shandong Agricultural University, Tai’an 271018,
China
| | - Ran Yang
- Department of Plant Protection, Shandong Agricultural University, Tai’an 271018,
China
| | - Min Zhang
- Department of Plant Protection, Shandong Agricultural University, Tai’an 271018,
China
| | - Qinjun Guo
- Department of Plant Protection, Shandong Agricultural University, Tai’an 271018,
China
| | - Kwang-Hyun Baek
- Department of Biotechnology, Yeungnam University, Gyeongsan, Gyeongbuk 38541,
Korea
- Co-corresponding authors: H. Xu, Phone) +86-538-824-1575, FAX) +86-538-824-1324, E-mail) . K.-H. Baek, Phone) +82-53-810-3029, FAX) +82-53-810-4769, E-mail)
| | - Houjuan Xu
- Department of Plant Protection, Shandong Agricultural University, Tai’an 271018,
China
- Co-corresponding authors: H. Xu, Phone) +86-538-824-1575, FAX) +86-538-824-1324, E-mail) . K.-H. Baek, Phone) +82-53-810-3029, FAX) +82-53-810-4769, E-mail)
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Simaan H, Lev S, Horwitz BA. Oxidant-Sensing Pathways in the Responses of Fungal Pathogens to Chemical Stress Signals. Front Microbiol 2019; 10:567. [PMID: 30941117 PMCID: PMC6433817 DOI: 10.3389/fmicb.2019.00567] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2018] [Accepted: 03/05/2019] [Indexed: 12/04/2022] Open
Abstract
Host defenses expose fungal pathogens to oxidants and antimicrobial chemicals. The fungal cell employs conserved eukaryotic signaling pathways and dedicated transcription factors to program its response to these stresses. The oxidant-sensitive transcription factor of yeast, YAP1, and its orthologs in filamentous fungi, are central to tolerance to oxidative stress. The C-terminal domain of YAP1 contains cysteine residues that, under oxidizing conditions, form an intramolecular disulfide bridge locking the molecule in a conformation where the nuclear export sequence is masked. YAP1 accumulates in the nucleus, promoting transcription of genes that provide the cell with the ability to counteract oxidative stress. Chemicals including xenobiotics and plant signals can also promote YAP1 nuclearization in yeast and filamentous fungi. This could happen via direct or indirect oxidative stress, or by a different biochemical pathway. Plant phenolics are known antioxidants, yet they have been shown to elicit cellular responses that would usually be triggered to counter oxidant stress. Here we will discuss the evidence that YAP1 and MAPK pathways respond to phenolic compounds. Following this and other examples, we explore here how oxidative-stress sensing networks of fungi might have evolved to detect chemical stressors. Furthermore, we draw functional parallels between fungal YAP1 and mammalian Keap1-Nrf2 signaling systems.
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Affiliation(s)
- Hiba Simaan
- Faculty of Biology, Technion - Israel Institute of Technology, Haifa, Israel
| | - Sophie Lev
- Centre for Infectious Diseases and Microbiology, The Westmead Institute for Medical Research, Westmead, NSW, Australia
| | - Benjamin A Horwitz
- Faculty of Biology, Technion - Israel Institute of Technology, Haifa, Israel
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Lin HC, Yu PL, Chen LH, Tsai HC, Chung KR. A Major Facilitator Superfamily Transporter Regulated by the Stress-Responsive Transcription Factor Yap1 Is Required for Resistance to Fungicides, Xenobiotics, and Oxidants and Full Virulence in Alternaria alternata. Front Microbiol 2018; 9:2229. [PMID: 30279684 PMCID: PMC6153361 DOI: 10.3389/fmicb.2018.02229] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2018] [Accepted: 08/31/2018] [Indexed: 11/29/2022] Open
Abstract
Alternaria alternata relies on the ability to produce a host-selective toxin and to detoxify reactive oxygen species to successfully colonize the host. An A. alternata major facilitator superfamily transporter designated AaMFS54 was functionally characterized by analysis of loss- and gain-of-function mutations to better understand the factors required for fungal pathogenesis. AaMFS54 was originally identified from a wild-type expression library after being subtracted with that of a mutant impaired for the oxidative stress-responsive transcription regulator Yap1. AaMFS54 contains 14 transmembrane helixes. Fungal mutant lacking AaMFS54 produced fewer conidia and increased sensitivity to many potent oxidants (potassium superoxide and singlet-oxygen generating compounds), xenobiotics (2,3,5-triiodobenzoic acid and 2-chloro-5-hydroxypyridine), and fungicides (clotrimazole, fludioxonil, vinclozolin, and iprodione). AaMFS54 mutant induced necrotic lesion sizes similar to those induced by wild-type on leaves of susceptible citrus cultivars after point inoculation with spore suspensions. However, the mutant produced smaller colonies and less fluffy hyphae on the affected leaves. Virulence assays on citrus leaves inoculated by spraying with spores revealed that AaMFS54 mutant induced less severe lesions than wild-type, indicating the requirement of AaMFS54 in pathogenesis. All defective phenotypes were restored in a strain re-acquiring a functional copy of AaMFS54. Northern blotting analysis revealed that the expression of AaMFS54 was suppressed by xenobiotics. The current studies indicate that the Yap1-mediated transporter plays a role in resistance to toxic oxidants and fungicides in A. alternata. The relationships of MFS transporters with other regulatory components conferring stress resistance and A. alternata pathogenesis are also discussed.
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Affiliation(s)
- Hsien-Che Lin
- Department of Plant Pathology, College of Agriculture and Natural Resources, National Chung-Hsing University, Taichung, Taiwan
| | - Pei-Ling Yu
- Department of Plant Pathology, College of Agriculture and Natural Resources, National Chung-Hsing University, Taichung, Taiwan
| | - Li-Hung Chen
- Department of Plant Pathology, College of Agriculture and Natural Resources, National Chung-Hsing University, Taichung, Taiwan
| | - Hsieh-Chin Tsai
- Department of Plant Pathology, College of Agriculture and Natural Resources, National Chung-Hsing University, Taichung, Taiwan
| | - Kuang-Ren Chung
- Department of Plant Pathology, College of Agriculture and Natural Resources, National Chung-Hsing University, Taichung, Taiwan
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Thioredoxin and Glutaredoxin Systems Required for Oxidative Stress Resistance, Fungicide Sensitivity, and Virulence of Alternaria alternata. Appl Environ Microbiol 2018; 84:AEM.00086-18. [PMID: 29752269 DOI: 10.1128/aem.00086-18] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2018] [Accepted: 05/04/2018] [Indexed: 01/07/2023] Open
Abstract
This study determined the function of thioredoxin and glutaredoxin systems in the phytopathogenic fungus Alternaria alternata via analyzing mutants obtained from the targeted deletion of genes encoding thioredoxin peroxidase (Tsa1), thioredoxin reductase (Trr1), and glutathione reductase (Glr1). Trr1 and Glr1, but not Tsa1, are required for growth and conidiation. The reduced growth and conidiation seen in the Trr1 or Glr1 deletion mutant can be restored by glutathione. Deletion mutants showing growth inhibition by oxidants are defective for H2O2 detoxification and induce smaller lesions on citrus leaves. Trr1 and Glr1, but not Tsa1, also contribute to NaCl resistance. Glr1 is required for sorbitol resistance and is responsible for resistance to mancozeb and boscalid but not chlorothalonil fungicides, a novel phenotype that has not been reported in fungi. Trr1 is required for resistance to boscalid and chlorothalonil fungicides but confers susceptibility to mancozeb. The Tsa1 deletion mutant displays wild-type sensitivity to the tested fungicides. The expression of Tsa1 and Trr1 is regulated by the oxidative stress responsive regulators Yap1, Hog1, and Skn7. The expression of Tsa1, but not Trr1, is also regulated indirectly by the NADPH oxidase. The results indicate that the capability to resist oxidative stress is required for virulence of A. alternataIMPORTANCE The thioredoxin and glutaredoxin systems are important thiol antioxidant systems in cells, and knowledge of these two systems in the plant-pathogenic fungus A. alternata is useful for finding new strategies to reduce the virulence of this pathogen. In this study, we demonstrated that thiol antioxidant system-related genes (Tsa1, Trr1, and Glr1) are required for H2O2 detoxification and virulence in A. alternata Moreover, deletion of Trr1 results in hypersensitivity to the fungicides chlorothalonil and boscalid, and Glr1 deletion mutants are highly sensitive to mancozeb, which is the fungicide mostly used in citrus fields. Therefore, our findings demonstrate that the ability to detoxify reactive oxygen species (ROS) plays a critical role in pathogenesis on citrus and provide novel insights into the physiological functions of thiol-containing systems in fungicide sensitivity for A. alternata.
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Hussain M, Raja NI, Mashwani ZUR, Naz F, Iqbal M, Aslam S. Green synthesis and characterisation of silver nanoparticles and their effects on antimicrobial efficacy and biochemical profiling in Citrus reticulata. IET Nanobiotechnol 2018; 12:514-519. [PMID: 29768240 PMCID: PMC8676029 DOI: 10.1049/iet-nbt.2017.0153] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2017] [Revised: 12/07/2017] [Accepted: 12/24/2017] [Indexed: 11/19/2022] Open
Abstract
The synthesis of nanoparticles by utilising plant extract has revolutionised the field of nanotechnology. In the present study, AgNPs were synthesised by utilising the leaves of Moringa oleifera as reducing and stabilising agent. UV-visible spectroscopy showed characteristic surface plasmon band in the range of 413-420 nm. Scanning electron microscopy (SEM) elucidated rectangular segments fused together. X-ray diffraction (XRD) analysis confirmed the crystalline nature of AgNPs and presence of metallic silver ions was confirmed by energy dispersive X-ray (EDX). The different concentrations (10, 20, 30 and 40 ppm) of AgNPs were exogenously applied on Citrus reticulata to record the disease incidence at different day intervals. The disease intensity was progressively increased in all the applied treatments with the passage of time. The 30 ppm concentration of AgNPs was found to be most suitable concentration for creating the resistance against brown spot disease. Moreover, the effects of AgNPs were also assessed for biochemical profiling in C. reticulata. The enhanced production of endogenous enzymes and non-enzymatic components was observed in response to 30 ppm concentration of AgNPs. The present work highlighted that green synthesised AgNPs can be as used as biological control of citrus diseases and the enhanced production of secondary metabolites antioxidants.
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Affiliation(s)
- Mubashir Hussain
- Department of Botany, PMAS Arid Agriculture University Rawalpindi, Pakistan.
| | - Naveed Iqbal Raja
- Department of Botany, PMAS Arid Agriculture University Rawalpindi, Pakistan
| | | | - Farah Naz
- Department of Plant Pathology, PMAS Arid Agriculture University Rawalpindi, Pakistan
| | - Muhammad Iqbal
- Department of Botany, PMAS Arid Agriculture University Rawalpindi, Pakistan
| | - Sumaira Aslam
- Department of Botany, PMAS Arid Agriculture University Rawalpindi, Pakistan
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Zhong Z, Li N, Liu L, He B, Igarashi Y, Luo F. Label-free differentially proteomic analysis of interspecific interaction between white-rot fungi highlights oxidative stress response and high metabolic activity. Fungal Biol 2018; 122:774-784. [PMID: 30007428 DOI: 10.1016/j.funbio.2018.04.005] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2017] [Revised: 03/31/2018] [Accepted: 04/09/2018] [Indexed: 10/17/2022]
Abstract
The laccase production by mycelial antagonistic interaction among white-rot fungi is a very important pathway for lignin degradation research. To gain a better understanding of competitive mechanisms under mycelial antagonistic interaction among three lignin-degrading white-rot basidiomycetes of Trametesversicolor (Tv), Pleurotusostreatus (Po) and Dichomitussqualens (Ds), mycelial morphology and proteins in three co-culture combinations TvPo (Tv cocultivated with Po), PoDs (Po cocultivated with Ds), TvDs (Tv cocultivated with Ds) were compared with corresponding each two mono-cultures. In this study, scanning electron microscopy detection of co-cultures indicated a highly close attachment of fungal hyphae with each other and conidiation could be inhibited under fungal interaction. In addition, a label-free proteomic analysis revealed changes on fungal proteomes existed in their counterpart competitors of co-culture. The maximum number of 1020 differentially expressed proteins (DEPs) were identified in PoDs relative to Po while the minimum number of 367 DEPs were identified in PoDs relative to Ds. Notably, we also found a large number of overexpressed proteins were oxidative stress-related proteins, followed by carbohydrate metabolism-related proteins and energy production-related proteins in all three co-culture combinations compared with control. These results were important for the future exploration of molecular mechanisms underlying lignin-degrading fungal interaction.
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Affiliation(s)
- Zixuan Zhong
- Research Center of Bioenergy and Bioremediation, College of Resources and Environment, Southwest University, Beibei, Chongqing 400715, China
| | - Nannan Li
- Research Center of Bioenergy and Bioremediation, College of Resources and Environment, Southwest University, Beibei, Chongqing 400715, China; Academy of Agricultural Sciences, Southwest University, Beibei, Chongqing 400715, China
| | - Li Liu
- Research Center of Bioenergy and Bioremediation, College of Resources and Environment, Southwest University, Beibei, Chongqing 400715, China
| | - Binghui He
- Research Center of Bioenergy and Bioremediation, College of Resources and Environment, Southwest University, Beibei, Chongqing 400715, China
| | - Yasuo Igarashi
- Research Center of Bioenergy and Bioremediation, College of Resources and Environment, Southwest University, Beibei, Chongqing 400715, China
| | - Feng Luo
- Research Center of Bioenergy and Bioremediation, College of Resources and Environment, Southwest University, Beibei, Chongqing 400715, China.
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Induced resistance in tomato fruit by γ-aminobutyric acid for the control of alternaria rot caused by Alternaria alternata. Food Chem 2017; 221:1014-1020. [DOI: 10.1016/j.foodchem.2016.11.061] [Citation(s) in RCA: 60] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2016] [Revised: 08/10/2016] [Accepted: 11/14/2016] [Indexed: 12/22/2022]
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Dalio RJD, Magalhães DM, Rodrigues CM, Arena GD, Oliveira TS, Souza-Neto RR, Picchi SC, Martins PMM, Santos PJC, Maximo HJ, Pacheco IS, De Souza AA, Machado MA. PAMPs, PRRs, effectors and R-genes associated with citrus-pathogen interactions. ANNALS OF BOTANY 2017; 119:749-774. [PMID: 28065920 PMCID: PMC5571375 DOI: 10.1093/aob/mcw238] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2016] [Revised: 07/08/2016] [Accepted: 10/22/2016] [Indexed: 05/08/2023]
Abstract
BACKGROUND Recent application of molecular-based technologies has considerably advanced our understanding of complex processes in plant-pathogen interactions and their key components such as PAMPs, PRRs, effectors and R-genes. To develop novel control strategies for disease prevention in citrus, it is essential to expand and consolidate our knowledge of the molecular interaction of citrus plants with their pathogens. SCOPE This review provides an overview of our understanding of citrus plant immunity, focusing on the molecular mechanisms involved in the interactions with viruses, bacteria, fungi, oomycetes and vectors related to the following diseases: tristeza, psorosis, citrus variegated chlorosis, citrus canker, huanglongbing, brown spot, post-bloom, anthracnose, gummosis and citrus root rot.
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Affiliation(s)
- Ronaldo J. D. Dalio
- Citrus Biotechnology Lab, Centro de Citricultura Sylvio Moreira, IAC, Cordeirópolis-SP, Brazil
| | - Diogo M. Magalhães
- Citrus Biotechnology Lab, Centro de Citricultura Sylvio Moreira, IAC, Cordeirópolis-SP, Brazil
| | - Carolina M. Rodrigues
- Citrus Biotechnology Lab, Centro de Citricultura Sylvio Moreira, IAC, Cordeirópolis-SP, Brazil
| | - Gabriella D. Arena
- Citrus Biotechnology Lab, Centro de Citricultura Sylvio Moreira, IAC, Cordeirópolis-SP, Brazil
| | - Tiago S. Oliveira
- Citrus Biotechnology Lab, Centro de Citricultura Sylvio Moreira, IAC, Cordeirópolis-SP, Brazil
| | - Reinaldo R. Souza-Neto
- Citrus Biotechnology Lab, Centro de Citricultura Sylvio Moreira, IAC, Cordeirópolis-SP, Brazil
| | - Simone C. Picchi
- Citrus Biotechnology Lab, Centro de Citricultura Sylvio Moreira, IAC, Cordeirópolis-SP, Brazil
| | - Paula M. M. Martins
- Citrus Biotechnology Lab, Centro de Citricultura Sylvio Moreira, IAC, Cordeirópolis-SP, Brazil
| | - Paulo J. C. Santos
- Citrus Biotechnology Lab, Centro de Citricultura Sylvio Moreira, IAC, Cordeirópolis-SP, Brazil
| | - Heros J. Maximo
- Citrus Biotechnology Lab, Centro de Citricultura Sylvio Moreira, IAC, Cordeirópolis-SP, Brazil
| | - Inaiara S. Pacheco
- Citrus Biotechnology Lab, Centro de Citricultura Sylvio Moreira, IAC, Cordeirópolis-SP, Brazil
| | - Alessandra A. De Souza
- Citrus Biotechnology Lab, Centro de Citricultura Sylvio Moreira, IAC, Cordeirópolis-SP, Brazil
| | - Marcos A. Machado
- Citrus Biotechnology Lab, Centro de Citricultura Sylvio Moreira, IAC, Cordeirópolis-SP, Brazil
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Chen LH, Tsai HC, Yu PL, Chung KR. A Major Facilitator Superfamily Transporter-Mediated Resistance to Oxidative Stress and Fungicides Requires Yap1, Skn7, and MAP Kinases in the Citrus Fungal Pathogen Alternaria alternata. PLoS One 2017; 12:e0169103. [PMID: 28060864 PMCID: PMC5218470 DOI: 10.1371/journal.pone.0169103] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2016] [Accepted: 12/12/2016] [Indexed: 12/19/2022] Open
Abstract
Major Facilitator Superfamily (MFS) transporters play an important role in multidrug resistance in fungi. We report an AaMFS19 gene encoding a MFS transporter required for cellular resistance to oxidative stress and fungicides in the phytopathogenic fungus Alternaria alternata. AaMFS19, containing 12 transmembrane domains, displays activity toward a broad range of substrates. Fungal mutants lacking AaMFS19 display profound hypersensitivities to cumyl hydroperoxide, potassium superoxide, many singlet oxygen-generating compounds (eosin Y, rose Bengal, hematoporphyrin, methylene blue, and cercosporin), and the cell wall biosynthesis inhibitor, Congo red. AaMFS19 mutants also increase sensitivity to copper ions, clotrimazole, fludioxonil, and kocide fungicides, 2-chloro-5-hydroxypyridine (CHP), and 2,3,5-triiodobenzoic acid (TIBA). AaMFS19 mutants induce smaller necrotic lesions on leaves of a susceptible citrus cultivar. All observed phenotypes in the mutant are restored by introducing and expressing a wild-type copy of AaMFS19. The wild-type strain of A. alternata treated with either CHP or TIBA reduces radial growth and formation and germination of conidia, increases hyphal branching, and results in decreased expression of the AaMFS19 gene. The expression of AaMFS19 is regulated by the Yap1 transcription activator, the Hog1 and Fus3 mitogen-activated protein (MAP) kinases, the ‘two component’ histidine kinase, and the Skn7 response regulator. Our results demonstrate that A. alternata confers resistance to different chemicals via a membrane-bound MFS transporter.
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Affiliation(s)
- Li-Hung Chen
- Department of Plant Pathology, College of Agriculture and Natural Resources, National Chung-Hsing University, Taichung, Taiwan
| | - Hsieh-Chin Tsai
- Department of Plant Pathology, College of Agriculture and Natural Resources, National Chung-Hsing University, Taichung, Taiwan
| | - Pei-Ling Yu
- Department of Plant Pathology, College of Agriculture and Natural Resources, National Chung-Hsing University, Taichung, Taiwan
| | - Kuang-Ren Chung
- Department of Plant Pathology, College of Agriculture and Natural Resources, National Chung-Hsing University, Taichung, Taiwan
- Biotechnology Center, NCHU, Taichung, Taiwan
- NCHU-UCD Plant and Food Biotechnology Center, NCHU, Taichung, Taiwan
- * E-mail:
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20
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Yu PL, Chen LH, Chung KR. How the Pathogenic Fungus Alternaria alternata Copes with Stress via the Response Regulators SSK1 and SHO1. PLoS One 2016; 11:e0149153. [PMID: 26863027 PMCID: PMC4749125 DOI: 10.1371/journal.pone.0149153] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2015] [Accepted: 01/27/2016] [Indexed: 01/06/2023] Open
Abstract
The tangerine pathotype of Alternaria alternata is a necrotrophic fungal pathogen causing brown spot disease on a number of citrus cultivars. To better understand the dynamics of signal regulation leading to oxidative and osmotic stress response and fungal infection on citrus, phenotypic characterization of the yeast SSK1 response regulator homolog was performed. It was determined that SSK1 responds to diverse environmental stimuli and plays a critical role in fungal pathogenesis. Experiments to determine the phenotypes resulting from the loss of SSK1 reveal that the SSK1 gene product may be fulfilling similar regulatory roles in signaling pathways involving a HOG1 MAP kinase during ROS resistance, osmotic resistance, fungicide sensitivity and fungal virulence. The SSK1 mutants display elevated sensitivity to oxidants, fail to detoxify H2O2 effectively, induce minor necrosis on susceptible citrus leaves, and displays resistance to dicarboximide and phenylpyrrole fungicides. Unlike the SKN7 response regulator, SSK1 and HOG1 confer resistance to salt-induced osmotic stress via an unknown kinase sensor rather than the “two component” histidine kinase HSK1. SSK1 and HOG1 play a moderate role in sugar-induced osmotic stress. We also show that SSK1 mutants are impaired in their ability to produce germ tubes from conidia, indicating a role for the gene product in cell differentiation. SSK1 also is involved in multi-drug resistance. However, deletion of the yeast SHO1 (synthetic high osmolarity) homolog resulted in no noticeable phenotypes. Nonetheless, our results show that A. alternata can sense and react to different types of stress via SSK1, HOG1 and SKN7 in a cooperative manner leading to proper physiological and pathological functions.
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Affiliation(s)
- Pei-Ling Yu
- Department of Plant Pathology, College of Agriculture and Natural Resources, National Chung-Hsing University, Taichung, Taiwan
| | - Li-Hung Chen
- Department of Plant Pathology, College of Agriculture and Natural Resources, National Chung-Hsing University, Taichung, Taiwan
| | - Kuang-Ren Chung
- Department of Plant Pathology, College of Agriculture and Natural Resources, National Chung-Hsing University, Taichung, Taiwan
- * E-mail:
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21
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Yang SL, Yu PL, Chung KR. The glutathione peroxidase-mediated reactive oxygen species resistance, fungicide sensitivity and cell wall construction in the citrus fungal pathogen Alternaria alternata. Environ Microbiol 2016; 18:923-35. [PMID: 26567914 DOI: 10.1111/1462-2920.13125] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2015] [Revised: 11/04/2015] [Accepted: 11/05/2015] [Indexed: 12/18/2022]
Abstract
The ability to detoxify reactive oxygen species (ROS) is critical for pathogenicity in the necrotrophic fungus Alternaria alternata. We report a glutathione peroxidase 3 (AaGPx3) involved in the complex signalling network that is essential for the detoxification of cellular stresses induced by ROS and for A. alternata pathogenesis in citrus. AaGPx3 deletion mutants displayed increased sensitivity to H2 O2 and many ROS-generating compounds. AaGPx3 is required for correct fungal development as the AaGPx3 mutant strains showed a severe reduction in conidiation. AaGPx3 mutants accumulated higher chitin content than the wild-type and were less sensitive to the cell wall-targeting compounds calcofluor white and Congo red, as well as the fungicides fludioxonil and vinclozolin, suggesting a role of the glutathione systems in fungal cell wall construction. Virulence assays revealed that AaGPx3 is required for full virulence. The expression of AaGPx3 was downregulated in fungal strains carrying defective NADPH oxidase (Nox) or the oxidative stress responsive regulators YAP1 and HOG1, all implicated in ROS resistance. These results further support the important role of ROS detoxification during A. alternata pathogenesis in citrus. Overall, our study provides genetic evidence to define the central role of AaGPx3 in the biological and pathological functions of A. alternata.
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Affiliation(s)
- Siwy Ling Yang
- Citrus Research and Education Center, Institute of Food and Agricultural Sciences, University of Florida, Lake Alfred, FL, USA
| | - Pei-Ling Yu
- Department of Plant Pathology, College of Agriculture and Natural Resources, National Chung-Hsing University, Taichung, Taiwan
| | - Kuang-Ren Chung
- Citrus Research and Education Center, Institute of Food and Agricultural Sciences, University of Florida, Lake Alfred, FL, USA.,Department of Plant Pathology, College of Agriculture and Natural Resources, National Chung-Hsing University, Taichung, Taiwan
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Kong S, Park SY, Lee YH. Systematic characterization of the bZIP transcription factor gene family in the rice blast fungus, Magnaporthe oryzae. Environ Microbiol 2014; 17:1425-43. [PMID: 25314920 DOI: 10.1111/1462-2920.12633] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2014] [Revised: 09/10/2014] [Accepted: 09/10/2014] [Indexed: 01/26/2023]
Abstract
Regulatory roles of the basic leucine zipper (bZIP) transcription factors (TFs) in fungi have been identified in diverse cellular processes such as development, nutrient utilization and various stress responses. In this study, the 22 Magnaporthe oryzae genes encoding bZIP TFs were systematically characterized. Phylogenetic analysis of fungal bZIP TFs revealed that seven MobZIPs are Magnaporthe-specific, while others belongs to 15 clades of orthologous Ascomycota genes. Expression patterns of MobZIPs under various conditions showed that they are highly stress responsive. We generated deletion mutants for 13 MobZIPs: nine with orthologues in other fungal species and four Magnaporthe-specific ones. Seven of them exhibited defects in mycelial growth, development and/or pathogenicity. Consistent with the conserved functions of the orthologues, MobZIP22 and MobZIP13 played a role in sulfur metabolism and iron homeostasis respectively. Along with MobZIP22 and MobZIP13, one Magnaporthe-specific gene, MobZIP11 is essential for pathogenicity in a reactive oxygen species-dependent manner. Taken together, our results will contribute to understanding the regulatory mechanisms of the bZIP TF gene family in fungal development, adaptation to environmental stresses and pathogenicity in the rice blast fungus.
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Affiliation(s)
- Sunghyung Kong
- Department of Agricultural Biotechnology, Center for Fungal Genetic Resources, and Center for Fungal Pathogenesis, Plant Genomics and Breeding Institute, and Research Institute for Agriculture and Life Sciences, Seoul National University, Seoul, Korea
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Tsai HC, Chung KR. Calcineurin phosphatase and phospholipase C are required for developmental and pathological functions in the citrus fungal pathogen Alternaria alternata. MICROBIOLOGY-SGM 2014; 160:1453-1465. [PMID: 24763426 DOI: 10.1099/mic.0.077818-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Excessive Ca(2+) or compounds interfering with phosphoinositide cycling have been found to inhibit the growth of the tangerine pathotype of Alternaria alternata, suggesting a crucial role of Ca(2+) homeostasis in this pathotype. The roles of PLC1, a phospholipase C-coding gene and CAL1, a calcineurin phosphatase-coding gene were investigated. Targeted gene disruption showed that both PLC1 and CAL1 were required for vegetative growth, conidial formation and pathogenesis in citrus. Fungal strains lacking PLC1 or CAL1 exhibited extremely slow growth and induced small lesions on calamondin leaves. Δplc1 mutants produced fewer conidia, which germinated at slower rates than wild-type. Δcal1 mutants produced abnormal hyphae and failed to produce any mature conidia, but instead produced highly melanized bulbous hyphae with distinct septae. Fluorescence microscopy using Fluo-3 dye as a Ca(2+) indicator revealed that the Δplc1 mutant hyphae emitted stronger cytosolic fluorescence, and the Δcal1 mutant hyphae emitted less cytosolic fluorescence, than those of wild-type. Infection assessed on detached calamondin leaves revealed that application of CaCl2 or neomycin 24 h prior to inoculation provided protection against Alt. alternata. These data indicate that a dynamic equilibrium of cellular Ca(2+) is critical for developmental and pathological processes of Alt. alternata.
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Affiliation(s)
- Hsieh-Chin Tsai
- Citrus Research and Education Center, Institute of Food and Agricultural Sciences (IFAS), University of Florida, 700 Experiment Station Road, Lake Alfred, FL 33850, USA
| | - Kuang-Ren Chung
- Department of Plant Pathology, IFAS, University of Florida, Gainesville, FL 32611, USA.,Citrus Research and Education Center, Institute of Food and Agricultural Sciences (IFAS), University of Florida, 700 Experiment Station Road, Lake Alfred, FL 33850, USA
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Chen LH, Yang SL, Chung KR. Resistance to oxidative stress via regulating siderophore-mediated iron acquisition by the citrus fungal pathogen Alternaria alternata. MICROBIOLOGY-SGM 2014; 160:970-979. [PMID: 24586035 DOI: 10.1099/mic.0.076182-0] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The ability of the necrotrophic fungus Alternaria alternata to detoxify reactive oxygen species (ROS) is crucial for pathogenesis to citrus. We report regulation of siderophore-mediated iron acquisition and ROS resistance by the NADPH oxidase (NOX), the redox activating yes-associated protein 1 (YAP1) regulator, and the high-osmolarity glycerol 1 (HOG1) mitogen-activated protein kinase (MAPK). The A. alternata nonribosomal peptide synthetase (NPS6) is essential for the biosynthesis of siderophores, contributing to iron uptake under low-iron conditions. Fungal strains impaired for NOX, YAP1, HOG1 or NPS6 all display increased sensitivity to ROS. Exogenous addition of iron at least partially rescues ROS sensitivity seen for NPS6, YAP1, HOG1, and NOX mutants. Importantly, expression of the NPS6 gene and biosynthesis of siderophores are regulated by NOX, YAP1 and HOG1, supporting a functional link among these regulatory pathways. Although iron fully rescues H2O2 sensitivity seen in mutants impaired for the response regulator SKN7, neither expression of NPS6 nor biosynthesis of siderophores is controlled by SKN7. Our results indicate that the acquisition of environmental iron has profound effects on ROS detoxification.
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Affiliation(s)
- Li-Hung Chen
- Citrus Research and Education Center, Institute of Food and Agricultural Sciences (IFAS), University of Florida, 700 Experiment Station Road, Lake Alfred, FL 33850, USA
| | - Siwy Ling Yang
- Department of Plant Pathology, IFAS, University of Florida, Gainesville, FL 32611, USA.,Citrus Research and Education Center, Institute of Food and Agricultural Sciences (IFAS), University of Florida, 700 Experiment Station Road, Lake Alfred, FL 33850, USA
| | - Kuang-Ren Chung
- Department of Plant Pathology, IFAS, University of Florida, Gainesville, FL 32611, USA.,Citrus Research and Education Center, Institute of Food and Agricultural Sciences (IFAS), University of Florida, 700 Experiment Station Road, Lake Alfred, FL 33850, USA
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Samalova M, Meyer AJ, Gurr SJ, Fricker MD. Robust anti-oxidant defences in the rice blast fungus Magnaporthe oryzae confer tolerance to the host oxidative burst. THE NEW PHYTOLOGIST 2014; 201:556-573. [PMID: 24117971 DOI: 10.1111/nph.12530] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/07/2013] [Accepted: 08/20/2013] [Indexed: 05/22/2023]
Abstract
Plants respond to pathogen attack via a rapid burst of reactive oxygen species (ROS). However, ROS are also produced by fungal metabolism and are required for the development of infection structures in Magnaporthe oryzae. To obtain a better understanding of redox regulation in M. oryzae, we measured the amount and redox potential of glutathione (E(GSH)), as the major cytoplasmic anti-oxidant, the rates of ROS production, and mitochondrial activity using multi-channel four-dimensional (x,y,z,t) confocal imaging of Grx1-roGFP2 and fluorescent reporters during spore germination, appressorium formation and infection. High levels of mitochondrial activity and ROS were localized to the growing germ tube and appressorium, but E(GSH) was highly reduced and tightly regulated during development. Furthermore, germlings were extremely resistant to external H2O2 exposure ex planta. EGSH remained highly reduced during successful infection of the susceptible rice cultivar CO39. By contrast, there was a dramatic reduction in the infection of resistant (IR68) rice, but the sparse hyphae that did form also maintained a similar reduced E(GSH). We conclude that M. oryzae has a robust anti-oxidant defence system and maintains tight control of EGSH despite substantial oxidative challenge. Furthermore, the magnitude of the host oxidative burst alone does not stress the pathogen sufficiently to prevent infection in this pathosystem.
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Affiliation(s)
- Marketa Samalova
- Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, OX1 3RB, UK
| | - Andreas J Meyer
- INRES, Universität Bonn, Friedrich-Ebert-Allee 144, D-53113, Bonn, Germany
| | - Sarah J Gurr
- Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, OX1 3RB, UK
- Biosciences, University of Exeter, Devon, EX4 4QD, UK
| | - Mark D Fricker
- Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, OX1 3RB, UK
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Daub ME, Herrero S, Chung KR. Reactive oxygen species in plant pathogenesis: the role of perylenequinone photosensitizers. Antioxid Redox Signal 2013; 19:970-89. [PMID: 23259634 DOI: 10.1089/ars.2012.5080] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
SIGNIFICANCE Reactive oxygen species (ROS) play multiple roles in interactions between plants and microbes, both as host defense mechanisms and as mediators of pathogenic and symbiotic associations. One source of ROS in these interactions are photoactivated, ROS-generating perylenequinone pigments produced via polyketide metabolic pathways in plant-associated fungi. These natural products, including cercosporin, elsinochromes, hypocrellins, and calphostin C, are being utilized as medicinal agents, enzyme inhibitors, and in tumor therapy, but in nature, they play a role in the establishment of pathogenic associations between fungi and their plant hosts. RECENT ADVANCES Photoactivated perylenequinones are photosensitizers that use light energy to form singlet oxygen (¹O₂) and free radical oxygen species which damage cellular components based on localization of the perylenequinone molecule. Production of perylenequinones during infection commonly results in lipid peroxidation and membrane damage, leading to leakage of nutrients from cells into the intercellular spaces colonized by the pathogen. Perylenequinones show almost universal toxicity against organisms, including plants, mice, bacteria, and most fungi. The producing fungi are resistant, however, and serve as models for understanding resistance mechanisms. CRITICAL ISSUES Studies of resistance mechanisms by perylenequinone-producing fungi such as Cercospora species are leading to an understanding of cellular resistance to ¹O₂ and oxidative stress. Recent studies show commonalities between resistance mechanisms in these fungi with extensive studies of ¹O₂ and oxidative stress responses in photosynthetic organisms. FUTURE DIRECTIONS Such studies hold promise both for improved medical use and for engineering crop plants for disease resistance.
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Affiliation(s)
- Margaret E Daub
- Department of Plant Biology, North Carolina State University, Raleigh, NC 27695, USA.
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Yang SL, Chung KR. Similar and distinct roles of NADPH oxidase components in the tangerine pathotype of Alternaria alternata. MOLECULAR PLANT PATHOLOGY 2013; 14:543-556. [PMID: 23527595 PMCID: PMC6638896 DOI: 10.1111/mpp.12026] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
The fungal nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (Nox) complex, which has been implicated in the production of low-level reactive oxygen species (ROS), contains mainly NoxA, NoxB (gp91(phox) homologues) and NoxR (p67(phox) homologue). Here, we report the developmental and pathological functions of NoxB and NoxR in the tangerine pathotype of Alternaria alternata. Loss-of-function genetics revealed that all three Nox components are required for the accumulation of cellular hydrogen peroxide (H₂O₂). Alternaria alternata strains lacking NoxA, NoxB or NoxR also displayed an increased sensitivity to H₂O₂ and many ROS-generating oxidants. These phenotypes are highly similar to those previously seen for the Δyap1 mutant lacking a YAP1 transcriptional regulator and for the Δhog1 mutant lacking a HOG1 mitogen-activated protein (MAP) kinase, implicating a possible link among them. A fungal strain carrying a NoxA NoxB or NoxA NoxR double mutation was more sensitive to the test compounds than the strain mutated at a single gene, implicating a synergistic function among Nox components. The ΔnoxB mutant strain failed to produce any conidia; both ΔnoxA and ΔnoxR mutant strains showed a severe reduction in sporulation. Mutant strains carrying defective NoxB had higher chitin content than the wild-type and were insensitive to calcofluor white, Congo red and the fungicides vinclozolin and fludioxonil. Virulence assays revealed that all three Nox components are required for the elaboration of the penetration process. The inability to penetrate the citrus host, observed for Δnox mutants, could be overcome by wounding and by reacquiring a dominant Nox gene. The A. alternata NoxR did not influence the expression of NoxB, but negatively regulated NoxA. Importantly, the expression of both YAP1 and HOG1 genes, whose products are involved in resistance to ROS, was down-regulated in fungi carrying defective NoxA, NoxB or NoxR. Our results highlight the requirement of Nox in ROS resistance and provide insights into its critical role in regulating both YAP1 and HOG1 in A. alternata.
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Affiliation(s)
- Siwy Ling Yang
- Citrus Research and Education Center, Institute of Food and Agricultural Sciences-IFAS, University of Florida, 700 Experiment Station Road, Lake Alfred, FL 33850, USA
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Chen LH, Lin CH, Chung KR. A nonribosomal peptide synthetase mediates siderophore production and virulence in the citrus fungal pathogen Alternaria alternata. MOLECULAR PLANT PATHOLOGY 2013; 14:497-505. [PMID: 23438010 PMCID: PMC6638914 DOI: 10.1111/mpp.12021] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
Alternaria species produce and excrete dimethyl coprogen siderophores to acquire iron. The Alternaria alternata gene AaNPS6, encoding a polypeptide analogous to fungal nonribosomal peptide synthetases, was found to be required for the production of siderophores and virulence on citrus. Siderophores purified from culture filtrates of the wild-type strain did not induce any phytotoxicity on the leaves of citrus. Fungal strains lacking AaNPS6 produced little or no detectable extracellular siderophores and displayed an increased sensitivity to H₂O₂, superoxide-generating compounds (KO₂ and menadione) and iron depletion. Δnps6 mutants were also defective for the production of melanin and conidia. The introduction of a wild-type AaNPS6 under the control of its endogenous promoter to a Δnps6 null mutant at least partially restored siderophore production and virulence to citrus, demonstrating a functional link between iron uptake and fungal pathogenesis. Elevated sensitivity to H₂O₂, seen for the Δnps6 null strain could be relieved by exogenous application of ferric iron. The expression of the AaNPS6 gene was highly up-regulated under low-iron conditions and apparently controlled by the redox-responsive yeast transcriptional regulator YAP1. Hence, the maintenance of iron homeostasis via siderophore-mediated iron uptake also plays an important role in resistance to toxic reactive oxygen species (ROS). Our results demonstrate further the critical role of ROS detoxification for the pathogenicity of A. alternata in citrus.
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Affiliation(s)
- Li-Hung Chen
- Citrus Research and Education Center, Institute of Food and Agricultural Sciences-IFAS, University of Florida, 700 Experiment Station Road, Lake Alfred, FL 33850, USA
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Llorens E, Fernández-Crespo E, Vicedo B, Lapeña L, García-Agustín P. Enhancement of the citrus immune system provides effective resistance against Alternaria brown spot disease. JOURNAL OF PLANT PHYSIOLOGY 2013; 170:146-54. [PMID: 23260526 DOI: 10.1016/j.jplph.2012.09.018] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/05/2012] [Revised: 09/12/2012] [Accepted: 09/13/2012] [Indexed: 05/08/2023]
Abstract
In addition to basal defense mechanisms, plants are able to develop enhanced defense mechanisms such as induced resistance (IR) upon appropriate stimulation. We recently described the means by which several carboxylic acids protect Arabidopsis and tomato plants against fungi. In this work, we demonstrate the effectiveness of hexanoic acid (Hx) in the control of Alternaria brown spot (ABS) disease via enhancement of the immune system of Fortune mandarin. The application of 1mM Hx in irrigation water to 2-year-old Fortune plants clearly reduced the incidence of the disease and led to smaller lesions. We observed that several of the most important mechanisms involved in induced resistance were affected by Hx application. Our results demonstrate enhanced callose deposition in infected plants treated with Hx, which suggests an Hx priming mechanism. Plants treated with the callose inhibitor 2-DDG were more susceptible to the fungus. Moreover, polygalacturonase-inhibiting protein (PGIP) gene expression was rapidly and significantly upregulated in treated plants. However, treatment with Hx decreased the levels of reactive oxygen species (ROS) in infected plants. Hormonal and gene analyses revealed that the jasmonic acid (JA) pathway was activated due to a greater accumulation of 12-oxo-phytodienoic acid (OPDA) and JA along with a rapid accumulation of JA-isoleucine (JA-Ile). Furthermore, we observed a more rapid accumulation of abscisic acid (ABA), which could act as a positive regulator of callose deposition. Thus, our results support the hypothesis that both enhanced physical barriers and the JA signaling pathway are involved in hexanoic acid-induced resistance (Hx-IR) to Alternaria alternata.
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Affiliation(s)
- Eugenio Llorens
- Grupo de Bioquímica y Biotecnología, Área de Fisiología Vegetal, Departamento de Ciencias Agrarias y del Medio Natural, ESTCE, Universitat Jaume I, 12071 Castellón, Spain.
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Chung KR. Stress Response and Pathogenicity of the Necrotrophic Fungal Pathogen Alternaria alternata. SCIENTIFICA 2012; 2012:635431. [PMID: 24278721 PMCID: PMC3820455 DOI: 10.6064/2012/635431] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/12/2012] [Accepted: 10/03/2012] [Indexed: 05/07/2023]
Abstract
The production of host-selective toxins by the necrotrophic fungus Alternaria alternata is essential for the pathogenesis. A. alternata infection in citrus leaves induces rapid lipid peroxidation, accumulation of hydrogen peroxide (H2O2), and cell death. The mechanisms by which A. alternata avoids killing by reactive oxygen species (ROS) after invasion have begun to be elucidated. The ability to coordinate of signaling pathways is essential for the detoxification of cellular stresses induced by ROS and for pathogenicity in A. alternata. A low level of H2O2, produced by the NADPH oxidase (NOX) complex, modulates ROS resistance and triggers conidiation partially via regulating the redox-responsive regulators (YAP1 and SKN7) and the mitogen-activated protein (MAP) kinase (HOG1) mediated pathways, which subsequently regulate the genes required for the biosynthesis of siderophore, an iron-chelating compound. Siderophore-mediated iron acquisition plays a key role in ROS detoxification because of the requirement of iron for the activities of antioxidants (e.g., catalase and SOD). Fungal strains impaired for the ROS-detoxifying system severely reduce the virulence on susceptible citrus cultivars. This paper summarizes the current state of knowledge of signaling pathways associated with cellular responses to multidrugs, oxidative and osmotic stress, and fungicides, as well as the pathogenicity/virulence in the tangerine pathotype of A. alternata.
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Affiliation(s)
- Kuang-Ren Chung
- Citrus Research and Education Center, Institute of Food and Agricultural Sciences (IFAS), University of Florida, 700 Experiment Station Road, Lake Alfred, FL 33850, USA
- Department of Plant Pathology, IFAS, University of Florida, Gainesville, FL 32611, USA
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Tsai HC, Yang SL, Chung KR. Cyclic AMP-dependent protein kinase A negatively regulates conidia formation by the tangerine pathotype of Alternaria alternata. World J Microbiol Biotechnol 2012; 29:289-300. [PMID: 23054702 DOI: 10.1007/s11274-012-1182-3] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2012] [Accepted: 09/24/2012] [Indexed: 01/24/2023]
Abstract
The necrotrophic fungal pathogen Alternaria alternata causes brown spot diseases in many citrus cultivars. The FUS3 and SLT2 mitogen-activated protein kinases (MAPK)-mediated signaling pathways have been shown to be required for conidiation. Exogenous application of cAMP to this fungal pathogen decreased conidia formation considerably. This study determined whether a cAMP-activated protein kinase A (PKA) is required for conidiation. Using loss-of-function mutations in PKA catalytic and regulatory subunit-coding genes, we demonstrated that PKA negatively regulates conidiation. Fungal mutants lacking PKA catalytic subunit gene (PKA ( cat )) reduced growth, lacked detectable PKA activity, and produced higher amounts of conidia compared to wild-type. Introduction of a functional copy of PKA ( cat ) into a null mutant partially restored PKA activity and produced wild-type level of conidia. In contrast, fungi lacking PKA regulatory subunit gene (PKA ( reg )) produced detectable PKA activity, exhibited severe growth reduction, formed swelling hyphal segments, and produced no mature conidia. Introduction of the PKA ( reg ) gene to a regulatory subunit mutant restored all phenotypes to wild type. PKA ( reg )-null mutants induced fewer necrotic lesions on citrus compared to wild-type, whereas PKA ( cat ) mutant displayed wild-type virulence. Overall, our studies indicate that PKA and FUS3-mediated signaling pathways apparently have very different roles in the regulation of conidia production and A. alternata pathogenesis in citrus.
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Affiliation(s)
- Hsieh-Chin Tsai
- Citrus Research and Education Center, Institute of Food and Agricultural Sciences (IFAS), University of Florida, 700 Experiment Station Road, Lake Alfred, FL 33850, USA
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Yang SL, Chung KR. The NADPH oxidase-mediated production of hydrogen peroxide (H(2)O(2)) and resistance to oxidative stress in the necrotrophic pathogen Alternaria alternata of citrus. MOLECULAR PLANT PATHOLOGY 2012; 13:900-14. [PMID: 22435666 PMCID: PMC6638813 DOI: 10.1111/j.1364-3703.2012.00799.x] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
It has become increasingly apparent that the production of reactive oxygen species (ROS) by the NADPH oxidase (Nox) complex is vital for cellular differentiation and signalling in fungi. We cloned and characterized an AaNoxA gene of the necrotrophic fungus Alternaria alternata, which encodes a polypeptide analogous to mammalian gp91(phox) and fungal Noxs implicated in the generation of ROS. Genetic analysis confirmed that AaNoxA is responsible for the production of ROS. Moreover, deletion of AaNoxA in A. alternata resulted in an elevated hypersensitivity to hydrogen peroxide (H(2)O(2)), menadione, potassium superoxide (KO(2)), diamide and many ROS-generating compounds. The results implicate the involvement of AaNoxA in cellular resistance to ROS stress. The impaired phenotypes strongly resemble those previously seen for the ap1 null mutant defective in a YAP1-like transcriptional regulator and for the hog1 mutant defective in a HOG1-like mitogen-activated protein (MAP) kinase. The noxA null mutant was also hypersensitive to Nox inhibitors, nitric oxide (NO(·)) donors and NO(·) synthase inhibitors, implying a role of AaNoxA in the NO(·) signalling pathway. Expression of AaNoxA was activated by H(2)O(2), menadione, KO(2), NO(·) donors and L-arginine (a substrate for NO(·) synthase). AaNoxA may be able to sense and respond to both ROS and nitric oxide. Moreover, AaNoxA is required for normal conidiation and full fungal virulence. AaNoxA promoted the expression of the AaAP1 and AaHOG1 genes in A. alternata. Inactivation of AaNoxA greatly reduced the transcriptional activation of AaAP1 in response to ROS stress. Thus, we conclude that the regulatory functions of AaNoxA conferring ROS resistance are modulated partially through the activation of the YAP1- and HOG1 MAP kinase-mediated signalling pathways.
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Affiliation(s)
- Siwy Ling Yang
- Citrus Research and Education Center and Department of Plant Pathology, Institute of Food and Agricultural Sciences, University of Florida, Lake Alfred, FL 33850, USA
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Chen LH, Lin CH, Chung KR. Roles for SKN7 response regulator in stress resistance, conidiation and virulence in the citrus pathogen Alternaria alternata. Fungal Genet Biol 2012; 49:802-13. [PMID: 22902811 DOI: 10.1016/j.fgb.2012.07.006] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2012] [Revised: 07/17/2012] [Accepted: 07/26/2012] [Indexed: 01/17/2023]
Abstract
"Two-component" histidine kinase (HSK1) is the primary regulator of resistance to sugar osmotic stress and sensitivity to dicarboximide or phenylpyrrole fungicides in the citrus fungal pathogen Alternaria alternata. On the other hand, the mitogen-activated protein kinase HOG1 confers resistance solely to salts and oxidative stress. We report here independent and shared functions of the SKN7-mediated signaling pathway with HSK1 and HOG1. SKN7, a putative transcription downstream regulator of HSK1, is primarily required for cellular resistance to oxidative and sugar-induced osmotic stress. SKN7, perhaps acting in parallel with HOG1, is required for resistance to H(2)O(2), tert-butyl hydroperoxide, and cumyl peroxide, but not to the superoxide-generating compounds - menadione, potassium superoxide, and diamide. Because of phenotypic commonalities, SKN7 is likely involved in resistance to sugar-induced osmotic stress via the HSK1 signaling pathway. However, mutants lacking SKN7 displayed wild-type sensitivity to NaCl and KCl salts. SKN7 is constitutively localized in the nucleus regardless of H(2)O(2) treatment. When compared to the wild type, skn7 mutants exhibited lower catalase, peroxidase, and superoxide dismutase activities and induced significantly fewer necrotic lesions on the susceptible citrus cultivar. The skn7 mutant exhibited fungicide resistance at levels between the hsk1 and the hog1 mutant strains. Skn7/hog1 double mutants exhibited fungicide resistance, similar to the strain with a single AaHSK1 gene mutation. Moreover, the A. alternata SKN7 plays a role in conidia formation. Conidia produced by the skn7 mutant are smaller and have fewer transverse septae than those produced by wild type. All altered phenotypes in the mutant were restored by introducing and expressing a wild-type copy of SKN7 under control of the endogenous promoter.
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Affiliation(s)
- Li-Hung Chen
- Citrus Research and Education Center, Institute of Food and Agricultural Sciences, University of Florida, Lake Alfred, FL 33850, USA
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Yago JI, Lin CH, Chung KR. The SLT2 mitogen-activated protein kinase-mediated signalling pathway governs conidiation, morphogenesis, fungal virulence and production of toxin and melanin in the tangerine pathotype of Alternaria alternata. MOLECULAR PLANT PATHOLOGY 2011; 12:653-65. [PMID: 21726368 PMCID: PMC6640243 DOI: 10.1111/j.1364-3703.2010.00701.x] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Fungi respond and adapt to different environmental stimuli via signal transduction systems. We determined the function of a yeast SLT2 mitogen-activated protein (MAP) kinase homologue (AaSLT2) in Alternaria alternata, the fungal pathogen of citrus. Analysis of the loss-of-function mutant indicated that AaSLT2 is required for the production of a host-selective toxin, and is crucial for fungal pathogenicity. Moreover, the A. alternata slt2 mutants displayed hypersensitivity to cell wall-degrading enzymes and chemicals such as Calcofluor white and Congo red. This implicates an important role of AaSLT2 in the maintenance of cell wall integrity in A. alternata. The A. alternata slt2 mutants were also hypersensitive to a heteroaromatic compound, 2-chloro-5-hydroxypyridine, and a plant growth regulator, 2,3,5-triiodobenzoic acid. Developmentally, the AaSLT2 gene product was shown to be critical for conidial formation and hyphal elongation. Compared with the wild-type, the mutants produced fewer but slightly larger conidia with less transverse septae. The mutants also accumulated lower levels of melanin and chitin. Unlike the wild-type progenitor, the A. alternata slt2 mutants produced globose, swollen hyphae that did not elongate in a straight radial direction. All defective phenotypes in the mutant were restored by transformation and expression of a wild-type copy of AaSLT2 under the control of its endogenous promoter. This study highlights an important role of the AaSLT2 MAP kinase-mediated signalling pathway, regulating diverse physiological, developmental and pathological functions, in the tangerine pathotype of A. alternata.
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Affiliation(s)
- Jonar Ingan Yago
- Citrus Research and Education Center and Department of Plant Pathology, Institute of Food and Agricultural Sciences, University of Florida, Lake Alfred, FL 33850, USA
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