1
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Tör M, Wood T, Webb A, Göl D, McDowell JM. Recent developments in plant-downy mildew interactions. Semin Cell Dev Biol 2023; 148-149:42-50. [PMID: 36670035 DOI: 10.1016/j.semcdb.2023.01.010] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2022] [Revised: 01/11/2023] [Accepted: 01/12/2023] [Indexed: 01/20/2023]
Abstract
Downy mildews are obligate oomycete pathogens that attack a wide range of plants and can cause significant economic impacts on commercial crops and ornamental plants. Traditionally, downy mildew disease control relied on an integrated strategies, that incorporate cultural practices, deployment of resistant cultivars, crop rotation, application of contact and systemic pesticides, and biopesticides. Recent advances in genomics provided data that significantly advanced understanding of downy mildew evolution, taxonomy and classification. In addition, downy mildew genomics also revealed that these obligate oomycetes have reduced numbers of virulence factor genes in comparison to hemibiotrophic and necrotrophic oomycetes. However, downy mildews do deploy significant arrays of virulence proteins, including so-called RXLR proteins that promote virulence or are recognized as avirulence factors. Pathogenomics are being applied to downy mildew population studies to determine the genetic diversity within the downy mildew populations and manage disease by selection of appropriate varieties and management strategies. Genome editing technologies have been used to manipulate host disease susceptibility genes in different plants including grapevine and sweet basil and thereby provide new soucres of resistance genes against downy mildews. Previously, it has proved difficult to transform and manipulate downy mildews because of their obligate lifestyle. However, recent exploitation of RNA interference machinery through Host-Induced Gene Silencing (HIGS) and Spray-Induced Gene Silencing (SIGS) indicate that functional genomics in downy mildews is now possible. Altogether, these breakthrough technologies and attendant fundamental understanding will advance our ability to mitigate downy mildew diseases.
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Affiliation(s)
- Mahmut Tör
- Department of Biology, School of Science and the Environment, University of Worcester, Henwick Grove, Worcester WR2 6AJ, UK.
| | | | | | - Deniz Göl
- Department of Biology, School of Science and the Environment, University of Worcester, Henwick Grove, Worcester WR2 6AJ, UK
| | - John M McDowell
- School of Plant and Environmental Sciences, Virginia Tech, Blacksburg, VA 24061-0329, USA
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2
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Wang W, Liu J, Mishra B, Mukhtar MS, McDowell JM. Sparking a sulfur war between plants and pathogens. Trends Plant Sci 2022; 27:1253-1265. [PMID: 36028431 DOI: 10.1016/j.tplants.2022.07.007] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/07/2021] [Revised: 07/03/2022] [Accepted: 07/21/2022] [Indexed: 06/15/2023]
Abstract
The biochemical versatility of sulfur (S) lends itself to myriad roles in plant-pathogen interactions. This review evaluates the current understanding of mechanisms by which pathogens acquire S from their plant hosts and highlights new evidence that plants can limit S availability during the immune responses. We discuss the discovery of host disease-susceptibility genes related to S that can be genetically manipulated to create new crop resistance. Finally, we summarize future research challenges and propose a research agenda that leverages systems biology approaches for a holistic understanding of this important element's diverse roles in plant disease resistance and susceptibility.
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Affiliation(s)
- Wei Wang
- School of Plant and Environmental Sciences, Virginia Tech, Blacksburg, VA 24061, USA
| | - Jinbao Liu
- Department of Biology, University of Alabama-Birmingham, Birmingham, AL 35294, USA
| | - Bharat Mishra
- Department of Biology, University of Alabama-Birmingham, Birmingham, AL 35294, USA
| | - M Shahid Mukhtar
- Department of Biology, University of Alabama-Birmingham, Birmingham, AL 35294, USA
| | - John M McDowell
- School of Plant and Environmental Sciences, Virginia Tech, Blacksburg, VA 24061, USA.
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3
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Bilir Ö, Göl D, Hong Y, McDowell JM, Tör M. Small RNA-based plant protection against diseases. Front Plant Sci 2022; 13:951097. [PMID: 36061762 PMCID: PMC9434005 DOI: 10.3389/fpls.2022.951097] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/23/2022] [Accepted: 07/28/2022] [Indexed: 06/15/2023]
Abstract
Plant diseases cause significant decreases in yield and quality of crops and consequently pose a very substantial threat to food security. In the continuous search for environmentally friendly crop protection, exploitation of RNA interferance machinery is showing promising results. It is well established that small RNAs (sRNAs) including microRNA (miRNA) and small interfering RNA (siRNA) are involved in the regulation of gene expression via both transcriptional and post-transcriptional RNA silencing. sRNAs from host plants can enter into pathogen cells during invasion and silence pathogen genes. This process has been exploited through Host-Induced Gene Silencing (HIGS), in which plant transgenes that produce sRNAs are engineered to silence pest and pathogen genes. Similarly, exogenously applied sRNAs can enter pest and pathogen cells, either directly or via the hosts, and silence target genes. This process has been exploited in Spray-Induced Gene Silencing (SIGS). Here, we focus on the role of sRNAs and review how they have recently been used against various plant pathogens through HIGS or SIGS-based methods and discuss advantages and drawbacks of these approaches.
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Affiliation(s)
- Özlem Bilir
- Department of Biotechnology, Trakya Agricultural Research Institute, Edirne, Turkey
| | - Deniz Göl
- Department of Biology, School of Science and the Environment, University of Worcester, Worcester, United Kingdom
| | - Yiguo Hong
- Department of Biology, School of Science and the Environment, University of Worcester, Worcester, United Kingdom
- Research Centre for Plant RNA Signaling, College of Life and Environmental Sciences, Hangzhou Normal University, Hangzhou, China
| | - John M. McDowell
- School of Plant and Environmental Sciences, Virginia Tech, Blacksburg, VA, United States
| | - Mahmut Tör
- Department of Biology, School of Science and the Environment, University of Worcester, Worcester, United Kingdom
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4
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Wilson RA, McDowell JM. Recent advances in understanding of fungal and oomycete effectors. Curr Opin Plant Biol 2022; 68:102228. [PMID: 35605341 DOI: 10.1016/j.pbi.2022.102228] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/10/2022] [Revised: 04/04/2022] [Accepted: 04/05/2022] [Indexed: 06/15/2023]
Abstract
Fungal and oomycete pathogens secrete complex arrays of proteins and small RNAs to interface with plant-host targets and manipulate plant regulatory networks to the microbes' advantage. Research on these important virulence factors has been accelerated by improved genome sequences, refined bioinformatic prediction tools, and exploitation of efficient platforms for understanding effector gene expression and function. Recent studies have validated the expectation that oomycetes and fungi target many of the same sectors in immune signaling networks, but the specific host plant targets and modes of action are diverse. Effector research has also contributed to deeper understanding of the mechanisms of effector-triggered immunity.
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Affiliation(s)
- Richard A Wilson
- Department of Plant Pathology, University of Nebraska-Lincoln, Lincoln, NE, USA
| | - John M McDowell
- School of Plant and Environmental Sciences, Virginia Tech, Blacksburg, VA, USA.
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5
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Dinkeloo K, Pelly Z, McDowell JM, Pilot G. A split green fluorescent protein system to enhance spatial and temporal sensitivity of translating ribosome affinity purification. Plant J 2022; 111:304-315. [PMID: 35436375 PMCID: PMC9544980 DOI: 10.1111/tpj.15779] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/19/2022] [Revised: 03/29/2022] [Accepted: 04/07/2022] [Indexed: 06/14/2023]
Abstract
Translating ribosome affinity purification (TRAP) utilizes transgenic plants expressing a ribosomal protein fused to a tag for affinity co-purification of ribosomes and the mRNAs that they are translating. This population of actively translated mRNAs (translatome) can be interrogated by quantitative PCR or RNA sequencing. Condition- or cell-specific promoters can be utilized to isolate the translatome of specific cell types, at different growth stages and/or in response to environmental variables. While advantageous for revealing differential expression, this approach may not provide sufficient sensitivity when activity of the condition/cell-specific promoter is weak, when ribosome turnover is low in the cells of interest, or when the targeted cells are ephemeral. In these situations, expressing tagged ribosomes under the control of these specific promoters may not yield sufficient polysomes for downstream analysis. Here, we describe a new TRAP system that employs two transgenes: One is constitutively expressed and encodes a ribosomal protein fused to one fragment of a split green fluorescent protein (GFP); the second is controlled by a stimulus-specific promoter and encodes the second GFP fragment fused to an affinity purification tag. In cells where both transgenes are active, the purification tag is attached to ribosomes by bi-molecular folding and assembly of the split GFP fragments. This approach provides increased sensitivity and better temporal resolution because it labels pre-existing ribosomes and does not depend on rapid ribosome turnover. We describe the optimization and key parameters of this system, and then apply it to a plant-pathogen interaction in which spatial and temporal resolution are difficult to achieve with current technologies.
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Affiliation(s)
- Kasia Dinkeloo
- School of Plant and Environmental Sciences, Virginia TechBlacksburgVirginia24061USA
| | - Zoe Pelly
- School of Plant and Environmental Sciences, Virginia TechBlacksburgVirginia24061USA
| | - John M. McDowell
- School of Plant and Environmental Sciences, Virginia TechBlacksburgVirginia24061USA
| | - Guillaume Pilot
- School of Plant and Environmental Sciences, Virginia TechBlacksburgVirginia24061USA
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6
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Lai Y, Lu XM, Daron J, Pan S, Wang J, Wang W, Tsuchiya T, Holub E, McDowell JM, Slotkin RK, Le Roch KG, Eulgem T. The Arabidopsis PHD-finger protein EDM2 has multiple roles in balancing NLR immune receptor gene expression. PLoS Genet 2020; 16:e1008993. [PMID: 32925902 PMCID: PMC7529245 DOI: 10.1371/journal.pgen.1008993] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2019] [Revised: 10/01/2020] [Accepted: 07/14/2020] [Indexed: 12/19/2022] Open
Abstract
Plant NLR-type receptors serve as sensitive triggers of host immunity. Their expression has to be well-balanced, due to their interference with various cellular processes and dose-dependency of their defense-inducing activity. A genetic “arms race” with fast-evolving pathogenic microbes requires plants to constantly innovate their NLR repertoires. We previously showed that insertion of the COPIA-R7 retrotransposon into RPP7 co-opted the epigenetic transposon silencing signal H3K9me2 to a new function promoting expression of this Arabidopsis thaliana NLR gene. Recruitment of the histone binding protein EDM2 to COPIA-R7-associated H3K9me2 is required for optimal expression of RPP7. By profiling of genome-wide effects of EDM2, we now uncovered additional examples illustrating effects of transposons on NLR gene expression, strongly suggesting that these mobile elements can play critical roles in the rapid evolution of plant NLR genes by providing the “raw material” for gene expression mechanisms. We further found EDM2 to have a global role in NLR expression control. Besides serving as a positive regulator of RPP7 and a small number of other NLR genes, EDM2 acts as a suppressor of a multitude of additional NLR genes. We speculate that the dual functionality of EDM2 in NLR expression control arose from the need to compensate for fitness penalties caused by high expression of some NLR genes by suppression of others. Moreover, we are providing new insights into functional relationships of EDM2 with its interaction partner, the RNA binding protein EDM3/AIPP1, and its target gene IBM1, encoding an H3K9-demethylase. We previously found the Arabidopsis thaliana PHD-finger protein EDM2 to serve as a chromatin-associated factor controlling expression of the NLR-type immune receptor gene RPP7. EDM2 binds to the transposon-silencing signal H3K9me2 and affects levels of this epigenetic mark at various loci. By genome-wide profiling of transcript- and H3K9me2-levels we now found EDM2 to have a broader role in controlling NLR gene expression. In order to mitigate fitness costs caused by its promoting effects on RPP7 expression and that of several other NLR genes, EDM2 seems to suppress expression of many additional members of this gene family. This observation is in line with multiple reports demonstrating the need for balanced expression of NLRs, which can substantially reduce overall plant fitness, but need to be present at certain minimal levels to confer sufficient immune protection. Our previous results demonstrated that the influence of EDM2 on RPP7 expression was co-opted to this immune receptor gene by the insertion of an EDM2-controlled transposon. Here, we are providing additional examples for transposon-associated effects on NLR gene expression, suggesting that these mobile elements play an important role for NLR genes by equipping members of this rapidly evolving gene family with regulatory mechanisms needed for balanced expression.
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Affiliation(s)
- Yan Lai
- Center for Plant Cell Biology, Institute of Integrative Genome Biology, Department of Botany and Plan Sciences, University of California at Riverside, Riverside, CA, United States of America
- College of Life Sciences, Fujian Agricultural and Forestry University, Fuzhou, Fujian, China
| | - Xueqing Maggie Lu
- Center for Infectious Disease and Vector Research, Institute of Integrative Genome Biology, Department of Molecular, Cell and Systems Biology, University of California at Riverside, Riverside, CA, United States of America
| | - Josquin Daron
- Department of Molecular Genetics, The Ohio State University, Columbus, Ohio, United States of America
| | - Songqin Pan
- Center for Plant Cell Biology, Institute of Integrative Genome Biology, Department of Botany and Plan Sciences, University of California at Riverside, Riverside, CA, United States of America
| | - Jianqiang Wang
- Center for Plant Cell Biology, Institute of Integrative Genome Biology, Department of Botany and Plan Sciences, University of California at Riverside, Riverside, CA, United States of America
| | - Wei Wang
- Department of Plant Pathology, Physiology, and Weed Science, Virginia Tech, Blacksburg, VA, United States of America
| | - Tokuji Tsuchiya
- College of Bioresource Sciences, Nihon University, Kanagawa, Japan
| | - Eric Holub
- School of Life Sciences, University of Warwick, Wellesbourne campus, United Kingdom
| | - John M. McDowell
- Department of Plant Pathology, Physiology, and Weed Science, Virginia Tech, Blacksburg, VA, United States of America
| | - R. Keith Slotkin
- Department of Molecular Genetics, The Ohio State University, Columbus, Ohio, United States of America
- Donald Danforth Plant Science Center, St. Louis, Missouri, United States of America
- Division of Biological Sciences, University of Missouri, Columbia, Missouri, United States of America
| | - Karine G. Le Roch
- Center for Infectious Disease and Vector Research, Institute of Integrative Genome Biology, Department of Molecular, Cell and Systems Biology, University of California at Riverside, Riverside, CA, United States of America
- * E-mail: (KGLR); (TE)
| | - Thomas Eulgem
- Center for Plant Cell Biology, Institute of Integrative Genome Biology, Department of Botany and Plan Sciences, University of California at Riverside, Riverside, CA, United States of America
- * E-mail: (KGLR); (TE)
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7
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Herlihy JH, Long TA, McDowell JM. Iron homeostasis and plant immune responses: Recent insights and translational implications. J Biol Chem 2020; 295:13444-13457. [PMID: 32732287 DOI: 10.1074/jbc.rev120.010856] [Citation(s) in RCA: 40] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2020] [Revised: 07/29/2020] [Indexed: 12/16/2022] Open
Abstract
Iron metabolism and the plant immune system are both critical for plant vigor in natural ecosystems and for reliable agricultural productivity. Mechanistic studies of plant iron home-ostasis and plant immunity have traditionally been carried out in isolation from each other; however, our growing understanding of both processes has uncovered significant connections. For example, iron plays a critical role in the generation of reactive oxygen intermediates during immunity and has been recently implicated as a critical factor for immune-initiated cell death via ferroptosis. Moreover, plant iron stress triggers immune activation, suggesting that sensing of iron depletion is a mechanism by which plants recognize a pathogen threat. The iron deficiency response engages hormone signaling sectors that are also utilized for plant immune signaling, providing a probable explanation for iron-immunity cross-talk. Finally, interference with iron acquisition by pathogens might be a critical component of the immune response. Efforts to address the global burden of iron deficiency-related anemia have focused on classical breeding and transgenic approaches to develop crops biofortified for iron content. However, our improved mechanistic understanding of plant iron metabolism suggests that such alterations could promote or impede plant immunity, depending on the nature of the alteration and the virulence strategy of the pathogen. Effects of iron biofortification on disease resistance should be evaluated while developing plants for iron biofortification.
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Affiliation(s)
- John H Herlihy
- School of Plant and Environmental Sciences, Virginia Tech, Latham Hall, Blacksburg, Virginia, USA
| | - Terri A Long
- Department of Plant and Microbial Biology, North Carolina State University, Raleigh, North Carolina, USA.
| | - John M McDowell
- School of Plant and Environmental Sciences, Virginia Tech, Latham Hall, Blacksburg, Virginia, USA.
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8
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Cui C, Herlihy JH, Bombarely A, McDowell JM, Haak DC. Draft Assembly of Phytophthora capsici from Long-Read Sequencing Uncovers Complexity. Mol Plant Microbe Interact 2019; 32:1559-1563. [PMID: 31479390 DOI: 10.1094/mpmi-04-19-0103-ta] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
Resolving complex plant pathogen genomes is important for identifying the genomic shifts associated with rapid adaptation to selective agents such as hosts and fungicides, yet assembling these genomes remains challenging and expensive. Phytophthora capsici is an important, globally distributed plant pathogen that exhibits widespread fungicide resistance and a broad host range. As with other pathogenic oomycetes, P. capsici has a complex life history and a complex genome. Here, we leverage Oxford Nanopore Technologies and existing short-read resources to rapidly generate a low-cost, improved assembly. We generated 10 Gbp from a single MinION flow cell resulting in >1.25 million reads with an N50 of 13 kb. The resulting assembly is 95.2 Mbp in 424 scaffolds with an N50 length of 313 kb. This assembly is approximately 30 Mbp bigger than the current reference genome of 64 Mbp. We confirmed this larger genome size using flow cytometry, with an estimated size of 110 Mbp. BUSCO analysis identified 97.4% complete orthologs (19.2% duplicated). Evolutionary analysis supports a recent whole-genome duplication in this group. Our work provides a blueprint for rapidly integrating benchtop long-read sequencing with existing short-read data, to dramatically improve assembly quality and integrity of complex genomes and offer novel insights into pathogen genome function and evolution.
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Affiliation(s)
- Chenming Cui
- School of Plant and Environmental Sciences, Virginia Tech, Blacksburg, VA 24061, U.S.A
| | - John H Herlihy
- School of Plant and Environmental Sciences, Virginia Tech, Blacksburg, VA 24061, U.S.A
| | - Aureliano Bombarely
- School of Plant and Environmental Sciences, Virginia Tech, Blacksburg, VA 24061, U.S.A
| | - John M McDowell
- School of Plant and Environmental Sciences, Virginia Tech, Blacksburg, VA 24061, U.S.A
| | - David C Haak
- School of Plant and Environmental Sciences, Virginia Tech, Blacksburg, VA 24061, U.S.A
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9
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Abstract
Arabidopsis plants in their natural environment are susceptible to infection by oomycete pathogens, in particular to downy mildew and white rust diseases. These naturally occurring infectious agents have imposed evolutionary pressures on Arabidopsis populations and are therefore highly relevant for the study of host-pathogen co-evolution. In addition, the study of oomycete diseases, including infections caused by several Phytophthora species, has led to many scientific discoveries on Arabidopsis immunity and disease. Herein, we describe the major oomycete species used for experiments on Arabidopsis, and how these pathosystems have been used to provide significant insights into mechanistic and evolutionary aspects of plant-oomycete interactions. We also highlight understudied aspects of plant-oomycete interactions, as well as translational approaches, that can be productively addressed using the reference pathosystems described in this article.
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Affiliation(s)
- John Herlihy
- School of Plant and Environmental Sciences, Virginia Tech, Blacksburg, VA 24061, USA
| | - Nora R. Ludwig
- Plant–Microbe Interactions, Department of Biology, Utrecht University, Padualaan 8, 3584 CH, Utrecht, the Netherlands
| | - Guido van den Ackerveken
- Plant–Microbe Interactions, Department of Biology, Utrecht University, Padualaan 8, 3584 CH, Utrecht, the Netherlands
| | - John M. McDowell
- School of Plant and Environmental Sciences, Virginia Tech, Blacksburg, VA 24061, USA
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10
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Lai Y, Cuzick A, Lu XM, Wang J, Katiyar N, Tsuchiya T, Le Roch K, McDowell JM, Holub E, Eulgem T. The Arabidopsis RRM domain protein EDM3 mediates race-specific disease resistance by controlling H3K9me2-dependent alternative polyadenylation of RPP7 immune receptor transcripts. Plant J 2019; 97:646-660. [PMID: 30407670 PMCID: PMC7138032 DOI: 10.1111/tpj.14148] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2018] [Revised: 09/27/2018] [Accepted: 10/26/2018] [Indexed: 05/18/2023]
Abstract
The NLR-receptor RPP7 mediates race-specific immunity in Arabidopsis. Previous screens for enhanced downy mildew (edm) mutants identified the co-chaperone SGT1b (EDM1) and the PHD-finger protein EDM2 as critical regulators of RPP7. Here, we describe a third edm mutant compromised in RPP7 immunity, edm3. EDM3 encodes a nuclear-localized protein featuring an RNA-recognition motif. Like EDM2, EDM3 promotes histone H3 lysine 9 dimethylation (H3K9me2) at RPP7. Global profiling of H3K9me2 showed EDM3 to affect this silencing mark at a large set of loci. Importantly, both EDM3 and EDM2 co-associate in vivo with H3K9me2-marked chromatin and transcripts at a critical proximal polyadenylation site of RPP7, where they suppress proximal transcript polyadeylation/termination. Our results highlight the complexity of plant NLR gene regulation, and establish a functional and physical link between a histone mark and NLR-transcript processing.
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Affiliation(s)
- Yan Lai
- Department of Botany and Plant Sciences, Center for Plant Cell Biology, Institute of Integrative Genome Biology, University of California at Riverside, Riverside, CA, 92521, USA
- College of Life Sciences, Fujian Agricultural and Forestry University, Fuzhou, Fujian, 350002, China
| | - Alayne Cuzick
- School of Life Sciences, University of Warwick, Wellesbourne Campus, Warwick, CV35 9EF, UK
- Biointeractions and Crop Protection, Rothamsted Research, Harpenden, AL5 2JQ, UK
| | - Xueqing M Lu
- Department of Molecular, Cell and Systems Biology, Center for Infectious Disease and Vector Research, Institute of Integrative Genome Biology, University of California at Riverside, Riverside, CA, 92521, USA
| | - Jianqiang Wang
- Department of Botany and Plant Sciences, Center for Plant Cell Biology, Institute of Integrative Genome Biology, University of California at Riverside, Riverside, CA, 92521, USA
| | - Neerja Katiyar
- Institute of Integrative Genome Biology, University of California at Riverside, Riverside, CA, 92521, USA
| | - Tokuji Tsuchiya
- College of Bioresource Sciences, Nihon University, Kanagawa, 252-0880, Japan
| | - Karine Le Roch
- Department of Molecular, Cell and Systems Biology, Center for Infectious Disease and Vector Research, Institute of Integrative Genome Biology, University of California at Riverside, Riverside, CA, 92521, USA
| | - John M McDowell
- Department of Plant Pathology, Physiology, and Weed Science, Virginia Tech, Blacksburg, VA, 24060-0329, USA
| | - Eric Holub
- School of Life Sciences, University of Warwick, Wellesbourne Campus, Warwick, CV35 9EF, UK
| | - Thomas Eulgem
- Department of Botany and Plant Sciences, Center for Plant Cell Biology, Institute of Integrative Genome Biology, University of California at Riverside, Riverside, CA, 92521, USA
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11
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Abstract
Plants perceive a variety of molecules produced by microbes, insects, and nematodes. These pathogen-derived components include so-called microbe-associated molecular patterns, or MAMPs, as well as effector proteins that are secreted to the exterior or interior of plant cells and these molecules can be recognized by receptor protein complexes on the exterior or interior of plant cells, thereby activating MAMP- or effector-triggered immunity (MTI or ETI, respectively). Because these processes are key components of plant disease resistance, they have been studied intensively. We are now in a golden age of ETI and MTI research, in which mechanistic and evolutionary understanding of both processes is emerging rapidly. Accordingly, in this Focus issue , we explore diverse aspects of MTI and ETI, with a unifying theme of integration at multiple levels.
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12
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Sonawala U, Dinkeloo K, Danna CH, McDowell JM, Pilot G. Review: Functional linkages between amino acid transporters and plant responses to pathogens. Plant Sci 2018; 277:79-88. [PMID: 30466603 DOI: 10.1016/j.plantsci.2018.09.009] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2018] [Revised: 08/11/2018] [Accepted: 09/12/2018] [Indexed: 06/09/2023]
Abstract
Upon infection, plant pathogens become dependent on their hosts for nutrition. Therefore, the interaction between the two organisms is tightly linked to the availability and flux of nutrients in the plant. The plant's nitrogen metabolism is reprogrammed during pathogen attack, likely reflecting plant's response to invasion by the pathogen and active modification by the pathogen to promote feeding. Several lines of evidence indicate that plant-derived amino acids are an important source of nitrogen for diverse pathogens. Moreover, amino acid homeostasis is interconnected with the plant's immune signaling pathways. Here, we critically examine the knowns and unknowns about connections between plant-encoded amino acid transporters and resistance or susceptibility to pathogens and pests. We use recent insights into sugar transporters to frame a perspective with potential applicability to amino acids and other nutrients. We emphasize different approaches that have provided insight in this topic and we conclude with suggestions to fill gaps in foundational knowledge and explore new avenues for disease control.
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Affiliation(s)
- Unnati Sonawala
- School of Plant and Environmental Sciences, Virginia Tech, Blacksburg, 24060 VA, USA
| | - Kasia Dinkeloo
- School of Plant and Environmental Sciences, Virginia Tech, Blacksburg, 24060 VA, USA
| | - Cristian H Danna
- Department of Biology, University of Virginia, Charlottesville, VA, USA
| | - John M McDowell
- School of Plant and Environmental Sciences, Virginia Tech, Blacksburg, 24060 VA, USA.
| | - Guillaume Pilot
- School of Plant and Environmental Sciences, Virginia Tech, Blacksburg, 24060 VA, USA.
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13
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Deb D, Mackey D, Opiyo SO, McDowell JM. Application of alignment-free bioinformatics methods to identify an oomycete protein with structural and functional similarity to the bacterial AvrE effector protein. PLoS One 2018; 13:e0195559. [PMID: 29641586 PMCID: PMC5895030 DOI: 10.1371/journal.pone.0195559] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2017] [Accepted: 03/23/2018] [Indexed: 11/23/2022] Open
Abstract
Diverse plant pathogens export effector proteins to reprogram host cells. One of the most challenging goals in the molecular plant-microbe field is to functionally characterize the complex repertoires of effectors secreted by these pathogens. For bacterial pathogens, the predominant class of effectors is delivered to host cells by Type III secretion. For oomycetes, the predominant class of effectors is defined by a signal peptide that mediates secretion from the oomycete and a conserved RxLR motif. Downy mildew pathogens and Phytophthora species maintain hundreds of candidate RxLR effector genes in their genomes. Although no primary sequence similarity is evident between bacterial Type III effectors (T3Es) and oomycete RXLR effectors, some bacterial and oomycete effectors have convergently evolved to target the same host proteins. Such effectors might have evolved domains that are functionally similar but sequence-unrelated. We reasoned that alignment-free bioinformatics approaches could be useful to identify structural similarities between bacterial and oomycete effectors. To test this approach, we used partial least squares regression, alignment-free bioinformatics methods to identify effector proteins from the genome of the oomycete Hyaloperonospora arabidopsidis that are similar to the well-studied AvrE1 effector from Pseudomonas syringae. This approach identified five RxLR proteins with putative structural similarity to AvrE1. We focused on one, HaRxL23, because it is an experimentally validated effector and it is conserved between distantly related oomycetes. Several experiments indicate that HaRxL23 is functionally similar to AvrE1, including the ability to partially rescue an AvrE1 loss-of-function mutant. This study provides an example of how an alignment-free bioinformatics approach can identify functionally similar effector proteins in the absence of primary sequence similarity. This approach could be useful to identify effectors that have convergently evolved regardless of whether the shared host target is known.
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Affiliation(s)
- Devdutta Deb
- Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Blacksburg, Virginia, United States of America
| | - David Mackey
- Departments of Horticulture and Crop Science and Molecular Genetics, Ohio State University, Columbus, Ohio, United States of America
| | - Stephen O. Opiyo
- Molecular and Cellular Imaging Center-Columbus, Ohio Agricultural Research and Development Center, Ohio State University, Columbus, Ohio, United States of America
- * E-mail: (SOO); (JMM)
| | - John M. McDowell
- Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Blacksburg, Virginia, United States of America
- * E-mail: (SOO); (JMM)
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Deb D, Anderson RG, How-Yew-Kin T, Tyler BM, McDowell JM. Conserved RxLR Effectors From Oomycetes Hyaloperonospora arabidopsidis and Phytophthora sojae Suppress PAMP- and Effector-Triggered Immunity in Diverse Plants. Mol Plant Microbe Interact 2018. [PMID: 29106332 DOI: 10.1094/mpmi-07-17-016-9-fi] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Effector proteins are exported to the interior of host cells by diverse plant pathogens. Many oomycete pathogens maintain large families of candidate effector genes, encoding proteins with a secretory leader followed by an RxLR motif. Although most of these genes are very divergent between oomycete species, several genes are conserved between Phytophthora species and Hyaloperonospora arabidopsidis, suggesting that they play important roles in pathogenicity. We describe a pair of conserved effector candidates, HaRxL23 and PsAvh73, from H. arabidopsidis and P. sojae respectively. We show that HaRxL23 is expressed early during infection of Arabidopsis. HaRxL23 triggers an ecotype-specific defense response in Arabidopsis, suggesting that it is recognized by a host surveillance protein. HaRxL23 and PsAvh73 can suppress pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) in Nicotiana benthamiana and effector-triggered immunity (ETI) in soybean. Transgenic Arabidopsis constitutively expressing HaRxL23 or PsAvh73 exhibit suppression of PTI and enhancement of bacterial and oomycete virulence. Together, our experiments demonstrate that these conserved oomycete RxLR effectors suppress PTI and ETI across diverse plant species.
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Affiliation(s)
- Devdutta Deb
- 1 Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Blacksburg, VA, 24061-0329, U.S.A
| | - Ryan G Anderson
- 1 Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Blacksburg, VA, 24061-0329, U.S.A
| | - Theresa How-Yew-Kin
- 1 Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Blacksburg, VA, 24061-0329, U.S.A
| | - Brett M Tyler
- 2 Center for Genome Research and Biocomputing, and Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331, U.S.A
| | - John M McDowell
- 1 Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Blacksburg, VA, 24061-0329, U.S.A
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Deb D, Anderson RG, How-Yew-Kin T, Tyler BM, McDowell JM. Conserved RxLR Effectors From Oomycetes Hyaloperonospora arabidopsidis and Phytophthora sojae Suppress PAMP- and Effector-Triggered Immunity in Diverse Plants. Mol Plant Microbe Interact 2018; 31:374-385. [PMID: 29106332 DOI: 10.1094/mpmi-07-17-0169-fi] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Effector proteins are exported to the interior of host cells by diverse plant pathogens. Many oomycete pathogens maintain large families of candidate effector genes, encoding proteins with a secretory leader followed by an RxLR motif. Although most of these genes are very divergent between oomycete species, several genes are conserved between Phytophthora species and Hyaloperonospora arabidopsidis, suggesting that they play important roles in pathogenicity. We describe a pair of conserved effector candidates, HaRxL23 and PsAvh73, from H. arabidopsidis and P. sojae respectively. We show that HaRxL23 is expressed early during infection of Arabidopsis. HaRxL23 triggers an ecotype-specific defense response in Arabidopsis, suggesting that it is recognized by a host surveillance protein. HaRxL23 and PsAvh73 can suppress pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) in Nicotiana benthamiana and effector-triggered immunity (ETI) in soybean. Transgenic Arabidopsis constitutively expressing HaRxL23 or PsAvh73 exhibit suppression of PTI and enhancement of bacterial and oomycete virulence. Together, our experiments demonstrate that these conserved oomycete RxLR effectors suppress PTI and ETI across diverse plant species.
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Affiliation(s)
- Devdutta Deb
- 1 Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Blacksburg, VA, 24061-0329, U.S.A
| | - Ryan G Anderson
- 1 Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Blacksburg, VA, 24061-0329, U.S.A
| | - Theresa How-Yew-Kin
- 1 Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Blacksburg, VA, 24061-0329, U.S.A
| | - Brett M Tyler
- 2 Center for Genome Research and Biocomputing, and Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331, U.S.A
| | - John M McDowell
- 1 Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Blacksburg, VA, 24061-0329, U.S.A
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Dalio RJD, Herlihy J, Oliveira TS, McDowell JM, Machado M. Effector Biology in Focus: A Primer for Computational Prediction and Functional Characterization. Mol Plant Microbe Interact 2018; 31:22-33. [PMID: 29023190 DOI: 10.1094/mpmi-07-17-0174-fi] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Plant-pathogen interactions are controlled by a multilayered immune system, which is activated by pathogen recognition in the host. Pathogens secrete effector molecules to interfere with the immune recognition or signaling network and reprogram cell structure or metabolism. Understanding the effector repertoires of diverse pathogens will contribute to unraveling the molecular mechanism of virulence and developing sustainable disease-control strategies for crops and natural ecosystems. Effector functionality has been investigated extensively in only a small number of pathogen species. However, many more pathogen genomes are becoming available, and much can be learned from a broader view of effector biology in diverse pathosystems. The purpose of this review is to summarize methodology for computational prediction of protein effectors, functional characterization of effector proteins and their targets, and the use of effectors as probes to screen for new sources of host resistance. Although these techniques were generally developed in model pathosystems, many of the approaches are directly applicable for exploration and exploitation of effector biology in pathosystems that are less well studied. We hope to facilitate such exploration, which will broaden understanding of the mechanisms that underpin the biological diversity of plant-pathogen interactions, and maximize the impact of new approaches that leverage effector biology for disease control.
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Affiliation(s)
- Ronaldo J D Dalio
- 1 Citrus Biotechnology Lab, Centro de Citricultura Sylvio Moreira, IA, Cordeirópolis-SP, Brazil; and
| | - John Herlihy
- 2 Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Blacksburg, VA, 24061-0329, U.S.A
| | - Tiago S Oliveira
- 1 Citrus Biotechnology Lab, Centro de Citricultura Sylvio Moreira, IA, Cordeirópolis-SP, Brazil; and
| | - John M McDowell
- 2 Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Blacksburg, VA, 24061-0329, U.S.A
| | - Marcos Machado
- 1 Citrus Biotechnology Lab, Centro de Citricultura Sylvio Moreira, IA, Cordeirópolis-SP, Brazil; and
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Abstract
Zoospore exudates play important roles in promoting zoospore communication, homing and germination during plant infection by Phytophthora. However, it is not clear whether exudates affect plant immunity. Zoospore-free fluid (ZFF) and zoospores of P. nicotianae were investigated comparatively for effects on resistance of Arabidopsis thaliana Col-0 and mutants that affect signaling mediated by salicylic acid (SA) and jasmonic acid (JA): eds16 (enhanced disease susceptibility16), pad4 (phytoalexin deficient4), and npr1 (nonexpressor of pathogenesis-related genes1). Col-0 attracted more zoospores and had severe tissue damage when flooded with a zoospore suspension in ZFF. Mutants treated with ZFF alone developed disease symptoms similar to those inoculated with zoospores and requirements of EDS16 and PAD4 for plant responses to zoospores and the exudates was apparent. Zoospore and ZFFs also induced expression of the PR1 and PDF1.2 marker genes for defense regulated by SA and JA, respectively. However, ZFF affected more JA defense signaling, down regulating PR1 when SA signaling or synthesis is deficient, which may be responsible for Arabidopsis mutant plants more susceptible to infection by high concentration of P. nicotianae zoospores. These results suggest that zoospore exudates can function as virulence factors and inducers of plant immune responses during plant infection by Phytophthora.
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Affiliation(s)
- Ping Kong
- Hampton Roads Agricultural Research and Extension Center, Virginia Tech, Virginia Beach, Virginia, United States of America
- * E-mail:
| | - John M. McDowell
- Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Blacksburg, Virginia, United States of America
| | - Chuanxue Hong
- Hampton Roads Agricultural Research and Extension Center, Virginia Tech, Virginia Beach, Virginia, United States of America
- Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Blacksburg, Virginia, United States of America
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Abstract
Some of the most devastating oomycete pathogens deploy effector proteins, with the signature amino acid motif RXLR, that enter plant cells to promote virulence. Research on the function and evolution of RXLR effectors has been very active over the decade that has transpired since their discovery. Comparative genomics indicate that RXLR genes play a major role in virulence for Phytophthora and downy mildew species. Importantly, gene-for-gene resistance against these oomycete lineages is based on recognition of RXLR proteins. Comparative genomics have revealed several mechanisms through which this resistance can be broken, most notably involving epigenetic control of RXLR gene expression. Structural studies have revealed a core fold that is present in the majority of RXLR proteins, providing a foundation for detailed mechanistic understanding of virulence and avirulence functions. Finally, functional studies have demonstrated that suppression of host immunity is a major function for RXLR proteins. Host protein targets are being identified in a variety of plant cell compartments. Some targets comprise hubs that are also manipulated by bacteria and fungi, thereby revealing key points of vulnerability in the plant immune network.
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Affiliation(s)
- Ryan G Anderson
- Department of Plant Pathology, Physiology, and Weed Science, Virginia Tech, Blacksburg, VA, U.S.A
| | - Devdutta Deb
- Department of Plant Pathology, Physiology, and Weed Science, Virginia Tech, Blacksburg, VA, U.S.A
| | - Kevin Fedkenheuer
- Department of Plant Pathology, Physiology, and Weed Science, Virginia Tech, Blacksburg, VA, U.S.A
| | - John M McDowell
- Department of Plant Pathology, Physiology, and Weed Science, Virginia Tech, Blacksburg, VA, U.S.A
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Anderson RG, McDowell JM. A PCR assay for the quantification of growth of the oomycete pathogen Hyaloperonospora arabidopsidis in Arabidopsis thaliana. Mol Plant Pathol 2015; 16:893-898. [PMID: 25676785 PMCID: PMC6638379 DOI: 10.1111/mpp.12247] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
The accurate quantification of disease severity is important for the assessment of host-pathogen interactions in laboratory or field settings. The interaction between Arabidopsis thaliana and its naturally occurring downy mildew pathogen, Hyaloperonospora arabidopsidis (Hpa), is a widely used reference pathosystem for plant-oomycete interactions. Current methods for the assessment of disease severity in the Arabidopsis-Hpa interaction rely on measurements at the terminal stage of pathogen development; namely, visual counts of spore-producing structures or the quantification of spore production with a haemocytometer. These assays are useful, but do not offer sensitivity for the robust quantification of small changes in virulence or the accurate quantification of pathogen growth prior to the reproductive stage. Here, we describe a quantitative real-time polymerase chain reaction (qPCR) assay for the monitoring of Hpa growth in planta. The protocol is rapid, inexpensive and can robustly distinguish small changes in virulence. We used this assay to investigate the dynamics of early Hpa mycelial growth and to demonstrate the proof of concept that this assay could be used in screens for novel oomycete growth inhibitors.
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Affiliation(s)
- Ryan G Anderson
- Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Blacksburg, VA, 24061-0329, USA
| | - John M McDowell
- Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Blacksburg, VA, 24061-0329, USA
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McDowell JM, Carr J, Lorito M. Focus on translational research. Mol Plant Microbe Interact 2014; 27:195. [PMID: 24499027 DOI: 10.1094/mpmi-27-03-0195] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Readers of this journal are well aware how far our field has progressed towards mechanistic understanding of pathogenesis and immunity. Almost concurrently, this new fundamental knowledge is being translated into new tools for reducing disease losses in crops. This is obviously exciting for our research community and our varied stakeholders. Thus, the MPMI editorial board decided that the time is right for a special issue devoted to the topic of Translational Research. This issue comprises reviews, invited by the editors, and primary reports submitted in response to an open call. We are gratified to introduce articles that collectively encompass a wide range of applications and clearly illustrate the practical value of fundamental understanding of molecular plant-microbe interactions. Click on Next Article or Table of Contents above to view the articles in this Focus Issue. (From the mobile site, go to the MPMI March 2014 issue.)
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Affiliation(s)
- John M. McDowell
- Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Blacksburg, VA 24061; and
| | - Blake C. Meyers
- Department of Plant and Soil Sciences, University of Delaware, Newark, DE 19716
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Zhang C, Xie Q, Anderson RG, Ng G, Seitz NC, Peterson T, McClung CR, McDowell JM, Kong D, Kwak JM, Lu H. Crosstalk between the circadian clock and innate immunity in Arabidopsis. PLoS Pathog 2013; 9:e1003370. [PMID: 23754942 PMCID: PMC3675028 DOI: 10.1371/journal.ppat.1003370] [Citation(s) in RCA: 123] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2012] [Accepted: 04/04/2013] [Indexed: 12/17/2022] Open
Abstract
The circadian clock integrates temporal information with environmental cues in regulating plant development and physiology. Recently, the circadian clock has been shown to affect plant responses to biotic cues. To further examine this role of the circadian clock, we tested disease resistance in mutants disrupted in CCA1 and LHY, which act synergistically to regulate clock activity. We found that cca1 and lhy mutants also synergistically affect basal and resistance gene-mediated defense against Pseudomonas syringae and Hyaloperonospora arabidopsidis. Disrupting the circadian clock caused by overexpression of CCA1 or LHY also resulted in severe susceptibility to P. syringae. We identified a downstream target of CCA1 and LHY, GRP7, a key constituent of a slave oscillator regulated by the circadian clock and previously shown to influence plant defense and stomatal activity. We show that the defense role of CCA1 and LHY against P. syringae is at least partially through circadian control of stomatal aperture but is independent of defense mediated by salicylic acid. Furthermore, we found defense activation by P. syringae infection and treatment with the elicitor flg22 can feedback-regulate clock activity. Together this data strongly supports a direct role of the circadian clock in defense control and reveal for the first time crosstalk between the circadian clock and plant innate immunity.
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Affiliation(s)
- Chong Zhang
- Department of Biological Sciences, University of Maryland Baltimore County, Baltimore, Maryland, United States of America
| | - Qiguang Xie
- Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire, United States of America
| | - Ryan G. Anderson
- Department of Plant Pathology, Physiology, and Weed Science, Virginia Tech, Blacksburg, Virginia, United States of America
| | - Gina Ng
- Department of Biological Sciences, University of Maryland Baltimore County, Baltimore, Maryland, United States of America
| | - Nicholas C. Seitz
- Department of Biological Sciences, University of Maryland Baltimore County, Baltimore, Maryland, United States of America
| | - Thomas Peterson
- Department of Biological Sciences, University of Maryland Baltimore County, Baltimore, Maryland, United States of America
| | - C. Robertson McClung
- Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire, United States of America
| | - John M. McDowell
- Department of Plant Pathology, Physiology, and Weed Science, Virginia Tech, Blacksburg, Virginia, United States of America
| | - Dongdong Kong
- Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, Maryland, United States of America
| | - June M. Kwak
- Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, Maryland, United States of America
- Department of Cell Biology and Molecular Genetics, Department of Plant Science and Landscape Architecture, University of Maryland, College Park, Maryland, United States of America
- Department of Plant Molecular Systems Biotechnology and Crop Biotech Institute, Kyung Hee University, Yongin, Republic of Korea
| | - Hua Lu
- Department of Biological Sciences, University of Maryland Baltimore County, Baltimore, Maryland, United States of America
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Affiliation(s)
- John M McDowell
- Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Blacksburg, VA, 24061-0329, USA
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Stegmann M, Anderson RG, Westphal L, Rosahl S, McDowell JM, Trujillo M. The exocyst subunit Exo70B1 is involved in the immune response of Arabidopsis thaliana to different pathogens and cell death. Plant Signal Behav 2013; 8:e27421. [PMID: 24389869 PMCID: PMC4091220 DOI: 10.4161/psb.27421] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/15/2013] [Revised: 12/03/2013] [Accepted: 12/03/2013] [Indexed: 05/20/2023]
Abstract
Components of the vesicle trafficking machinery are central to the immune response in plants. The role of vesicle trafficking during pre-invasive penetration resistance has been well documented. However, emerging evidence also implicates vesicle trafficking in early immune signaling. Here we report that Exo70B1, a subunit of the exocyst complex which mediates early tethering during exocytosis is involved in resistance. We show that exo70B1 mutants display pathogen-specific immuno-compromised phenotypes. We also show that exo70B1 mutants display lesion-mimic cell death, which in combination with the reduced responsiveness to pathogen-associated molecular patterns (PAMPs) results in complex immunity-related phenotypes.
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Affiliation(s)
- Martin Stegmann
- Leibniz Institute of Plant Biochemistry; Halle, (Saale) Germany
| | - Ryan G Anderson
- Department of Plant Pathology, Physiology, & Weed Science; Virginia Tech; Blacksburg, VA USA
| | - Lore Westphal
- Leibniz Institute of Plant Biochemistry; Halle, (Saale) Germany
| | - Sabine Rosahl
- Leibniz Institute of Plant Biochemistry; Halle, (Saale) Germany
| | - John M McDowell
- Department of Plant Pathology, Physiology, & Weed Science; Virginia Tech; Blacksburg, VA USA
| | - Marco Trujillo
- Leibniz Institute of Plant Biochemistry; Halle, (Saale) Germany
- Correspondence to: Marco Trujillo,
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Anderson RG, Casady MS, Fee RA, Vaughan MM, Deb D, Fedkenheuer K, Huffaker A, Schmelz EA, Tyler BM, McDowell JM. Homologous RXLR effectors from Hyaloperonospora arabidopsidis and Phytophthora sojae suppress immunity in distantly related plants. Plant J 2012; 72:882-93. [PMID: 22709376 DOI: 10.1111/j.1365-313x.2012.05079.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Diverse pathogens secrete effector proteins into plant cells to manipulate host cellular processes. Oomycete pathogens contain large complements of predicted effector genes defined by an RXLR host cell entry motif. The genome of Hyaloperonospora arabidopsidis (Hpa, downy mildew of Arabidopsis) contains at least 134 candidate RXLR effector genes. Only a small subset of these genes is conserved in related oomycetes from the Phytophthora genus. Here, we describe a comparative functional characterization of the Hpa RXLR effector gene HaRxL96 and a homologous gene, PsAvh163, from the Glycine max (soybean) pathogen Phytophthora sojae. HaRxL96 and PsAvh163 are induced during the early stages of infection and carry a functional RXLR motif that is sufficient for protein uptake into plant cells. Both effectors can suppress immune responses in soybean. HaRxL96 suppresses immunity in Nicotiana benthamiana, whereas PsAvh163 induces an HR-like cell death response in Nicotiana that is dependent on RAR1 and Hsp90.1. Transgenic Arabidopsis plants expressing HaRxL96 or PsAvh163 exhibit elevated susceptibility to virulent and avirulent Hpa, as well as decreased callose deposition in response to non-pathogenic Pseudomonas syringae. Both effectors interfere with defense marker gene induction, but do not affect salicylic acid biosynthesis. Together, these experiments demonstrate that evolutionarily conserved effectors from different oomycete species can suppress immunity in plant species that are divergent from the source pathogen's host.
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Affiliation(s)
- Ryan G Anderson
- Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Blacksburg, VA 24061-0329, USAChemistry Research Unit, Center of Medical, Agricultural, and Veterinary Entomology, US Department of Agriculture, Agricultural Research Service, Gainesville, FL 32608, USAVirginia Bioinformatics Institute, Virginia Tech, Blacksburg, VA 24061-0329, USA
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Stegmann M, Anderson RG, Ichimura K, Pecenkova T, Reuter P, Žárský V, McDowell JM, Shirasu K, Trujillo M. The ubiquitin ligase PUB22 targets a subunit of the exocyst complex required for PAMP-triggered responses in Arabidopsis. Plant Cell 2012; 24:4703-16. [PMID: 23170036 PMCID: PMC3531861 DOI: 10.1105/tpc.112.104463] [Citation(s) in RCA: 173] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2012] [Revised: 10/11/2012] [Accepted: 10/26/2012] [Indexed: 05/19/2023]
Abstract
Plant pathogens are perceived by pattern recognition receptors, which are activated upon binding to pathogen-associated molecular patterns (PAMPs). Ubiquitination and vesicle trafficking have been linked to the regulation of immune signaling. However, little information exists about components of vesicle trafficking involved in immune signaling and the mechanisms that regulate them. In this study, we identified Arabidopsis thaliana Exo70B2, a subunit of the exocyst complex that mediates vesicle tethering during exocytosis, as a target of the plant U-box-type ubiquitin ligase 22 (PUB22), which acts in concert with PUB23 and PUB24 as a negative regulator of PAMP-triggered responses. We show that Exo70B2 is required for both immediate and later responses triggered by all tested PAMPs, suggestive of a role in signaling. Exo70B2 is also necessary for the immune response against different pathogens. Our data demonstrate that PUB22 mediates the ubiquitination and degradation of Exo70B2 via the 26S Proteasome. Furthermore, degradation is regulated by the autocatalytic turnover of PUB22, which is stabilized upon PAMP perception. We therefore propose a mechanism by which PUB22-mediated degradation of Exo70B2 contributes to the attenuation of PAMP-induced signaling.
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Affiliation(s)
- Martin Stegmann
- Leibniz Institute of Plant Biochemistry, D-06120 Halle (Saale), Germany
- Julius-Maximilans-University of Würzburg, Julius-von-Sachs Institute, D-97082 Wuerzburg, Germany
| | - Ryan G. Anderson
- Department of Plant Pathology, Physiology, and Weed Science, Virginia Tech, Blacksburg, Virginia 24061-0329, USA
| | - Kazuya Ichimura
- Faculty of Agriculture, Kagawa University, Miki, Kagawa 761-0795, Japan
| | - Tamara Pecenkova
- Institute of Experimental Botany, Academy of Sciences of the Czech Republic Rozvojova 263, Prague 6, CZ-165 02, Czech Republic
| | - Patrick Reuter
- Julius-Maximilans-University of Würzburg, Julius-von-Sachs Institute, D-97082 Wuerzburg, Germany
| | - Viktor Žárský
- Department of Experimental Plant Biology, Faculty of Sciences, Charles University, 12844 Prague 2, Czech Republic
| | - John M. McDowell
- Department of Plant Pathology, Physiology, and Weed Science, Virginia Tech, Blacksburg, Virginia 24061-0329, USA
| | - Ken Shirasu
- RIKEN Plant Science Center, Tsurumi-ku, Yokohama 230-0045, Japan
| | - Marco Trujillo
- Leibniz Institute of Plant Biochemistry, D-06120 Halle (Saale), Germany
- Address correspondence to
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McDowell JM, Johnson GM, Bradnam LV. Towards a neurophysiological mechanisms-based classification of adverse reactions to acupuncture. Physical Therapy Reviews 2011. [DOI: 10.1179/1743288x11y.0000000008] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
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McDowell JM, Hoff T, Anderson RG, Deegan D. Propagation, storage, and assays with Hyaloperonospora arabidopsidis: A model oomycete pathogen of Arabidopsis. Methods Mol Biol 2011; 712:137-51. [PMID: 21359806 DOI: 10.1007/978-1-61737-998-7_12] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
The oomycete pathogen Hyaloperonospora arabidopsidis is a natural pathogen of Arabidopsis thaliana and a laboratory model for (1) understanding how Arabidopsis responds to pathogen attack; (2) comparative and functional genomics of oomycetes; and (3) the molecular basis and evolution of obligate biotrophy. Here, we describe procedures for propagation and long-term storage of H. arabidopsidis, which address complications arising from its biotrophic lifestyle that precludes growth on synthetic media. We also describe four assays that provide information on different facets of the H. arabidopsidis-Arabidopsis interaction.
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Affiliation(s)
- John M McDowell
- Department of Plant Pathology, Physiology, and Weed Science, Virginia Tech, Blacksburg, VA, USA.
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29
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Baxter L, Tripathy S, Ishaque N, Boot N, Cabral A, Kemen E, Thines M, Ah-Fong A, Anderson R, Badejoko W, Bittner-Eddy P, Boore JL, Chibucos MC, Coates M, Dehal P, Delehaunty K, Dong S, Downton P, Dumas B, Fabro G, Fronick C, Fuerstenberg SI, Fulton L, Gaulin E, Govers F, Hughes L, Humphray S, Jiang RHY, Judelson H, Kamoun S, Kyung K, Meijer H, Minx P, Morris P, Nelson J, Phuntumart V, Qutob D, Rehmany A, Rougon-Cardoso A, Ryden P, Torto-Alalibo T, Studholme D, Wang Y, Win J, Wood J, Clifton SW, Rogers J, Van den Ackerveken G, Jones JDG, McDowell JM, Beynon J, Tyler BM. Signatures of adaptation to obligate biotrophy in the Hyaloperonospora arabidopsidis genome. Science 2010; 330:1549-1551. [PMID: 21148394 PMCID: PMC3971456 DOI: 10.1126/science.1195203] [Citation(s) in RCA: 321] [Impact Index Per Article: 22.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Many oomycete and fungal plant pathogens are obligate biotrophs, which extract nutrients only from living plant tissue and cannot grow apart from their hosts. Although these pathogens cause substantial crop losses, little is known about the molecular basis or evolution of obligate biotrophy. Here, we report the genome sequence of the oomycete Hyaloperonospora arabidopsidis (Hpa), an obligate biotroph and natural pathogen of Arabidopsis thaliana. In comparison with genomes of related, hemibiotrophic Phytophthora species, the Hpa genome exhibits dramatic reductions in genes encoding (i) RXLR effectors and other secreted pathogenicity proteins, (ii) enzymes for assimilation of inorganic nitrogen and sulfur, and (iii) proteins associated with zoospore formation and motility. These attributes comprise a genomic signature of evolution toward obligate biotrophy.
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Affiliation(s)
- Laura Baxter
- School of Life Sciences, Warwick University, Wellesbourne, CV35 9EF, UK
| | - Sucheta Tripathy
- Virginia Bioinformatics Institute, Virginia Tech, Blacksburg, VA, 24061, USA
| | - Naveed Ishaque
- Sainsbury Laboratory, University of East Anglia, John Innes Centre, Norwich NR4 7UH, UK
| | - Nico Boot
- Centre for Biosystems Genomics, P.O. Box 98,6700 AB Wageningen, The Netherlands
| | - Adriana Cabral
- Centre for Biosystems Genomics, P.O. Box 98,6700 AB Wageningen, The Netherlands
| | - Eric Kemen
- Sainsbury Laboratory, University of East Anglia, John Innes Centre, Norwich NR4 7UH, UK
| | - Marco Thines
- Sainsbury Laboratory, University of East Anglia, John Innes Centre, Norwich NR4 7UH, UK
- Biodiversity and Climate Research Centre (BiK-F), Senckenberganlage 25, D-60325 Frankfurt (Main), Germany
- Johann Wolfgang Goethe University, Department of Biological Sciences, Institute of Ecology, Evolution and Diversity, Siesmayerstr. 70, D-60323 Frankfurt (Main), Germany
| | - Audrey Ah-Fong
- Department of Plant Pathology and Microbiology, University of California, Riverside, CA 92521, USA
| | - Ryan Anderson
- Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Blacksburg, VA 24061, USA
| | - Wole Badejoko
- School of Life Sciences, Warwick University, Wellesbourne, CV35 9EF, UK
| | | | - Jeffrey L Boore
- Department of Integrative Biology, University of California, Berkeley, USA
| | - Marcus C Chibucos
- Virginia Bioinformatics Institute, Virginia Tech, Blacksburg, VA, 24061, USA
| | - Mary Coates
- School of Life Sciences, Warwick University, Wellesbourne, CV35 9EF, UK
| | - Paramvir Dehal
- Lawrence Berkeley National Laboratories, Berkeley, CA, 94720, USA
| | - Kim Delehaunty
- Genome Sequencing Centre, Washington University School of Medicine, St Louis, MO63110, USA
| | - Suomeng Dong
- Agriculture and Agri-Food Canada, London, Ontario, N5V 4T3, Canada
- Department of Plant Pathology, Nanjing Agricultural University, China
| | - Polly Downton
- School of Life Sciences, Warwick University, Wellesbourne, CV35 9EF, UK
| | - Bernard Dumas
- Université de Toulouse, UPS, Surfaces Cellulaires et Signalisation chez les Végétaux, 24 chemin de Borde Rouge, BP42617, Auzeville, F-31326, Castanet-Tolosan, France
- CNRS, Surfaces Cellulaires et Signalisation chez les Végétaux, 24 chemin de Borde Rouge, BP42617, Auzeville, F-31326, Castanet-Tolosan, France
| | - Georgina Fabro
- Sainsbury Laboratory, University of East Anglia, John Innes Centre, Norwich NR4 7UH, UK
| | - Catrina Fronick
- Genome Sequencing Centre, Washington University School of Medicine, St Louis, MO63110, USA
| | | | - Lucinda Fulton
- Genome Sequencing Centre, Washington University School of Medicine, St Louis, MO63110, USA
| | - Elodie Gaulin
- Université de Toulouse, UPS, Surfaces Cellulaires et Signalisation chez les Végétaux, 24 chemin de Borde Rouge, BP42617, Auzeville, F-31326, Castanet-Tolosan, France
- CNRS, Surfaces Cellulaires et Signalisation chez les Végétaux, 24 chemin de Borde Rouge, BP42617, Auzeville, F-31326, Castanet-Tolosan, France
| | - Francine Govers
- Laboratory of Phytopathology, Wageningen University, and Centre for BioSystems Genomics, NL-1-6708 PB Wageningen, The Netherlands
| | - Linda Hughes
- School of Life Sciences, Warwick University, Wellesbourne, CV35 9EF, UK
| | - Sean Humphray
- Sanger, Wellcome Trust Genome Campus, Hinxton, Cambridge, CB10 1SA, UK
| | - Rays H Y Jiang
- Laboratory of Phytopathology, Wageningen University, and Centre for BioSystems Genomics, NL-1-6708 PB Wageningen, The Netherlands
- The Broad Institute of MIT and Harvard, Cambridge, MA 02141-2023, USA
| | - Howard Judelson
- Department of Plant Pathology and Microbiology, University of California, Riverside, CA 92521, USA
| | - Sophien Kamoun
- Sainsbury Laboratory, University of East Anglia, John Innes Centre, Norwich NR4 7UH, UK
| | - Kim Kyung
- Genome Sequencing Centre, Washington University School of Medicine, St Louis, MO63110, USA
| | - Harold Meijer
- Laboratory of Phytopathology, Wageningen University, and Centre for BioSystems Genomics, NL-1-6708 PB Wageningen, The Netherlands
| | - Patrick Minx
- Genome Sequencing Centre, Washington University School of Medicine, St Louis, MO63110, USA
| | - Paul Morris
- Department of Biological Sciences, Bowling Green State University, Bowling Green, Ohio 43403-0212, USA
| | - Joanne Nelson
- Genome Sequencing Centre, Washington University School of Medicine, St Louis, MO63110, USA
| | - Vipa Phuntumart
- Department of Biological Sciences, Bowling Green State University, Bowling Green, Ohio 43403-0212, USA
| | - Dinah Qutob
- Agriculture and Agri-Food Canada, London, Ontario, N5V 4T3, Canada
| | - Anne Rehmany
- School of Life Sciences, Warwick University, Wellesbourne, CV35 9EF, UK
| | | | - Peter Ryden
- School of Life Sciences, Warwick University, Wellesbourne, CV35 9EF, UK
| | - Trudy Torto-Alalibo
- Virginia Bioinformatics Institute, Virginia Tech, Blacksburg, VA, 24061, USA
| | - David Studholme
- Sainsbury Laboratory, University of East Anglia, John Innes Centre, Norwich NR4 7UH, UK
| | - Yuanchao Wang
- Department of Plant Pathology, Nanjing Agricultural University, China
| | - Joe Win
- Sainsbury Laboratory, University of East Anglia, John Innes Centre, Norwich NR4 7UH, UK
| | - Jo Wood
- Sanger, Wellcome Trust Genome Campus, Hinxton, Cambridge, CB10 1SA, UK
| | - Sandra W Clifton
- Genome Sequencing Centre, Washington University School of Medicine, St Louis, MO63110, USA
| | - Jane Rogers
- Sanger, Wellcome Trust Genome Campus, Hinxton, Cambridge, CB10 1SA, UK
| | - Guido Van den Ackerveken
- Johann Wolfgang Goethe University, Department of Biological Sciences, Institute of Ecology, Evolution and Diversity, Siesmayerstr. 70, D-60323 Frankfurt (Main), Germany
| | - Jonathan D G Jones
- Sainsbury Laboratory, University of East Anglia, John Innes Centre, Norwich NR4 7UH, UK
| | - John M McDowell
- Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Blacksburg, VA 24061, USA
| | - Jim Beynon
- School of Life Sciences, Warwick University, Wellesbourne, CV35 9EF, UK
| | - Brett M Tyler
- Virginia Bioinformatics Institute, Virginia Tech, Blacksburg, VA, 24061, USA
- Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Blacksburg, VA 24061, USA
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Mohr TJ, Mammarella ND, Hoff T, Woffenden BJ, Jelesko JG, McDowell JM. The Arabidopsis downy mildew resistance gene RPP8 is induced by pathogens and salicylic acid and is regulated by W box cis elements. Mol Plant Microbe Interact 2010; 23:1303-15. [PMID: 20831409 DOI: 10.1094/mpmi-01-10-0022] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Plants disease resistance (R) genes encode specialized receptors that are quantitative, rate-limiting defense regulators. R genes must be expressed at optimum levels to function properly. If expression is too low, downstream defense responses are not activated efficiently. Conversely, overexpression of R genes can trigger autoactivation of defenses with deleterious consequences for the plant. Little is known about R gene regulation, particularly under defense-inducing conditions. We examined regulation of the Arabidopsis thaliana gene RPP8 (resistance to Hyaloperonospora arabidopsidis, isolate Emco5). RPP8 was induced in response to challenge with H. arabidopsidis or application of salicylic acid, as shown with RPP8-Luciferase transgenic plants and quantitative reverse-transcription polymerase chain reaction of endogenous alleles. The RPP1 and RPP4 genes were also induced by H. arabidopsidis and salicylic acid, suggesting that some RPP genes are subject to feedback amplification. The RPP8 promoter contains three W box cis elements. Site-directed mutagenesis of all three W boxes greatly diminished RPP8 basal expression, inducibility, and resistance in transgenic plants. Motif searches indicated that the W box is the only known cis element that is statistically overrepresented in Arabidopsis nucleotide-binding leucine-rich repeat promoters. These results indicate that WRKY transcription factors can regulate expression of surveillance genes at the top of the defense-signaling cascade.
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Affiliation(s)
- Toni J Mohr
- Department of Plant Pathology, Physiology, and Weed Science, Virginia Tech, Blacksburg, VA 24060, USA
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31
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Genger RK, Jurkowski GI, McDowell JM, Lu H, Jung HW, Greenberg JT, Bent AF. Signaling pathways that regulate the enhanced disease resistance of Arabidopsis "defense, no death" mutants. Mol Plant Microbe Interact 2008; 21:1285-96. [PMID: 18785824 PMCID: PMC2923831 DOI: 10.1094/mpmi-21-10-1285] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Arabidopsis dnd1 and dnd2 mutants lack cyclic nucleotide-gated ion channel proteins and carry out avirulence or resistance gene-mediated defense with a greatly reduced hypersensitive response (HR). They also exhibit elevated broad-spectrum disease resistance and constitutively elevated salicylic acid (SA) levels. We examined the contributions of NPR1, SID2 (EDS16), NDR1, and EIN2 to dnd phenotypes. Mutations that affect SA accumulation or signaling (sid2, npr1, and ndr1) abolished the enhanced resistance of dnd mutants against Pseudomonas syringae pv. tomato and Hyaloperonospora parasitica but not Botrytis cinerea. When SA-associated pathways were disrupted, the constitutive activation of NPR1-dependent and NPR1-independent and SA-dependent pathways was redirected toward PDF1.2-associated pathways. This PDF1.2 overexpression was downregulated after infection by P. syringae. Disruption of ethylene signaling abolished the enhanced resistance to B. cinerea but not P. syringae or H. parasitica. However, loss of NPR1, SID2, NDR1, or EIN2 did not detectably alter the reduced HR in dnd mutants. The susceptibility of dnd ein2 plants to B. cinerea despite their reduced-HR phenotype suggests that cell death repression is not the primary cause of dnd resistance to necrotrophic pathogens. The partial restoration of resistance to B. cinerea in dnd1 npr1 ein2 triple mutants indicated that this resistance is not entirely EIN2 dependent. The above findings indicate that the broad-spectrum resistance of dnd mutants occurs due to activation or sensitization of multiple defense pathways, yet none of the investigated pathways are required for the reduced-HR phenotype.
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Affiliation(s)
- Ruth K Genger
- Department of Plant Pathology, University of Wisconsin-Madison, Madison, WI 53706, USA
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32
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Dou D, Kale SD, Wang X, Chen Y, Wang Q, Wang X, Jiang RHY, Arredondo FD, Anderson RG, Thakur PB, McDowell JM, Wang Y, Tyler BM. Conserved C-terminal motifs required for avirulence and suppression of cell death by Phytophthora sojae effector Avr1b. Plant Cell 2008; 20:1118-33. [PMID: 18390593 PMCID: PMC2390733 DOI: 10.1105/tpc.107.057067] [Citation(s) in RCA: 221] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2007] [Revised: 02/26/2008] [Accepted: 03/17/2008] [Indexed: 05/17/2023]
Abstract
The sequenced genomes of oomycete plant pathogens contain large superfamilies of effector proteins containing the protein translocation motif RXLR-dEER. However, the contributions of these effectors to pathogenicity remain poorly understood. Here, we show that the Phytophthora sojae effector protein Avr1b can contribute positively to virulence and can suppress programmed cell death (PCD) triggered by the mouse BAX protein in yeast, soybean (Glycine max), and Nicotiana benthamiana cells. We identify three conserved motifs (K, W, and Y) in the C terminus of the Avr1b protein and show that mutations in the conserved residues of the W and Y motifs reduce or abolish the ability of Avr1b to suppress PCD and also abolish the avirulence interaction of Avr1b with the Rps1b resistance gene in soybean. W and Y motifs are present in at least half of the identified oomycete RXLR-dEER effector candidates, and we show that three of these candidates also suppress PCD in soybean. Together, these results indicate that the W and Y motifs are critical for the interaction of Avr1b with host plant target proteins and support the hypothesis that these motifs are critical for the functions of the very large number of predicted oomycete effectors that contain them.
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Affiliation(s)
- Daolong Dou
- Virginia Bioinformatics Institute, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA
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33
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McDowell JM, Simon SA. Molecular diversity at the plant-pathogen interface. Dev Comp Immunol 2008; 32:736-44. [PMID: 18191204 DOI: 10.1016/j.dci.2007.11.005] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/04/2007] [Revised: 11/20/2007] [Accepted: 11/21/2007] [Indexed: 05/08/2023]
Abstract
Plants have evolved a robust innate immune system that exhibits striking similarities as well as significant differences with various metazoan innate immune systems. For example, plants are capable of perceiving pathogen-associated molecular patterns through pattern recognition receptors that bear structural similarities to animal Toll-like receptors. In addition, plants have evolved a second surveillance system based on cytoplasmic "NB-LRR" proteins (nucleotide-binding, leucine-rich repeat) that are structurally similar to animal nucleotide-binding and oligomerization domain (NOD)-like receptors. Plant NB-LRR proteins do not detect PAMPs; rather, they perceive effector proteins that pathogens secrete into plant cells to promote virulence. This review summarizes the current state of knowledge about the molecular functionality and evolution of these immune surveillance genes.
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Affiliation(s)
- John M McDowell
- Department of Plant Pathology, Physiology, and Weed Science, Latham Hall, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0390, USA.
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34
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Eulgem T, Tsuchiya T, Wang XJ, Beasley B, Cuzick A, Tör M, Zhu T, McDowell JM, Holub E, Dangl JL. EDM2 is required for RPP7-dependent disease resistance in Arabidopsis and affects RPP7 transcript levels. Plant J 2007; 49:829-39. [PMID: 17253987 DOI: 10.1111/j.1365-313x.2006.02999.x] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
Specific disease resistance of Arabidopsis thaliana against the Hyaloperonospora parasitica isolate Hiks1 (HpHiks1) is mediated by RPP7. Although this disease resistance gene encodes a typical nucleotide binding site leucine-rich repeat (NB-LRR) disease resistance protein, its function is independent of the defense hormone salicylic acid and most known genes required for plant immune responses. We identified EDM2 (enhanced downy mildew 2) in a genetic screen for RPP7 suppressors. Mutations of EDM2 phenocopy RPP7 mutations, but do not affect other tested disease resistance genes. We isolated EDM2 by map-based cloning. The predicted EDM2 protein is structurally unrelated to previously identified components of the plant immune system, bears typical features of transcriptional regulators, including plant homeodomain (PHD)-finger-like domains, and defines a plant-specific protein family. In edm2 mutants both constitutive and HpHiks1-induced RPP7 transcript levels are reduced, suggesting that EDM2 is either a direct or an indirect regulator of RPP7 expression. Microarray analyses defined a set of defense-associated genes, the expression of which is suppressed during successful HpHiks1 colonization of either rpp7 or edm2 plants. This transcriptional phenotype is counteracted by an EDM2/RPP7-dependent mechanism.
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Affiliation(s)
- Thomas Eulgem
- Department of Biology, CB#3280 University of North Carolina at Chapel Hill, NC 27599, USA.
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Abstract
SUMMARY Plants are under strong evolutionary pressure to maintain surveillance against pathogens. Resistance (R) gene-dependent recognition of pathogen avirulence (Avr) determinants plays a major role in plant defence. Here we highlight recent insights into the molecular mechanisms and selective forces that drive the evolution of NB-LRR (nucleotide binding-leucine-rich repeat) resistance genes. New implications for models of R gene evolution have been raised by demonstrations that R proteins can detect cognate Avr proteins indirectly by 'guarding' virulence targets, and by evidence that R protein signalling is regulated by intramolecular interactions between different R functional domains. Comparative genomic surveys of NB-LRR diversity in different species have revealed ancient NB-LRR lineages that are unequally represented among plant taxa, consistent with a Birth and Death Model of evolution. The physical distribution of NB-LRRs in plant genomes indicates that tandem and segmental duplication are important factors in R gene proliferation. The majority of R genes reside in clusters, and the frequency of recombination between clustered genes can vary strikingly, even within a single cluster. Biotic and abiotic factors have been shown to increase the frequency of recombination in reporter transgene-based assays, suggesting that external stressors can affect genome stability. Fitness penalties have been associated with some R genes, and population studies have provided evidence for maintenance of ancient R allelic diversity by balancing selection. The available data suggest that different R genes can follow strikingly distinct evolutionary trajectories, indicating that it will be difficult to formulate universally applicable models of R gene evolution.
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Affiliation(s)
- John M McDowell
- Department of Plant Pathology, Physiology, and Weed Science, and Fralin Biotechnology Center, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0346, USA
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36
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Affiliation(s)
- Jeffery L Dangl
- Departments of Biology and Microbiology and Immunology, Curriculum in Genetics, Carolina Center for Genome Sciences, University of North Carolina, Chapel Hill, NC 27599-3280, USA.
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McDowell JM, Williams SG, Funderburg NT, Eulgem T, Dangl JL. Genetic analysis of developmentally regulated resistance to downy mildew (Hyaloperonospora parasitica) in Arabidopsis thaliana. Mol Plant Microbe Interact 2005; 18:1226-34. [PMID: 16353557 DOI: 10.1094/mpmi-18-1226] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Although developmentally regulated disease resistance has been observed in a variety of plant-pathogen interactions, the molecular basis of this phenomenon is not well understood. Arabidopsis thaliana ecotype Columbia-0 (Col-0) expresses a developmentally regulated resistance to Hyaloperonospora parasitica isolate Emco5. Col-0 seedlings support profuse mycelial growth and asexual spore formation in the cotyledons. In contrast, Emco5 growth and reproduction is dramatically (but not completely) restricted in the first set of true leaves. Subsequent leaves exhibit progresssively increased resistance. This adult resistance is strongly suppressed by expression of the salicylic acid-degrading transgene NahG and by loss-of-function mutations in the defense-response regulators PAD4, NDR1, RAR1, PBS3, and NPR1. In contrast to Col-0, the Wassilewskija-0 (Ws-0) ecotype supports profuse growth of Emco5 at all stages of development. Gene-dosage experiments and segregation patterns indicate that adult susceptibility in Ws-0 is incomepletely dominant to adult resistance in Col-0. Genetic mapping in a Col x Ws F2 population revealed a major locus on the bottom arm of chromosome 5, which we named RPP31. Analysis of T-DNA insertion lines indicated that the Columbia allele of RPP8, though tightly linked to RPP31, is not necessary for adult resistance.
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Affiliation(s)
- John M McDowell
- Department of Plant Pathology, Physiology, and Weed Science, and Fralin Biotechnology Center, Virginia Polytechnic Institute and State University, Blacksburg 24061-0346, USA.
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38
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Abstract
The Arabidopsis thaliana agd2-like defense response protein1 (ald1) mutant was previously found to be hypersusceptible to the virulent bacterial pathogen Pseudomonas syringae and had reduced accumulation of the defense signal salicylic acid (SA). ALD1 was shown to possess aminotransferase activity in vitro, suggesting it generates an amino acid-derived defense signal. We now find ALD1 to be a key defense component that acts in multiple contexts and partially requires the PHYTOALEXIN DEFICIENT4 (PAD4) defense regulatory gene for its expression in response to infection. ald1 plants have increased susceptibility to avirulent P. syringae strains, are unable to activate systemic acquired resistance and are compromised for resistance to the oomycete pathogen Peronospora parasitica in mutants with constitutively active defenses. ALD1 and PAD4 can act additively to control SA, PATHOGENESIS RELATED GENE1 (PR1) transcript and camalexin (an antimicrobial metabolite) accumulation as well as disease resistance. Finally, ALD1 and PAD4 can mutually affect each other's expression in a constitutive defense mutant, suggesting that these two genes can act in a signal amplification loop.
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Affiliation(s)
- Jong Tae Song
- Department of Molecular Genetics and Cell Biology, Erman Biology Center, The University of Chicago, 1103 East 57th Street, Chicago, IL 60637, USA
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39
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Abstract
The resistance genes Rpg1-b in soybean and RPM1 in Arabidopsis recognize the same bacterial avirulence protein (AvrB). Recent map-based cloning of Rpg1-b has provided the first opportunity to compare functionally analogous R genes in distantly related species. Rpg1-b and RPM1 are not orthologs. Rather, these genes descended from distinct evolutionary lineages in which recognition of AvrB has probably evolved independently. This result, together with new insights into RPM1-mediated recognition of AvrB, provides an exciting opportunity to reconsider classical views on the evolution of pathogen recognition specificity.
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Affiliation(s)
- John M McDowell
- Department of Plant Pathology, Physiology, and Weed Science, Fralin Biotechnology Center, Virginia Tech, Blacksburg, VA 24061-0346, USA.
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40
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Eulgem T, Weigman VJ, Chang HS, McDowell JM, Holub EB, Glazebrook J, Zhu T, Dangl JL. Gene expression signatures from three genetically separable resistance gene signaling pathways for downy mildew resistance. Plant Physiol 2004; 135:1129-44. [PMID: 15181204 PMCID: PMC514145 DOI: 10.1104/pp.104.040444] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
Resistance gene-dependent disease resistance to pathogenic microorganisms is mediated by genetically separable regulatory pathways. Using the GeneChip Arabidopsis genome array, we compared the expression profiles of approximately 8,000 Arabidopsis genes following activation of three RPP genes directed against the pathogenic oomycete Peronospora parasitica. Judicious choice of P. parasitica isolates and loss of resistance plant mutants allowed us to compare the responses controlled by three genetically distinct resistance gene-mediated signaling pathways. We found that all three pathways can converge, leading to up-regulation of common sets of target genes. At least two temporal patterns of gene activation are triggered by two of the pathways examined. Many genes defined by their early and transient increases in expression encode proteins that execute defense biochemistry, while genes exhibiting a sustained or delayed expression increase predominantly encode putative signaling proteins. Previously defined and novel sequence motifs were found to be enriched in the promoters of genes coregulated by the local defense-signaling network. These putative promoter elements may operate downstream from signal convergence points.
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Affiliation(s)
- Thomas Eulgem
- Department of Biology, University of North Carolina, Chapel Hill, North Carolina 27599, USA
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41
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Chen Z, Kloek AP, Cuzick A, Moeder W, Tang D, Innes RW, Klessig DF, McDowell JM, Kunkel BN. The Pseudomonas syringae type III effector AvrRpt2 functions downstream or independently of SA to promote virulence on Arabidopsis thaliana. Plant J 2004; 37:494-504. [PMID: 14756766 DOI: 10.1111/j.1365-313x.2003.01984.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
AvrRpt2, a Pseudomonas syringae type III effector protein, functions from inside plant cells to promote the virulence of P. syringae pv. tomato strain DC3000 (PstDC3000) on Arabidopsis thaliana plants lacking a functional copy of the corresponding RPS2 resistance gene. In this study, we extended our understanding of AvrRpt2 virulence activity by exploring the hypothesis that AvrRpt2 promotes PstDC3000 virulence by suppressing plant defenses. When delivered by PstDC3000, AvrRpt2 suppresses pathogen-related (PR) gene expression during infection, suggesting that AvrRpt2 suppresses defenses mediated by salicylic acid (SA). However, AvrRpt2 promotes PstDC3000 growth on transgenic plants expressing the SA-degrading enzyme NahG, indicating that AvrRpt2 does not promote bacterial virulence by modulating SA levels during infection. AvrRpt2 general virulence activity does not depend on the RPM1 resistance gene, as mutations in RPM1 had no effect on AvrRpt2-induced phenotypes. Transgenic plants expressing AvrRpt2 displayed enhanced susceptibility to PstDC3000 strains defective in type III secretion, indicating that enhanced susceptibility of these plants is not because of suppression of defense responses elicited by other type III effectors. Additionally, avrRpt2 transgenic plants did not exhibit increased susceptibility to Peronospora parasitica and Erysiphe cichoracearum, suggesting that AvrRpt2 virulence activity is specific to P. syringae.
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Affiliation(s)
- Zhongying Chen
- Department of Biology, Washington University in St Louis, St Louis, MO 63130, USA
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42
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Abstract
Plant disease resistance genes (R genes) encode proteins that detect pathogens. R genes have been used in resistance breeding programs for decades, with varying degrees of success. Recent molecular research on R proteins and downstream signal transduction networks has provided exciting insights, which will enhance the use of R genes for disease control. Definition of conserved structural motifs in R proteins has facilitated the cloning of useful R genes, including several that are functional in multiple crop species and/or provide resistance to a relatively wide range of pathogens. Numerous signal transduction components in the defense network have been defined, and several are being exploited as switches by which resistance can be activated against diverse pathogens.
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Affiliation(s)
- John M McDowell
- Department of Plant Pathology, Physiology and Weed Science, Fralin Biotechnology Center, Virginia Tech, Blacksburg, VA 24061-0346, USA.
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Beers EP, McDowell JM. Regulation and execution of programmed cell death in response to pathogens, stress and developmental cues. Curr Opin Plant Biol 2001; 4:561-567. [PMID: 11641074 DOI: 10.1016/s1369-5266(00)00216-8] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Recent studies have expanded our view of the interactions between small molecule signals that regulate the hypersensitive response and other forms of cell suicide in plants. The mitochondrion has received increasing support as a mediator of at least some forms of programmed cell death in plants. In addition, new information provides a glimpse of how plant hormone signaling may be integrated with extensive autolysis, sensitivity to reactive oxygen intermediates and cell death.
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Affiliation(s)
- E P Beers
- Department of Horticulture, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA.
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McDowell JM, Cuzick A, Can C, Beynon J, Dangl JL, Holub EB. Downy mildew (Peronospora parasitica) resistance genes in Arabidopsis vary in functional requirements for NDR1, EDS1, NPR1 and salicylic acid accumulation. Plant J 2000; 22:523-9. [PMID: 10886772 DOI: 10.1046/j.1365-313x.2000.00771.x] [Citation(s) in RCA: 139] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
To better understand the genetic requirements for R gene-dependent defense activation in Arabidopsis, we tested the effect of several defense response mutants on resistance specified by eight RPP genes (for resistance to Peronospora parasitica) expressed in the Col-0 background. In most cases, resistance was not suppressed by a mutation in the SAR regulatory gene NPR1 or by expression of the NahG transgene. Thus, salicylic acid accumulation and NPR1 function are not necessary for resistance mediated by these RPP genes. In addition, resistance conferred by two of these genes, RPP7 and RPP8, was not significantly suppressed by mutations in either EDS1 or NDR1. RPP7 resistance was also not compromised by mutations in EIN2, JAR1 or COI1 which affect ethylene or jasmonic acid signaling. Double mutants were therefore tested. RPP7 and RPP8 were weakly suppressed in an eds1-2/ndr1-1 background, suggesting that these RPP genes operate additively through EDS1, NDR1 and as-yet-undefined signaling components. RPP7 was not compromised in coi1/npr1 or coi1/NahG backgrounds. These observations suggest that RPP7 initiates resistance through a novel signaling pathway that functions independently of salicylic acid accumulation or jasmonic acid response components.
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Affiliation(s)
- J M McDowell
- Department of Biology, University of North Carolina, Chapel Hill 27599-3280, USA
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45
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Abstract
Complementary biochemical and genetic approaches are being used to dissect the signaling network that regulates the innate immune response in plants. Receptor-mediated recognition of invading pathogens triggers a signal amplification loop that is based on synergistic interactions between nitric oxide, reactive oxygen intermediates and salicylic acid. Alternative resistance mechanisms in Arabidopsis are deployed against different types of pathogens; these mechanisms are mediated by either salicylic acid or the growth regulators jasmonic acid and ethylene.
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Affiliation(s)
- J M McDowell
- Dept of Plant Pathology, Plant Physiology, and Weed Science, Virginia Polytechnic Institute, Blacksburg, VA 24061-0331, USA
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Grant MR, McDowell JM, Sharpe AG, de Torres Zabala M, Lydiate DJ, Dangl JL. Independent deletions of a pathogen-resistance gene in Brassica and Arabidopsis. Proc Natl Acad Sci U S A 1998; 95:15843-8. [PMID: 9861058 PMCID: PMC28132 DOI: 10.1073/pnas.95.26.15843] [Citation(s) in RCA: 102] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Plant disease resistance (R) genes confer race-specific resistance to pathogens and are genetically defined on the basis of intra-specific functional polymorphism. Little is known about the evolutionary mechanisms that generate this polymorphism. Most R loci examined to date contain alternate alleles and/or linked homologs even in disease-susceptible plant genotypes. In contrast, the resistance to Pseudomonas syringae pathovar maculicola (RPM1) bacterial resistance gene is completely absent (rpm1-null) in 5/5 Arabidopsis thaliana accessions that lack RPM1 function. The rpm1-null locus contains a 98-bp segment of unknown origin in place of the RPM1 gene. We undertook comparative mapping of RPM1 and flanking genes in Brassica napus to determine the ancestral state of the RPM1 locus. We cloned two B. napus RPM1 homologs encoding hypothetical proteins with approximately 81% amino acid identity to Arabidopsis RPM1. Collinearity of genes flanking RPM1 is conserved between B. napus and Arabidopsis. Surprisingly, we found four additional B. napus loci in which the flanking marker synteny is maintained but RPM1 is absent. These B. napus rpm1-null loci have no detectable nucleotide similarity to the Arabidopsis rpm1-null allele. We conclude that RPM1 evolved before the divergence of the Brassicaceae and has been deleted independently in the Brassica and Arabidopsis lineages. These results suggest that functional polymorphism at R gene loci can arise from gene deletions.
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Affiliation(s)
- M R Grant
- Department of Biological Sciences, Wye College, Wye, Ashford, TN, USA
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47
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McDowell JM, Dhandaydham M, Long TA, Aarts MG, Goff S, Holub EB, Dangl JL. Intragenic recombination and diversifying selection contribute to the evolution of downy mildew resistance at the RPP8 locus of Arabidopsis. Plant Cell 1998; 10:1861-74. [PMID: 9811794 PMCID: PMC143965 DOI: 10.1105/tpc.10.11.1861] [Citation(s) in RCA: 189] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Pathogen resistance (R) genes of the NBS-LRR class (for nucleotide binding site and leucine-rich repeat) are found in many plant species and confer resistance to a diverse spectrum of pathogens. Little is known about the mechanisms that drive NBS-LRR gene evolution in the host-pathogen arms race. We cloned the RPP8 gene (for resistance to Peronospora parasitica) and compared the structure of alleles at this locus in resistant Landsberg erecta (Ler-0) and susceptible Columbia (Col-0) accessions. RPP8-Ler encodes an NBS-LRR protein with a putative N-terminal leucine zipper and is more closely related to previously cloned R genes that confer resistance to bacterial pathogens than it is to other known RPP genes. The RPP8 haplotype in Ler-0 contains the functional RPP8-Ler gene and a nonfunctional homolog, RPH8A. In contrast, the rpp8 locus in Col-0 contains a single chimeric gene, which was likely derived from unequal crossing over between RPP8-Ler and RPH8A ancestors within a Ler-like haplotype. Sequence divergence among RPP8 family members has been accelerated by positive selection on the putative ligand binding region in the LRRs. These observations indicate that NBS-LRR molecular evolution is driven by the same mechanisms that promote rapid sequence diversification among other genes involved in non-self-recognition.
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Affiliation(s)
- J M McDowell
- Department of Biology, C.B. 3280 Coker Hall, University of North Carolina, Chapel Hill, North Carolina 27599-3280, USA
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48
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McDowell JM, Dhandaydham M, Long TA, Aarts MG, Goff S, Holub EB, Dangl JL. Intragenic recombination and diversifying selection contribute to the evolution of downy mildew resistance at the RPP8 locus of Arabidopsis. Plant Cell 1998; 10:1861-1874. [PMID: 9811794 DOI: 10.2307/3870909] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Pathogen resistance (R) genes of the NBS-LRR class (for nucleotide binding site and leucine-rich repeat) are found in many plant species and confer resistance to a diverse spectrum of pathogens. Little is known about the mechanisms that drive NBS-LRR gene evolution in the host-pathogen arms race. We cloned the RPP8 gene (for resistance to Peronospora parasitica) and compared the structure of alleles at this locus in resistant Landsberg erecta (Ler-0) and susceptible Columbia (Col-0) accessions. RPP8-Ler encodes an NBS-LRR protein with a putative N-terminal leucine zipper and is more closely related to previously cloned R genes that confer resistance to bacterial pathogens than it is to other known RPP genes. The RPP8 haplotype in Ler-0 contains the functional RPP8-Ler gene and a nonfunctional homolog, RPH8A. In contrast, the rpp8 locus in Col-0 contains a single chimeric gene, which was likely derived from unequal crossing over between RPP8-Ler and RPH8A ancestors within a Ler-like haplotype. Sequence divergence among RPP8 family members has been accelerated by positive selection on the putative ligand binding region in the LRRs. These observations indicate that NBS-LRR molecular evolution is driven by the same mechanisms that promote rapid sequence diversification among other genes involved in non-self-recognition.
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Affiliation(s)
- J M McDowell
- Department of Biology, C.B. 3280 Coker Hall, University of North Carolina, Chapel Hill, North Carolina 27599-3280, USA
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Huang S, An YQ, McDowell JM, McKinney EC, Meagher RB. The Arabidopsis ACT11 actin gene is strongly expressed in tissues of the emerging inflorescence, pollen, and developing ovules. Plant Mol Biol 1997; 33:125-39. [PMID: 9037165 DOI: 10.1023/a:1005741514764] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
ACT11 represents a unique and ancient actin subclass in the complex Arabidopsis actin gene family. We have isolated and characterized the Arabidopsis ACT11 actin gene and examined its expression. Southern blotting with a 5' gene-specific probe showed that ACT11 was a single-copy gene in the genome. Northern analysis with a 3' gene-specific probe and reverse transcriptase-mediated PCR (RT-PCR) using gene-specific primers detected ACT11 mRNA at low levels in seedling, root, leaf, and silique tissue; at moderate levels in the inflorescence stem and flower; and at very high levels in pollen. The 5' region of the ACT11 gene, including the promoter region, the 5'-untranslated leader, the intron within the leader, and the first 19 actin codons, was fused to a beta-glucuronidase (GUS) reporter gene. The expression of the ACT11/GUS fusion was examined histochemically in numerous independent transgenic Arabidopsis plants. Strong ACT11/GUS activity was detected in rapidly elongating tissues and organs (e.g., etiolated hypocotyls, expanding leaves, stems) and in floral organ primordia. As the floral buds developed into mature flowers, strong GUS activity was gradually restricted to mature pollen and developing ovules. ACT11 appears to be the only Arabidopsis actin gene expressed at significant levels in ovule, embryo, and endosperm. The unique expression patterns in reproductive organs and the sequence divergence of the ACT11 actin gene suggest that the ACT11 isovariant plays distinct and required roles during Arabidopsis development.
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Affiliation(s)
- S Huang
- Department of Genetics, University of Georgia, Athens 30602-7223, USA
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50
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Huang S, An YQ, McDowell JM, McKinney EC, Meagher RB. The Arabidopsis thaliana ACT4/ACT12 actin gene subclass is strongly expressed throughout pollen development. Plant J 1996; 10:189-202. [PMID: 8771777 DOI: 10.1046/j.1365-313x.1996.10020189.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
Plants contain complex actin gene families composed of several diverse and ancient subclasses of genes. One Arabidopsis actin gene subclass represented by the ACT4 and ACT12 genes has been isolated and characterized. Both actin genes have typical plant actin gene structures, including three small introns interrupting the coding region and an intron within the mRNA leader. Their encoded proteins differ from each other in only one amino acid, whereas they differ in 3-10% of their amino acids from the other five Arabidopsis actin subclasses. They also share a few small blocks of DNA sequence homology in the 5' flanking region near their TATA boxs, but not in their introns, 3' flanking regions, or degenerate positions within codons. Southern analysis with gene-specific probes from 5' flanking sequences showed that both were single copy genes in the genome. Both RNA gel blot analysis with 3' gene-specific probes and reverse transcriptase-mediated polymerase chain reactions (RT-PCR) with gene-specific primers detected low levels of ACT4 and ACT12 mRNAs in flowers and very high levels in pollen. The RT-PCR detected very low levels of these mRNAs in the vegetative organs. The 5' region from both genes, including the promoter region, TATA box, the sequence for the mRNA leader and its intron, and the first 19 actin codons, was fused to a beta-glucuronidase (GUS) reporter gene. Expression of the GUS fusions were examined histochemically in 40 independent transgenic Arabidopsis plants. Expression of the ACT4/GUS fusion was restricted to young vascular tissues, tapetum, and developing and mature pollen. Similar expression patterns in these tissues and cell types were observed for ACT12/GUS fusion, yet unlike ACT4, ACT12 was also strongly expressed in the root cap and in a ring of pericycle tissues during lateral root initiation and early development. The unique expression patterns of the ACT4/ACT12 actin gene subclass are discussed in light of recent data on the other expressed members of the Arabidopsis actin gene family.
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MESH Headings
- Actins/genetics
- Arabidopsis/genetics
- Arabidopsis/growth & development
- Arabidopsis/metabolism
- Base Sequence
- Cloning, Molecular
- Conserved Sequence
- DNA, Plant/genetics
- Gene Expression Regulation, Plant
- Genes, Plant
- Genes, Reporter
- Genome, Plant
- Glucuronidase/genetics
- Introns
- Molecular Sequence Data
- Multigene Family
- Plants, Genetically Modified
- Pollen/genetics
- Pollen/growth & development
- Pollen/metabolism
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- RNA, Plant/genetics
- RNA, Plant/metabolism
- Sequence Homology, Nucleic Acid
- Tissue Distribution
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Affiliation(s)
- S Huang
- Department of Genetics, University of Georgia, Athens 30602, USA
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