Extreme Resistance to Viruses in Potato and Soybean

Plant pathogens, including viruses, negatively impact global crop production. Plants have evolved complex immune responses to pathogens. These responses are often controlled by nucleotide-binding leucine-rich repeat proteins (NLRs), which recognize intracellular, pathogen-derived proteins. Genetic resistance to plant viruses is often phenotypically characterized by programmed cell death at or near the infection site; a reaction termed the hypersensitive response. Although visualization of the hypersensitive response is often used as a hallmark of resistance, the molecular mechanisms leading to the hypersensitive response and associated cell death vary. Plants with extreme resistance to viruses rarely exhibit symptoms and have little to no detectable virus replication or spread beyond the infection site. Both extreme resistance and the hypersensitive response can be activated by the same NLR genes. In many cases, genes that normally provide an extreme resistance phenotype can be stimulated to cause a hypersensitive response by experimentally increasing cellular levels of pathogen-derived elicitor protein(s). The molecular mechanisms of extreme resistance and its relationship to the hypersensitive response are largely uncharacterized. Studies on potato and soybean cultivars that are resistant to strains of Potato virus Y (PVY), Potato virus X (PVX), and Soybean mosaic virus (SMV) indicate that abscisic acid (ABA)-mediated signaling and NLR nuclear translocation are important for the extreme resistance response. Recent research also indicates that some of the same proteins are involved in both extreme resistance and the hypersensitive response. Herein, we review and synthesize published studies on extreme resistance in potato and soybean, and describe studies in additional species, including model plant species, to highlight future research avenues that may bridge the gaps in our knowledge of plant antiviral defense mechanisms.

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The Plant Gene CCD1 Selectively Blocks Cell Death During the Hypersensitive Response to Cauliflower Mosaic Virus Infection

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-18-0212 ◽

2005 ◽

Vol 18 (3) ◽

pp. 212-219 ◽

Cited By ~ 23

Author(s):

John Cawly ◽

Anthony B. Cole ◽

Lóránt Király ◽

Wenping Qiu ◽

James E. Schoelz

Keyword(s):

Cell Death ◽

Mosaic Virus ◽

Hypersensitive Response ◽

Plant Pathogens ◽

Plant Viruses ◽

Cauliflower Mosaic Virus ◽

Plant Gene ◽

Cell Death Pathway ◽

Resistance Pathway ◽

Key Characteristics

The P6 protein of Cauliflower mosaic virus (CaMV) W260 elicits a hypersensitive response (HR) on inoculated leaves of Nicotiana edwardsonii. This defense response, common to many plant pathogens, has two key characteristics, cell death within the initially infected tissues and restriction of the pathogen to this area. We present evidence that a plant gene designated CCD1, originally identified in N. bigelovii, can selectively block the cell death pathway during HR, whereas the resistance pathway against W260 remains intact. Suppression of cell death was evident not only macroscopically but also microscopically. The suppression of HR-mediated cell death was specific to CaMV, as Tobacco mosaic virus was able to elicit HR in the plants that contained CCD1. CCD1 also blocks the development of a systemic cell death symptom induced specifically by the P6 protein of W260 in N. clevelandii. Introgression of CCD1 from N. bigelovii into N. clevelandii blocked the development of systemic cell death in response to W260 infection but could not prevent systemic cell death induced by Tomato bushy stunt virus. Thus, CCD1 blocks both local and systemic cell death induced by P6 of W260 but does not act as a general suppressor of cell death induced by other plant viruses. Furthermore, experiments with CCD1 provide further evidence that cell death could be uncoupled from resistance in the HR of Nicotiana edwardsonii to CaMV W260.

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The mirid bug Apolygus lucorum deploys a glutathione peroxidase as a candidate effector to enhance plant susceptibility

Journal of Experimental Botany ◽

10.1093/jxb/eraa015 ◽

2020 ◽

Vol 71 (9) ◽

pp. 2701-2712

Author(s):

Yumei Dong ◽

Maofeng Jing ◽

Danyu Shen ◽

Chenyang Wang ◽

Meiqian Zhang ◽

...

Keyword(s):

Cell Death ◽

Salivary Gland ◽

Glutathione Peroxidase ◽

Large Scale ◽

Plant Pathogens ◽

Molecular Mechanisms ◽

Mechanism Analysis ◽

Apolygus Lucorum ◽

Mirid Bug ◽

Plant Susceptibility

Abstract The mirid bug Apolygus lucorum has become a major agricultural pest since the large-scale cultivation of Bt-cotton. It was assumed that A. lucorum, similarly to other phloem sap insects, could secrete saliva that contains effector proteins into plant interfaces to perturb host cellular processes during feeding. However, the secreted effectors of A. lucorum are still uncharacterized and unstudied. In this study, 1878 putative secreted proteins were identified from the transcriptome of A. lucorum, which either had homology with published aphid effectors or shared common features with plant pathogens and insect effectors. One hundred and seventy-two candidate effectors were used for cell death-inducing/suppressing assays, and a putative salivary gland effector, Apolygus lucorum cell death inhibitor 6 (Al6), was characterized. The mRNAs of Al6 were enriched at feeding stages (nymph and adult) and, in particular, in salivary glands. Moreover, we revealed that the secreted Al6 encoded an active glutathione peroxidase that reduced reactive oxygen species (ROS) accumulation induced by INF1 or Flg22. Expression of the Al6 gene in planta altered insect feeding behavior and promoted plant pathogen infections. Inhibition of cell death and enhanced plant susceptibility to insect and pathogens are dependent on glutathione peroxidase activity of Al6. Thus, this study shows that a candidate salivary gland effector, Al6, functions as a glutathione peroxidase and suppresses ROS induced by pathogen-associated molecular pattern to inhibit pattern-triggered immunity (PTI)-induced cell death. The identification and molecular mechanism analysis of the Al6 candidate effector in A. lucorum will provide new insight into the molecular mechanisms of insect–plant interactions.

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Adaptation of Soybean mosaic virus Avirulent Chimeras Containing P3 Sequences from Virulent Strains to Rsv1-Genotype Soybeans Is Mediated by Mutations in HC-Pro

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-21-7-0937 ◽

2008 ◽

Vol 21 (7) ◽

pp. 937-946 ◽

Cited By ~ 31

Author(s):

M. R. Hajimorad ◽

A. L. Eggenberger ◽

J. H. Hill

Keyword(s):

Amino Acids ◽

Mosaic Virus ◽

Hypersensitive Response ◽

Soybean Mosaic Virus ◽

Extreme Resistance ◽

Sequence Analyses ◽

Virulent Strains ◽

N Terminus ◽

Helper Component Proteinase ◽

Avirulent Isolate

In Rsv1-genotype soybean, Soybean mosaic virus (SMV)-N (an avirulent isolate of strain G2) elicits extreme resistance (ER) whereas strain SMV-G7 provokes a lethal systemic hypersensitive response (LSHR). SMV-G7d, an experimentally evolved variant of SMV-G7, induces systemic mosaic. Thus, for Rsv1-genotype soybean, SMV-N is avirulent whereas SMV-G7 and SMV-G7d are both virulent. Exploiting these differential interactions, we recently mapped the elicitor functions of SMV provoking Rsv1-mediated ER and LSHR to the N-terminal 271 amino acids of P3 from SMV-N and SMV-G7, respectively. The phenotype of both SMV-G7 and SMV-G7d were rendered avirulent on Rsv1-genotype soybean when the part of the genome encoding the N-terminus or the entire P3 cistron was replaced with that from SMV-N; however, reciprocal exchanges did not confer virulence to SMV-N-derived P3 chimeras. Here, we describe virulent SMV-N-derived P3 chimeras containing the full-length or the N-terminal P3 from SMV-G7 or SMV-G7d, with or without additional mutations in P3, that were selected on Rsv1-genotype soybean by sequential transfers on rsv1 and Rsv1-genotype soybean. Sequence analyses of the P3 and helper-component proteinase (HC-Pro) cistrons of progeny recovered from Rsv1-genotype soybean consistently revealed the presence of mutations in HC-Pro. Interestingly, the precise mutations in HC-Pro required for the adaptation varied among the chimeras. No mutation was detected in the HC-Pro of progeny passaged continuously in rsv1-genotype soybean, suggesting that selection is a consequence of pressure imposed by Rsv1. Mutations in HC-Pro alone failed to confer virulence to SMV-N; however, reconstruction of mutations in HC-Pro of the SMV-N-derived P3 chimeras resulted in virulence. Taken together, the data suggest that HC-Pro complementation of P3 is essential for SMV virulence on Rsv1-genotype soybean.

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Gain of Virulence on Rsv1-Genotype Soybean by an Avirulent Soybean mosaic virus Requires Concurrent Mutations in Both P3 and HC-Pro

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-21-7-0931 ◽

2008 ◽

Vol 21 (7) ◽

pp. 931-936 ◽

Cited By ~ 63

Author(s):

A. L. Eggenberger ◽

M. R. Hajimorad ◽

J. H. Hill

Keyword(s):

Amino Acids ◽

Mosaic Virus ◽

Resistance Gene ◽

Hypersensitive Response ◽

Soybean Mosaic Virus ◽

Cytoplasmic Inclusion ◽

Virulence Determinants ◽

Extreme Resistance ◽

Helper Component ◽

Helper Component Proteinase

In soybean, Rsv1, a single dominant resistance gene, invokes extreme resistance (ER) against most Soybean mosaic virus (SMV) strains, including SMV-N, but not SMV-G7, which provokes a virulent lethal systemic hypersensitive response (LSHR). The elicitor functions of the two viruses provoking Rsv1-mediated ER and LSHR have been mapped to the N-terminal 271 amino acids of P3 from SMV-N and SMV-G7, respectively, which differ by nine residues between the two strains. To identify amino acids of P3 from SMV-N provoking Rsv1-mediated ER, the unique residues of SMV-G7 were substituted with those of SMV-N. Of the mutants tested on Rsv1-genotype soybean, only SMV-G7I788R and SMV-G7T948A lost virulence. However, substitution of amino acids of SMV-N, individually or in combination, with the reciprocal residues from SMV-G7 at these two positions failed to confer virulence to SMV-N. In the search for additional virulence determinants, a series of SMV-N chimeras was generated in which fragments within a region from near the middle of the helper-component proteinase (HC-Pro) cistron to the 5′ end of the cytoplasmic inclusion cistron, nucleotides 1,605 to 3,787, were replaced with those of SMV-G7. Only SMV-N-derived chimeras harboring the 3′ region of HC-Pro, at least from nucleotide 2,013, and the entire 5′ end of P3 (nucleotides 2,430 to 3,237) from SMV-G7 were virulent whereas reciprocal exchanges resulted in loss of SMV-G7 virulence. This region of HC-Pro differs by three amino acids between SMV-N and SMV-G7. Analyses of SMV-G7-derived HC-Pro site-directed mutants showed that only SMV-G7M683R lost virulence on Rsv1-genotype soybean; however, SMV-NR682M failed to gain virulence. Nevertheless, an SMV-N derived mutant with three concurrent substitutions, R682M+R787I+A947T, gained virulence. The data indicate that both P3 and HC-Pro are involved in virulence of SMV on Rsv1-genotype soybean.

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Strain-Specific Cylindrical Inclusion Protein of Soybean mosaic virus Elicits Extreme Resistance and a Lethal Systemic Hypersensitive Response in Two Resistant Soybean Cultivars

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-22-9-1151 ◽

2009 ◽

Vol 22 (9) ◽

pp. 1151-1159 ◽

Cited By ~ 42

Author(s):

Jang-Kyun Seo ◽

Suk-Ha Lee ◽

Kook-Hyung Kim

Keyword(s):

Amino Acid ◽

Mosaic Virus ◽

Amino Acid Substitution ◽

Hypersensitive Response ◽

Soybean Mosaic Virus ◽

Cylindrical Inclusion ◽

Single Amino Acid ◽

Extreme Resistance ◽

Soybean Genotypes ◽

Pathogenic Determinant

In the Soybean mosaic virus (SMV)–soybean pathosystem, three independent genes (Rsv1, Rsv3, and Rsv4) conferring resistance to SMV have been identified. Recently, we constructed infectious cDNA clones of SMV G7H and G5H strains and found that these two strains differ in their ability to infect soybean genotypes possessing different SMV resistance genes despite a difference of only 33 amino acids. In particular, pSMV-G7H induced mosaic symptoms systemically in L29 (Rsv3) and provoked a lethal systemic hypersensitive response (LSHR) in Jinpumkong-2, whereas pSMV-G5H could not infect these soybean genotypes. To identify the responsible pathogenic determinants of SMV, we exploited the differential responses of pSMV-G7H- and pSMV-G5H-derived chimeric viruses and amino acid substitution mutant viruses in several soybean genotypes and demonstrated that cylindrical inclusion (CI) protein is the elicitor of Rsv3-mediated extreme resistance and a pathogenic determinant provoking LSHR in Jinpumkong-2. A single amino acid substitution in CI was found to be responsible for gain or loss of elicitor function of CI. Our finding provides a role for CI as a pathogenic determinant in the SMV–soybean pathosystem, and increases the understanding of the basis of the different disease responses of SMV strains.

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The secreted hypersensitive response inducing protein 1 fromBotrytis cinereadisplays non-canonical PAMP-activity

10.1101/2020.12.16.423131 ◽

2020 ◽

Author(s):

Tanja Jeblick ◽

Thomas Leisen ◽

Christina E. Steidele ◽

Jonas Müller ◽

Florian Mahler ◽

...

Keyword(s):

Cell Death ◽

Plant Cell ◽

Hypersensitive Response ◽

Plant Pathogens ◽

Infection Process ◽

Host Cells ◽

Plant Responses ◽

Cell Wall Degrading Enzymes ◽

Molecular Pattern ◽

Biotrophic Pathogens

AbstractAccording to their lifestyle, plant pathogens are divided into biotrophic and necrotrophic organisms. While biotrophic pathogens establish a relationship with living host cells, necrotrophic pathogens rapidly kill host cells and feed on the cell debris. To this end, the necrotrophic ascomycete fungusBotrytis cinereasecretes large amounts of phytotoxic proteins and cell wall degrading enzymes. However, the precise role of these proteins during the infection process is unknown. Here we report on the identification and characterization of the previously unknown toxic protein hypersensitive response inducing protein 1 (Hip1), which induces plant cell death. We found the adoption of a folded protein structure to be a prerequisite for Hip1 to exert its necrosis-inducing activity inNicotiana benthamiana. Localization and the induction of specific plant responses by Hip1 indicate recognition as pathogen-associated molecular pattern at the plant plasma membrane. Our results demonstrate that recognition of Hip1, even in the absence of obvious enzymatic or poreforming activity, induces strong plant defense reactions eventually leading to plant cell death.

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Molecular mechanisms of host cell manipulation by plant pathogens

Acta Crystallographica Section A Foundations and Advances ◽

10.1107/s2053273314091980 ◽

2014 ◽

Vol 70 (a1) ◽

pp. C801-C801

Author(s):

Richard Hughes ◽

Stuart King ◽

Abbas Maqbool ◽

Hazel McLellan ◽

Tolga Bozkurt ◽

...

Keyword(s):

Cell Death ◽

Crop Production ◽

Plant Pathogens ◽

Molecular Mechanisms ◽

Complex Structure ◽

Effector Proteins ◽

Plant Diseases ◽

Cell Manipulation ◽

Cell Physiology ◽

Structural Studies

An estimated 15% of global crop production is lost to pre-harvest disease every year. New ways to manage plant diseases are required. A mechanistic understanding of how plant pathogens re-program their hosts to enable colonisation may provide novel genetic or chemical opportunities to interfere with disease. One notorious plant parasite is the Irish potato famine pathogen Phytophthora infestans. This pathogen remains a considerable threat to potato/tomato crops today as the agent of late blight. Plant pathogens secrete effector proteins outside of and into plant cells to suppress host defences and manipulate cell physiology. Structural studies have provided insights into effector evolution and enabled experiments to probe function [1-3]. Crystal structures of 4 Phytophthora RXLR-type effectors, which are unrelated in primary sequence, revealed similarities in the fold of these proteins. This fold was proposed to act as a stable scaffold that supports diversification of effectors. Further, molecular modelling has enabled mapping of single-site variants responsible for specialisation of a Phytophthora Cystatin-like effector, revealing how effectors can adapt to new hosts after a "host jump". Structural studies describing how RXLR-effectors interact with host targets are lacking. We have used Y2H/co-IP studies to identify host proteins that interact with P. infestans effectors PexRD2 and PexRD54. PexRD2 interacts with MAPKKKe, a component of plant immune signalling pathways, and suppressed cell death activities of this protein. We used the structure of PexRD2 to design mutants that fail to interact with MAPKKKe, and no longer suppress cell-death activities. We found that PexRD54 interacts with potato homologues of the autophagy protein ATG8. We have obtained a crystal structure for PexRD54 in the presence of ATG8. We are now using X-ray scattering to verify the complex structure in solution prior to establishing the role of this interaction during infection.

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The CC domain structure from the wheat stem rust resistance protein Sr33 challenges paradigms for dimerization in plant NLR proteins

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1609922113 ◽

2016 ◽

Vol 113 (45) ◽

pp. 12856-12861 ◽

Cited By ~ 54

Author(s):

Lachlan W. Casey ◽

Peter Lavrencic ◽

Adam R. Bentham ◽

Stella Cesari ◽

Daniel J. Ericsson ◽

...

Keyword(s):

Cell Death ◽

Stem Rust ◽

Plant Pathogens ◽

Molecular Mechanisms ◽

Structural Basis ◽

Wheat Stem Rust ◽

Pathogen Effector ◽

Resistance Protein ◽

Cell Death Signaling ◽

Self Association

Plants use intracellular immunity receptors, known as nucleotide-binding oligomerization domain-like receptors (NLRs), to recognize specific pathogen effector proteins and induce immune responses. These proteins provide resistance to many of the world’s most destructive plant pathogens, yet we have a limited understanding of the molecular mechanisms that lead to defense signaling. We examined the wheat NLR protein, Sr33, which is responsible for strain-specific resistance to the wheat stem rust pathogen, Puccinia graminis f. sp. tritici. We present the solution structure of a coiled-coil (CC) fragment from Sr33, which adopts a four-helix bundle conformation. Unexpectedly, this structure differs from the published dimeric crystal structure of the equivalent region from the orthologous barley powdery mildew resistance protein, MLA10, but is similar to the structure of the distantly related potato NLR protein, Rx. We demonstrate that these regions are, in fact, largely monomeric and adopt similar folds in solution in all three proteins, suggesting that the CC domains from plant NLRs adopt a conserved fold. However, larger C-terminal fragments of Sr33 and MLA10 can self-associate both in vitro and in planta, and this self-association correlates with their cell death signaling activity. The minimal region of the CC domain required for both cell death signaling and self-association extends to amino acid 142, thus including 22 residues absent from previous biochemical and structural protein studies. These data suggest that self-association of the minimal CC domain is necessary for signaling but is likely to involve a different structural basis than previously suggested by the MLA10 crystallographic dimer.

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Survival and Transmission of Potato Virus Y, Pepino Mosaic Virus, and Potato Spindle Tuber Viroid in Water

Applied and Environmental Microbiology ◽

10.1128/aem.03349-13 ◽

2013 ◽

Vol 80 (4) ◽

pp. 1455-1462 ◽

Cited By ~ 34

Author(s):

N. Mehle ◽

I. Gutiérrez-Aguirre ◽

N. Prezelj ◽

D. Delić ◽

U. Vidic ◽

...

Keyword(s):

Mosaic Virus ◽

Potato Virus ◽

Plant Pathogens ◽

Potato Virus Y ◽

Potato Spindle Tuber Viroid ◽

Plant Viruses ◽

Detection Methods ◽

Mechanical Transmission ◽

Pepino Mosaic Virus ◽

Viroid Infection

ABSTRACTHydroponic systems and intensive irrigation are used widely in horticulture and thus have the potential for rapid spread of water-transmissible plant pathogens. Numerous plant viruses have been reported to occur in aqueous environments, although information on their survival and transmission is minimal, due mainly to the lack of effective detection methods and to the complexity of the required transmission experiments. We have assessed the role of water as a source of plant infection using three mechanically transmissible plant pathogens that constitute a serious threat to tomato and potato production: pepino mosaic virus (PepMV), potato virus Y (PVY), and potato spindle tuber viroid (PSTVd). PepMV remains infectious in water at 20 ± 4°C for up to 3 weeks, PVY (NTN strain) for up to 1 week, and PSTVd for up to 7 weeks. Experiments using a hydroponic system show that PepMV (Ch2 genotype) and PVY (NTN strain) can be released from plant roots into the nutrient solution and can infect healthy plants through their roots, ultimately spreading to the green parts, where they can be detected after a few months. In addition, tubers developed on plants grown in substrate watered with PSTVd-infested water were confirmed to be the source of viroid infection. Our data indicate that although well-known pathways of virus spread are more rapid than water-mediated infection, like insect or mechanical transmission through leaves, water is a route that provides a significant bridge for rapid virus/viroid spread. Consequently, water should be taken into account in future epidemiology and risk assessment studies.

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Loss and Gain of Elicitor Function of Soybean Mosaic Virus G7 Provoking Rsv1-Mediated Lethal Systemic Hypersensitive Response Maps to P3

Journal of Virology ◽

10.1128/jvi.79.2.1215-1222.2005 ◽

2005 ◽

Vol 79 (2) ◽

pp. 1215-1222 ◽

Cited By ~ 63

Author(s):

M. R. Hajimorad ◽

A. L. Eggenberger ◽

J. H. Hill

Keyword(s):

Amino Acid ◽

Mosaic Virus ◽

Amino Acid Substitution ◽

Hypersensitive Response ◽

Soybean Mosaic Virus ◽

The Other ◽

Single Amino Acid ◽

Amino Acid Substitutions ◽

Extreme Resistance ◽

Nucleotide Substitutions

ABSTRACT Rsv1, a single dominant resistance gene in soybean PI 96983 (Rsv1), confers extreme resistance against all known American strains of Soybean mosaic virus (SMV), except G7 and G7d. SMV-G7 provokes a lethal systemic hypersensitive response (LSHR), whereas SMV-G7d, an experimentally evolved variant of SMV-G7, induces systemic mosaic. To identify the elicitor of Rsv1-mediated LSHR, chimeras were constructed by exchanging fragments between the molecularly cloned SMV-G7 (pSMV-G7) and SMV-G7d (pSMV-G7d), and their elicitor functions were assessed on PI 96983 (Rsv1). pSMV-G7-derived chimeras containing only P3 of SMV-G7d lost the elicitor function, while the reciprocal chimera of pSMV-G7d gained the function. The P3 regions of the two viruses differ by six nucleotides, of which two are translationally silent. The four amino acid differences are located at positions 823, 915, 953, and 1112 of the precursor polypeptide. Analyses of the site-directed point mutants of both the viruses revealed that nucleotide substitutions leading to translationally silent mutations as well as reciprocal amino acid substitution at position 915 did not influence the loss or gain of the elicitor function. pSMV-G7-derived mutants with amino acid substitutions at any of the other three positions lost the ability to provoke LSHR but induced SHR instead. Two concomitant amino acid substitutions at positions 823 (V to M) and 953 (K to E) abolished pSMV-G7 elicitor function, provoking Rsv1-mediated SHR. Conversely, pSMV-G7d gained the elicitor function of Rsv1-mediated LSHR by a single amino acid substitution at position 823 (M to V), and mutants with amino acid substitutions at position 953 or 1112 induced SHR instead of mosaic. Taken together, the data suggest that strain-specific P3 of SMV is the elicitor of Rsv1-mediated LSHR.

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