Basal Defenses Induced in Pepper by Lipopolysaccharides Are Suppressed by Xanthomonas campestris pv. vesicatoria

The nonpathogenic hrcC mutant of Xanthomonas campestris pv. vesicatoria 85-10∷hrpA22 multiplied in pepper leaves if it was mixed with pathogenic strains of X. campestris pv. vesicatoria. Reactions to the mutant alone included localized deposition of phenolics and callose in papillae, and alterations to the plant cell wall leading to increased electron density. Electron microscopy showed that the localized responses were suppressed in the presence of wild-type bacteria but other wall changes occurred at some sites, involving cellulose-rich ingrowth of the wall. Multiplication of the hrp mutant in mixed inocula was confirmed by tagging 85-10∷hrpA22 using immunocytochemical location of AvrBs3 expressed from the plasmid pD36. Elicitors of callose deposition and other wall changes were isolated from the hrcC mutant. Activity in extracts of bacteria was attributed to the presence of high molecular weight lipopolysaccharides (LPS). Wild-type X. campestris pv. vesicatoria suppressed induction of structural changes caused by purified LPS. Results obtained suggest that effector proteins produced by phytopathogenic bacteria and delivered by the type III secretion system may have a key role in suppressing the basal defense responses activated by bacterial LPS, which lead to restricted multiplication of nonpathogens such as hrp mutants.

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Xanthomonas campestris pv. vesicatoria Effector AvrBsT Induces Cell Death in Pepper, but Suppresses Defense Responses in Tomato

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-23-8-1069 ◽

2010 ◽

Vol 23 (8) ◽

pp. 1069-1082 ◽

Cited By ~ 30

Author(s):

Nak Hyun Kim ◽

Hyong Woo Choi ◽

Byung Kook Hwang

Keyword(s):

Xanthomonas Campestris ◽

Marker Gene ◽

Defense Responses ◽

Gene Expressions ◽

Callose Deposition ◽

Tomato Plants ◽

Type Iii Effector ◽

Type Iii ◽

Pepper Leaves ◽

Pepper Plants

A type III effector protein, AvrBsT, is secreted into plant cells from Xanthomonas campestris pv. vesicatoria Bv5-4a, which causes bacterial spot disease on pepper (Capsicum annuum) and tomato (Solanum lycopersicum). To define the function and recognition of AvrBsT in the two host plants, avrBsT was introduced into the virulent pepper strain X. campestris pv. vesicatoria Ds1. Expression of AvrBsT in Ds1 rendered the strain avirulent to pepper plants. Infection of pepper leaves with Ds1 (avrBsT) expressing AvrBsT but not with near-isogenic control strains triggered a hypersensitive response (HR) accompanied by strong H2O2 generation, callose deposition, and defense-marker gene expressions. Mutation of avrBsT, however, compromised HR induction by X. campestris pv. vesicatoria Bv5-4a, suggesting its avirulence function in pepper plants. In contrast, AvrBsT acted as a virulence factor in tomato plants. Growth of strains Ds1 (avrBsT) and Bv5-4a ΔavrBsT was significantly enhanced and reduced, respectively, in tomato leaves. X. campestris pv. vesicatoria-expressed AvrBsT also significantly compromised callose deposition and defense-marker gene expression in tomato plants. Together, these results suggest that the X. campestris pv. vesicatoria type III effector AvrBsT is differentially recognized by pepper and tomato plants.

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Changes in Methanol Evolution and Pectin Methylesterification in Resistant and Susceptible Pepper Leaves Inoculated with Xanthomonas campestris pv. vesicatoria

Journal of the American Society for Horticultural Science ◽

10.21273/jashs.123.6.980 ◽

1998 ◽

Vol 123 (6) ◽

pp. 980-986 ◽

Cited By ~ 1

Author(s):

Suparna R. Mundodi ◽

Jeffrey A. Anderson ◽

Niels O. Maness ◽

Michael W. Smith ◽

Bjorn Martin ◽

...

Keyword(s):

Cell Wall ◽

Xanthomonas Campestris ◽

Time Course ◽

Structural Changes ◽

Plant Cell Wall ◽

Water Control ◽

Methanol Production ◽

Pepper Leaves ◽

Race 1 ◽

The Relationship

The hypersensitive response in resistant plants exposed to incompatible pathogens involves structural changes in the plant cell wall and plasma membrane. Cell wall changes may include pectin deesterification resulting in release of methanol. The time course of methanol production was characterized from `Early Calwonder 20R' pepper (Capsicum annuum L.) leaves infiltrated with the incompatible pathogen, Xanthomonas campestris pv. vesicatoria (Doidge) Dye race 1 (XCV). In the first time course experiment, leaves were infiltrated with either 108 colony-forming units/mL of XCV or water control. Leaf panels (1 × 5 cm) were excised after dissipation of water soaking, then incubated in vials at 24 °C. Headspace gas was analyzed at 6-hour intervals up to 24 hours. The rate of methanol production from resistant pepper leaves infiltrated with XCV was greatest during the first 12 hours after excision. In another experiment, leaf panels were harvested at 6-hour intervals up to 24 hours after inoculation and incubated for 12 hours at 24 °C to determine the relationship between the interval from inoculation to leaf excision and methanol production. The highest rate of methanol production was obtained when the interval between bacterial infiltration and leaf excision was 18 hours. The relationship between methanol release and changes in the degree of methylesterification (DOM) of cell wall pectin was determined in near isogenic lines of `Early Calwonder' pepper plants resistant (20R) and susceptible (10R) to XCV race 1. Cell walls were prepared from resistant and susceptible pepper leaves infiltrated with XCV or water. XCV-treated resistant leaves had 18% DOM and 9.7 nmol·g-1·h-1 of headspace methanol, and the susceptible leaves had 48% DOM with 0.2 nmol·g-1·h-1 methanol. Susceptible and resistant control leaves infiltrated with water had 55% and 54% DOM, respectively, with no detectable methanol production. Increased methanol production in resistant pepper leaves inoculated with XCV coincided with an increase in cell wall pH. Intercellular washing fluid of resistant pepper leaves had a significantly higher pH (6.9) compared to susceptible leaves (pH 5.1) and control leaves infiltrated with water (pH 5.1). Both 10R and 20R pepper leaves infiltrated with buffer at increasing pH's of 5.1, 6.9 or 8.7 had increased methanol production. Since deesterified pectin is more susceptible to degradation, demethylation may facilitate formation of pectic oligomers with defensive signalling activity.

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Transgenic Plants Producing the Bacterial Pheromone N-Acyl-Homoserine Lactone Exhibit Enhanced Resistance to the Bacterial Phytopathogen Erwinia carotovora

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi.2001.14.9.1035 ◽

2001 ◽

Vol 14 (9) ◽

pp. 1035-1042 ◽

Cited By ~ 108

Author(s):

Andres Mäe ◽

Marcos Montesano ◽

Viia Koiv ◽

E. Tapio Palva

Keyword(s):

Quorum Sensing ◽

Transgenic Tobacco ◽

Plant Cell Wall ◽

Ectopic Expression ◽

Erwinia Carotovora ◽

Homoserine Lactone ◽

Defense Responses ◽

Dependent Manner ◽

Wild Type ◽

Enhanced Resistance

Bacterial pheromones, mainly different homoserine lactones, are central to a number of bacterial signaling processes, including those involved in plant pathogenicity. We previously demonstrated that N-oxoacyl-homoserine lactone (OHL) is essential for quorum sensing in the soft-rot phytopathogen Erwinia carotovora. In this pathogen, OHL controls the coordinate activation of genes encoding the main virulence determinants, extracellular plant cell wall degrading enzymes (PCWDEs), in a cell density-dependent manner. We suggest that E. carotovora employ quorum sensing to avoid the premature production of PCWDEs and subsequent activation of plant defense responses. To test whether modulating this sensory system would affect the outcome of a plant-pathogen interaction, we generated transgenic tobacco, producing OHL. This was accomplished by ectopic expression in tobacco of the E. carotovora gene expI, which is responsible for OHL biosynthesis. We show that expI-positive transgenic tobacco lines produced the active pheromone and partially complemented the avirulent phenotype of expI mutants. The OHL-producing tobacco lines exhibited enhanced resistance to infection by wild-type E. carotovora. The results were confirmed by exogenous addition of OHL to wild-type plants, which also resulted in increased resistance to E. carotovora.

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Xanthan Pyruvilation Is Essential for the Virulence of Xanthomonas campestris pv. campestris

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-06-16-0106-r ◽

2016 ◽

Vol 29 (9) ◽

pp. 688-699 ◽

Cited By ~ 11

Author(s):

María Isabel Bianco ◽

Laila Toum ◽

Pablo Marcelo Yaryura ◽

Natalia Mielnichuk ◽

Gustavo Eduardo Gudesblat ◽

...

Keyword(s):

Xanthomonas Campestris ◽

Defense Responses ◽

Plant Defense Responses ◽

In Planta ◽

Callose Deposition ◽

Disease Symptoms ◽

The Relationship ◽

Plant Surfaces ◽

Xanthomonas Campestris Pv Campestris ◽

Successful Colonization

Xanthan, the main exopolysaccharide (EPS) synthesized by Xanthomonas spp., contributes to bacterial stress tolerance and enhances attachment to plant surfaces by helping in biofilm formation. Therefore, xanthan is essential for successful colonization and growth in planta and has also been proposed to be involved in the promotion of pathogenesis by calcium ion chelation and, hence, in the suppression of the plant defense responses in which this cation acts as a signal. The aim of this work was to study the relationship between xanthan structure and its role as a virulence factor. We analyzed four Xanthomonas campestris pv. campestris mutants that synthesize structural variants of xanthan. We found that the lack of acetyl groups that decorate the internal mannose residues, ketal-pyruvate groups, and external mannose residues affects bacterial adhesion and biofilm architecture. In addition, the mutants that synthesized EPS without pyruvilation or without the external mannose residues did not develop disease symptoms in Arabidopsis thaliana. We also observed that the presence of the external mannose residues and, hence, pyruvilation is required for xanthan to suppress callose deposition as well as to interfere with stomatal defense. In conclusion, pyruvilation of xanthan seems to be essential for Xanthomonas campestris pv. campestris virulence.

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The Type III Secretion Chaperone HpaB Controls the Translocation of Effector and Noneffector Proteins From Xanthomonas campestris pv. vesicatoria

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-06-17-0138-r ◽

2018 ◽

Vol 31 (1) ◽

pp. 61-74 ◽

Cited By ~ 6

Author(s):

Felix Scheibner ◽

Nadine Hartmann ◽

Jens Hausner ◽

Christian Lorenz ◽

Anne-Katrin Hoffmeister ◽

...

Keyword(s):

Type Iii Secretion ◽

Type Strain ◽

Xanthomonas Campestris ◽

Molecular Mechanisms ◽

Wild Type Strain ◽

Effector Proteins ◽

Wild Type ◽

Type Iii ◽

In The Wild ◽

Secretion Chaperone

Pathogenicity of the gram-negative bacterium Xanthomonas campestris pv. vesicatoria depends on a type III secretion (T3S) system, which translocates effector proteins into plant cells. Effector proteins contain N-terminal T3S and translocation signals and interact with the T3S chaperone HpaB, which presumably escorts effectors to the secretion apparatus. The molecular mechanisms underlying the recognition of effectors by the T3S system are not yet understood. In the present study, we analyzed T3S and translocation signals in the type III effectors XopE2 and XopJ from X. campestris pv. vesicatoria. Both effectors contain minimal translocation signals, which are only recognized in the absence of HpaB. Additional N-terminal signals promote translocation of XopE2 and XopJ in the wild-type strain. The results of translocation and interaction studies revealed that the interaction of XopE2 and XopJ with HpaB and a predicted cytoplasmic substrate docking site of the T3S system is not sufficient for translocation. In agreement with this finding, we show that the presence of an artificial HpaB-binding site does not promote translocation of the noneffector XopA in the wild-type strain. Our data, therefore, suggest that the T3S chaperone HpaB not only acts as an escort protein but also controls the recognition of translocation signals.

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Identification of MAMP-Responsive Plasma Membrane-Associated Proteins in Arabidopsis thaliana Following Challenge with Different LPS Chemotypes from Xanthomonas campestris

Pathogens ◽

10.3390/pathogens9100787 ◽

2020 ◽

Vol 9 (10) ◽

pp. 787

Author(s):

Raeesa H. Hussan ◽

Ian A. Dubery ◽

Lizelle A. Piater

Keyword(s):

Arabidopsis Thaliana ◽

Plasma Membrane ◽

Xanthomonas Campestris ◽

Induced Defense ◽

Defense Responses ◽

Structural Features ◽

Wild Type ◽

Core Oligosaccharide ◽

Associated Proteins ◽

Induced Defense Responses

Lipopolysaccharides (LPS) are recognized as microbe-associated molecular patterns (MAMPs) responsible for eliciting defense-related responses and while the effects have been well-documented in mammals, there is a lack of knowledge regarding the mechanism of perception in plant systems and recognized structural moieties within the macromolecular lipoglycan structure. Thus, identification of the LPS plasma membrane (PM) receptor(s)/receptor complex in Arabidopsis thaliana through proteomics will contribute to a deeper understanding of induced defense responses. As such, structurally characterized LPS chemotypes from Xanthomonas campestris pv. campestris (Xcc) wild-type 8004 (prototypical smooth-type LPS) and mutant 8530 (truncated core with no O–chain) strains were utilized to pre-treat A. thaliana plants. The associated proteomic response/changes within the PM were compared over a 24 h period using mass spectrometry-based methodologies following three variants of LPS-immobilized affinity chromatography. This resulted in the identification of proteins from several functional categories, but importantly, those involved in perception and defense. The distinct structural features between wild-type and mutant LPS are likely responsible for the differential changes to the proteome profiles, and many of the significant proteins were identified in response to the wild-type Xcc LPS where it is suggested that the core oligosaccharide and O-chain participate in recognition by receptor-like kinases (RLKs) in a multiprotein complex and, notably, varied from that of the mutant chemotype.

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Cytochemistry of defense responses in cassava infected by Xanthomonas campestris pv. manihotis

Canadian Journal of Microbiology ◽

10.1139/m96-145 ◽

1996 ◽

Vol 42 (11) ◽

pp. 1131-1143 ◽

Cited By ~ 56

Author(s):

K. Kpémoua ◽

B. Boher ◽

M. Nicole ◽

P. Calatayud ◽

J. P. Geiger

Keyword(s):

Cell Wall ◽

Bacterial Growth ◽

Xanthomonas Campestris ◽

Secondary Cell Wall ◽

Defense Responses ◽

Resistant Variety ◽

Xylem Parenchyma ◽

Callose Deposition ◽

Wide Range ◽

Parenchyma Cells

Stems of susceptible and resistant cassava plants have been cytologically investigated for their defense reactions to an aggressive strain of Xanthomonas campestris pv. manihotis. Histochemistry, in conjunction with gold cytochemistry, revealed that in susceptible and resistant plants, phloem and xylem parenchyma cells displayed a wide range of responses that limited the bacterial growth within the infected plants. Lignification and suberization associated with callose deposition were effective mechanisms that reinforced host barriers in the phloem. In the infected xylem, vessels were plugged by a material of pectic and (or) lignin-like origin. Flavonoids have been seen to be incorporated in secondary cell wall coatings. These reactions occurred at a higher intensity in the resistant plants. The number of phoem and xylem cells producing autofluorescent compounds was higher in infected resistant plants than in susceptible plants. Reactions have been observed in the resistant variety only, such as secretion of phenol-like molecules by tyloses and hyperplasic activity of phloem cells that compartmentalized bacterial lysis pockets, which are potent secondary inoculum sources.Key words: lignin, suberin, callose, phenol, tylose, flavonoid, pectin.

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Stage-Specific Suppression of Basal Defense Discriminates Barley Plants Containing Fast- and Delayed-Acting Mla Powdery Mildew Resistance Alleles

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-19-0939 ◽

2006 ◽

Vol 19 (9) ◽

pp. 939-947 ◽

Cited By ~ 52

Author(s):

Rico A. Caldo ◽

Dan Nettleton ◽

Jiqing Peng ◽

Roger P. Wise

Keyword(s):

Powdery Mildew ◽

Meta Analysis ◽

Defense Responses ◽

Resistance Locus ◽

Wild Type ◽

Mildew Resistance ◽

Basal Defense ◽

Fast Acting ◽

Compatible Interactions ◽

Incompatible Interactions

Nonspecific recognition of pathogen-derived general elicitors triggers the first line of plant basal defense, which in turn, preconditions the host towards resistance or susceptibility. To elucidate how basal defense responses influence the onset of Mla (mildew resistance locus a)-specified resistance, we performed a meta-analysis of GeneChip mRNA expression for 155 basal defense-related genes of barley (Hordeum vulgare) challenged with Blumeria graminis f. sp. hordei, the causal agent of powdery mildew disease. In plants containing the fast-acting Mla1, Mla6, or Mla13 alleles, transcripts hyper-accumulated from 0 to 16 h after inoculation (hai) in both compatible and incompatible interactions. Suppression of basal defense-related transcripts was observed after 16 hai only in compatible interactions, whereas these transcripts were sustained or increased in incompatible interactions. By contrast, in plants containing wild-type and mutants of the delayed-acting Mla12 allele, an early hyper-induction of transcripts from 0 to 8 hai was observed, but the expression of many of these genes is markedly suppressed from 8 to 16 hai. These results suggest that the inhibition of basal defense facilitates the development of haustoria by the pathogen, consequently delaying the onset of host resistance responses. Thus, we hypothesize that the regulation of basal defense influences host-cell accessibility to the fungal pathogen and drives allelic diversification of gene-specific resistance phenotypes.

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Genetic Deletion of Interleukin-15 Is Not Associated with Major Structural Changes Following Experimental Post-Traumatic Knee Osteoarthritis in Rats

Applied Sciences ◽

10.3390/app11157118 ◽

2021 ◽

Vol 11 (15) ◽

pp. 7118

Author(s):

Ermina Hadzic ◽

Garth Blackler ◽

Holly Dupuis ◽

Stephen James Renaud ◽

Christopher Thomas Appleton ◽

...

Keyword(s):

Articular Cartilage ◽

Subchondral Bone ◽

Structural Changes ◽

Cartilage Damage ◽

Wild Type ◽

Significant Difference ◽

Post Traumatic ◽

Interleukin 15 ◽

Joint Trauma ◽

Surgically Induced

Post-traumatic osteoarthritis (PTOA) is a degenerative joint disease, leading to articular cartilage breakdown, osteophyte formation, and synovitis, caused by an initial joint trauma. Pro-inflammatory cytokines increase catabolic activity and may perpetuate inflammation following joint trauma. Interleukin-15 (IL-15), a pro-inflammatory cytokine, is increased in OA patients, although its roles in PTOA pathophysiology are not well characterized. Here, we utilized Il15 deficient rats to examine the role of IL-15 in PTOA pathogenesis in an injury-induced model. OA was surgically induced in Il15 deficient Holtzman Sprague-Dawley rats and control wild-type rats to compare PTOA progression. Semi-quantitative scoring of the articular cartilage, subchondral bone, osteophyte size, and synovium was performed by two blinded observers. There was no significant difference between Il15 deficient rats and wild-type rats following PTOA-induction across articular cartilage damage, subchondral bone damage, and osteophyte scoring. Similarly, synovitis scoring across six parameters found no significant difference between genetic variants. Overall, IL-15 does not appear to play a key role in the development of structural changes in this surgically-induced rat model of PTOA.

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Brown Spiders’ Phospholipases-D with Potential Therapeutic Applications: Functional Assessment of Mutant Isoforms

Biomedicines ◽

10.3390/biomedicines9030320 ◽

2021 ◽

Vol 9 (3) ◽

pp. 320

Author(s):

Thaís Pereira da Silva ◽

Fernando Jacomini de Castro ◽

Larissa Vuitika ◽

Nayanne Louise Costacurta Polli ◽

Bruno César Antunes ◽

...

Keyword(s):

Structural Changes ◽

Capillary Permeability ◽

Structural Data ◽

Histopathological Analysis ◽

Amino Acid Residues ◽

Wild Type ◽

Antigenic Properties ◽

Harmful Effects

Phospholipases-D (PLDs) found in Loxosceles spiders’ venoms are responsible for the dermonecrosis triggered by envenomation. PLDs can also induce other local and systemic effects, such as massive inflammatory response, edema, and hemolysis. Recombinant PLDs reproduce all of the deleterious effects induced by Loxosceles whole venoms. Herein, wild type and mutant PLDs of two species involved in accidents—L. gaucho and L. laeta—were recombinantly expressed and characterized. The mutations are related to amino acid residues relevant for catalysis (H12-H47), magnesium ion coordination (E32-D34) and binding to phospholipid substrates (Y228 and Y228-Y229-W230). Circular dichroism and structural data demonstrated that the mutant isoforms did not undergo significant structural changes. Immunoassays showed that mutant PLDs exhibit conserved epitopes and kept their antigenic properties despite the mutations. Both in vitro (sphingomyelinase activity and hemolysis) and in vivo (capillary permeability, dermonecrotic activity, and histopathological analysis) assays showed that the PLDs with mutations H12-H47, E32-D34, and Y228-Y229-W230 displayed only residual activities. Results indicate that these mutant toxins are suitable for use as antigens to obtain neutralizing antisera with enhanced properties since they will be based on the most deleterious toxins in the venom and without causing severe harmful effects to the animals in which these sera are produced.

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