Introductory Plant Pathology

Class 17

Toxins

Objectives for Today's Class
Reference: Agrios Chapter 3		Basic outline and references for bacterial toxins from PPA 660: Plant-Microbe Interactions I (University of Kentucky) Dr. Chris Schardl

How Pathogens Attack Plants

When one considers the relative sizes and masses of host cells/cell walls in light of the necessity of parasites to invade hosts for their own survival, if is obvious that parasites have some mechanism, or mechanisms, for invasion of a suitable host. Mechanical penetration is available to some organisms (certain nematodes and fungi); while others are virtually helpless without chemical or mechanical events.

Chemical Methods of Pathogenesis

Microbial Toxins ^R

In general, i.e. teleological, terms it is not to the advantage of the parasite to kill its host; therefore, the production of a toxin by the parasite, whether specific or non-specific, must be for some other function than the death.

Toxin Organism Structure Mechanism of Action

Non-host-specific toxins

Tabtoxin Pseudomonas syringae pv. tabaci irreversibly inhibits glutamine synthetase

Phaseolotoxin Pseudomonas syringae pv. phaseolicola competitively inhibits ornithine carbamoyl transferase

Tentoxin Alternaria alternata chloroplast F(1)-ATPase (CF(1)) is strongly affected

Fusicoccin Fusicoccum amygdali plasma membrane (PM) H+-ATPase

Host-specific toxins

Victorin Helminthosporium victoriae Membranes and Permeability

HMT-toxin Helminthosporium maydis Race T Mitochondria
Texas male-sterile cytoplasm (T-cms)

AK-toxin

AM-toxin

Toxin	Organism	Mechanism of Action
Non-host-specific toxins
Tabtoxin	Pseudomonas syringae pv. tabaci	irreversibly inhibits glutamine synthetase
Phaseolotoxin	Pseudomonas syringae pv. phaseolicola	competitively inhibits ornithine carbamoyl transferase
Tentoxin	Alternaria alternata	chloroplast F(1)-ATPase (CF(1)) is strongly affected
Fusicoccin	Fusicoccum amygdali	plasma membrane (PM) H+-ATPase
Host-specific toxins
Victorin	Helminthosporium victoriae	Membranes and Permeability
HMT-toxin	Helminthosporium maydis Race T	Mitochondria Texas male-sterile cytoplasm (T-cms)
AK-toxin
AM-toxin

Toxin classes based on biological activity

Specificity
- host-specific: Unlike some of the fungal toxins, bacterial toxins not usually host-specific.
  [Recall Southern Corn Leaf Blight and Victoria Blight]
- nonspecific: common of bacterial toxins
Effect on pathogenesis
- primary determinant (pathogenicity factor; little evidence for bacteria)
- secondary determinants (virulence factor; more evidence for bacteria)
Alternative roles against competing microbes (niche protection)

Toxin classes based on chemical structures:

lipodepsipeptides, peptidolactones
Pseudophomin = beta-hydroxydodecanoyl-L-Leu-D-Glu-D-allo-Thr-D-Ile-D-Leu-D-Ser-L-Leu-D-Ser-L-Ile monohydrate

coronatine, polyketide (coronafacic acid plus coronamic acid (a leucine-related moiety)
tabtoxin, monocyclic b-lactam
phaseolotoxin, sulpho-diamino-phosphinyl peptide

Model systems

Pseudomonas syringae pv tabaci and tabtoxin :
- Mode of action:
  - Tabtoxin is an inactive protoxin that is cleaved by plant proteinase to yield tabtoxinine-b-lactam,
    
    which:
  - inhibits glutamine synthetase, leading to ammonium accumulation to toxic levels.
- Symptoms: chlorosis
- Pathogen self-protection: detoxification by lactamase and acetyltransferase (Anzai et al 1989)
Pseudomonas syringae pv phaseolicola and phaseolotoxin

Mode of action: inhibitor of ornithine carbamoyltransferase, blocking arginine biosynthesis

From: http://crch.org/ProfileBachmann.htm

Symptoms: chlorosis
Pathogen self-protection: target site resistance due to a phaseolotoxin-resistant ornithine carbamoyltransferase
Pseudomonas syringae pv and coronatine

The coronatine molecules is cleaved in the plant to yield coronafacic and coronamic acids. The mode of action of these toxins is thought to be due, in part, their mimic of plant signals jasmonate (JA) and methyljasmonate (MeJA); but their may be additional activity(ies) as well

Induces cell expansion (promotes potato tuberization) and reduces division (inhibits soybean callus growth), suggesting MeJA agonism

Symptoms: chlorosis
Pathogen self-protection: unknown; Can you think of at least three possibilities?
Pseudomonas syringae pv syringae and syringomycins, syringotoxins and fuscopeptins

Mode of action:

Syringomycin is an amphipathic, cyclic lipodepsipeptide which inserts to biological and artificial lipid bilayers to form cation (K+, H+, Ca2+) permeable channels. Monomers aggregate to form a voltage-dependent pore complex which may possibly be a homohexamer. The channel may catalyze K+: H+ antiport under certain conditions. It is produced by the plant pathogen, Pseudomonas syringae and targets host plants, inducing necrosis. The channel radius is about 1nm, sufficient to allow the release of nutrients from the plant cell which then can be used by the bacteria. Bender

Syringomycin is a necrosis-inducing lipopeptide toxin synthesized and secreted by the phytopathogen, Pseudomonas syringae pv. syringae. Although small quantities of syringomycin are known to activate a cascade of physiological events in plasma membranes, the mechanism of action of the phytotoxin has never been fully characterized. Hutchison. et.al.
A low concentration activates proton-pump ATPase, perhaps by uncoupling.
At higher concentrations, inhibits K⁺/H⁺ATPase, so that the apoplast becomes more alkaline (where have we discussed this before?).
Synergistic action of the lipodepsipeptides
Syringomycin, a phytotoxin produced by Pseudomonas syringae pv. syringae, decreases stomatal aperture by stimulating K+ efflux from guard cells. Shope et al.

Symptoms: necrosis
Pathogen self-protection ;
Another lipodepsipeptide toxin, tolaasin, is produced by Pseudomonas tolaasii, a mushroom pathogen

Regulation by the gacA/lemA two-component system ( lemA being the environmental sensor) in some but not all pathovars .

References

Anzai H, Yoneyama K, Yamaguchi I (1989) Transgenic tobacco resistant to a bacterial disease by the detoxification of a pathogenic toxin. Mol Gen Genet 219: 492-494

Ballio A, Barra D, Bossa F, Collina A, Grgurina I, Marino G,Moneti G, Paci M, Pucci P, Segre A, Simmaco M (1991) Syringopeptins, new phytotoxic lipodepsipeptides of Pseudomonas syringae pv syringae. FEBS Letters 291: 109-112

Ballio A, Bossa F, Collina A, Gallo M, Iacobellis NS, Paci M,Pucci P, Scaloni A, Segre A, Simmaco M (1990) Structure of syringotoxin, a bioactive metabolite of Pseudomonas syringae pv syringae. FEBS Lett 269: 377-380

Batoko H, D'Exaerde AD, Kinet JM, Bouharmont J, Gage RA, Maraite H, Boutry M (1998) Modulation of plant plasma membrane H+-ATPase by phytotoxic lipodepsipeptides produced by the plant pathogen Pseudomonas fuscovaginae. Biochimica et Biophysica Acta: Bio-Membranes 1372: 216-226

Bender CL, Liyanage H, Palmer D, Ullrich M, Young S, Mitchell R(1993) Characterization of the genes controlling the biosynthesis of the polyketide phytotoxin coronatine including conjugation between coronafacic and coronamic acid. Gene 133: 31-38

Coiro VM, Segre AL, Di Nola A, Paci M, Grottesi A, Veglia G, Ballio A (1998): Solution conformation of the Pseudomonas syringae MSU 16H phytotoxic lipodepsipeptide Pseudomycin A determined by computer simulations using distance geometry and molecular dynamics from NMR data. Eur J Biochem 257: 449-456.

Dalla Serra M, Bernhart I, Nordera P, Di Giorgio D, Ballio A, Menestrina G (1999a): Conductive properties and gating of channels formed by syringopeptin 25a, a bioactive lipodepsipeptide from Pseudomonas syringae pv. syringae, in planar lipid membranes. Molecular Plant Microbe Interactions 12: 401&endash;409.

Dalla Serra M, Fagiuoli G, Nordera P, Bernhart I, Della Volpe C, Di Giorgio D, Ballio A, Menestrina G (1999b): The interaction of lipodepsipeptide toxins from Pseudomonas syringae pv. syringae with biological and model membranes: a comparison of syringotoxin, syringomycin, and two syringopeptins. Molecular Plant Microbe Interactions 12: 391&endash;400.

Durbin RD (1991) Bacterial phytotoxins: mechanisms of action. Experientia 47: 776-783

Feys BJF, Benedetti CE, Penfold CN, Turner JG (1994) Arabidopsis mutants selected for resistance to the phytotoxin coronatine are male sterile, insensitive to methyl jasmonate, and resistant to a bacterial pathogen. Plant Cell 6: 751-759

Hutchison ML, Gross DC (1997) Lipopeptide phytotoxins produced by Pseudomonas syringae pv syringae: Comparison of the biosurfactant and ion channel-forming activities of syringopeptin and syringomycin. Mol Plant-Microbe Int 10: 347-354

Hutchison ML, Johnstone K (1993) Evidence for the involvement of the surface active properties of the extracellular toxin tolaasin in the manifestation of brown blotch disease symptoms by Pseudomonas tolaasii on Agaricus bisporus/ Physiol Mol Plant Pathol 42: 373-384

Kitten T, Kinscherf TG, McEvoy JL, Willis DK (1998) A newly identified regulator is required for virulence and toxin production in Pseudomonas syringae. Mol Microbiol 28: 917-929

Kloek AP, Verbsky ML, Sharma SB, Schoelz JE, Vogel J, Klessig DF, Kunkel BN (2001): Resistance to Pseudomonas syringae conferred by an Arabidopsis thaliana coronatine-insensitive (coi1) mutation occurs through two distinct mechanisms. Plant J 26:509-522.

Koda Y, Takahashi K, Kikuta Y, Greulich F, Toshima H, Ichihara A (1996) Similarities of the biological activities of coronatine and coronafacic acid to those of jasmonic acid. Phytochemistry 41: 93-96

McKay AC, Ophel KM (1993) Toxigenic Clavibacter/Anguina associations infecting grass seedheads. Ann Rev Phytopathol 31: 151-167

Mosqueda G, Van den Broeck G, Saucedo O, Bailey AM,Alvarez-Morales A, Herrera-Estrella L (1990) Isolation and characterization of the gene from Pseudomonas syringae pv. phaseolicola encoding the phaseolotoxin-insensitive ornithine carbamoyltransferase. Mol Gen Genet 222: 461-466

Palmer DA, Bender CL (1995) Ultrastructure of tomato leaf tissue treated with the Pseudomonad phytotoxin coronatine and comparison with methyl jasmonate. Mol Plant-Microbe Interact 8: 683-692

Peet RC, Lindgren PB, Willis DK, Panopoulos NJ (1986) Identification and cloning of genes involved in phaseolotoxin production by Pseudomonas syringae pv. phaseolicola. J Bacteriol 166: 1096-1105

Penfold CN, Bender CL, Turner JG (1996) Characterisation of genes involved in biosynthesis of coronafacic acid, the polyketide component of the phytotoxin coronatine. Gene 183: 167-173

Templeton MD, Sullivan PA, Shepherd MG (1986) Phaseolotoxin-insensitive L-ornithine transcarbamoylase from Pseudomonas syringae pv. phaseolicola. Phys Mol Plant Pathol 29: 393-403

Völksch, B. and H. Weingart (1998). "Toxin production by pathovars of Pseudomonas syringae and their antagonistic activities against epiphytic microorganisms." J Basic Microbiol. 38: 135-145.

DoubleClick Any Word to get a Definition