Plant interactions with

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Plant interactions with bacterial Pathogens
Handout 1 Luis Mur lum_at_aber.ac.uk users.aber.ac
.uk/lum
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The variety of plant - bacterial interactions
From Agrios G.N. Plant Pathology (4thed.)
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NECROTROPHIC BACTERIAL INTERACTIONS
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Cell-wall polymers
(A) Cellulose
Unbranched polymer (1000-1500 Units) of glucose
residues joined at C1-4
.
(B) Matrix Polymers
-"molecular glue"
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(2) pectic polygalacturonic acids
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Degrading the Cell wall Erwinia carotovora
Pectic lyases attach the a 1-4 glucosidic
linkage by b-elimination to produce unsaturated
products.


H

Polygalacturonidase cleaves pectate polymers by
hydrolysis


-
OH
OH
Poly galacturondiase
CO
CO
O
O
O
HO
H20
OH
OH
H
O
OH
OH

BUT resistance to Erwinia in e.g. potato is
associated with the methylation of pectate. So
some strains of Erwinia also produce a
methyltransferase
-
Pectic methyltransferases
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Another type of virulence function Quorum
sensing
But first Quorum sensing in Vibrio fischeri.
The range of acyl homoserine lactams (AHL)
associated with plant pathogens
Quorum sensing in Erwinia.
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BIOTROPHIC BACTERIAL INTERACTIONS
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Phaseolotoxin is produced by P. syringae p.v.
phaseolicola which cauyse halo blight on legumes
and bacterial canker. It consists of a
sulphodiaminophosphinyl moiety linked to a
tri-peptide consisting of ornithine, alanine and
homoarginine (Fig. 1).
PHASEOTOXIN
Fig. 1. The structure of phaseolotoxin. Plant
peptidase cleave phasolotoxin (arrow) to release
the alanine and homooarginine residues, a
reaction that results in octicidine (Psorn)
formation.
Phaseolotoxin competitively inhibit ornithine
carbamoyl transferase (OCTase), a critical enzyme
in the Urea cycle which converts ornithine and
carbamoyl phosphate to citrulline (Fig.2). Psorn
(Nd-Nsulphodiaminophosphyinyl) L-
orthinine)is an irreversible inhibitor of OCTase.
Inhibition of OCTasa casues an accumulation of
ornithine and a defiency in the intracellular
pools of argnine, leading to necrosis.
Fig. 2. Mechanism of action of octicidine
(Psorn), the toxic moiety Of phaseolotoxin.
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Vascular Wilts Ralstonia (Pseudomonas)
solanacearum
N-acetylglucosamide monomers of EPS in
Pseudomonas solanaceraum
Amine group
.