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Plant interactions with bacterial Pathogens

Plant interactions with bacterial Pathogens. Handout 1: Luis Mur lum@aber.ac.uk users.aber.ac.uk/lum. The variety of plant - bacterial interactions. From Agrios G.N.: Plant Pathology (4thed.). NECROTROPHIC BACTERIAL INTERACTIONS. H. CH. OH. CH. OH. OH. 6. 2. 2. O. O. 5. O.

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Plant interactions with bacterial Pathogens

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  1. Plant interactions with bacterial Pathogens Handout 1: Luis Mur lum@aber.ac.uk users.aber.ac.uk/lum

  2. The variety of plant - bacterial interactions From Agrios G.N.: Plant Pathology (4thed.)

  3. NECROTROPHIC BACTERIAL INTERACTIONS

  4. H CH OH CH OH OH 6 2 2 O O 5 O O H H H H H H 4 1 OH H OH H O H O H H O 3 2 H OH H OH CH OH 2 O O O (1) hemicellulases - mainly xyloglucans . Xylose C5 sugar in pyranose (C5 ring) form CH CH 2 2 CH 2 Further OH OH substituent O(H) 2 3 sugars: HO OH e.g. galactose OH HO OH 1 OH HO OH 4 OH O O O 5 O C o o o o cellulose o o o Cell-wall polymers (A) Cellulose Unbranched polymer (1000-1500 Units) of glucose residues joined at C1-4 . (B) Matrix Polymers -"molecular glue"

  5. - - O O C=O 6 C=O O O occasional rhamnose 5 C1-4 linked O HO sugars in chain galacturonic acids 4 1 OH OH O OH 3 2 OH OH (2) pectic polygalacturonic acids:

  6. Degrading the Cell wall:Erwinia carotovora OH OH C=O C=O PECTIC O LYASE O O =O OH OH O OH OH CH OH 2 PECTIN PECTATE C=O C=O Methyl O O transferase O OH OH O OH OH 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 C=O C=O O O HO O + H20 OH OH +H O OH OH BUT resistance toErwinia in e.g. potato is associated withthe methylation of pectate. So some strains of Erwinia also produce a methyltransferase - Pectic methyltransferases

  7. 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.

  8. BIOTROPHIC BACTERIAL INTERACTIONS

  9. Toxins Produced byP. syringae pathovars Toxin Pathovar Function or Target Symptoms Syringomycin syringae Forms pores in plasma membrane Necrosis Syringopeptin syringae Coronatine e.g. tomato, Molecular Mimic of the plant Chlorosis signal, jasmonic acid. Tagetitoxin tagetis Inhibitor of chloroplast RNA Chlorosis polymersase Phaseolotoxin phaseolicola Inhibitor of ornthine Chlorosis carbamoyltransferase Tabtoxin tabaci Inhibitor of glutamine synthase Chlorosis

  10. 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-[N’sulphodiaminophosphyinyl) – 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.

  11. H CH OH CH OH 6 2 2 O O 5 O O H H H H H H 4 1 OH H OH H O H H O H O 3 2 H NH H NH d- d- d- C=O C=O CH3 CH3 CH OH 2 Vascular Wilts : Ralstonia(Pseudomonas) solanacearum N-acetylglucosamide monomers of EPS in Pseudomonas solanaceraum Amine group .

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