Article: article from journal or magazin.
Manipulation of salicylate content in Arabidopsis thaliana by the expression of an engineered bacterial salicylate synthase.
Salicylic acid (SA) plays a central role as a signalling molecule involved in plant defense against microbial attack. Genetic manipulation of SA biosynthesis may therefore help to generate plants that are more disease-resistant. By fusing the two bacterial genes pchA and pchB from Pseudomonas aeruginosa, which encode isochorismate synthase and isochorismate pyruvate-lyase, respectively, we have engineered a novel hybrid enzyme with salicylate synthase (SAS) activity. The pchB-A fusion was expressed in Arabidopsis thaliana under the control of the constitutive cauliflower mosaic virus (CaMV) 35S promoter, with targeting of the gene product either to the cytosol (c-SAS plants) or to the chloroplast (p-SAS plants). In p-SAS plants, the amount of free and conjugated SA was increased more than 20-fold above wild type (WT) level, indicating that SAS is functional in Arabidopsis. P-SAS plants showed a strongly dwarfed phenotype and produced very few seeds. Dwarfism could be caused by the high SA levels per se or, perhaps more likely, by a depletion of the chorismate or isochorismate pools of the chloroplast. Targeting of SAS to the cytosol caused a slight increase in free SA and a significant threefold increase in conjugated SA, probably reflecting limited chorismate availability in this compartment. Although this modest increase in total SA content did not strongly induce the resistance marker PR-1, it resulted nevertheless in enhanced disease resistance towards a virulent isolate of Peronospora parasitica. Increased resistance of c-SAS lines was paralleled with reduced seed production. Taken together, these results illustrate that SAS is a potent tool for the manipulation of SA levels in plants.
Amino Acid Sequence, Arabidopsis/genetics, Arabidopsis/physiology, Base Sequence, Caulimovirus/enzymology, Caulimovirus/genetics, Codon, Intramolecular Transferases/genetics, Intramolecular Transferases/metabolism, Lyases/genetics, Lyases/metabolism, Molecular Sequence Data, Phenols/metabolism, Plant Leaves/enzymology, Plants, Genetically Modified, Pseudomonas aeruginosa/enzymology, Pseudomonas aeruginosa/genetics, Recombinant Fusion Proteins/metabolism, Restriction Mapping, Salicylates/metabolism, Thiazoles
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