Identification and characterization of thaxtomin resistance genes in Arabidopsis, and genetic engineering of sacab-resistant potato

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Thaxtomin A is a phytotoxin produced by Streptomyces scabies, the causal agent of scab disease in potato. Thaxtomin A causes cell-swelling phenotypes in many plant species, and experimental evidence suggests it acts as cellulose synthesis inhibitor. Several complementation groups of thaxtomin resistant (txr) Arabidopsis mutants have been isolated and we have already identified one of the TXR loci by recombinational mapping. The TXR1 gene encodes a novel, small protein of unknown function with homologs in all fully sequenced eukaryotic genomes. The txr1 mutant shows a strongly reduced uptake of thaxtomin A, suggesting that TXR1 is a component, or regulator of a transport mechanism. Experimental goals of the present proposal are (1) to genetically engineer scab resistance in potato by down-regulation of the potato TXR1 ortholog(s), (2) to identify the plant cell wall target and understand the mode-of-action of thaxtomin by identifying additional txr-loci, and by characterizing the metabolic and transcriptional responses of Arabidopsis after treatment with the phytotoxin, and (3) to further elucidate the biological function and to pinpoint the molecular partners of the evolutionarily conserved TXR1 protein.