Submitted to: International Congress on Molecular Plant-Microbe Interactions
Publication Type: Abstract Only
Publication Acceptance Date: 9/20/2005
Publication Date: 12/15/2005
Citation: Johnson, E., Wach, M., Joshi, M., Loria, R., Gibson, D.M. 2005. Plant-pathogenic streptomyces: breaching the wall by sensing the wall [abstract]. International Congress on Molecular Plant-Microbe Interactions. p.91. Interpretive Summary:
Technical Abstract: The thaxtomin family of phytotoxins, produced by plant-pathogenic Streptomyces species that cause common scab of potato, are required for disease development. These phytotoxins disrupt plant cell wall formation by inhibiting cellulose synthesis. Significant production of thaxtomins in culture only occurs in media containing plant material. Oat-based media, such as oat bran broth, strongly induce thaxtomin production. This suggests that plant-derived compound(s) trigger expression of pathogenicity genes in plant-pathogenic Streptomyces species. Serial extractions of oat bran, using a range of solvents from hydrophobic to hydrophilic, were performed to search for the thaxtomin inducing compound(s). The extracted materials were added to a basal medium and tested for thaxtomin induction. The greatest thaxtomin production was induced by the solvent-insoluble fraction, which is comprised mostly of cell wall materials. Further studies with specific cell wall components added to a minimal medium demonstrated that degradation products of xylans and other cell wall polymers were responsible for induction of thaxtomin biosynthesis. Current studies are focusing on the ability of cellobiose and other disaccharides derived from cell wall components to induce thaxtomin production in plant-pathogenic Streptomyces species. Structure modeling of these compounds is being used to determine a recognition motif used by plant-pathogenic Streptomyces species to detect plant roots.