Submitted to: Physiological and Molecular Plant Pathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/25/2007
Publication Date: 1/10/2008
Citation: Johnson, E.G., Joshi, M.V., Gibson, D.M., Loria, R. 2008. Cello-oligosaccharides released from host plants induce pathogenicity in scab-causing Streptomyces species. Physiological and Molecular Plant Pathology. 71:18-25. Interpretive Summary: Several Streptomyces species cause “scab” diseases on potato tubers, sweet potatoes, and tap roots of radish, beet and similar crops, due to the presence of a family of phytotoxins, thaxtomins, that are critical for pathogenicity. Thaxtomin inhibits cellulose biosynthesis by some unknown mechanism. This work describes a series of experiments that identify cellobiose and cellotriose, the smallest units of cellulose, as triggers for thaxtomin production by the plant pathogen. Cellobiose was shown to turn on the genes involved in biosynthesis, while cellotriose was shown to be released by the plant cell wall. These studies provide a model for plant pathogenic Streptomyces-host interactions where the cell wall components are key mediators.
Technical Abstract: Thaxtomin, a phytotoxic dipeptide that inhibits cellulose synthesis in expanding plant cells, is a pathogenicity determinant in scab-causing Streptomyces species. Cellobiose and cellotriose, the smallest subunits of cellulose, stimulated thaxtomin production in a defined medium, while other oligosaccharides did not. Cellobiose up-regulated transcription of thaxtomin biosynthetic genes. Streptomyces scabies, S. acidiscabies, and S. turgidiscabies did not hydrolyze cellulose, suggesting that these cello-oligosaccharides are plant derived. Cellotriose was released from rapidly growing plant seedlings growing in vitro. These data support a model in which scab-causing pathogens up-regulate thaxtomin production in response to cellotriose released from thaxtomin-sensitive plant tissue.