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Streptomyces turgidiscabies Possesses a Functional Cytokinin Biosynthetic Pathway and Produces Leafy Galls

July 2007 , Volume 20 , Number  7
Pages  751 - 758

Madhumita V. Joshi and Rosemary Loria

Department of Plant Pathology, Cornell University, Ithaca, NY 14850, U.S.A.

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Accepted 5 March 2007.

Streptomyces turgidiscabies, a cause of potato scab, possesses a mobilizable pathogenicity island containing multiple virulence genes and a cytokinin biosynthetic pathway. These biosynthetic genes are homologous and collinear with the fas operon in Rhodococcus fascians. Reverse-transcriptase polymerase chain reaction of S. turgidiscabies demonstrated that all six genes were transcribed in oat bran broth with and without glucose, though transcription was partially repressed by glucose. The supernatant of S. turgidiscabies cultures had cytokinin activity in callus initiation and differentiation assays. Arabidopsis and tobacco plants inoculated with a thaxtomin-deficient mutant (Δnos) produced leafy galls, indistinguishable from those produced by R. fascians. Deletion of the ipt gene in the pathway eliminated gall phenotype. Other symptoms on tobacco included production of hairy roots and de novo meristems.

Additional keywords: cytokinin biosynthesis .

© 2007 The American Phytopathological Society