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Crop Biotech Update

Rhodococcus Requires Only a Single Cytokinin to Cause Gall Symptoms.

July 23, 2014

Rhodococcus, a member of the Actinobacteria, can cause gall symptoms and deformities and are pathogens to a wide range of plants. A current belief is that pathogenic Rhodococcus isolates contain the fas operon. This fas operon produces a mixture of growth-regulating cytokinins which, in turn, cause hormonal imbalance in plants, resulting in abnormal growth.

Researchers from Oregon State University compared 20 isolates of Rhodococcus to study the mechanisms of infection in these bacteria. Although the fas operon is present in most phytopathogenic isolates, it is absent from pathogenic isolate A21d2. Instead, this isolate has a gene chimera that encodes a protein capable of catalyzing and activating several cytokinins. Analysis of an archetypal isolate with the fas operon revealed that only one active cytokinin type, isopentenyladenine cytokinin, was specifically synthesized.

These results show that only isopentenyladenine cytokinin is necessary for Rhodococcus pathogenicity, contrary to the belief that a mixture of cytokinins was necessary for Rhodococcus to cause gall symptoms.

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