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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