The ORF8 gene product of Agrobacterium rhizogenes TL-DNA has tryptophan 2-monooxygenase activity

The open reading frame 8 (ORF8) is located on the TL-DNA of the phytopathog enic soil bacterium Agrobacterium rhizogenes strain A4. The predicted ORF8 protein has a particular structure and is possibly a natural fusion protein . The N-terminal domain shows homology to the A. rhizogenes rolB protein an d may modulate the auxin responsiveness of host cells. The C terminus has u p to 38% homology to tryptophan 2-monooxygenases (t2m). We show that ORF8 o verexpressing plants contain a five-fold higher concentration of indole-3-a cetamide (IAM) than untransformed plants. Protein extracts from seedlings a nd Escherichia coli overexpressing ORF8 show significantly higher turnover rates of tryptophan to IAM than negative controls. We conclude that the ORF 8 gene product has tryptophan 2-monooxygenase activity.