The invention provides isolated and at least partially-purified dicamba-degrading enzymes, isolated DNA molecules coding for dicamba-degrading enzymes, DNA constructs coding for dicamba-degrading enzymes, transgenic host cells comprising DNA coding for dicamba-degrading enzymes, and transgenic plants and plant parts comprising one or more cells comprising DNA coding for dicamba-degrading enzymes. Expression of the dicamba-degrading enzymes results in the production of dicamba-degrading organisms, including dicamba-tolerant plants. Finally, the invention provides a method of selecting transformed plants and plant cells based on dicamba tolerance and a method of selecting or screening transformed host cells, intact organisms and parts of organisms based on the fluorescence of 3,6-dichlorosalicylic acid produced as a result of dicamba degradation.
