Searching for the Phenolic Receptor(s) of Agrobacterium Tumefaciens: Developing a Chiral Molecule to be Used in a Novel Mutant Selection
Conclusive evidence that a specific xenognostic receptor exists in Agrobacterium tumefaciens has been presented through the testing of structurally varying phenols and the development of a novel genetic screen to isolate mutants which exhibit a hypersensitive response to the highly active inducer, acetosyringone. It has also been demonstrated that only a' single enantiomer of the chiral inducers, (-)-transdehydroferulate dimethylester and (+)-trans- cyclopropyl cinnamyl alcohol (CCA), are active, thus indicating the presence of an enantioselective receptor. Attempts to identify this receptor via another novel genetic screen that would employ the inactive (-)-trans- CCA would be unsuccessful as a result of this compound's relatively low inducing activity and the toxicity of phenolic compounds in general. It is well established that dimethoxy phenols have significantly higher activities than their monomethoxy counterparts and herin the synthesis of the dimethoxy version of trans-CCA, trans-4- hydroxy-3,5-dimethoxy cyclopropyl cinnamyl alcohol (DCP), is presented. The activity of the active (S,S)-trans-DCP, determined by a f3-galactosidase assay, is compared to that of the active (S,S)-trans-CCA and indeed it possesses notably higher activity such that the utilization of its inactive form, (R,R)-trans-DCP, for a novel mutant selection appears promising. Comparison of the activities of both enantiomers of trans-DCP to ensure a significant difference in activity will confirm the feasibility of this novel genetic screen for the isolation of mutants. The mutants would most likely exhibit a difference in the region of the xenognositc receptor that recognizes the chirality in the inducing phenol, thus providing specific structural as well as genetic information on the receptor.
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