GENETIC-ENGINEERING OF PLANT SECONDARY METABOLISM - ACCUMULATION OF 4-HYDROXYBENZOATE GLUCOSIDES AS A RESULT OF THE EXPRESSION OF THE BACTERIAL UBIC GENE IN TOBACCO

The ubiC gene of Escherichia coli encodes chorismate pyruvate-lyase, a n enzyme that converts chorismate into 4-hydroxybenzoate (4HB) and is not normally present in plants. The ubiC gene was expressed in Nicotia na tabacum L. plants under control of a constitutive plant promoter. T he gene product was targeted into the plastid by fusing it to the sequ ence for the chloroplast transit peptide of the small subunit of ribul ose-1,5-bisphosphate carboxylase/oxygenase. Transgenic plants showed h igh chorismate pyruvate-lyase activity and accumulated 4HB as beta-glu cosides, with the glucose attached to either the hydroxy or the carbox yl function of 4HB. The total content of 4HB glucosides was approximat ely 0.52% of dry weight, which exceeded the content of untransformed p lants by at least a factor of 1000. Feeding experiments with [1,7-C-13 (2)]shikimic acid unequivocally proved that the 4HB that was formed in the transgenic plants was not derived from the conventional phenylpro panoid pathway but from the newly introduced chorismate pyruvate-lyase reaction.