THE PLEIOTROPIC EFFECTS INDUCED BY THE ROLC GENE IN TRANSGENIC PLANTSARE CAUSED BY EXPRESSION RESTRICTED TO PROTOPHLOEM AND COMPANION CELLS

Expression of the rolC gene from Agrobacterium rhizogenes causes morph ological and developmental alterations in transgenic plants. The histo logical alterations underlying the macroscopic changes and the cellula r localization of the site of expression of the rolC gene have shown t hat: (i) the expression of the rolC gene is developmentally regulated, (ii) in vegetative transgenic plants, the expression of the rolC gene under the control of its own promoter is restricted to companion and protophloem cells, (iii) the site of action of the product(s) of the a ctivity of the rolC enzyme is distinct from its site of expression, (i v) precise localization of the rolC peptide has been achieved by immun ocytochemistry but not by the histochemical GUS assay. These results i mply that the sites of action and expression of the rolC gene in trans genic plants are physically separated. Thus the product(s) of the acti vity of the rolC enzyme must be a factor capable of being transported. Current models for rolC gene action are discussed taking into account the reported results.