Alterations in Auxin and Cytokinin Metabolism of Higher Plants Due to Expression of Specific Genes From Pathogenic Bacteria: a Review

Abstract

This review deals with the physiological and morphological effects of altering the auxin/cytokinin balance in transgenic plants by expressing specific genes from pathogenic bacteria. Genes which have been used to alter auxin levels or sensitivity in transgenic plants include the iaaM/iaaH genes from Agrobacterium tumefaciens and A. rhizogenes; gene 5 and possibly gene 6b from A. tumefaciens; the rol B and possibly the rol A gene from A. rhizogenes and the iaaL gene from Pseudomonas syringae subsp. savastanoi (P. savastanoi). Genes which have been used to alter cytokinin levels in transgenic plants include the ipt gene from A. tumefaciens and the rol C gene from A. rhizogenes. A variety of biochemical mechanisms have been identified which result in alterations to phytohormone levels following expression of these genes in transgenic plants. Many of the effects on plant development are consistent with observations made following exogenous auxin and/or cytokinin application to plant tissues, and the availability of these genes offers a new approach to the study of plant physiology using transformation methodology.