Functions of rol genes in plant secondary metabolism.

For a long time, the Agrobacterium rhizogenes rolA, rolB and rolC oncogenes have been considered to be modulators of plant growth and cell differentiation. A new function of the rol genes in plant-Agrobacterium interaction became apparent with the discovery that these genes are potential activators of secondary metabolism in transformed cells from the Solanaceae, Araliaceae, Rubiaceae, Vitaceae and Rosaceae families. In some cases, the activator effect of individual rol genes is sufficient to overcome the inability of cultured plant cells to produce large amounts of secondary metabolites. Here, I summarize the available evidence that shows that genetic transformation by single Agrobacterium rol genes may be used as a powerful tool to manipulate secondary metabolites in cultured plant cells. Although it is known that the rol genes act via transcriptional activation of defense genes, the mechanism of activation is unclear. In this review, evidence is presented to support the hypothesis that the rol genes mediate uncommon signal transduction pathways in plants.