Genetic analysis of the individual T-DNA genes of Agrobacterium tumefaciens; further evidence that two genes are involved in indole-3-acetic acid synthesis

Abstract

The T-DNA genes of Ti plasmids of Agrobacterium tumefaciens can induce tumorous growth on a wide range of dicotyledonous plants. We subcloned the individual onc genes of the pTiC58 T-DNA and reintroduced them in the T-region of the Ti plasmid gene vector pGV3850 (from which the onc genes had been removed (Zambryski et al. 1983)). These experiments were designed to analyze the contribution of each onc gene to the development of a tumor and have fulfilled two purposes. First, it was found that only the strains carrying gene 4 produced tumors without the aid of other T-DNA genes; in cell culture these tumors sprout shoots. Second, the shoot-forming phenotype of tumors induced by agrobacteria carrying Ti plasmids defective in either gene 1 or gene 2 can be restored to wildtype phenotype by simple coinfection with Agrobacterium strains whose Ti plasmids contain respectively only gene 2, or only gene 1 in their T-region. A parallel experiment demonstrated that the combined action of genes 1 and 2 is sufficient to induce tumor formation on tobacco plantlets. The external addition of α-naphthalene acetic acid (NAA) restores to wild-type the phenotype of tumors induced by mutants in gene 1 or in gene 2. However, α-naphthalene acetamide can only restore to wild-type the phenotype of mutants in gene 1. These data indicate that the product of the T-DNA gene 2 participates in the conversion of α-naphthalene acetamide to a biologically active auxin, presumably NAA, and suggest that gene 1 codes for an enzyme involved in the synthesis of an indole-3-acetyl derivative. © 1984 Springer-Verlag.