Biological activity of the rolB-like 5 ' end of the A4-orf8 gene from the Agrobacterium rhizogenes TL-DNA

The iaaM gene from different plant-associated bacteria encodes a tryptophan monooxygenase (IaaM) that catalyzes the synthesis of indole-3-acetamide (I AM), a precursor of indole-3-acetic acid (IAA), Unlike the IaaM proteins fr om other bacteria, Agrobacterium spp, T-DNA-encoded IaaM proteins carry a 2 00 amino acid N-terminal extension with low homology to various members of the RolB protein family. This family is composed of 18 highly divergent T-D NA-encoded proteins, the basic functions of which are still largely undeter mined. Deletion of the 5' rolB-like extension of the iaaM gene from Agrobac terium tumefaciens strain Ach5 did not lead to a reduction in IAM synthesis in plants. When expressed in tobacco, the rolB-like fragment did not affec t growth or morphology. An iaaM homolog (A4-orf8) from the TL-DNA of Agro-b acterium rhizogenes strain A4 also was investigated. Neither the full-size A4-orf8 gene nor the 5'-truncated form induced detectable IAM synthesis. Pl ants expressing the rolB-like part of the A4-orf8 gene, however, were dwarf ed and mottled to various extents and synthesized abnormally high amounts o f glucose, fructose, sucrose, and starch.