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Biological Activity of the rolB-like 5′ End of the A4-orf8 Gene from the Agrobacterium rhizogenes TL-DNA

March 2001 , Volume 14 , Number  3
Pages  405 - 411

Léon Otten and Anne Helfer

Department of Cell Biology, Plant Molecular Biology Institute of the C.N.R.S., Rue du Général Zimmer 12, Strasbourg 67084, France

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Accepted 17 November 2000.

The iaaM gene from different plant-associated bacteria encodes a tryptophan monooxygenase (IaaM) that catalyzes the synthesis of indole-3-acetamide (IAM), a precursor of indole-3-acetic acid (IAA). Unlike the IaaM proteins from other bacteria, Agrobacterium spp. T-DNA-encoded IaaM proteins carry a 200 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-DNA-encoded proteins, the basic functions of which are still largely undetermined. Deletion of the 5′rolB-like extension of the iaaM gene from Agrobacterium tumefaciens strain Ach5 did not lead to a reduction in IAM synthesis in plants. When expressed in tobacco, the rolB-like fragment did not affect growth or morphology. An iaaM homolog (A4-orf8) from the TL-DNA of Agrobacterium rhizogenes strain A4 also was investigated. Neither the full-size A4-orf8 gene nor the 5′-truncated form induced detectable IAM synthesis. Plants expressing the rolB-like part of the A4-orf8 gene, however, were dwarfed and mottled to various extents and synthesized abnormally high amounts of glucose, fructose, sucrose, and starch.

Additional keywords: crown gall tumors, hairy roots, starch synthesis, T-DNA evolution.

© 2001 The American Phytopathological Society