Reduction of polar auxin transport in tobacco by the tumorigenic Agrobacterium tumefaciens AK-6b gene

• Published in: Planta 2006-01, Vol.223 (2), p.237-247
• Main Authors: Kakiuchi, Y, Galis, I, Tamogami, S, Wabiko, H
• Format: Article
• Language: English
• Subjects: Aerial parts; Agrobacterium tumefaciens; Agrobacterium tumefaciens - genetics; Agronomy. Soil science and plant productions; Auxins; bacterial proteins; Biological and medical sciences; Biological Transport; Cotyledons; crown galls; Cytokinins; Flavonoids; Flavonoids - metabolism; Fundamental and applied biological sciences. Psychology; Gene expression; Genes, Bacterial - physiology; Genetic engineering applications; Genetics and breeding of economic plants; Hypocotyls; indole acetic acid; Indoleacetic Acids - metabolism; Insulin antibodies; Liquid chromatography; Nicotiana - anatomy & histology; Nicotiana - genetics; Nicotiana - metabolism; Nicotiana tabacum; Phenols; phenylpropanoids; Phenylpropionates - metabolism; physiological transport; Plant breeding: fundamental aspects and methodology; plant growth; plant morphology; plant pathogenic bacteria; Plant Tumors - genetics; plant vascular system; Plants; Plants, Genetically Modified - metabolism; Recombinant Proteins - metabolism; Seedlings; Seedlings - anatomy & histology; Seedlings - genetics; Seedlings - physiology; signal transduction; soil bacteria; Tobacco; Transgenic plants
• ISSN: 0032-0935; 1432-2048
• DOI: 10.1007/s00425-005-0080-4

The plant-tumorigenic 6b (AK-6b) gene of Agrobacterium tumefaciens strain AKE10 induces morphological alterations to tobacco plants, Nicotiana tabacum. To investigate the molecular mechanisms underlying these processes, we generated transgenic tobacco harboring the AK-6b gene under the control of a dexamethazone-inducible promoter. Upon induction, transgenic tobacco seedlings exhibited distinct classes of aberrant morphologies, most notably adventitious outgrowths and stunted epicotyls. Histological analysis revealed massive proliferation and altered venation in the newly established outgrowths. Prominent vascular development suggested that auxin metabolism or signaling had been altered. Indeed, basipetal auxin transport in the hypocotyls of the transgenic seedlings was reduced by 50-80%, whereas intracellular auxin contents were only slightly reduced. Analysis of cell extracts by HPLC revealed a large accumulation of phenolic compounds, including the flavonoid kaempferol-3-rutinoside, in transgenic plants compared with wild-type seedlings. As some naturally occurring flavonoids have been shown to affect auxin transport, we suggest that the AK-6b gene expression impairs auxin transport via modulation of phenylpropanoid metabolism, and ultimately results in the observed morphological alterations.