Phenotype and hormonal status of transgenic tobacco plants overexpressing the rolA gene of Agrobacterium rhizogenes T-DNA

Christoph Dehio 1 , Klaus Grossmann 2 , Jeff Schell 1 , and Thomas Schmülling 3

Plant Mol Biol 23: 1199-1210.

1 Max-Planck-Institut fⁿr Züchtungsforschung, Carl-von-Linné-Weg 10, 50829 Köln, FRG
2 Landwirtschaftliche Versuchsstation der BASF, 67117 Limburgerhof, FRG
3 Universität Tübingen, Lehrstuhl fⁿr Allgemeine Genetik, Auf der Morgenstelle 28, 72076 Tübingen, FRG

Abstract

The rolA gene of the T L -DNA of Agrobacterium rhizogenes Ri-plasmid plays a major role in establishing the hairy root syndrome in transgenic plants. Transgenic tobacco plants ( Nicotiana tabacum L.) expressing constitutively the rolA gene under the transcriptional control of the 35S RNA promoter show pronounced phenotypical alterations. P 35S - rolA transgenic tobacco plants are characterized by stunted growth, dark green wrinkled leaves with an altered length-to-width ratio, condensed inflorescences, retarded onset of flowering, a reduced number of flowers and shortened styles. To investigate whether the pleiotropic alterations of growth and development are linked to an altered hormonal status we have compared the immunoreactive content of indole-3-acetic acid, cytokinins, abscisic acid, gibberellin and the ethylene precursor ACC (1-aminocyclopropane-1-carboxylic acid) of seedlings and different tissues of P 35S - rolA transgenic plants, transgenic plants expressing the rolA gene under control of its own phloem specific promoter and wild type plants. Multiple tissue-specific alterations of phytohormone concentrations are the consequence of rolA gene activity. Changes of phytohormonal content can explain part of the rolA induced phenotypic alterations. Most strikingly, in young and fully developed leaves of rolA and P 35S - rolA transgenic clones a 40 - 60% reduction of immunoreactive gibberellin A 1 was found, when compared to wild type leaves. Treatment of wild type tobacco plants with inhibitors of gibberellin biosynthesis phenotypic alterations similar to those of rolA transgenic plants. This suggests that the reduction of gibberellic acid content is indirectly but causally involved in rolA induced alterations of stem elongation and planar leaf blade growth.