Transgenic Tobacco Plants Coexpressing the Agrobacterium tumefaciens iaaM and iaaH Genes Display Altered Growth and Indoleacetic Acid Metabolism.

Transgenic tobacco (Nicotiana tabacum) SR1 plants expressing the Agrobacterium tumefaciens nopaline transferred DNA iaaH gene were transformed with a 35S-iaaM construct. The transformants displayed several morphological aberrations, such as adventitious root formation on stem and leaves, dwarfism, epinastic leaf growth, increased apical dominance, and an overall retardation in development. In addition, xylem lignification was higher than in wild type. Free and conjugated indoleacetic acid (IAA) levels were quantified by gas chromatography-multiple ion monitoring-mass spectrometry in leaves and internodes of wild-type plants and two transformed lines with different phenotypes. Both transformed lines contained elevated levels of free and conjugated IAA, which was associated with increased transcription of the iaaM gene. The line with the highest IAA level also had the most altered pattern of growth and development. These IAA-overproducing plants will provide a model system for studies on IAA metabolism, IAA interactions with other phytohormones, and IAA roles in regulating plant growth and development.