PHENOTYPIC CHARACTERIZATION OF PETUNIA PLANTS EXPRESSING AN INDOLEACETIC ACID (IAA)-LYSINE SYNTHETASE TRANSGENE DRIVEN BY A SHOOT SPECIFIC PROMOTER

Chemical plant growth regulators are used on many ornamental species to control internode length and/or increase branching.
Transgenes that reduce whole-plant auxin activity produce plants with the desirable compact, well-branched phenotype but with poor root development.
In this study, petunia ‘Marco Polo Odyssey’ were transformed with an auxin inactivating indoleacetic acid-lysine synthetase (iaaL) gene from Pseudomonas syringae driven by a shoot specific promoter or with a constitutively controlled MADS-box gene that affects shoot morphological development (TOBM1 from Nicotiana tobacum). Phenotypic expression of this fusion gene was characterized for selected transgenic lines (12 TOBM1 lines and 15 iaaL lines) and the non-transformed wild-type by quantifying leaf shape, internode length, leaf area, number of lateral branches, and dry weight distribution between leaves, stems, flowers, and roots.
The most obvious effects of transgene expression were on leaf morphology and lateral branch development.
Overall phenotypic expression of TOBM1 petunias was similar to that of plants expressing down-regulated auxin (iaaL). Similar phenotypes would be expected if high cytokinin to auxin ratios (resulting from iaaL activity) trigger expression of the TOBM1 gene, or of genes that have functions similar to TOBM1 in petunia.
Alternatively, TOBM1 may regulate the concentration of auxin or cytokinin so that a high cytokinin to auxin ratio is achieved in TOBM1 plants.