Tobacco etch virus leader sequence enhances inducible indoleacetic acid-lysine synthetase activity in transgenic plants

Indole-3-acetic acid (IAA) is one of several plant hormones that interact t o coordinate growth and differentiation in higher plants. IAA has been iden tified in all species investigated and is found not only in its free form b ut also as sugar ester, peptide and amino acid conjugates. Plant processes ranging from the induction of cell division and expansion to the maintenanc e of apical dominance are dependent on free IAA levels. The objective of th is study was to construct and characterize transgenic plants that contain t he tetracycline (Tc)-specific inducible system to control the expression of the IAA-lysine synthetase gene (iaaL). The enzyme activity (IAA-L) encoded by iaaL conjugates free IAA with lysine to produce a foreign inactive conj ugate IAA-lysine (IAA-Lys). Characterization of independent tobacco (Nicoti ana tabacum cv. Wisconsin 38) transformants identified inducible plants com pletely repressed in the absence of tetracycline and derepressed to high IA A-L levels in the presence of inducer. The incorporation of the tobacco etc h virus non-translated leader sequence (NTR) in context of the tetracycline -regulatable CaMV 35S triple-op promoter enhanced IAA-L activity 7-fold. Un like tetracycline, the tetracycline analog anhydrotetracycline (ATc) did no t inhibit the growth of callus at concentrations up to 50 mug(.)mL(-1) on s olid medium. In the selected plants, IAA-Lys accumulation is dose-dependent upon the presence of the inducer molecule, and IAA-L activity in the derep ressed state is similar to a plant that constitutively expresses iaaL at hi gh levels from the native CaMV 35S promoter. (C) 2001 Editions scientifique s et medicales Elsevier SAS.