PROMOTER SPECIFICITY AND DELETION ANALYSIS OF 3 HEAT-STRESS TRANSCRIPTION FACTORS OF TOMATO

Transient expression assays in transformed tobacco (Nicotiana plumbagi nifolia) mesophyll protoplasts were used to test the activity of three tomato heat stress transcription factors, HSF24, HSF8 and HSF30, in a trans-activation and a trans-repression assay. The results document d ifferences between the three HSFs with respect to their response to th e configuration of heat stress promoter elements (HSEs) in the reporte r construct (promoter specificity) and to the stress regime used for a ctivation. Analysis of C-terminal deletions identified acidic sequence elements with a central tryptophan residue, which are important for H SF activity control. Surprisingly, heterologous HSFs from Drosophila a nd human cells, but not from yeast, were also functional as heat stres s-induced transcription factors in this tobacco protoplast system.