TISSUE-SPECIFIC ACTIVATION OF THE OSMOTIN GENE BY ABA, C2H4 AND NACL INVOLVES THE SAME PROMOTER REGION

The gene encoding the antifungal protein osmotin is induced by several hormonal and environmental signals. In this study, tissue-specific an d inducer-mediated expression of the reporter gene beta-glucuronidase (uidA) fused to different fragment lengths of the osmotin promoter was evaluated in transgenic tobacco (Nicotiana tabacum). The region of th e promoter between -248 to -108 (Fragment A) was found to be essential and sufficient for inducer (abscisic acid (ABA), C2H4 and NaCl)-media ted expression of the reporter gene. Expression of the reporter gene w as developmentally regulated and increased with maturity of leaves, st em and flowers. Expression also was tissue-specific being most highly expressed in epidermis and vascular parenchyma of the stem. The regula tors ABA, C2H4 and NaCl exhibited tissue-specific induction of this pr omoter. The promoter was specifically responsive to C2H4 in flowers at virtually all stages of development, but not responsive in these tiss ues to ABA or NaCl. Conversely, ABA and NaCl were able to induce repor ter gene activity using promoter Fragment A in specific tissues of roo t where C2H4 was unable to induce activity. Further dissection of the promoter Fragment A into fragments containing either the conserved GCC element (PR); PR/AT; or G/AT sequences, and subsequent testing of the se fragments fused to GUS in transgenic plants was performed. These ex periments revealed that the promoter fragment containing PR element al one, although required, was barely able to allow responsiveness to C2H 4 However, significant C2H4-induced activity was obtained with a promo ter fragment containing the AT and PR elements together.