STRUCTURE AND DIFFERENTIAL RESPONSE TO ABSCISIC-ACID OF 2 PROMOTERS FOR THE CYTOSOLIC COPPER ZINC-SUPEROXIDE DISMUTASE GENES, SODCC1 AND SODCC2, IN RICE PROTOPLASTS

We determined the 5'-flanking sequences of two nuclear genes (SodCc1 a nd SodCc2) encoding cytosolic copper/zinc-superoxide dismutase in rice (Oryza sativa L.). Utilizing transient P-glucuronidase (GUS) reporter assays, functional promoter-GUS analysis was performed in rice protop lasts exposed to the phytohormone abscisic acid (ABA) or the antioxida nt sulfhydryl reagent, dithiothreitol (DTT). Transcriptional activitie s from both SodCc-GUS fusions were stimulated by DTT, which induces th e promoter activity of the tobacco SodCc gene [Proc. Natl. Acad. Sci. USA 90 (1993) 3108-3112]. ABA had no effect on SodCc1-GUS expression b ut specifically induced the gene expression of the SodCc2-GUS fusion. The simultaneous application of ABA and gibberellin A(3), however, abo lished the enhancing effect of ABA. These results indicated that two r ice SodCc promoters differentially respond to externally supplied ABA and that one of the regulatory factors for plant SodCc expression is A BA in addition to cellular redox-modulating antioxidants.