THE TOMATO GENE FOR THE CHLOROPLASTIC CU,ZN SUPEROXIDE-DISMUTASE - REGULATION OF EXPRESSION IMPOSED IN TRANSGENIC TOBACCO PLANTS BY A SHORTPROMOTER

The chloroplastic Cu,Zn superoxide dismutase (SOD) has an important ro le in the defense against damage by oxygen radicals in the chloroplast s. Here, for the first time, we report on the isolation of a genomic D NA clone from tomato that contains all the coding sequence for the chl oroplastic Cu,Zn SOD as well as a 442 bp DNA fragment upstream of the translational initiation site. The latter upstream sequence has a puta tive TATA box and a 285 bp promoter region, 5' of the apparent transcr iptional initiation and a 157 bp leader region. The coding sequence is composed of 8 exons that are interspaced by 7 introns; we termed this gene SODCp;Le:1. The 442 bp fragment was cloned into a pBI101 vector, upstream of the uidA (GUS) gene, via transcriptional fusion. Agrobact erium-mediated transformation resulted in transgenic tobacco plants. T he progeny (after self-pollination) of 14 transformed plants, which ex pressed GUS above a threshold of 1 nmol/min per mg protein, were found to fall into two distinct groups. In the seedlings of 10 lines (group A) GUS expression was enhanced by exposure to light. In 4 lines of th is group maintenance for 3 days in the dark eliminated GUS activity. T he seedlings of group B expressed GUS regardless of the light/dark reg ime. In plants of group A, GUS expression was also developmentally reg ulated: high GUS activity in young leaves, low activity in mature leav es and no activity in the roots. The results suggest that this short c hloroplastic Cu,Zn SOD promoter contains motifs for developmental (spa tial) regulation as well as motifs responsive to light (or to oxygen r adicals resulting from light-driven photosynthesis).