THE HEAT-SHOCK ELEMENT IS A FUNCTIONAL COMPONENT OF THE ARABIDOPSIS APX1 GENE PROMOTER

Ascorbate peroxidases are important enzymes that detoxify hydrogen per oxide within the cytosol and chloroplasts of plant cells. To better un derstand their role in oxidative stress tolerance, the transcriptional regulation of the apx1 gene from Arabidopsis was studied. The apx1 ge ne was expressed in all tested organs of Arabidopsis; mRNA levels were low in roots, leaves, and stems and high in flowers. Steady-state mRN A levels in leaves or cell suspensions increased after treatment with methyl viologen, ethephon, high temperature, and illumination of etiol ated seedlings. A putative heat-shock cis element found in the apx1 pr omoter was shown to be recognized by the tomato (Lycopersicon esculent um) heat-shock factor in vitro and to be responsible for the in vivo h eat-shock induction of the gene. The heat-shock cis element also contr ibuted partially to the induction of the gene by oxidative stress. By using in vivo dimethyl sulfate footprinting, we showed that proteins i nteracted with a G/C-rich element found in the apx1 promoter.