Reactive oxygen species are common causes of cellular damages in all aerobic organisms. In Escherichia coli, the oxyR gene product is a positive regulator of the oxyR regulon that is induced in response to H202 stress. To identify genes involved in counteracting oxidative stress in plants, we transformed a AoxyR mutant of E. coli with an Arabidopsis thaliana cDNA library and selected for clones that restored the ability of the AoxyR mutant to grow in the presence of H202. Using this approach, we isolated a cDNA that has strong homology with the annexin super-gene family. The complemented mutant showed higher catalase activity. mRNA expression of the annexin gene in A. thaliana was higher in roots as compared with other organs and was also increased when the plants were exposed to H202 stress or salicylic acid. Based on the results presented in this study, we propose a novel physiological role for annexin in counteracting H202 stress.