ARABIDOPSIS-THALIANA NADPH OXIDOREDUCTASE HOMOLOGS CONFER TOLERANCE OF YEASTS TOWARD THE THIOL-OXIDIZING DRUG DIAMIDE

To isolate new plant genes involved in the defense against oxidative stress, an Arabidopsis cDNA library in a yeast expression vector was transformed into a yeast strain deficient in the YAP1 gene, which encodes a b-Zip transcription factor and regulates general stress response in yeasts. Cells from approximate to 10(5) primary transformants were subjected to a tolerance screen toward the thiol-oxidizing drug diamide, which depletes the reduced glutathione in the cell, Four types of Arobidopsis cDNAs were isolated, Three of these cDNAs (PI, Pa, and P4) belong to a plant zeta-crystallin family and P3 is an Arabidopsis homolog of isoflavonoid reductases. As such, all four isolated cDNAs are homologous to NADPH oxidoreductases. PI, P2, and PS steady-state mRNAs accumulated rapidly in Arabidopsis plants under various oxidative stress conditions, such as treatment with paraquat, t-butylhydroperoxide, diamide, and menadione. The data suggested that proteins encoded by the isolated cDNAs play a distinct role in plant antioxidant defense and are possibly involved in NAD(P)/NAD(P)H homeostasis.