A novel stress-inducible 12-oxophytodienoate reductase from Arabidopsis thaliana provides a potential link between Brassinosteroid-action and Jasmonic-acid synthesis

To isolate brassinosteroid (BR) inducible genes, a subtractive cDNA-cloning strategy was applied. One of the isolated genes encodes a plant homologue to yeast old yellow enzymes (OYE) with strong sequence similarity to two cl oned 12-oxo-phylodienoic acid reductases (OPR1 and OPR2) from A. thaliana a nd was termed 12-oxophytodienoate reductase 3 (OPR3; accession number: AJ23 8149). The expression of the OPR3 gene is induced by brassinosteroids, jasm onic acid (JA), and by a variety of stimuli like UV-light, touch, wind, wou nding, and application of a detergent. Recombinant OPR3 protein converts 12 -oxophytodienoate (OPDA) into 12-oxo phytoenoic acid (OPC8:0), indicating t he participation of OPR3 in the biosynthesis of JA from linolenic acid via the Vick-Zimmerman-pathway. In plants, OPC8:0 is inevitably metabolized to JA by three cycles of P-oxidation. Both OPDA and JA are signal molecules in volved in developmental processes and stress responses. Depending on enviro nmental or developmental conditions, OPR potentially regulates the ratio be tween these two signal molecules. The yeast old yellow enzymes act on vario us enones and phenols including steroids, catalyzing reduction and dispropo rtionation reactions. Thus, in addition to OPDA to OPC8:0 conversion, OPR3 might be involved in further biosynthetic or degradative pathways in plants . As OPR3 expression is increased through treatment with brassinosteroids, it provides a potential link between brassinosteroid action and JA synthesi s. BRs may thus influence the stress responses of plants through stimulatio n of JA synthesis.