12-oxophytodienoate reductase 3 (OPR3) is the isoenzyme involved in jasmonate biosynthesis

In addition to OPR1 and OPR2, two isoenzymes of 12-oxophytodienoate reducta se, a third isoform (OPR3) has recently been identified in Arabidopsis thal iana (L.) Heynh. The expression of the OPR3 gene is induced not only by a v ariety of stimuli, such as touch. wind, wounding, UV-light and application of detergent, but also by brassinosteroids. The three enzymes were expresse d in a functional form in Escherichia coli, and OPR2 was additionally expre ssed in insect cell cultures and overexpressed in A. thaliana. Substrate co nversion was analyzed using a stereospecific assay. The results show that O PR3 effectively converts the natural (9S,13S)-12-oxophytodienoic acid [K-m = 35 mu M, V-max 53.7 nkat (mg protein)(-1)] to the corresponding 3-2(2'(Z) -pentenyl) cyclopentane-1-octanoic acid (OPC-8:0) stereoisomer while OPR1 a nd OPR2 convert (9S,13S)-12-oxophytodienoic acid with greatly reduced effic iency compared to OPR3. Thus, OPR3 is the isoenzyme relevant for jasmonate biosynthesis.