New Assay Method for Allene Oxide Cyclase, an Important Enzyme in Jasmonic Acid Biosynthesis

Aims: Allene oxide cyclase (AOC) (EC 5.3.99.6) is an important enzyme of jasmonates (JAs) biosynthesis. JAs are important signals that play a pivotal role in defense response of plants to environmental cues. Regulation JA biosynthesis is believed useful for elucidating the mechanism of plant defense system. Despite the high potential of AOC as a target for JA biosynthesis inhibitors, an efficient assay method suitable for screening AOC inhibitors is still not available. The aim of this work is to develop an efficient AOC assay method.

Study Design: Using excess amount of purified recombinant allene oxide synthase (AOS) combined with 13(S)-hydroperxy-9(Z), 11(E), 15(Z)-octadecatrienoic acid (13-HPOT), we established an efficient method to generate (12,13S)-epoxyoctadecatrienoic acid (EOT), the substrate of AOC. The AOS produced EOT was subsequently converted to (9S,13S)-12-oxo-(10,15Z)-phytodienoic acid (OPDA) by using purified recombinant AOC in a real time manner and the amount of OPDA was determined by HPLC.

Place and Duration of Study: All the experiments were conducted from October 2009 to March 2013 at Akita Prefectural University, Japan.

Methodology: The recombinant AOS and AOC were expressed in E. coli. The target proteins were purified using affinity chromatography, respectively. The unstable EOT was generated by using excess AOS combined with 13(S)-hydroperxy-9(Z), 11(E), 15(Z)-octadecatrienoic acid. The AOC synthesized OPDA was characterized by the comparison of HPLC retention time with the OPDA standard. AOC activity was calculated by determine the amount of OPDA in the assay system.

Results: We found in the presence of 50 nmol of purified AOS together with 20 mM 13-HPOT, the synthesis of OPDA was saturated when using 5 nmol of purified AOC in the enzyme reaction for 30 min. Our results indicated that the AOC activity can be determined by dual enzyme system.

Conclusion: We established an efficient assay method for AOC which may be applied for screening of AOC inhibitors.