MOLECULAR CHARACTERIZATION OF AN ARABIDOPSIS GENE ENCODING HYDROPEROXIDE LYASE, A CYTOCHROME-P-450 THAT IS WOUND-INDUCIBLE

Hydroperoxide lyase (HPL) cleaves lipid hydroperoxides to produce vola tile flavor molecules and also potential signal molecules. We have cha racterized a gene from Arabidopsis that is homologous to a recently cl oned HPL from green pepper (Capsicum annuum). The deduced protein sequ ence indicates that this gene encodes a cytochrome P-450 with a struct ure similar to that of allene oxide synthase. The gene was cloned into an expression vector and expressed in Escherichia coli to demonstrate HPL activity. Significant HPL activity was evident when 13S-hydropero xy-9(Z), 11(E), 15(Z)-octadecatrienoic acid was used as the substrate, whereas activity with 13S-hydroperoxy-9(Z),11(E)-octadecadienoic acid was approximately 10-fold lower. Analysis of headspace volatiles by g as chromatography-mass spectrometry, after addition of the substrate t o E. coli extracts expressing the protein, confirmed enzyme-activity d ata, since cis-3-hexenal was produced by the enzymatic activity of the encoded protein, whereas hexanal production was limited. Molecular ch aracterization of this gene indicates that it is expressed at high lev els in floral tissue and is wound inducible but, unlike allene oxide s ynthase, it is not induced by treatment with methyl jasmonate.