Functional Characterization of Two 13-Lipoxygenase Genes from Olive Fruit in Relation to the Biosynthesis of Volatile Compounds of Virgin Olive Oil

Two LOX cDNA clones, Oep1LOX2 and Oep2LOX2, have been isolated from olive (Olea europaea cv. Picual). Both deduced amino acid sequences showed significant similarity to known plant LOX2, and they contain an N-terminal chloroplastic transit peptide. Genomic Southern blot analyses suggest that at least three copies of Oep1LOX2 and one copy of Oep2LOX2 should be present in the olive genome. Linolenic acid proved to be the preferred substrate for both olive recombinant LOXs, and analyses of reaction products revealed that both enzymes produce primarily 13-hydroperoxides from linoleic and linolenic acids. Expression levels of both genes were measured in the mesocarp and seeds during development and ripening of Picual and Arbequina olive fruit along with the level of volatile compounds in the corresponding virgin olive oils. Biochemical and gene expression data suggest a major involvement of the Oep2LOX2 gene in the biosynthesis of virgin olive oil aroma compounds.