A novel lipoxygenase in olives (Olea europaea L.), with dual positional specificity, expressed late during fruit development

Plant lipoxygenases (LOXs) are a class of widespread dioxygenase catalyzing the hydroperoxidation of polyunsaturated fatty acids. Although multiple isoforms of LOX have been detected in a wide range of plants, their physiological role is still unclear. With the aim to clarify the occurrence of LOXs and their contribution to the elaboration of the olive oil aroma, we carried out the biochemical and molecular characterization of the LOX isoform expressed during olive development. A full-length cDNA was isolated by Reverse Transcription PCR and Rapid amplification of cDNA end carried out on total RNA from mature olives. The 2852 bp sequence displays an open reading frame of 2592 bp encoding a putative polypeptide of 864 amino acids with a calculated molecular mass of 98.4 kDa and a pI of 5.95. The olive LOX is a type-1 LOX and shows a high degree of identity towards hazelnut (77.3%), tobacco (76.3%) and almond (75.5%) LOXs. The recombinant enzyme produced in E. coli shows a dual positional specificity, as it releases both 9- and 13-hydroperoxide of linoleic acid in a 2:1 ratio. Although LOX activity was detected throughout the olive development, the 9/13-LOX is mainly expressed at late developmental stages. Our data suggest the presence of at least two LOX isoforms in black olives, and that the 9/13-LOX is associated with the ripening and senescence processes. However, due to its dual positional specificity ant its expression pattern, its contribution to the elaboration of the olive oil aroma might be considered.