The location and timing of domestication of the olive tree, a key crop in Early Mediterranean societies, remain hotly debated. Here, we unravel the history of wild olives (oleasters), and then infer the primary origins of the domesticated olive. Phylogeography and Bayesian molecular dating analyses based on plastid genome profiling of 1263 oleasters and 534 cultivated genotypes reveal three main lineages of pre-Quaternary origin. Regional hotspots of plastid diversity, species distribution modelling and macrofossils support the existence of three long-term refugia; namely the Near East (including Cyprus), the Aegean area and the Strait of Gibraltar. These ancestral wild gene pools have provided the essential foundations for cultivated olive breeding. Comparison of the geographical pattern of plastid diversity between wild and cultivated olives indicates the cradle of first domestication in the northern Levant followed by dispersals across the Mediterranean basin in parallel with the expansion of civilizations and human exchanges in this part of the world.

In higher plants, the lipoxygenase enzymatic pathway combined actions of several enzymes to convert lipid substrates into signaling and defense molecules called phytooxylipins including short chain volatile aldehydes, alcohols, and esters, known as green leaf volatiles (GLVs). GLVs are synthesized from C18:2 and C18:3 fatty acids that are oxygenated by lipoxygenase (LOX) to form corresponding hydroperoxides, then the action of hydroperoxide lyase (HPL) produces C6 or C9 aldehydes that can undergo isomerization, dehydrogenation, and esterification. GLVs are commonly used as flavors to confer a fresh green odor of vegetable to perfumes, cosmetics, and food products. Given the increasing demand in these natural flavors, biocatalytic processes using the LOX pathway reactions constitute an interesting application. Vegetable oils, chosen for their lipid profile are converted in natural GLVs with high added value. This review describes the enzymatic reactions of GLVs biosynthesis in the plant, as well as the structural and functional properties of the enzymes involved. The various stages of the biocatalytic production processes are approached from the lipid substrate to the corresponding aldehyde or alcoholic aromas, as well as the biotechnological improvements to enhance the production potential of the enzymatic catalysts.

Volatile C6-aldehydes are the main contributors to the characteristic odor of plants known as "green note" and are widely used by the flavor industry. Biotechnological processes were developed to fulfill the high demand in C6-aldehydes in natural flavorants and odorants. Recombinant hydroperoxide lyases (HPLs) constitute an interesting alternative to overcome drawbacks arising from the use of HPL from plant extracts. Thus, olive recombinant 13-HPL was assayed as biocatalysts to produce C6-aldehydes. Firstly, a cDNA encoding for olive HPL of Leccino variety was isolated and cloned in pQE-30 expression vector. In order to improve the enzyme solubility, its chloroplast transit peptide was deleted. Both enzymes (HPL wild type and HPL deleted) were expressed into Escherichia coli strain M15, purified, characterized, and then used for bioconversion of 13-hydroperoxides of linoleic and linolenic acids. Aldehydes produced were extracted, then identified and quantified using gas chromatography and mass spectrometry. Recombinant HPL wild type (HPLwt) allowed producing 5.61 mM of hexanal and 4.39 mM of 3Z-hexenal, corresponding to high conversion yields of 93.5 and 73 %, respectively. Using HPL deleted (HPLdel) instead of HPLwt failed to obtain greater quantities of hexanal or 3Z-hexenal. No undesirable products were formed, and no isomerization of 3Z-hexenal in 2E-hexenal occurred. The olive recombinant HPLwt appears to be a promising efficient biocatalyst for the production of C6-aldehydes.