Characterization and validation of olive FAD and SAD gene families: expression analysis in different tissues and during fruit development

Stearoyl-ACP desaturases (SADs) and fatty acid desaturases (FADs) play a critical role in plant lipid metabolism and also affect oil fatty acid composition introducing double bonds into the hydrocarbon chains to produce unsaturated fatty acids. In the present study, the genomic sequences of threeSADand threeFADcandidate genes were characterized in olive and their expression was evaluated in different plant tissues.OeSADgenes corresponded to oliveSAD1andSAD2and to a newly identifiedOeSAD4, sharing the conserved protein structure with other plant species. On the other hand, the full-length genomic sequences of two microsomalOeFADgenes (FAD2-1andFAD2-2) and the plastidialFAD6, were released. When the level of expression was tested on different tissues of cv. Leccino,OeSAD1andOeSAD2were mainly expressed in the fruits, whileOeFADgenes showed the lowest expression in this tissue. The mRNA profiling of all genes was directly studied in fruits of Leccino and Coratina cultivars during fruit development. In both genotypes, the expression level ofOeSAD1andOeSAD2had the highest value during and after the pit-hardening period, when oil accumulation in fruit mesocarp is intensively increasing. Furthermore, the expression level of bothOeFAD2genes, which were the main candidates for oleic acid desaturation, were almost negligible during fruit ripening. These results have made possible to define candidate genes of the machinery regulation of fatty acid composition in olive oil, providing information on their sequence, gene structure and chromosomal location.