Identifying genes involved in fatty acid synthesis in olive

Olive accumulates oil triacylglycerols (TAGs) in the fruit mesocarp and the study of the genetic determinants affecting TAG biosynthesis, including the early steps of fatty acid (FA) elongation, is extremely important to clarify the mechanisms that regulate or restrict this pathway. We have identified and characterized four main gene families involved in FA elongation and desaturation: Acyl Carrier Protein (ACP), ?-ketoacyl-ACP synthase I (KAS I) and II (KAS II), and stearoyl-ACP-desaturase (SAD). ACP is the central cofactor protein for plastidial FA synthesis, KAS I catalyzes the substrate C4:0-ACP to produce C16:0-ACP, KAS II conduces the final elongation from C16:0-ACP to C18:0-ACP and SAD desaturates stearoyl-ACP to oleoyl-ACP in the plastid. Three OeACP genes have been identified at genomic and cDNA level and numerous haplotypes have been distinguished within olive cultivars. Their expression has been characterized in different olive tissues and an OeACP cDNA has been overexpressed in tobacco plants, in order to alter the levels of ACP and analyze the possible consequences on lipid biosynthesis. The phenotypic analysis of tobacco transformants expressing high amounts of olive ACP in different tissues is currently in progress. The analysis of preliminary olive genomic sequence data and fruit EST (Expressed Sequence Tags) collections have allowed to identify three OeKASI copies carrying seven exons. Their sequence has been characterized, many polymorphisms have been identified and expression analyses carried out on RNA of fruit mesocarp accumulating oil allowed to identify the most strong candidates involved in the FA synthesis of olive oil. The same approach has been used to identify two OeSAD variants, respectively carrying two and three exons and four OeKASII copies, all carrying 12 exons. The identification of haplotype variants and the analysis of their expression in oil-accumulating tissues is currently in progress.