Molecular cloning and characterization of genes encoding two microsomal oleate desaturases (FAD2) from olive

Two different cDNA sequences, designated OepFAD2-1 and OepFAD2-2, encoding two microsomal oleate desaturases (FAD2) have been isolated from olive (Olea europaea cv. Picual) using a PCR approach. Both deduced amino acid sequences showed the three histidine boxes characteristic of all membrane-bound desaturases, and possess a C-terminal endoplasmic reticulum retention signal. Phylogenetic analysis shows that OepFAD2-1 and OepFAD2-2 are grouped with other plant FAD2 sequences. Functional expression of the corresponding FAD2 cDNAs in yeast confirmed that they encode microsomal oleate desaturases. Genomic Southern blot analysis is consistent with the presence of at least two copies of each OepFAD2 gene in the olive genome. OepFAD2-1 transcript was strongly detected in very young seeds and in leaves, showing low levels in mesocarps, while the transcript of the OepFAD2-2 gene was moderately expressed in developing seeds, ripening mesocarp and leaves. These expression data suggest differential functions for the two olive microsomal oleate desaturase genes, with FAD2-1 possibly responsible for the desaturation of reserve lipids in the young seed, while FAD2-2 may be mainly involved in storage lipid desaturation in the mature seeds and the mesocarp.