TEMPORAL AND TRANSIENT EXPRESSION OF STEAROYL-ACP CARRIER PROTEIN DESATURASE GENE DURING OLIVE FRUIT-DEVELOPMENT

To study the regulation of gene expression during olive (Olea europaea ) fruit development, a full length cDNA encoding the stearoyl-ACP desa turase (EC 1.14.99.6), which catalyses the conversion of saturated ste aric acid to mono-unsaturated oleic acid was isolated. The primary str ucture of the protein as deduced from the nucleotide sequence of the c DNA includes a putative 27-amino acid transit peptide, Amino acid sequ ence comparison showed substantial similarity to de-desaturases isolat ed from other plant species, The two conserved motifs D/EEXXH, involve d in the catalytic reaction are localized in similar positions to the other desaturases. Delta 9-desaturase gene expression is developmental ly regulated, Comparative Northern blot analysis exhibited distinct pa tterns of temporal gene regulation and mRNA accumulation in the three tissues of the developing olive fruit, In embryos and in the correspon ding endosperms, Delta 9-desaturase expression starts early during hea rt-stage, while in the mesocarp it starts later, Maximum expression an d transcript accumulation in embryos and endosperms is observed at 13- 14 WAF (early torpedo stage), whereas at 22 WAF (late torpedo stage), the Delta 9-desaturase message was almost undetectable. In the mesocar p, gene expression and mRNA accumulation is active upto 28 WAF. This a ccumulation during fruit growth parallels the synthesis of oil in this oleogenic tissue, ABA modulates transiently Delta 9-desaturase gene e xpression in immature olive embryos, Short exposures to ABA positively influenced gene expression whereas longer exposures decreased mRNA ac cumulation. Fluridone, an inhibitor of ABA synthesis and accumulation, decreased mRNA levels while ABA added to fluridone supplemented media restored Delta 9-desaturase transcript accumulation, These results su ggest that Delta 9-desaturase gene expression in olives is temporally and developmentally regulated in olive fruit.