Developmental regulation and spatial expression of a plastidial fatty aciddesaturase from Olea europaea

Trienoic fatty acids are major components of chloroplast membranes and are also precursors of the oxylipins, such as methyl jasmonate, that play impor tant roles in signal transduction pathways relating to plant development an d responses to stress. A cDNA encoding a plastidial omega-3 fatty acid desa turase responsible for trienoic formation has been isolated from a library made from ripening fruits of Olea europaea L. The predicted protein contain s 436 amino acid residues including a consensus chloroplast specific transi t peptide. Alignment with other desaturase sequences showed strong homology with the plastidial omega-3 desaturases fad7 and fad8. Since fad8 is only expressed at low temperatures and the olive fruit were developing at > 20 d egrees C, it is concluded that the isolated cDNA is most likely to be deriv ed from fad7. Northern hybridisation showed a transient expression of the p utative fad7 gene at early stages of drupe (5-7 WAF) and mesocarp (16-19 WA F) development. In situ hybridisation showed particularly prominent express ion in the palisade and vascular tissue of young leaves, the embryo sac and transmitting tissue of the carpel, and the tapetum, pollen grains and vasc ular tissue of anthers. The distinctive spatial, temporal and environmental regulation of the putative fad7 gene is consistent with major roles, not o nly in thylakoid membrane formation, but also in the provision of alpha-lin olenate-derived signalling molecules that are particularly important in pla nt tissues involved in transportation and reproduction. (C) Elsevier, Paris .