Expression of a plastidial ?9 desaturase in different tissues and in response to physical stresses in potato

The solubic plastid enzyme stearoyl-acyl carrier protein desaturase (EC 1.14.99.6) catalyzes the initial desaturation step of C18 fatty acids in higher plants and therefore it plays a key role in the regulation of fatty acid composition of plant cellular and sub cellular membranes. Hcrc we report the molecular cloning and charactcrization of a gene encoding a A9 stearoyl-acyl carrier protein (ACP) desaturase from Solanum commersonii, a cold tolerant potato wild species. A full length clone (ScDes4.1) was isolated from a leaf cDNA library of 3-day cold acclimated S. commersonii plantlets. The 1800 bp cDNA contained a 1179 bp open reading frame encoding a precursor polypeptide of 393 amino acids which includcs a putative transit pcptide for chloroplast targeting of 30 amino acid residues. Despite the considerable homology with other cloned plant A9 desaturases the pattern of exprcssion of this genc is remarkably differcnt in that it is expressed in leaf tissues as well as in stem and tubcrs and not specifically in storagc organs as found for other A9 desaturases. Moreover the level of expression of the A 9 stearoyl-ACP desaturase was modulated by environmental changes such as cold acclimation and adaptation to low water potentials. A preliminary characterization of a A9 stearoyl-ACP desaturase genomic clone, isolated from a S. commersonii genomic library screened with ScDes4.1, is also reported.