Nucleotide Sequence of a Complementary DNA Clone Encoding Stearoyl-Acyl Carrier Protein Desaturase from Simmondsia chinensis

Stearoyl-ACP' desaturase (EC 1.14.99.6) converts stearoyl[ 18:0]-ACP to oleoyl[ 18:1(9)]-ACP in the unsaturated fatty acid synthesis of plants and plays a role in the regulation of fatty acid composition of plant membranes and seed oils (1). Several cDNA clones ofmRNAs encoding plant stearoylACP desaturase have now been described (2-4). The coding sequences for the mature enzyme are highly homologous. We have isolated a corresponding stearoyl-ACP desaturase cDNA from a cDNA bank made using embryo mRNA from jojoba, Simmondsia chinensis (Link). Many workers (5) consider jojoba to be a single species in a single genus in the single family Simmondsiaceae. Because of its unique evolutionary position, we anticipated a divergent stearoyl-ACP desaturase structure in jojoba. However, the high degree of peptide homology (approximately 80%) observed between jojoba and safflower did not suggest any obvious conserved regions specifically relating to the enzyme activity.