A gene encoding a delta12 desaturase in Solanum commersonii

It has been widely proved that the regulation of the extent of unsaturation of fatty acids (FAs) plays a pivotal role in maintaining membrane fluidity upon en- vironmental changes. The first step of FA unsaturation is controlled by a chloro- plastic soluble stearoyl-ACP-desaturase, while a delta12_oleoyl-desaturase, bound to the endoplasmic reticulum (ER), is responsible of further poly-unsaturation. A full-length cDNA clone (pScDll) coding for the latter enzyme has been cloned from a library of a wild potato species (Solanum commersonii) and further char- acterized The ORF of pScDll is 383 amino acid residue long. The deduced amino acid sequence from the cDNA showed homology to other desaturases from Arabidopsis, soybean as well as to an oleate hydroxylase from Ricinus communis. Southem blot analysis revealed that at least two copies were present per haploid genome. The hydropathy plot revealed six-candidate membrane spanning se- quences, and sequence analysis identified histidine-rich motifs, highly conserved in other desaturases, which putatively may contribute to an iron binding site in the cytoplasmic domain of the enzyme. This gene was found to be transcriptionally up-regulated in potato cells upon cold acclimation in the cold tolerant species S. commersonii, but not in S. tuberosum, the cultivated specie s, known to be unable to cold-acclimate.