Fatty acid desaturases constitute a group of enzymes that introduce double bonds into the hydrocarbon chains of fatty acids to produce unsaturated fatty acids. In plants, seed-specific delta-12 fatty acid desaturase 2 (FAD2) is responsible for the high content of linoleic acid by inserting a double bond at the delta-12 (omega-6) position of oleic acid. In this study, sixteen FAD2 and FAD2-2 protein sequences from oilseeds were analyzed by computational tools including two databases of the NCBI and EXPASY and data management tools such as SignalP, TMHMM, Psort, ProtParam, TargetP, PLACE and PlantCARE. These services were used to predict the protein properties such as molecular mass, pI, signal peptide, transmembrane and conserved domains, secondary and spatial structures. The polypeptide sequences were aligned and a neighbour-joining tree was constructed using MEGA5.1 to elucidate phylogenetic relationships among FAD2 genes. Based on the phylogenetic analysis species with high similarity in FAD2 sequence grouped together. FAD2 proteins include highly conserved histidine-rich motifs (HECGHH, HRRHH and HV[A/C/T]HH) that are located by three to five transmembrane anchors. For further investigations Sesamum indicum FAD2 was selected and analyzed by bioinformatics tools. Analysis showed no N-terminal signal peptide for probable localization of FAD2 protein in cytoplasmic organelles such as chloroplast, mitochondria and Golgi. Instead the C-terminal signaling motif YNNKL, Y(K/N)NKF or YRNKI allows FAD2 protein to selectively bind to and embed in the endoplasmic reticulum. FAD2 promoter contains different cis-regulatory elements involve in the biotic and abiotic stresses response or control of gene expression specifically in seeds.

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The low artemisinin content in Artemisia has caused this compound to be expensive among medicines. Several attempts have been made to increase its production by altering the expression of different genes. However, no approach has been cost-effective. In this study, the expression levels of SQS and DBR2 genes were quantified by qRT-PCR, and artemisinin content was measured by HPLC in Artemisia annua cell suspension culture under nano cobalt particles elicitation. For this purpose, nano cobalt particles were used in 0.25, 2.5, and 5 mg L -1 concentrations and samples were collected after 8, 24, 48, and 72 h. The highest artemisinin content was observed 24 h after 5 mg L -1 nano cobalt treatment. In this case, artemisinin production was 2.25-fold (113.35 mg g -1 dw) higher than that of the control. Simultaneously, the expression levels of SQS and DBR2 genes decreased. It appears that the decrease in the expression of SQS and DBR2 genes caused the artemisinin content to increase by high concentrations of the nano cobalt particles.

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