Abstract:

The quality of peanut oil largely depends on the quantity of oleic (18:1) and linoleic acid (18:2), which comprise more than 80% of the total fatty acids in peanut. Oleic acid is a monounsaturated fatty acid and has the function of reducing the content of low-density lipoprotein (LDL) in human bodies. Therefore, the increase of the content of oleic acid in peanut will not only improve oil stability and favor but also be good for the health of consumers. And Δ¹²-fatty acid desaturase (FAD) gene is an important gene to maintain a high content of oleic acid.
The objectives of the present research were to further study the roles of the FAD gene in the growth and development of peanut cells and to reveal the regulation mechanisms in fatty acid metabolism，using different types of peanut genotypes. On the basis of the conservative sequence of Δ¹²-fatty acid desaturase, a cDNA was isolated, which consisted of 1 140 bp and encoded a polypeptide of 379 amino acid resides with a calculated molecular weight of 42 kDa. The putative amino acid sequence had three histidine conservative regions sharing integral-protease specificity and the hydrophobicity analysis showed that the sequence of the encoded amino acids had two hydrophobic structures sharing the characteristics of membrane-anchored protein，which totally crossed the membrane four times. These analyses revealed the obtained sequence was Δ¹²-fatty acid desaturase. The phylogenetic-tree analysis demonstrated that in Arachis the FDA sequence was conservative and highly homogenous to those in other species. Amino acid sequence comparison of peanut with other lipid-modifying enzymes provides insight to the evolution of enzyme structure/function relationships. The results of this study will provide molecular evidence for probing the phylogenetic relationships among the plants of Arachis. The significance of these findings and the evolution of plant fatty acid diversity were discussed.

Key words: Arachis, Fatty acid desaturase, Sequence analysis, Evolution relationship