Based on the whole genome clarified the evolution and expression process of fatty acid desaturase genes in three soybeans.

Soybean is an important oil crop cultivated worldwide. With the increasing global population crossed with growing challenging cultivation conditions, improving soybean breeding by selecting important traits is urgent needed. Genes coding for plant fatty acid desaturases (FADs) genes are major candidates for that, because they are involving in controlling fatty acid composition and holding membrane fluidity under abiotic stress. Here, 75 FADs were found in three soybean genomes, which were further classified into four sub-groups. Phylogenetic tree, gene structure, motif and promoter analysis showed that the FAD gene family was conserved in the three soybeans. In addition, the numbers of omega desaturase from Chinese cultivated varieties were significantly higher than those in Chinese wild soybean and ancient polyploid soybean, respectively. However, it was the opposite for the sphingolipid subfamily. These results indicated that each subfamily was subjected to different selection pressures during cultivation and domestication. As the extra genes of the subfamily were very close to other family members' positions on chromosomes, they should be produced by duplication. The cis-element analysis of FAD promoter sequences revealed that upstream sequences of FAD contained abundant light, hormone and abiotic stress responsive cis-elements, suggesting that the quality of soybean could be improved by regulating these stresses. Expression analysis of Chinese wild soybean under salt stress showed that GsDES1.1, GsDES1.2, GsFAD2.1 and GsSLD1 in leaves and GsSLD2, GsSLD5 and GsSLD6 in roots were not closely related to salt stress response. Therefore, we explored the significant role of conserved, duplicated and neofunctionalized FAD in the domestication of soybean, which contributes to the importance of soybean as a global oil crop.