Overexpression of SiDGAT1, a gene encoding acyl-CoA:diacylglycerol acyltransferase from Sesamum indicum L. increases oil content in transgenic Arabidopsis and soybean

Diacylglycerol acyltransferase (DGAT1; EC 2.3.1.20) is the key enzyme governing the terminal step of triacylglycerol synthesis in plant seeds. The aims here were to isolate and characterize a full-length cDNA encoding DGAT1 from the sesame (Sesamum indicum L.) cultivar 'Wanzhi1' (oil content 55 +/- A 2 %; SiDGAT1); and to over-express that gene in Arabidopsis (Arabidopsis thaliana L.) and soybean (Glycine max L. Merr.). The 1,629-bp open reading frame of the SiDGAT1 cDNA encoded a protein of 543 amino acids, which showed high similarity to other plant DGAT1s. The transcript of the SiDGAT1 gene was differentially abundant among organs in sesame. The highest transcript abundance was found in the developing seeds. The expression of the SiDGAT1 cDNA driven by the cauliflower mosaic virus 35S-promoter was able to restore to near normal oil content and the fatty acid composition phenotypes of the Arabidopsis mutant AS11 (an AtDGAT1). Over-expression of SiDGAT1 in several lines of Arabidopsis thaliana 'Col 0' resulted in increases in oil content; and in seed weight. The ratio of eicosenoic acid (C20:1) was increased, whereas that of oleic acid (C18:1) was decreased in transgenic Arabidopsis plants. The SiDGAT1 was also used to transform soybean. Compared to controls, the mean increase in oil content was 1.75 and 1.39 % respectively in T2 and T3 transgenic soybean lines. Further, SiDGAT1 transcript abundance was correlated with increased seed size and 100-seed weight, but did not alter the fatty acid composition of the seed oil.