Summary Soybean ( Glycine max [L.] Merr.) is a commodity crop highly valued for its protein and oil content. The high percentage of polyunsaturated fatty acids in soybean oil results in low oxidative stability, which is a key parameter for usage in baking, high temperature frying applications, and affects shelf life of packaged products containing soybean oil. Introduction of a seed‐specific expression cassette carrying the Arabidopsis transcription factor WRINKLED 1 (At WRI 1) into soybean, led to seed oil with levels of palmitate up to approximately 20%. Stacking of the At WRI 1 transgenic allele with a transgenic locus harbouring the mangosteen steroyl‐ ACP thioesterase (GmFatA) resulted in oil with total saturates up to 30%. The creation of a triple stack in soybean, wherein the At WRI 1 and GmFatA alleles were combined with a FAD 2‐1 silencing allele led to the synthesis of an oil with 28% saturates and approximately 60% oleate. Constructs were then assembled that carry a dual FAD 2‐1 silencing element/GmFatA expression cassette, alone or combined with an At WRI 1 cassette. These plasmids are designated pPTN 1289 and pPTN 1301, respectively. Transgenic events carrying the T‐ DNA of pPTN 1289 displayed an oil with stearate levels between 18% and 25%, and oleate in the upper 60%, with reduced palmitate (<5%). While soybean events harboring transgenic alleles of pPTN 1301 had similar levels of stearic and oleate levels as that of the pPTRN 1289 events, but with levels of palmitate closer to wild type. The modified fatty acid composition results in an oil with higher oxidative stability, and functionality attributes for end use in baking applications.

Triacylglycerol (TAG) is the major carbon storage reserve in oilseeds such as Arabidopsis. Acyl-CoA:diacylglycerol acyltransferase (DGAT) catalyses the final step of the TAG synthesis pathway. Although TAG is mainly accumulated during seed development, and DGAT has presumably the highest activity in developing seeds, we show here that TAG synthesis is also actively taking place during germination and seedling development in Arabidopsis. The expression pattern of the DGAT1 gene was studied in transgenic plants containing the reporter gene beta-glucuronidase (GUS) fused with DNA sequences flanking the DGAT1 coding region. GUS activity was not only detected in developing seeds and pollen, which normally accumulate storage TAG, but also in germinating seeds and seedlings. Western blots showed that DGAT1 protein is present in several tissues, though is most abundant in developing seeds. In seedlings, DGAT1 is expressed in shoot and root apical regions, correlating with rapid cell division and growth. The expression of GUS in seedlings was consistent with the results of RNA gel blot analyses, precursor feeding and DGAT assay. In addition, DGAT1 gene expression is up-regulated by glucose and associated with glucose-induced changes in seedling development.