Polyunsaturated fatty acids (PUFAs) are essential membrane components in higher eukaryotes and are the precursors of many lipid-derived signaling molecules. Here, pathways for PUFA synthesis are described that do not require desaturation and elongation of saturated fatty acids. These pathways are catalyzed by polyketide synthases (PKSs) that are distinct from previously recognized PKSs in both structure and mechanism. Generation of cis double bonds probably involves position-specific isomerases; such enzymes might be useful in the production of new families of antibiotics. It is likely that PUFA synthesis in cold marine ecosystems is accomplished in part by these PKS enzymes.

We report the identification and biotechnological utility of a plant gene encoding the tocopherol (vitamin E) biosynthetic enzyme 2-methyl-6-phytylbenzoquinol methyltransferase. This gene was identified by map-based cloning of the Arabidopsis mutation vitamin E pathway gene3-1 ( vte3-1 ), which causes increased accumulation of ␦ -tocopherol and decreased ␥ -tocopherol in the seed. Enzyme assays of recombinant protein supported the hypothesis that At-VTE3 encodes a 2-methyl-6-phytylbenzoquinol methyltransferase. Seed-specific expression of At-VTE3 in transgenic soybean reduced seed ␦ -tocopherol from 20 to 2%. These results confirm that At-VTE3 protein catalyzes the methylation of 2-methyl-6-phytylbenzoquinol in planta and show the utility of this gene in altering soybean tocopherol composition. When At-VTE3 was coexpressed with At-VTE4 ( ␥ -tocopherol methyltransferase) in soybean, the seed accumulated to Ͼ 95% ␣ -tocopherol, a dramatic change from the normal 10%, resulting in a greater than eightfold increase of ␣ -tocopherol and an up to fivefold increase in seed vitamin E activity. These findings demonstrate the utility of a gene identified in Arabidopsis to alter the tocopherol composition of commercial seed oils, a result with both nutritional and food quality implications.

Oilseeds are the main source of lipids used in both food and biofuels. The growing demand for vegetable oil has focused research toward increasing the amount of this valuable component in oilseed crops. Globally, soybean (Glycine max) is one of the most important oilseed crops grown, contributing about 30% of the vegetable oil used for food, feed, and industrial applications. Breeding efforts in soy have shown that multiple loci contribute to the final content of oil and protein stored in seeds. Genetically, the levels of these two storage products appear to be inversely correlated with an increase in oil coming at the expense of protein and vice versa. One way to overcome the linkage between oil and protein is to introduce a transgene that can specifically modulate one pathway without disrupting the other. We describe the first, to our knowledge, transgenic soy crop with increased oil that shows no major impact on protein content or yield. This was achieved by expressing a codon-optimized version of a diacylglycerol acyltransferase 2A from the soil fungus Umbelopsis (formerly Mortierella) ramanniana in soybean seed during development, resulting in an absolute increase in oil of 1.5% (by weight) in the mature seed.

Lysophosphatidic acid acyltransferase acylates the sn-2 hydroxyl group of lysophosphatidic acid to form phosphatidic acid, a precursor to triacylglycerol. A cDNA encoding lysophosphatidic acid acyltransferase was isolated from developing seeds of meadowfoam (Limnanthes alba alba). The cDNA encodes a 281-amino acid protein with a molecular m a s of 32 kD. The cDNA was expressed in developing seeds of transgenic high-erucic-acid rapeseed (Brassica napus) using a napin expression cassette. Erucic acid was present at the sn-2 position of triacylglycerols from transgenic plants but was absent from that position of seed oil extracted from control plants. Trierucin was present in the transgenic oil. Alteration of the sn-2 erucic acid composition did not affect the total erucic acid content. These experiments demonstrate the feasibility of using acyltransferases to alter the stereochemical composition of transgenic seed oils and also representa necessary step toward increasing the erucic acid content of rapeseed oil.