October 2005

From the Lab: Biotechnology

New publications, experiments, and breakthroughs in biotechnology -- and what they mean

By TR Staff

Fatty-Acid Factories
Engineered seeds produce healthful oils

Results: Canadian researchers have engineered mustard seeds to make very-long-chain polyunsaturated fatty acids such as omega-3 fatty acids that are known to reduce the risk of death from heart attacks and strokes. By transplanting genes from six sources, including marine fungi and marigolds, into the mustard plant, the researchers built new metabolic pathways that enabled the plants' seeds to convert two fatty acids they ordinarily make into two omega-3 fatty acids they don't normally make: eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The seeds produced a commercially viable amount of EPA, which topped out at 15 percent of the total fatty acids in the seed oil, and a detectable but not commercially viable amount of DHA, at 1.5 percent.

Why It Matters: Omega-3 acids are found primarily in fish oils, and food manufacturers have recently been extracting them and adding them to eggs, milk, juice, butter, breads, and other foods. But while these acids are good for people's health, their source, fish oil, can contain high levels of toxic chemicals such as mercury. By turning mustard seeds--chosen because they normally produce large amounts of oils and can easily incorporate new genes--into fatty-acid factories, the researchers hope to produce a safe source of omega-3 acids not limited by the supply of fish. Previously engineered plants produced low levels of EPA and no DHA. Here, an engineered mustard seed produced DHA for the first time and high enough levels of EPA to make it a potential commercial source.

Methods: Led by Xiao Qiu of Bioriginal Food and Science in Saskatoon, Saskatchewan, the researchers introduced three to nine genes from plants and microrganisms into the cells of India mustard seedlings, then analyzed the oils in the seeds those plants produced. The new genes produced enzymes that in a series of steps transformed the two normally present fatty acids into the omega-3 fatty acids. By adding genes successively in a series of experiments, the researchers could see how each gene changed fatty-acid production, which allowed them to understand in detail the metabolic pathways involved and to try different genes that would produce higher yields of the target fatty acids.

Next Step: The researchers are attempting to increase the seeds' production of DHA by adding more genes to the omega-3 fatty-acid pathways. -- By Kevin Bullis

Source: Wu, G., et al. 2005. Stepwise engineering to produce high yields of very long-chain polyunsaturated fatty acids in plants. Nature Biotechnology 23:1013-1017.