Engineered Plant Produces Compounds for Plastics

John Shanklin (Brookhaven National Lab)

Plants may have in theory the kinds of raw materials for plastics obtained from petroleum-based chemicals, but in reality, getting plants to accumulate these desired products in any meaningful quantity has been an elusive goal. In a step toward industrial-scale green production, scientists from the U.S. Department of Energy’s Brookhaven National Laboratory in Upton, New York and collaborators at Dow AgroSciences report engineering a plant that produces industrially relevant levels of compounds with the potential to make plastics.

Dow AgroSciences in Indianapolis, Indiana, is a subsidiary of Dow Chemical Company.

“We’ve engineered a new metabolic pathway in plants for producing a kind of fatty acid that could be used as a source of precursors to chemical building blocks for making plastics such as polyethylene,” says Brookhaven biochemist John Shanklin (left), who led the research. Shanklin adds, “Additional technology to efficiently convert the plant fatty acids into chemical building blocks is needed, but our research shows that high levels of the appropriate feedstock can be made in plants.”

The method builds on Shanklin’s interest in fatty acids — the building blocks for plant oils — and the enzymes that control their production. Plants that naturally produce the desired fatty acids, called omega-7 fatty acids, in their seeds — such as cat’s claw vine and milkweed — found that their yields and growth characteristics are not suitable for commercial production. Attempts to express the relevant genes in more suitable plant species resulted in much lower levels of the desired oils than are produced in plants from which the genes were isolated.

Shanklin and colleagues then tried, as a proof-of-concept, a series of systematic metabolic engineering experiments to optimize the accumulation of omega-7 fatty acids in transgenic plants, using Arabidopsis, a common laboratory plant. Having tested various traits individually, the scientists then combined the most promising traits into a single new plant.

The result was an accumulation of the desired omega-7 fatty acid at levels of about 71 percent in the best-engineered line of Arabidopsis. This was much higher than the omega-7 fatty acid levels in milkweed, and equivalent to those seen in cat’s claw vine. Growth and development of the engineered Arabidopsis plants were unaffected by the genetic modifications and accumulation of omega-7 fatty acid.

The research is reported online in Plant Physiology, and will appear in print in the December issue.

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