Submitted to: Plant Biotechnology Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/6/2008
Publication Date: 10/1/2008
Citation: Burgal, J., Shockey, J., Lu, C., Dyer, J., Larson, T., Graham, I., Browse, J. 2008. Metabolic engineering of hydroxy fatty acid production in plants: rcdgat2 drives dramatic increases in ricinoleate levels in seed oil. Plant Biotechnology Journal. 6(8):819-831. Interpretive Summary: Many laboratories in government, academia, and private industry seek to create new types of oilseed crops that produce oils with value-added traits. These new oils could replace petroleum-based compounds in many everyday products such as nylons, plastics, inks, and dyes. One way to accomplish this goal is to engineer common oilseed plants, such as soybean, canola, or Arabidopsis thaliana (thale cress), to contain foreign genes from other plants that produce the value-added oils, such as castor bean. Many labs, including ours, have created thale cress plants containing one gene from castor, called FAH12. Introduction of the FAH12 gene into thale cress results in production of only 17% of the novel fatty acid produced by castor. Such small yields of the desired product are common when trying to produce such novel fatty acids by these methods. One idea as to why the “single novel gene” approach does not work effectively is that many other genes are needed to produce oils in plants. Probably between five and ten other genes may be necessary. Some or all of the other ten genes present in the new host plant might not be well-suited to use the novel fatty acids being produced by the single new gene. In the present study, we have found an additional new gene from castor, called DGAT2, that enables thale cress plants already containing the FAH12 gene to increase their castor-like fatty acid content from 17% to 30%. Such a finding confirms the need for additional oil-producing genes from the novel plants, and should help guide the design of more successful oil engineering studies.
Technical Abstract: A central goal of green chemistry is to produce industrially-useful fatty acids in oilseed crops. Although genes encoding suitable modification enzymes are available from many wild species, progress has been stymied because expression of these in transgenic plants produces poor yields of the desired products. For example, the Ricinus communis FAH12 hydroxylase produces a maximum of only 17% hydroxy fatty acids (HFAs) when expressed in Arabidopsis thaliana. We identified cDNAs encoding R. communis isozymes for additional steps in seed-lipid synthesis. Expression of these in FAH12-transgenics revealed that the R. communis isozyme of Type-2 acyl-CoA:diacylglycerol acyltransferase (RcDGAT2) could increase HFAs from 17% to nearly 30%. Overexpression of A. thaliana DGAT2 did not increase HFAs. When expressed in yeast, recombinant RcDGAT2 showed a strong preference for HFA-containing diacylglycerol substrate. Our results demonstrate that pathway engineering approaches can be successfully used to increase the yields of industrial feedstocks in plants.