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Title: Castor phospholipid:diacylglycerol acyltransferase facilitates efficient metabolism of hydroxy fatty acids in transgenic Arabidopsis

item VAN ERP, HARRIE - Washington State University
item BATES, PHILIP - Washington State University
item BURGAL, JULIE - Washington State University
item Shockey, Jay
item BROWSE, JOHN - Washington State University

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/17/2010
Publication Date: 2/1/2011
Citation: Van Erp, H., Bates, P.D., Burgal, J., Shockey, J., Browse, J. 2011. Castor phospholipid:diacylglycerol acyltransferase facilitates efficient metabolism of hydroxy fatty acids in transgenic Arabidopsis. Plant Physiology. 155:683-693.

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 or mouse ear cress), to produce foreign proteins 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. This yield is much smaller than what is observed in castor bean seeds (nearly 90%). Improvements to the “single novel gene” approach involve adding many other genes from the exotic plant into the single-gene thale cress host plant are needed to produce oils in plants. In the present study, we have found an additional new gene from castor, called PDAT1A, that enables thale cress plants already containing the FAH12 gene to increase their castor-like fatty acid content from 17% to almost 30%. This study details the analysis of the oil content and quality produced from seeds producing both the FAH12 and PDAT1A proteins.

Technical Abstract: Producing unusual fatty acids (FAs) in crop plants has been a long-standing goal of green chemistry. However, expression of the enzymes that catalyze the primary synthesis of these unusual FAs in transgenic plants typically results in low levels of the desired FA. For example, seed-specific expression of castor (Ricinus communis) fatty acid hydroxylase (RcFAH) in Arabidopsis (Arabidopsis thaliana) resulted in only 17% hydroxy fatty acids (HFAs) in the seed oil. In order to increase HFA levels, we investigated castor phospholipid:diacylglycerol acyltransferase (PDAT). We cloned cDNAs encoding three putative PDAT enzymes from a castor seed cDNA library and coexpressed them with RcFAH12. One isoform, RcPDAT1A, increased HFA levels to 27%. Analysis of HFA-triacylglycerol molecular species and regiochemistry, along with analysis of the HFA content of phosphatidylcholine, indicates that RcPDAT1A functions as a PDAT in vivo. Expression of RcFAH12 alone leads to a significant decrease in FA content of seeds. Coexpression of RcPDAT1A and RcDGAT2 (for diacylglycerol acyltransferase 2) with RcFAH12 restored FA levels to nearly wild-type levels, and this was accompanied by a major increase in the mass of HFAs accumulating in the seeds. We show the usefulness of RcPDAT1A for engineering plants with high levels of HFAs and alleviating bottlenecks due to the production of unusual FAs in transgenic oilseeds.