Identification of bottlenecks in the accumulation of cyclic fatty acids in camelina seed oil

Xiao-Hong Yu, Stony Brook University
Rebecca E. Cahoon, University of Nebraska - Lincoln
Patrick J. Horn, University of North Texas
Hai Shi, Brookhaven National Laboratory
Richa R. Prakash, Stony Brook University
Yuanheng Cai, Stony Brook University
Maegan Hearney, Brookhaven National Laboratory
Kent D. Chapman, University of North Texas
Edgar B. Cahoon, University of Nebraska - Lincoln
Jorg Schwender, Brookhaven National Laboratory
John Shanklin, Brookhaven National Laboratory

Document Type Article

Copyright 2017 The Authors. This is an open access article under the terms of the Creative Commons Attribution License.

Abstract

Modified fatty acids (mFA) have diverse uses; for example, cyclopropane fatty acids (CPA) are feedstocks for producing coatings, lubricants, plastics and cosmetics. The expression of mFAproducing enzymes in crop and model plants generally results in lower levels of mFA accumulation than in their natural-occurring source plants. Thus, to further our understanding of metabolic bottlenecks that limit mFA accumulation, we generated transgenic Camelina sativa lines co-expressing Escherichia coli cyclopropane synthase (EcCPS) and Sterculia foetida lysophosphatidic acid acyltransferase (SfLPAT). In contrast to transgenic CPA-accumulating Arabidopsis, CPA accumulation in camelina caused only minor changes in seed weight, germination rate, oil accumulation and seedling development. CPA accumulated to much higher levels in membrane than storage lipids, comprising more than 60% of total fatty acid in both phosphatidylcholine (PC) and phosphatidylethanolamine (PE) versus 26% in diacylglycerol (DAG) and 12% in triacylglycerol (TAG) indicating bottlenecks in the transfer of CPA from PC to DAG and from DAG to TAG. Upon co-expression of SfLPAT with EcCPS, di-CPA-PC increased by ~50% relative to lines expressing EcCPS alone with the di-CPA-PC primarily observed in the embryonic axis and mono-CPA-PC primarily in cotyledon tissue. EcCPS-SfLPAT lines revealed a redistribution of CPA from the sn-1 to sn-2 positions within PC and PE that was associated with a doubling of CPA accumulation in both DAG and TAG. The identification of metabolic bottlenecks in acyl transfer between site of synthesis (phospholipids) and deposition in storage oils (TAGs) lays the foundation for the optimizing CPA accumulation through directed engineering of oil synthesis in target crops.