All plant cells produce fatty acids from acetyl-CoA by a common pathway localized in plastids. Although the biochemistry of this pathway is now well understood, much less is known about how plants control the very different amounts and types of lipids produced in different tissues. Thus, a central challenge for plant lipid research is to provide a molecular understanding of how plants regulate the major differences in lipid metabolism found, for example, in mesophyll, epidermal, or developing seed cells. Acetyl-CoA carboxylase (ACCase) is one control point that regulates rates of fatty acid synthesis. However, the biochemical modulators that act on ACCase and the factors that in turn control these modulators are poorly understood. In addition, little is known about how the expression of genes involved in fatty acid synthesis is controlled. This review evaluates current knowledge of regulation of plant fatty metabolism and attempts to identify the major unanswered questions.

Regulation of fatty acid synthesis

The contribution of membrane lipids, particularly the level of unsaturation of fatty acids, to chilling sensitivity of plants has been intensively discussed for many years. We have demonstrated that the chilling sensitivity can be manipulated by modulating levels of unsaturation of fatty acids of membrane lipids by the action of acyl-lipid desaturases and glycerol-3-phosphate acyltransferase. This review covers recent studies on genetic manipulation of these enzymes in transgenic tobacco and cyanobacteria with special emphasis on the crucial importance of the unsaturation of membrane lipids in protecting the photosynthetic machinery from photoinhibition under cold conditions. Furthermore, we review the molecular mechanism of temperature-induced desaturation of fatty acids and introduce our hypothesis that changes in the membrane fluidity is the initial event of the expression of desaturase genes.

CHILLING SENSITIVITY IN PLANTS AND CYANOBACTERIA: The Crucial Contribution of Membrane Lipids

Medium-chain fatty acids (FAs), found in storage lipids of certain plants, are an important renewable resource. Seeds of undomesticated California bay accumulate laurate (12:0), and a 12:0-acyl-carrier protein thioesterase (BTE) has been purified from this tissue. Sequencing of BTE enabled the cloning of a complementary DNA coding for a plastid-targeted preprotein. Expression of the complementary DNA in the seeds of Arabidopsis thaliana resulted in BTE activity, and medium chains accumulated at the expense of long-chain (greater than or equal to 16) FAs. Laurate became the most abundant FA species and was deposited in the storage triacylglycerols. These results demonstrate a mechanism for medium-chain FA synthesis in plants.

http://science.sciencemag.org/content/sci/257/5066/72.full.pdf

Fatty acid biosynthesis redirected to medium chains in transgenic oilseed plants.

World consumption of soybean ( Glycine max ) in 2008 was over 221 million metric tons, with approximately 50% of this supply coming from U.S. production, where soybean plantings on an annual basis are over 77 million ha. Soybeans are desired on the marketplace as a valuable source of protein and oil

https://www.jstor.org/stable/pdfplus/40537933.pdf

Soybean Oil: Genetic Approaches for Modification of Functionality and Total Content

Metabolic engineering of fatty acid biosynthesis in plants.

Molecular gene transfer techniques have been used to engineer the fatty acid composition of Brassica rapa and Brassica napus (canola) oil. Stearoyl-acyl carrier protein (stearoyl-ACP) desaturase (EC 1.14.99.6) catalyzes the first desaturation step in seed oil biosynthesis, converting stearoyl-ACP to oleoyl-ACP. Seed-specific antisense gene constructs of B. rapa stearoyl-ACP desaturase were used to reduce the protein concentration and enzyme activity of stearoyl-ACP desaturase in developing rapeseed embryos during storage lipid biosynthesis. The resulting transgenic plants showed dramatically increased stearate levels in the seeds. A continuous distribution of stearate levels from 2% to 40% was observed in seeds of a transgenic B. napus plant, illustrating the potential to engineer specialized seed oil compositions.

https://www.pnas.org/content/pnas/89/7/2624.full.pdf

W B Johnson

Papers

Modification of Brassica seed oil by antisense expression of a stearoyl-acyl carrier protein desaturase gene