Using Deep Transcriptional Profiling to Improve Plant Oils.

Using 454 pyrosequencing we have obtained over 8 million ESTs from the developing seeds of four different oil producing plants: Brassica napus (canola), Euonymus alatus (burning bush), Ricinus communis (castor) and Tropaeoleum majus (nasturtium). The seed storage oil of Euonymus is comprised of acetyl-triacylglycerols (acTAGs), unusual triacylglycerols (TAGs) that possess an sn-3 acetate group instead of a long chain fatty acid. AcTAGs possess a lower viscosity than other seed oils, and could be useful as a direct use biodiesel, as well as for other industrial and nutritional applications.  As Euonymus is not a suitable oil seed crop, isolating the enzymes responsible for the synthesis of acTAGs represented the first step in developing transgenic plants capable of producing acTAGs.  The greater depth of the 454 transcriptional profiling compared to conventional EST sequencing allowed us to quantitatively compare expression values, even for genes encoding acyltransferase enzymes involved in lipid production, which are expressed at low levels. With this approach, we identified the acyltransferase responsible for the synthesis of acTAGs in Euonymus endosperm. Expression of this novel Euonymus acyltransferase in Arabidopsis resulted in the accumulation of high levels of acTAGs, up to 65 mol%, in the seed oil of the transgenic plants.