Abstract
BackgroundJatropha curcas is recognized as a new energy crop due to the presence of the high amount of oil in its seeds that can be converted into biodiesel. The quality and performance of the biodiesel depends on the chemical composition of the fatty acids present in the oil. The fatty acids profile of the oil has a direct impact on ignition quality, heat of combustion and oxidative stability. An ideal biodiesel composition should have more monounsaturated fatty acids and less polyunsaturated acids. Jatropha seed oil contains 30% to 50% polyunsaturated fatty acids (mainly linoleic acid) which negatively impacts the oxidative stability and causes high rate of nitrogen oxides emission.ResultsThe enzyme 1-acyl-2-oleoyl-sn-glycero-3-phosphocholine delta 12-desaturase (FAD2) is the key enzyme responsible for the production of linoleic acid in plants. We identified three putative delta 12 fatty acid desaturase genes in Jatropha (JcFAD2s) through genome-wide analysis and downregulated the expression of one of these genes, JcFAD2-1, in a seed-specific manner by RNA interference technology. The resulting JcFAD2-1 RNA interference transgenic plants showed a dramatic increase of oleic acid (> 78%) and a corresponding reduction in polyunsaturated fatty acids (< 3%) in its seed oil. The control Jatropha had around 37% oleic acid and 41% polyunsaturated fatty acids. This indicates that FAD2-1 is the major enzyme responsible for converting oleic acid to linoleic acid in Jatropha. Due to the changes in the fatty acids profile, the oil of the JcFAD2-1 RNA interference seed was estimated to yield a cetane number as high as 60.2, which is similar to the required cetane number for conventional premium diesel fuels (60) in Europe. The presence of high seed oleic acid did not have a negative impact on other Jatropha agronomic traits based on our preliminary data of the original plants under greenhouse conditions. Further, we developed a marker-free system to generate the transgenic Jatropha that will help reduce public concerns for environmental issues surrounding genetically modified plants.ConclusionIn this study we produced seed-specific JcFAD2-1 RNA interference transgenic Jatropha without a selectable marker. We successfully increased the proportion of oleic acid versus linoleic in Jatropha through genetic engineering, enhancing the quality of its oil.
Highlights
Jatropha curcas is recognized as a new energy crop due to the presence of the high amount of oil in its seeds that can be converted into biodiesel
JcFAD2-1 has identical amino acid sequences to Arabidopsis thaliana fatty acid desaturase 2 (FAD2) at its enzyme active center in three conserved His-rich boxes, while JcFAD2-2 has a variation on a key residue Ala in active site His-rich box 3 (Thr in JcFAD2-2; Additional file 2)
The change of small hydrophobic Ala substituted with polar Thr could potentially alter FAD2-2 substrate specificity and enzyme activity because the hydrophobic core environment is crucial for its activity [12]
Summary
Jatropha curcas is recognized as a new energy crop due to the presence of the high amount of oil in its seeds that can be converted into biodiesel. It is known that biodiesel with high monounsaturated fatty acid content (oleate) has excellent characteristics with respect to ignition quality, nitrogen oxides (NOx) emissions and fuel stability [2]. Most plant oils used as biodiesel feedstock have a high level of polyunsaturated fatty acids (linoleate and linolenate acids) which negatively impacts the biodiesel quality. The biodiesel derived from plant oil with high oleate content is expected to have better fuel qualities This has been shown in soybean, where lines with high levels of oleic acid and low levels of polyunsaturated fatty acids were developed using a transgenic strategy that downregulates the expression of fatty acid desaturase 2 (FAD2) gene [2,4]. Biodiesel derived from these high oleic soybean oils displayed improved fuel characteristics with regard to fuel stability and NOx missions [2,4]
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