SummaryWe used expressed sequence tag library and whole genome sequence mining to identify a suite of putative desaturase genes representing the four main activities required for production of polyunsaturated fatty acids in hemp seed oil. Phylogenetic-based classification and developing seed transcriptome analysis informed selection for further analysis of one of seven D12 desaturases and one of three D15 desaturases that we designate CSFAD2A and CSFAD3A, respectively. Heterologous expression of corresponding cDNAs in Saccharomyces cerevisiae showed CSFAD2A to have Dx+3 activity, while CSFAD3A activity was exclusively at the D15 position. TILLING of an ethyl methane sulphonate mutagenized population identified multiple alleles including non-sense mutations in both genes and fatty acid composition of seed oil confirmed these to be the major D12 and D15 desaturases in developing hemp seed. Following four backcrosses and sibling crosses to achieve homozygosity, csfad2a-1 was grown in the field and found to produce a 70 molar per cent high oleic acid (18:1 D9 ) oil at yields similar to wild type. Cold-pressed high oleic oil produced fewer volatiles and had a sevenfold increase in shelf life compared to wild type. Two low abundance octadecadienoic acids, 18:2 D6,9 and 18:2 D9,15 , were identified in the high oleic oil, and their presence suggests remaining endogenous desaturase activities utilize the increased levels of oleic acid as substrate. Consistent with this, CSFAD3A produces 18:2 D9,15 from endogenous 18:1 D9 when expressed in S. cerevisiae. This work lays the foundation for the development of additional novel oil varieties in this multipurpose low input crop.
Summary Oilseed rape (Brassica napus) is the third largest source of vegetable oil globally. In addition to food uses, there are industrial applications that exploit the ability of the species to accumulate the very‐long‐chain fatty acid (VLCFA) erucic acid in its seed oil, controlled by orthologues of FATTY ACID ELONGASE 1 (Bna.FAE1.A8 and Bna.FAE1.C3). The proportion of polyunsaturated fatty acids (PUFAs) in rapeseed oil is predicted to affect its thermal stability and is controlled by orthologues of FATTY ACID DESATURASE 2, particularly Bna.FAD2.C5. Our aim was to develop rapeseed lines combining high erucic and low PUFA characters and to assess the impact on thermal stability of the oil they produce. The new type of rapeseed oil (high erucic low polyunsaturate; HELP) contained a substantially greater proportion of erucic acid (54%) compared with high erucic rapeseed oil (46%). Although the total VLCFA content was greater in oil from HELP lines (64%) than from high erucic rapeseed (57%), analysis of triacylglycerol composition showed negligible incorporation of VLCFAs into the sn‐2 position. Rancimat analysis showed that the thermal stability of rapeseed oil was improved greatly as a consequence of reduction of PUFA content, from 3.8 and 4.2 h in conventional low erucic and high erucic rapeseed oils, respectively, to 11.3 and 16.4 h in high oleic low PUFA (HOLP) and HELP oils, respectively. Our results demonstrate that engineering of the lipid biosynthetic pathway of rapeseed, using traditional approaches, enables the production of renewable industrial oils with novel composition and properties.
The high oil content and suitable fatty acid composition of the seeds are two arguments to promote Jatropha curcas L. as a promising biodiesel crop. For seed yielding crops as J. curcas, it can be expected that successful pollination is a key process affecting oil yield and oil quality. Field experiments were conducted in Zambia to study the effects of different pollination treatments (autonomous autogamy, open natural, open pollen supplemented, self, and cross-pollination) on seed morphology, seed oil content (g), seed oil concentration (%), and oil fatty acid composition of J. curcas in 2-and 5-year-old plantations. For this experiment, 100 inflorescences per plantation were selected. Autonomous autogamy and self-pollination treatments reduced oil yield with 70 and 29 % respectively, compared to open pollination. Cross-and self-pollinations resulted in longer seeds than open pollination but did not affect oil content and concentration. The oil has high unsaturated fatty acid content (80 %) and is composed of nine fatty acids. Pollination treatments had an effect on fatty acid composition of oil from mature trees (5 years old), but had not for 2-year-old trees. The oleic acid content, a determinant fatty acid component for quality biodiesel production was lower for artificial self-pollination (9 % reduction) compared to open pollination. This research demonstrates that overall oil yield and quality are the highest under natural pollination. This shows the importance of safeguarding the quality and effectiveness of open natural pollination. This can be done by enhancing the presence of insects identified as J. curcas pollinators, particularly those pollinators enhancing cross-pollination.
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