Abstract
BackgroundCrambe abyssinica produces high erucic acid (C22:1, 55-60%) in the seed oil, which can be further increased by reduction of polyunsaturated fatty acid (PUFA) levels. The omega-6 fatty acid desaturase enzyme (FAD2) is known to be involved in PUFA biosynthesis. In crambe, three CaFAD2 genes, CaFAD2-C1, CaFAD2-C2 and CaFAD2-C3 are expressed.ResultsThe individual effect of each CaFAD2 gene on oil composition was investigated through studying transgenic lines (CaFAD2-RNAi) for differential expression levels in relation to the composition of seed-oil. Six first generation transgenic plants (T1) showed C18:1 increase (by 6% to 10.5%) and PUFA reduction (by 8.6% to 10.2%). The silencing effect in these T1-plants ranged from the moderate silencing (40% to 50% reduction) of all three CaFAD2 genes to strong silencing (95% reduction) of CaFAD2-C3 alone. The progeny of two T1-plants (WG4-4 and WG19-6) was further analysed. Four or five transgene insertions are characterized in the progeny (T2) of WG19-6 in contrast to a single insertion in the T2 progeny of WG4-4. For the individual T2-plants of both families (WG19-6 and WG4-4), seed-specific silencing of CaFAD2-C1 and CaFAD2-C2 was observed in several individual T2-plants but, on average in both families, the level of silencing of these genes was not significant. A significant reduction in expression level (P < 0.01) in both families was only observed for CaFAD2-C3 together with significantly different C18:1 and PUFA levels in oil.ConclusionsCaFAD2-C3 expression is highly correlated to levels of C18:1 (r = -0.78) and PUFA (r = 0.75), which suggests that CaFAD2-C3 is the most important one for changing the oil composition of crambe.
Highlights
Crambe abyssinica produces high erucic acid (C22:1, 55-60%) in the seed oil, which can be further increased by reduction of polyunsaturated fatty acid (PUFA) levels
CaFAD2-RNAi lines We have previously shown that the major expressed CaFAD2 gene in developing crambe seeds is CaFAD2-C3, while the other two genes CaFAD2-C1 and CaFAD2-C2 are naturally expressed to much lower levels (4 and 100 times lower than CaFAD2-C3 respectively) [32]
Two primary transgenic plants (T0 generation,WG4 and WG19) that showed significantly lower contents of C18:2 and C18:3, but higher level of C18:1 in the seed-oil were used in this study [29]. For these two independent transgenic lines, the effect of RNAi-silencing on the expression of the individual CaFAD2 genes and the composition of the seed-oil were analysed for the seeds produced by the first generation (T1) and the second generation (T2)
Summary
Crambe abyssinica produces high erucic acid (C22:1, 55-60%) in the seed oil, which can be further increased by reduction of polyunsaturated fatty acid (PUFA) levels. The seed oil of crambe contains a high content of erucic acid (C22:1, 55% to 60%) and this oil has applications as industrial oil [1]. The cultivation of crambe yields up to 1 t ha-1 of oil, comparative to that of high erucic acid rapeseed (HEAR). The high yield and the fact that crambe is not able to cross with food oil crops in nature make crambe an ideal platform to produce industrial oils [6,7]. In addition to high erucic acid (C22:1), crambe oil contains certain amounts of oleic acid (C18:1), linoleic acid (C18:2) and linolenic acid (C18:3)
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