Abstract
BackgroundStearoyl-acyl carrier protein desaturase (SAD) is a key enzyme that catalyses the conversion of stearoyl-acyl carrier protein (ACP) to oleoyl-ACP, a precursor for the biosynthesis of polyunsaturated fatty acids. ZmSAD1 (GenBank: KU949326) is a major QTL for stearic acid content in maize seeds. To investigate the biological function and the application potential of maize ZmSAD1 in oil biosynthesis, we isolated the full-length ZmSAD1 cDNA from maize B73 and overexpressed it in Arabidopsis and maize.ResultsUnder seed-specific overexpression of ZmSAD1 in Arabidopsis, the stearic acid content and the ratio of saturated to unsaturated fatty acids in the seeds were significantly decreased relative to those in the control. Conversely, in transgenic ZmSAD1 RNAi Arabidopsis seeds, the contents of stearic acid and long-chain saturated acids and the ratio of saturated to unsaturated fatty acids were significantly increased; in addition, the oleic acid content was significantly decreased. More importantly, transgenic ZmSAD1 maize that expressed high levels of ZmSAD1 in its mature seeds showed reduced stearic acid content (1.57 %) and a lower saturated to unsaturated fatty acid ratio (20.40 %) relative to those (1.64 % and 20.61 %, respectively) of the control. Conversely, down-regulation of ZmSAD1 in maize resulted in increased levels of stearic acid (1.78 %), long-chain saturated acids (0.85 %) and the ratio of saturated to unsaturated fatty acids (21.54 %) relative to those (1.64 %, 0.74 %, and 20.61 %, respectively) of the control, whereas the oleic acid (32.01 %) level was significantly decreased relative to that (32.68 %) of the control.ConclusionsOur work demonstrates that the contents of stearic acid, oleic acid, and long-chain saturated acids, and the ratio of saturated to unsaturated fatty acids, are modified in maize seeds by seed-specific overexpression or down-regulation of ZmSAD1. Therefore, the ZmSAD1 gene is a useful tool for engineering the seed oil composition in maize and other crops.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0827-z) contains supplementary material, which is available to authorized users.
Highlights
Introduction of theZmSAD1 gene into maize Our results confirmed that the composition of fatty acids in the Arabidopsis seeds was modified by the introduction of an exogenous ZmSAD1 gene and suppressed by ZmSAD1 RNAi
Endogenous Stearoyl-acyl carrier protein desaturase (SAD) expression levels are altered in transgenic Arabidopsis We obtained the full-length cDNA of ZmSAD1 from B73 using the 5’-rapid-amplification of cDNA ends (RACE) technique [19]
The ZmSAD1 overexpression (ZmSAD1), antisense ZmSAD1, and ZmSAD1 RNA interference (ZmSAD1 RNAi) constructs were generated in the pBI121 vector (Additional file 1: Figure S1), and their expression was under control of the Fatty Acid Elongation 1 (FAE1) promoter, a seed-specific promoter [21]
Summary
Introduction of theZmSAD1 gene into maize Our results confirmed that the composition of fatty acids in the Arabidopsis seeds was modified by the introduction of an exogenous ZmSAD1 gene and suppressed by ZmSAD1 RNAi. The ZmSAD1 expression levels in the A188(ZmSAD1 RNAi) mature seeds are lower than that in the control, indicating that the ZmSAD1 RNAi construct effectively suppresses expression of the endogenous ZmSAD1 gene in maize (Fig. 4). Stearoyl-acyl carrier protein desaturase (SAD) is a key enzyme that catalyses the conversion of stearoyl-acyl carrier protein (ACP) to oleoyl-ACP, a precursor for the biosynthesis of polyunsaturated fatty acids. The desaturation of long-chain fatty acids is accomplished in sequential steps and begins with the conversion of stearoyl-acyl carrier protein (ACP) to oleoyl-ACP, catalysed by stearoyl-ACP desaturase (SAD, EC 1.12.99.6) [6, 7]. SAD may serve as a useful tool for engineering maize plants that produce a balanced content of stearic and oleic acids in their seeds
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