Transcriptional Regulation of Stearoyl-Acyl Carrier Protein Desaturase Genes in Response to Abiotic Stresses Leads to Changes in the Unsaturated Fatty Acids Composition of Olive Mesocarp

Abstract

In higher plants, the stearoyl-acyl carrier protein desaturase (SAD) catalyzes the first desaturation step leading to oleic acid, which can be further desaturated to linoleic and α-linolenic acids. Therefore, SAD plays an essential role in determining the overall content of unsaturated fatty acids (UFA). We have investigated how SAD genes expression and UFA composition are regulated in olive (Olea europaea) mesocarp tissue from Picual and Arbequina cultivars in response to different abiotic stresses. The results showed that olive SAD genes are transcriptionally regulated by temperature, darkness and wounding. The increase in SAD genes expression levels observed in Picual mesocarp exposed to low temperature brought about a modification in the UFA content of microsomal membrane lipids. In addition, darkness caused the down-regulation of SAD genes transcripts, together with a decrease in the UFA content of chloroplast lipids. The differential role of olive SAD genes in the wounding response was also demonstrated. These data point out that different environmental stresses can modify the UFA composition of olive mesocarp through the transcriptional regulation of SAD genes, affecting olive oil quality.

Keywords: Olea europaea; abiotic stress; gene expression; olive; stearoyl-ACP desaturase; unsaturated fatty acids.

FIGURE 1

Effect of low temperature on the unsaturated fatty acids content (A) and the relative expression levels of olive SAD1, SAD2, and SAD3 genes (B) in the mesocarp tissue from cultivars Picual and Arbequina. Branches with about 100 olive fruit (28 WAF) were incubated using standard conditions except that the temperature was 15°C. At the indicated times, fatty acid composition was analyzed by gas chromatography, and relative expressions levels were determined by qRT-PCR using the expression level of the corresponding gene at zero time as calibrator. Data are presented as means ± SD of three biological replicates. ^∗Indicates significantly different to time 0 h (p < 0.05) by two-way ANOVA with a Bonferroni post-test.

FIGURE 2

Effect of high temperature on the unsaturated fatty acids content (A) and the relative expression levels of olive SAD1, SAD2, and SAD3 genes (B) in the mesocarp tissue from cultivars Picual and Arbequina. Branches with about 100 olive fruit (28 WAF) were incubated using standard conditions except that the temperature was 35°C. At the indicated times, fatty acid composition was analyzed by gas chromatography, and relative expressions levels were determined by qRT-PCR using the expression level of the corresponding gene at zero time as calibrator. Data are presented as means ± SD of three biological replicates. ^∗Indicates significantly different to time 0 h (p < 0.05) by two-way ANOVA with a Bonferroni post-test.

FIGURE 3

Effect of darkness on the unsaturated fatty acids content (A) and the relative expression levels of olive SAD1, SAD2, and SAD3 genes (B) in the mesocarp tissue from cultivars Picual and Arbequina. Branches with about 100 olive fruit (28 WAF) were incubated at 25°C under darkness conditions. At the indicated times, fatty acid composition was analyzed by gas chromatography, and relative expressions levels were determined by qRT-PCR using the expression level of the corresponding gene at zero time as calibrator. Data are presented as means ± SD of three biological replicates. ^∗Indicates significantly different to time 0 h (p < 0.05) by two-way ANOVA with a Bonferroni post-test.

FIGURE 4

Effect of darkness on the galactolipids unsaturated fatty acid content in the mesocarp tissue from cultivars Picual and Arbequina. Branches with about 100 olive fruit (28 WAF) were incubated at 25°C under darkness conditions. At the indicated times, fatty acid composition of galactolipids were analyzed by gas chromatography a Triangles, monogalactosyldiacylglycerol; circles, digalactosyldiacylglycerol. Data are presented as means ± SD of three biological replicates. ^∗Indicates significantly different to time 0 h (p < 0.05) by two-way ANOVA with a Bonferroni post-test.

FIGURE 5

Effect of wounding on the unsaturated fatty acids content (A) and the relative expression levels of olive SAD1, SAD2 and SAD3 genes (B) in the mesocarp tissue from cultivars Picual and Arbequina. Branches with about 100 olive fruit (28 WAF) were incubated using standard conditions except that the olive fruit were mechanically damaged at zero time. At the indicated times, fatty acid composition was analyzed by gas chromatography, and relative expressions levels were determined by qRT-PCR using the expression level of the corresponding gene at zero time as calibrator. Data are presented as means ± SD of three biological replicates. ^∗Indicates significantly different to time 0 h (p < 0.05) by two-way ANOVA with a Bonferroni post-test.